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ROBE TOWN WATER SUPPLY PROJECT - FINAL DETAIL DESIGN REPORT TABLE OF CONTENTS 1. INTRODUCTION.....................................................1-1 1.1 FORMATION OF ROBE TOWN WATER SUPPLY AND SEWERAGE SERVICE.................1-1 1.2 PROJECT COMPONENTS..................................................1-1 2. PRESENT STATUS...................................................2-1 2.1 ROBE TOWN WATER SUPPLY AND SANITATION.................................2-1 2.1.1. Water Supply.................................................................................................................................. 2-1 3. POPULATION AND WATER DEMAND PROJECTION...........................3-1 3.1 POPULATION PROJECTION............................................3-1 3.1.1 Base Population and Growth Rate............................................................................................... 3-1 3.1.2 Population Projection................................................................................................................... 3-1 3.2 WATER DEMAND PROJECTION..........................................3-1 3.2.1 Domestic Water Demand.............................................................................................................. 3-1 3.2.2 Non-Domestic Water Demand...................................................................................................... 3-3 3.2.3 Non Revenue Water....................................................................................................................... 3-5 3.3 AVERAGE DAY WATER DEMAND.........................................3-5 3.4 MAXIMUM DAY WATER DEMAND.........................................3-6 3.5 PEAK HOUR WATER DEMAND...........................................3-6 3.6 SUMMARY OF WATER DEMAND..........................................3-7 4. ANALYSIS OF THE EXISTING WATER SOURCES...........................4-1 4.1 EXISTING WATER SOURCE............................................4-1 4.2 GROUNDWATER SOURCE...............................................4-1 4.3 REGIONAL GEOLOGY.................................................4-1 4.3.1 Local Geology................................................................................................................................ 4-1 4.3.2 Structural Geology........................................................................................................................ 4-2 4.4 HYDROGEOLOGY.....................................................4-2 4.4.1 Water Point Inventory................................................................................................................... 4-2 4.4.2 Recharge Area and Catchments................................................................................................... 4-4 4.5 THE PROPOSED WATER SOURCE........................................4-4 4.6 LOLA RIVER.......................................................4-5 5. INTAKE WORKS.....................................................5-1 5.1 LOCATION.........................................................5-1 5.2 GENERAL..........................................................5-1 5.3 PROJECT IMPROVEMENTS.............................................5-1 5.3.1 Intake Structures........................................................................................................................... 5-2 5.3.2 Aerator, Raw Water Gravity Main and Header Tank.................................................................. 5-4 6. RAW WATER MAIN...................................................6-1 6.1 ROUTE ALIGNMENT.................................................... 6-1 6.2 SELECTED PIPE MATERIAL..............................................6-1 6.3 HYDRAULIC DESIGN....................................................6-1 6.4 INSTALLATION OF PIPES...............................................6-1 ARMA Engineering PLC i

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Page 1: Robe-Detail Design Report

ROBE TOWN WATER SUPPLY PROJECT - FINAL DETAIL DESIGN REPORT

TABLE OF CONTENTS

1. INTRODUCTION...............................................................................................................................1-1

1.1 FORMATION OF ROBE TOWN WATER SUPPLY AND SEWERAGE SERVICE.............................................1-11.2 PROJECT COMPONENTS..........................................................................................................................1-1

2. PRESENT STATUS............................................................................................................................2-1

2.1 ROBE TOWN WATER SUPPLY AND SANITATION...................................................................................2-12.1.1. Water Supply.........................................................................................................................................2-1

3. POPULATION AND WATER DEMAND PROJECTION............................................................3-1

3.1 POPULATION PROJECTION.............................................................................................................3-13.1.1 Base Population and Growth Rate........................................................................................................3-13.1.2 Population Projection...........................................................................................................................3-13.2 WATER DEMAND PROJECTION.....................................................................................................3-13.2.1 Domestic Water Demand......................................................................................................................3-13.2.2 Non-Domestic Water Demand..............................................................................................................3-33.2.3 Non Revenue Water...............................................................................................................................3-53.3 AVERAGE DAY WATER DEMAND................................................................................................3-53.4 MAXIMUM DAY WATER DEMAND...............................................................................................3-63.5 PEAK HOUR WATER DEMAND......................................................................................................3-63.6 SUMMARY OF WATER DEMAND..................................................................................................3-7

4. ANALYSIS OF THE EXISTING WATER SOURCES..................................................................4-1

4.1 EXISTING WATER SOURCE............................................................................................................4-14.2 GROUNDWATER SOURCE...............................................................................................................4-14.3 REGIONAL GEOLOGY......................................................................................................................4-14.3.1 Local Geology.......................................................................................................................................4-14.3.2 Structural Geology................................................................................................................................4-24.4 HYDROGEOLOGY.............................................................................................................................4-24.4.1 Water Point Inventory...........................................................................................................................4-24.4.2 Recharge Area and Catchments............................................................................................................4-44.5 THE PROPOSED WATER SOURCE.................................................................................................4-44.6 LOLA RIVER.......................................................................................................................................4-5

5. INTAKE WORKS...............................................................................................................................5-1

5.1 LOCATION..........................................................................................................................................5-15.2 GENERAL............................................................................................................................................5-15.3 PROJECT IMPROVEMENTS.............................................................................................................5-15.3.1 Intake Structures...................................................................................................................................5-25.3.2 Aerator, Raw Water Gravity Main and Header Tank...........................................................................5-4

6. RAW WATER MAIN.........................................................................................................................6-1

6.1 ROUTE ALIGNMENT...............................................................................................................................6-16.2 SELECTED PIPE MATERIAL....................................................................................................................6-16.3 HYDRAULIC DESIGN..............................................................................................................................6-16.4 INSTALLATION OF PIPES........................................................................................................................6-1

7. NEW WATER TREATMENT WORKS..........................................................................................7-1

7.1 GENERAL............................................................................................................................................7-17.2 TREATMENT SYSTEM......................................................................................................................7-17.3 TREATMENT WORKS UNITS..........................................................................................................7-77.5.1. Aeration Unit.........................................................................................................................................7-77.5.2. Chemical Mixing and Dosing Building.................................................................................................7-97.5.3. Rapid Mix............................................................................................................................................7-137.5.4. Flocculation........................................................................................................................................7-16

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7.5.5. Filters, Filter Gallery and Control Room...........................................................................................7-257.5.6. Filter Backwashing Unit.....................................................................................................................7-277.5.7. Chlorine Mixing and Chlorine Dosing Room.....................................................................................7-377.5.8. Clear Water Tank................................................................................................................................7-407.5.9. Pump House Design Sizing of Pump House.......................................................................................7-417.5.10. Building Works....................................................................................................................................7-427.5.11. Electrical Works..................................................................................................................................7-437.5.12. Site Works...........................................................................................................................................7-45

8. DISTRIBUTION SYSTEM AND STORAGE RESERVOIRS......................................................8-1

8.1 EXISTING DISTRIBUTION SYSTEM..............................................................................................8-18.2 PROPOSED DISTRIBUTION SYSTEM............................................................................................8-18.3 DISTRIBUTION SYSTEM DESIGN CRITERIA...............................................................................8-18.3.1. Water Demand......................................................................................................................................8-18.3.2. Pipelines................................................................................................................................................8-18.3.3. Accessories............................................................................................................................................8-38.3.4. Pipeline Appurtenant Structures...........................................................................................................8-48.4 CLEAR WATER GRAVITY MAIN....................................................................................................8-48.4.1. Route Alignment....................................................................................................................................8-48.4.2. Selected Pipe Material..........................................................................................................................8-58.4.3. Hydraulic Design..................................................................................................................................8-58.4.4. Installation of Pipes..............................................................................................................................8-58.5 DISTRIBUTION SYSTEM..................................................................................................................8-78.5.1. Goba Road Main Subsystem (GBR-Main-1-3)....................................................................................8-78.5.2. Western Main Subsystem (West-Main-1 to West-Main-13)..................................................................8-78.5.3. Goba Road Branch Subsystem (GBR-BR-1-to ADM-BR-3).................................................................8-78.5.4. Eastern Main Subsystem (East-Main-1 TO East-BR-2).......................................................................8-78.5.5. Eastern Main Subsystem (East-Main-2 TO AAR-BR-10).....................................................................8-78.5.6. Western Branch Subsystem (wst-br-1-2 TO wst-BR-6).........................................................................8-78.5.7. Eastern Main Subsystem (East-Main-6 TO East-SBR-5).....................................................................8-78.5.8. Eastern Main Subsystem (East-Main-9 TO East-Main-16)..................................................................8-88.5.9. Addis Ababa Road Subsystem (AAR-BR-1TO AAR-BR-4)..................................................................8-88.5.10. Addis Ababa Road Subsystem (AAR-BR-7 TO AAR-BR-4).................................................................8-88.6 STORAGE RESERVOIRS...................................................................................................................8-88.6.1. Goba Road Service Reservoir (GRSR)..................................................................................................8-98.6.2. Bulk Meters...........................................................................................................................................8-98.7 NETWORK ANALYSIS.............................................................................................................................8-98.7.1. General..................................................................................................................................................8-98.7.2. System Simulation.................................................................................................................................8-98.8 RESULTS AND CONCLUSION.......................................................................................................8-10

9. ENVIRONMENTAL IMPACTS OF THE SCHEME....................................................................9-1

9.1 IMPACTS DURING THE CONSTRUCTION PERIOD.....................................................................9-19.2 LONGTERM IMPACT........................................................................................................................9-2

10. PROJECT COSTS............................................................................................................................10-1

10.1 COST ESTIMATES.................................................................................................................................10-110.2 CRITERIA FOR COSTING.......................................................................................................................10-210.2.1 General................................................................................................................................................10-210.2.2 Pipeline Costs.....................................................................................................................................10-210.2.3 Supply of Pipes & Fittings..................................................................................................................10-210.2.4 Civil and Construction Works.............................................................................................................10-210.2.5 Pumping Plant, Compressors Costs....................................................................................................10-210.2.6 Treatment Works Costs.......................................................................................................................10-210.2.7 Storage Reservoir Costs......................................................................................................................10-210.2.8 EEPCO Power Line Connection and road Crossings.......................................................................10-210.2.9 Total Gross Costs................................................................................................................................10-2

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APPENDICES

Appendix '1' - HYDRAULIC CALCULATIONS

Appendix '2' - DESIGN OF STRUCTURES

Appendix '3' - ELECTROMECHANICAL DESIGN REPORTS

Appendix '4' - Raw water Quality analysis result

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1. INTRODUCTION

Robe town is situated in Bale Zone of south east Oromia Regional State at latitude of 7o 08' N and longitude 380 36' E. at a road distance of 430 km from Finfine in Sinana Woreda. The town is situated at the foot of Bale Mountain on a plain terrain with an average ground elevation from 2419 - 2560m ASL. The total proposed area of the town is 8024 hectares according to area measured from the base map of the town. For administrative purpose the town is divided into three kebeles, 01, 02, &03, i.e., Oda Robe, Caffee Donsa, and Baha Biftu.

The power supply for town is from National Grid line which serves for 24 hrs. The town is accessible by asphalt road and all weather gravel road covering a distance of 427km.

1.1 Formation of Robe Town Water Supply and Sewerage Service

In 1937 water for domestic use of Robe town was obtained from Bamo River of Goba town area. Later on the production of water for domestic use from this river stopped in 1968. In the same year from Shaya River production of water for domestic use started to function. The water from Shaya river was pumped scheme and was supplied to the town without adequate treatment but with only intermittent disinfection besides most of the township was not supplied. Due to inadequacy of this supply the town inhabitants were obtaining water from shallow wells and traditional dug wells. To alleviate the problem the water supply of the town has been incorporated in the Robe Meliyu Water supply project.

At present the water supply and sewerage enterprise is administered by the Town Water Board. The Town Water Board has been established based on the Region’s proclamation for the administration and management of urban water supply schemes. The water supply system is administered under the Town Water Board whose chairperson is the zonal water resources office head and the utility head being the secretary. The Town Water Board consist members from the municipality, Zone Water resources office, Zone women affair, EEPCO office at Robe, Community representative and Water Supply and sewerage Service as secretary.

It is the intention of the RWSSE to provide service to areas which are not covered at present but which are part of the town.

1.2 Project Components

Existing Water SupplyRobe town water supply is from Robe-Maliyu water Supply project, constructed to serve rural population from spring source. The implementation of the project was started in 1996 G.C., and phase one of the project was completed in 1997 G.C. the project was implemented by four organizations; the Oromia water resources Bureau and Oromia Health bureau were implementers of the project by assigning their staff. Oromia Disaster Prevention and Preparedness Bureau was involved by making overall coordination and assisted by supervising foreign procurement. WaterAid was the main financer of the project. The project was implemented through community participation in providing labour and financial contribution. The construction of the project has taken about six years. The scheme was designed to serve 18 rural kebeles and Robe town population for 15 to 20 years.

The town water supply pays 0.75Birr/m3 of water received from the rural water board measured by bulk water meter installed at the entrance to the town.

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The system consists the following units.a)Raw Water Gravity Main – ND 150 mm uPVC 2 km, up to junction point,b) Distribution Network consists of DCI, uPVC, HPDE and Gs pipes with diameter ranging

from ND 50 to ND 300, totaling 39.8km,c)Three Storage Reservoirs each having volume of 150m3

This Report covers the Draft Final Designs for augmentation of the present Water Supply System to cater for water demands for increased population up to the Year 2030. The Draft Final Design Project components detailed in this Report are as follows: -

New 'Raw' Intake Weir Constructed across Lola River , located at ‘x,y’ coordinates of 601484 & 779560 at an elevation of 2790masl.

New 'Raw' Gravity Water Main, approximate length 762 metres. DCI pipe nominal size 400 mm diameter

New Treatment Works at the New Treatment Plant Site, located at (x,y) coordinates ranges of x coordinates 601980, 602,160 and y coordinates 779560, 779680 for a capacity 12,001 m3/d briefly comprising of: - Chemical Dosing Building incorporating stilling well and inlet works

- Distribution Pipe to Clarifiers- DN of 400 & 300mm

- Upflow Sludge Blanket Clarifier - 3Nr each L 9.1 m, W = 8 m, Hmax = 6.7m, inclined length 6.02 m

- Rapid Gravity Sand Filters – 4 Nr each 4.3 m x 6.6 m (WxL)

- Filter Gallery and Pipework

- Chlorine Dosing and pH Correction Room

- Generator Room - floor area 50 m2

- Backwash Collection Pond and Sludge Drying Beds

- Site Works including Access Road, Fencing, etc.- Operators dwelling house,- Workshop,- Administration building

Water Mains: Varying in diameter from 150 mm to 400 mm in materials uPVC and lined DCI pipes - approximate length 106.00 km. Associated works included like installation of valves, fire hydrants, flow meters, etc. and construction of chambers, etc.

Storage & Service Reservoirs:

TP Clear Water Reservoir (R.C.) 1 Nr capacity 2500 m3

Service Reservoir nearby Goba road (R.C.) - 1000 m3

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2. PRESENT STATUS

The system consists the following units.d) Raw Water Gravity Main – ND 150 mm uPVC 2 km, up to junction point,e)Distribution Network consists of DCI, uPVC, HPDE and Gs pipes with diameter ranging

from ND 50 to ND 300, totaling 39.8km,f) Three Storage Reservoirs each having volume of 150m3

2.1 Robe Town Water Supply and Sanitation

2.1.1. Water Supply

The first water supply for the town was started in 1937 water for domestic use of Robe town was obtained from Bamo River of Goba town area. Later on the production of water for domestic use from this river stopped in 1968. In the same year from Shaya River production of water for domestic use started to function. The water from Shaya river was pumped scheme and was supplied to the town without adequate treatment but with only intermittent disinfection besides most of the township was not supplied. Due to inadequacy of this supply the town inhabitants were obtaining water from shallow wells and traditional dug wells. To alleviate the problem the water supply of the town has been incorporated in the Robe Meliyu Water supply project.

Robe town water supply is from Robe-Maliyu water Supply project, which is gravity system from Spring source. The implementation of the project was started in 1996 G.C., and phase one of the project was completed in 1997 G.C. The project was implemented through community participation in providing labour and contributed costs. The construction of the project has taken about six years. The scheme was designed to serve 18 rural kebeles and Robe town population for 15 to 20 years.

The distribution system consist the following .The distribution pipes are DCI, uPVC and GS and the size varies from 50mm to 300mm. The total distribution line length in the town is as indicated below.

S/n Diameter in mm Length in m Type Remark 1 300 1374 uPVC2 250 198 DCI

250 1002 uPVC3 200 504 uPVC4 150 6192 uPVC5 100 3936 uPVC6 80 4080 uPVC

65 2196 HPDE7 50 2544 uPVC

50 11426 HPDETotal 39,878

The total existing customers are 5026 out of this private connection are 4380, Commerce 533 and governments 81.

The number of public water points is 16. All the public water points are constructed with concrete and have four faucets. The water points were constructed in 1997 G.C.

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There is no distribution pipes layout drawing available. The distribution lines also do not follow the present master plan of the town.

Mio capped spring

Spring outlet box

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Raw Water Main

The Raw Water Rising Main is DN 150mm DCI and it, conveys water from the spring to the benefiting community and to reservoirs located in the town from which distribution net work is laid within the town

Existing 150m3 each reservoirs

Existing Treatment Plant

There is no treatment facility except shock chlorination.

Distribution Network

The existing Water Distribution Network consists of two types of pipe material, i.e DCI unPlasticised Polyvinyl Chloride (uPVC) and HDPE pipes, ranging in diameters from 50 mm to 300 mm. The total length is approximately 39.79 km.

Water Storage

The water tank/Storage reservoirs are three masonry with capacity of 150m3 located in the west southeast of the town.

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3. POPULATION AND WATER DEMAND PROJECTION

3.1 POPULATION PROJECTION

3.1.1 Base Population and Growth Rate

The base population as indicated in the Feasibility Study and preliminary engineering design Report is that of the year 2007 CSA draft report. This figure is projected using the medium growth rate for Oromia towns as indicated in the 1998 CSA analytical report. Accordingly, the CSA report for 2007 has been project to year 2010 to be used as base year.

3.1.2 Population Projection

CSA has also produced regional growth rates for different periods up to year 2030 and for three alternative scenarios with high, medium and low growth rates. The efforts of implementing government policies on population regulation in the Robe town are anticipated to be successful to a moderate extent. Hence, the population of the town is expected to show medium growth rate.

Table 3.1 shows the projected population for the Robe town for different years.

Year Growth Rate Projected Population2010 4.6 61,2302015 4.4 76,2972020 4.2 94,1262025 4.0 114,9652030 3.8 139,0212035 3.6 166,4382040 3.6 199,263

3.2 WATER DEMAND PROJECTION

Water demand projection is based on the determination of domestic water demand, non-domestic water demand and Non Revenue Water and their projections accordingly. Thus the water demand projection for ROBE town has been computed as indicated hereunder.

3.2.1 Domestic Water Demand

Domestic water demand includes water for drinking, for food preparation, for washing and cleaning and miscellaneous domestic purposes. The amount of water used for domestic purposes varies depending on the lifestyle, living standard, climate, mode of service and above all on the affordability of the users.

3.2.1.1 Mode of Service

The Feasibility Study and preliminary engineering design carried out under this Project have identified three major mode of services for domestic water consumers. Accordingly, these three services have been adopted for the water demand study of the ROBE town and are as follows: House Connections (HC) Yard Connections (YC) Yard Connections Shared (YCS) Public Fountains (PF)

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3.2.1.2 Projection of Service Level

Considering the overall future development trend of the town, the target service level has been projected up to the design horizon, year 2030. The present and projected service levels in percentage are presented in Table 3.2.

Table 3.2: Projected Service Level

Mode of Service Year2010 2015 2020 2025 2030 2035 2040

House Connection 3.2% 7.7% 12.1% 16.6% 21.0% 23.0% 25.0%Yard Connection 29.0% 33.2% 37.4% 41.6% 45.8% 50.4% 55.0%Yard tap shared 29.0% 28.1% 27.1% 26.2% 25.2% 20.1% 15.0%Public Fountain 11.0% 10.3% 9.5% 8.8% 8.0% 6.5% 5.0%

72.20% 79.30% 86.10% 93.20% 100.00% 100.0% 100.0%

The table indicate that yard tap shared and public fountain users decrease while yard connection and house connection increase.

3.2.1.3 Domestic Demand Adjustment Factors

In determining the socio-economic and climatic factors for the Robe town, the design criteria have presented the following guidelines. In the case of socio-economic factor determination, it is more of a personal judgment while in the latter case the mean annual precipitation is the governing factor.

Table 3.3: Socio Economic FactorsGroup Description Factor

A Towns enjoying high living standards and with high potential for development

1.10

B Towns having a very high potential for development, but lower living standards at present

1.05

C Towns under normal Ethiopian conditions 1.00D Advanced rural towns 0.90

Table 3.4: Climatic Effects FactorsGroup Mean Annual Precipitation - mm Factor

A 600 or less 1.10B 601-900 1.05C 901 or more 1.00

The development potential is considered in group C. Accordingly a socio-economic factor of 1.00 is utilized. The town has a mean annual rainfall of 1,490 mm and there is no dry month in a year which makes its climatic factor 1.0.

3.2.1.4 Per Capita Demand and Its Projection

In determining per capita water demand, previous studies on urban water supply schemes have been utilized. In principle water demand depends on water usage for different purposes. In line to this the consultant has studied water usage for different purposes for the four towns under this project. The basis for the study is the national Water Policy, previous study such as the Oromia

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six towns water supply project, the Environmental Support Project (ESP) and 25 towns water supply project. It is expected that as the people get more and more education and enjoy higher living standard their water demand will increase. Previous studies indicate that a demand growth rate of 1% for public tap users and 2% for yard and house connections were assumed realistic. Demand Responsive Approach state that the beneficiaries should decide on the service level that they want and can afford.

Table 3.5: Consumption of Water for Different Purposes (lpcd)

Service level HTU YTU NTU PTUYear 2010 2029 2010 2029 2010 2029 2010 2029Usage Drinking 3 3 3 3 3 3 2 3Cooking 5 5 4 4 3 4 2 3Ablution 6 6 5 5 3 4 1 2Washing Dishes 3 6 3 4 3 4 3 3Washing Clothes 5 10 4 6 3 4 3 3House cleaning 5 6 2 5 2 3 2 3Bath or shower 6 15 4 8 3 3 2 3Flushing Toilet 7 9            Watering animals   0   0        Total 40 60 25 35 20 25 15 20

3.2.1.5 Consumption by Mode of Service

Following the above procedure the projected per capita water demand, for the four mode of services in the two Project stages with the consideration of socioeconomic and climatic factor, is shown in Table 3.6. in estimating the projected water demand for ROBE town is done using the adjusted per capita demand for the mode of services considered for the township and estimation is made for each mode of service.

Table 3.6: Projected Per Capita Water Demand by Mode of Service (lpcd)Mode of Service Year Adjusted (socioeconomic &

climatic, 1.00&1)2011 2030 2040

HTU 35 60 60 60YTU 30 35 35 35NTU 20 25 25 25PTU 20 20 20 20Average 26.25 35 35 35

3.2.2 Non-Domestic Water Demand

Non-domestic water demand can be broadly divided into two main categories:

Public water demands; and Industrial water demands.

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3.2.2.1 Public Water Demand

The water required for schools, hospitals, hotels, public facilities, offices, commercial establishments, military camps and other public purposes is classified as public water demand.

Educational Water Demand

Day schoolThe number of students attending schools is expected to grow faster than the total population. The assumptions adopted in the determination of the school water demand in the ROBE town include:

1. 85 percent of the students in the age group of 7 to 12 will attend school by the year 2015 and 100 per cent by year 2030;

2. 85 percent of the students in the age group of 13 to 14 will attend school by the year 2015 and 98 per cent by year 2030;

3. 75 percent of the students in the age group of 15 to 18 will attend school by the year 2015 and 95 per cent by year 2030;

4. Factors of 10% and 5% are adopted in order to include the demand of staff and pupils, respectively, from the surrounding areas; and

5. The ratio of school age children to the total population of the Robe town is considered to be same as the ratio of school age children to the total population in Oromia region.

The above assumptions are based on the 1994 Population and Housing Census Report and the Analytical Report of the same published in 1998.

It is considered that 5 liters to be the normal daily demand per pupil in a day school. The working day demand of the teachers and other workers in day schools is taken to be equal to 5 l/day. From the total number of students, and allowing for teachers and administrative staff, the day school demand for the Robe town is estimated to 121 m3/day and 220 m3/day for year 2015 and 2030, respectively.

University60 liters is considered to be the daily demand per pupil and residing staff in a boarding school. Also, the working day demand for staff residing outside the premises of the boarding school is assumed at 5 l/day per employee. The total estimated demand for Meda Wolabu University is 389 m3/day and 600 m3/day for year 2015 and 2030, respectively.

Health Water DemandHealth, water demand for ROBE town has been estimated to be 5% of average domestic day demand. Accordingly, the total water demand for health institutions in the Robe town is estimated at 81.5 m3/day and 256.2 m3/day for years 2015 and 2030, respectively.

Commercial Water DemandHotels, bars, restaurants, traditional winery houses, small shops, and workshops are among the existing commercial activities in the Robe town. The demand for such category varies 20%-40% of the domestic water demand as indicated in the guideline for urban water supply by ministry of water and mines. The adopted commercial demand is 20% of average domestic day demand. This is because Robe is commerce center for the for Bale zone and Somali regions which boarders it in the low lands hence, there is high activity in this center. The total water demand

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for commercial sector in the Robe town is estimated at 326 m3/day for year 2015 and 1025 m3/day year 2030, respectively.

Other Public UsesOther public uses include water demand for public offices, mosques, abattoirs, public facilities and prison houses and it is estimated to be 20% of average domestic day demand. The estimated demand for other public uses is 326 m3/day and 1025 m3/day for year 2015 and year 2030 respectively.

Fire RequirementsThe annual volume required for firefighting purpose is small. However, during periods of need, the demand may be exceedingly large and in many cases govern the design of distribution storage and pumping requirements. In this case the fire fighting water requirements is considered to be met by stopping supply to consumers and directing it for this purpose. This demand is taken care of by increasing the volume of storage tanks by 10 percent.

3.2.2.2 Industrial Water Demand

Industrial water demand for ROBE town is estimated to be 10% of average domestic day demand. Accordingly, industrial domestic demand is estimated to 163 m3/day and 512 m3/day for year 2015 and year 2010 respectively.

3.2.3 Non Revenue Water

Non Revenue Water includes water losses in the water supply system, illegal connections, overflow from reservoirs, improper metering and losses in the treatment plants. The amount is expressed as a percentage of the sum of domestic demand, public demand, and the industrial demand covered from the water supply system. The percentage usually varies from 10 to 30 % depending on the age of the pipes and the complexity of the system. Here, the percentage is based on the expected condition of the system in each stage of development, the contribution of the existing system to the new development being the main factor. Here, non revenue water varying from of 20% to 25% has been adopted.

3.3 AVERAGE DAY WATER DEMAND

The average day demand is the sum of the domestic demand, public demand, industrial demand and non revenue water.

The water demand in a day varies with time according to the consumers' life style which is expected to improve with time. Hence, the adopted hourly flow factors, fractions of average daily demand, for the design period Table 3.7.

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Table 3.7: Recommended Hourly Demand Factors

Time Year 202900-01 0.3001-02 0.3002-03 0.3003-04 0.3004-05 1.2005-06 1.3006-07 1.4007-08 1.5008-09 1.5009-10 1.5010-11 1.5011-12 1.6012-13 1.5013-14 1.5014-15 1.5015-16 1.5016-17 1.4017-18 1.2018-19 1.0019-20 0.5020-21 0.3021-22 0.3022-23 0.3023-24 0.30

Total 24.0

3.4 MAXIMUM DAY WATER DEMANDTable 3.8: Maximum day and peak hour as presented in the design guideline of the Ministry of Water and Energy May 2003. Settlement category Maximum-day factor Peak-hour factorRural (<2,000)

1.23 – 4

Small towns (2,000 – 10,000) 2.5 – 3.0Medium towns (10,000 – 50,000) 1.15 1.8 – 2.2

Large towns (50,000 – 80,000) 1.1 1.5 – 1.8

Very large towns (> 80,000) 1.5

The water consumption varies from day to day. The maximum day water demand is considered to meet water consumption changes with seasons and days of the week. The ratio of the maximum daily consumption to the mean annual daily consumption is the maximum day factor. The maximum day factors as indicated above vary from 1.1 to 1.2 depending on the population size of the town. In this Project the maximum day factor adopted is 1.1.

3.5 PEAK HOUR WATER DEMAND

Peak hour demand occurs particularly when all the water taps are opened at a particular rush hour. Such an event is likely to happen during morning hours when most people use water for bathing, cooking and it could also occur towards the end of the day due to peoples' need for water for the same purpose after working hours. It is greatly influenced by the size of the town, mode of service and social activity pattern. The peak hour factor in a day used is 1.7 up to year

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2017. From Year 2017 onwards a peak factor of 1.5 has been used based on the guideline shown in the above table as Robe town is assumed to be very large town.

3.6 SUMMARY OF WATER DEMAND

The total demand projections of the ROBE town for each demand category are summarized in Table 3.9.

Table 3.9: Summary of Projected Water Demand

Item Year Unit 2011 2015 2030 2040

1 Population  

1.1 Growth % 4.4% 4.4% 3.8% 3.6%

1.2 Population No 63,984 76,297 139,021 199,263

1.3 Rural Population No 1,287 1,445 2,234 2,987

1.4 Medawolabu University population No 5,295 6,475 10,000 10,000

1.5 College Student - from Robe No 1,896 2,261 4,120 5,905

1.6 Total population No 70,566 84,217 151,255 212,250

2 Demand  

2.1 Domestic Demand m³/day 1,168 1,630 5,125 7,832

2.2 Non-Domestic m³/day 743 1,017 3,039 4,623

2.2.1 Public m³/day 627 854 2,526 3,840

2.2.1.1 Schools m³/day 101 121 220 315

2.2.1.2 Health m³/day 58 81 256 392

2.2.1.3 Commercial m³/day 234 326 1,025 1,566

2.2.1.4 Other Public & Gov institutions m³/day 234 326 1,025 1,566

2.2.2 Industrial m³/day 117 163 512 783

2.2.3 Medawolabu University m³/day 318 389 600 600

2.4 Total Demand m³/day 2,229 3,035 8,763 13,055

2.5 Unaccounted-for Water % 18% 20% 20% 25%

2.6 Average Day Demand m³/day 2,635 3,642 10,516 16,318

    l/s 30.5 42.2 121.7 188.9

2.7 Mean Percapita Demand l/c/d 37 43 70 76

2.8 Max. Day Factor   1.10 1.10 1.10 1.10

2.9 Max. Day Demand - Mains Capacity  

2.9.1   m³/day 2,899 4,007 11,568 17,950

2.9.2   l/s 34 46 134 208

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Table 3.9: Summary of Projected Water Demand continued

Item Year Unit 2011 2015 2030 2040

2.10 Peak Hour Factor   1.7 1.70 1.50 1.50

2.11Peak Hour Demand- Distribution Capacity l/s 57.0 78.8 227.6 353.2

2.12 Abstraction and treatment loses (SW) % 7% 7% 7% 7%

2.13 Abstraction and treatment loses (GW) % 3% 3% 3% 3%

2.14 Total Water production (SW)  

2.14.1   m³/day 3,102 4,287 12,377 19,207

2.14.2   l/s 35.9 49.6 143.3 222.3

2.15 Total Water production (GW)  

2.15.1   m³/day 2,986 4,127 11,915 18,489

2.15.2   l/s 34.6 47.8 137.9 214.0

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4. ANALYSIS OF THE EXISTING WATER SOURCES

4.1 EXISTING WATER SOURCE

Robe town water supply is from Robe-Maliyu water Supply project, which is gravity system from Spring source. The implementation of the project was started in 1996 G.C., and phase one of the project was completed in 1997 G.C. The project was implemented through community participation in providing labour and contributed costs. The construction of the project has taken about six years. The scheme was designed to serve 18 rural kebeles and Robe town population for 15 to 20 years.

At present the scheme is inadequate to serve Robe town and the rural communities and hence this project has been envisaged to study and design new water supply scheme specifically for Robe town.

4.2 GROUNDWATER SOURCE

The geomorphology of the area and the region in its vicinity is composed of extensive flat land and a long belt of a Chain Mountain starting from Sebesibe Washa to the summit of Tulu Dimtu which stands high up in the center of Senete plateau. This area distinctively represents the second higher topographic region in the Country. The present topographic setting of the surface is the result of the aforementioned geological activities that shapes the surface the way it manifests itself. The mountains in this area were built up by volcanic activities. The Senet plateau is marking the regional catchments divide line (Weyib River basin and Genale River basin). The altitudes of the plateau start from about 4600m a.s.l at the summit of Tulu Dimtu and start to fall to the south and to the north directions. In the north direction it becomes 2780m at the proposed intake and finally made the Robe plain and Weyib Catchment’s basin. The plateau is the beginning places for the streams and drainages that are flowing to Shaya and Weyib, the two prominent Rivers in the region. The drainages are joined each other dendritically to form the Shaya and Weyib rivers. Shaya is the second largest river next to Weyib and is the tributary for the later. Dendritically joined drainage pattern depicts that the fracturing of the subsurface formation are interconnected hydraulically. However, the density of the streams and drainages are dispersed indicating that the abundance of secondary porosities is insignificant.

4.3 REGIONAL GEOLOGY

The geology of this area when viewed at a large scale encloses the Arsi - Bale units that covered an extensive area due to huge eruption that comprises compositionally diversified rock formations (from Acidic to Basic). According to the Hydro geological map of Ethiopia scaled to one to two million, the geological time scale that marks the geological activity in this area is Upper Oligocene to Upper Miocene. The geological occurrences that were evolved during this time are mainly the basaltic rocks that often connected to the main volcanic center to form volcanic edifices. This geological unit as described by the same source has got the thickness of 100m to 600m. The map notifies that it become siliceous in composition in the upper portion of the stratification. But this thickness seems to be more than the stated figure above (100m to 600m), for the reason that the elevation difference at Senete plateau (4600m) and Robe (2480m) is far more than that. Since the geology of the area from Senete plateau to Robe plain is continuously basaltic rock.

4.3.1 Local Geology

There is no significant difference between the regional geology and the local geology since the volcanic eruption exhibits more or less homogeneous mode of occurrences due to the edifice

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(huge) mode of eruption. But the geology around the plain land contains scoria and scoracious basalt while the geology in the high land and plateaus lacks these formations. The scoracious basalt and scoria are available around Robe towns and may have covered substantial area overlying the basaltic rock formation. Hence the probable stratigraphic sequence might exhibit following succession.- Black cotton soil- Scoria/scoracious basalt- Basaltic rockThe basalt that will be helpful for construction during the implementation of the water supply system is available at and around river intake site.

4.3.2 Structural Geology

There are two major faults that regional affect the block. The first fault runs in the east-west direction whose up thrown part contains Dinsho-Goba ridge while the down throw part contains the Robe plain land. The second fault runs in the north-south direction making the slope that dips toward the Robe Town from Dinsho to Robe. In addition to these faults there exist several minor faults that facilitate convenient situation for the developments of cliffs through sliding around the mountainous area. At the intended river intake, this structure was clearly observed that was formed by fracturing and later followed by landslide to form almost ninety degree down fall from the horizontal surface which creates a favorable condition for the development of water fall.

4.4 HYDROGEOLOGY

There are some occurrences of groundwater system and surface water from the upper weathered parts of basaltic rock formation. These occurrences of groundwater is manifesting through several perennial springs along the fault plane whose discharges are considerably large. Several Rivers starts from the foot of Senete plateau and flow to Shaya –Weyib basin.

4.4.1 Water Point Inventory

The occurrences of groundwater that were observed as spring and productive bore holes are recorded with its coordinate points below:

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Table 4.1 Shows locations of water point Inventories

Water points Source type X(m)

Y(m)

Z(m)

Depth(m)

SWL(m)

ApproximateYield (l/sec)

Specific Capacity(l/m)

Remark

1 Oda spring 0599343 0785563 2652 22 Currently supplying The Town

2 Tebel two near Mio

spring 0597980 0785844 2614 More than 75 Occupied for Ginir

3 Ulandhula spring 0594356 0785262 2898 Approx. 54 Burqitu spring 0594553 0786323 2886 Approx. 35 Halqitii spring 0608481 0770003 2770 Approx. 56 RRC Compound

Robe townDW - - - 78 13 Estimate-d to 4

t0 57 NCA Compound

Robe TownDW - - - 84 12 Estimated to

3.58 Agarfa DW 96 0 29 Robe (instate of

teacherDW 96 13 Estimated to be

2.5

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There are more springs than listed above, but most of them possessed less discharges while the others with the big discharges were occupied by the existing water supplies of Mio Gasara, Robe Town water supply and by the future plan for Ginir water supply scheme.

As one can observe from the above table the groundwater resource is not sufficient for Robe town water supply since the demand of the Town is much bigger than the discharge of the boreholes drilled before. The aquifer for both the bore holes (deep seated groundwater) and the springs (the groundwater flow around the recharge area) were the fractured basaltic rock formation whose yield is very less for the Town that needs higher discharge to support the design demand. However, the groundwater in this area receives a major infiltration having an extensive recharge area combined with the substantial precipitation prevailing in the region. Its yield in storage area (Robe Plain) is very poor probably pertinent to the out pouring of the major groundwater in the recharge area as springs through the aforementioned East – West trending fault plane that cut across groundwater flow line. This is the situation that might describe the big discharges of the groundwater as springs in the recharge area and the low discharges in the storage area. Among the surface water source Shaya river is located relatively nearby Robe town but this source requires pumping hence it is not considered as a first priority. For this reason Lola River is the preferred source for Robe Town water supply project as it does not require pumping, low turbidity even during rainy season .

4.4.2 Recharge Area and Catchments

There is an extensively wide catchments area that brings a lot of tributaries for Lola River. All the rivers in this area start from Senete Plateau with bimodal rainfall and substantially brings a big discharge to the river almost constantly throughout the year.

4.5 THE PROPOSED WATER SOURCE

The proposed water source is Lola river which has an estimated catchment area of 26 km2 at the proposed intake site and at upstream of the proposed intake it has three major tributaries among which Adoda is one. Based on the preliminary assessment the intake is assumed to be gravity.

Lola river is un-gauged and its minimum and maximum flows are not known however, during the preliminary assessment elders leaving nearby the stream has been asked about the severe drought flow. Their response is that the stream is perennial and they have not seen any remarkable dry period flow during the recent drought that has occurred in the country.

In the absence of recorded stream flow data the Consultant has estimated the flow using twenty two year rainfall data and empirical formulae.

Thus in this chapter adequacy or otherwise requirement for other additional water source is conducted.

The, peak discharge is estimated by the following equation, which is derived by the triangular unit hydrograph concept.

Q = 0.2083*A*R/(0.5*Tc^0.5+0.6*Tc)

where,A = catchment area (km2)R = Runoff depth (mm)Tc = Time of concentration (hrs)Q = Peak discharge (m3/sec)

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Tc is determined by Kirpich's formula:

Tc = 0.0195*(L/S^0.5)^0.77/60

where,L = River length (meters)S = slope of the river bed

Runoff has been estimated using Khosla’s formula for estimating un-gauged stream.R = Pm - Lm

Where Lm = monthly lossPm = monthly precipitation,

Lm = 0.48* Tm, for Tm > 4.50C

Tm = monthly mean temperature

After estimating the peak discharge based on the above formulae the mean minimum flow of Lola river has been estimated, Table 4.2 Refers.

4.6 LOLA RIVER

Minimum flow of the Lola stream as determined from twenty two year rainfall data and the formulae mentioned above is as indicated in Table 4.2.

Lola river at the proposed intake site

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Table 4.2 : Estimated flow in m3/sSource Lola River estimated mean flow in m3/s

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

  1985 1.64 2.16 1.83 1.62 1.29 1.50 1.77 1.66 1.56 1.30 0.94 1.30  1986 1.53 1.70 1.82 1.66 1.56 1.64 1.53 1.56 1.35 1.02 1.00 1.40  1987 1.43 1.73 1.61 1.54 1.52 1.64 1.60 1.44 1.42 1.45 1.10 1.43

  1988 1.75 1.76 1.70 1.56 1.61 1.84 1.59 1.44 1.37 1.27 0.51 0.82

  1989 1.41 1.48 0.75 1.11 1.33 1.58 1.51 1.49 1.38 1.22 1.11 1.65

  1990 1.49 1.97 1.53 1.52 1.71 1.93 1.81 1.87 1.54 1.36 1.27 1.21

  1991 1.70 1.84 1.91 1.62 1.63 2.14 1.68 1.75 1.57 1.38 1.41 1.58

  1992 1.80 1.79 1.95 1.88 1.49 1.87 1.60 1.50 1.41 1.35 0.93 1.36

  1993 1.49 1.39 1.36 1.51 1.46 1.99 1.72 1.72 1.65 1.38 1.15 1.34

  1994 1.58 1.93 1.90 1.82 1.65 2.09 1.74 1.48 1.54 1.31 1.11 1.24

  1995 1.56 2.26 1.94 1.75 1.50 1.74 1.90 1.82 1.69 1.54 1.07 1.62

  1996 1.88 1.83 1.87 1.72 1.56 1.66 1.61 1.69 1.56 1.13 1.02 1.16

  1997 1.67 1.75 1.72 1.75 1.54 1.69 1.58 1.58 1.47 1.50 1.40 1.46

  1998 1.75 1.89 1.67 1.72 1.82 2.07 1.75 1.63 1.55 1.46 0.62 0.90

  1999 1.57 1.75 0.83 1.38 1.43 1.74 1.53 1.51 1.46 1.43 0.95 1.41

  2000 1.65 1.87 1.82 1.71 1.76 1.85 1.91 1.81 1.57 1.60 1.46 1.47

  2001 1.64 1.87 1.83 1.70 1.77 1.93 1.76 1.78 1.65 1.54 1.22 1.61

  2002 1.88 1.76 1.95 1.91 1.86 2.24 1.99 1.93 1.68 1.54 1.49 1.55

  2003 1.73 2.14 2.11 1.96 1.80 2.15 1.83 1.85 1.89 1.46 1.44 1.84

  2004 1.82 2.16 2.17 2.09 1.86 2.03 1.67 1.80 1.94 1.63 1.27 1.40

  2005 1.86 2.19 2.08 1.92 1.84 1.93 1.65 2.03 1.92 1.65 1.46 1.34

  2006 1.77 2.08 2.02 1.73 1.61 2.06 1.84 1.78 1.67 1.61 1.38 1.61Mean m3/s   1.66 1.88 1.75 1.69 1.62 1.88 1.71 1.69 1.58 1.42 1.15 1.40Max m3/s   1.88 2.26 2.17 2.09 1.86 2.24 1.99 2.03 1.94 1.65 1.49 1.84

Min m3/s   1.41 1.39 0.75 1.11 1.29 1.50 1.51 1.44 1.35 1.02 0.51 0.82

Mean +mean 1.62

Low Mean 1.15

High Max 2.26

Low Min 0.51

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The minimum estimated flow is considered as the draught flow of the stream and 50% of the drought flow must be allowed to flow over the intake weir for downstream users. Thus the raw water abstraction from the source for design year should not be more than 50% drought flow. This is checked as indicated below.

Qi=CwLhdi3/2

Where: Qi Discharge (m3/s)L Length of over flow section of the weir (m)hdi Head over weir crest (m)Cw Weir discharge coefficient (1.5 for broad crested weir)

Table 4.3 Analysis of Raw Water Abstraction

DischargeLength

(L)Head Over crest (hd)

Flow through div. Intake

% of river flow  

(m3/s) (m) (m) (l/s)    0.51 0.5 0.77 222 43.6% low

flow1.05 0.5 1.25 222 21.2% Low

Mean1.53 7.0 0.28 222 14.6% Average2.16 15.0 0.21 222 10.3% Flood

flow10.80 21.8 0.48 222 2.1% 5 x FF

The minimum flow estimated using empirical formulae and rainfall record of twenty two years as seen from Table 4.2, is 0.51m3/s which occurs in November and the peak day demand for year 2040 is 222.3 l/s which is 43.6% and 21.2% of the minimum and low mean flow, respectively. As the flow over the weir is over 50% of the minimum flow the Consultant proposes construction of simple grated weir intake across the river. Thus, it is assumed that Lola river is adequate to supply the water supply demand up to year 2040 with no storage facility.

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5. INTAKE WORKS

5.1 LOCATION

The proposed Intake is grated weir to be constructed across Lola river located at X,Y, coordinates 601,313m, 779,640m and at an elevation of 2790masl. It is approximately 730 m from the proposed treatment Plant Site which is located at (X, Y) coordinates 601,998, 779634m.

5.2 GENERAL

The proposed intake structure is grated weir which will be constructed across Lola River located at about 9.5 km west of Robe town. The raw water potential of this river is expected to deliver the Year 2030 maximum day water demand of 143.3 l/s and the additional demand of 79.0 l/s to augment the total demand of 222.3 l/s for Year 2040 including abstraction and treatment losses.

The estimated minimum monthly flow of Lola River as presented in the previous chapter over the weir is expected to provide an average of 510 l/s. The maximum intake required is 222.3l/s for year 2040, this flow is 43.3% of the minimum estimated flow thus the River is assumed to supply the maximum day demand of Robe town without the requirement of impounding structure. The water from the weir intake will be gravitated to the treatment plant via 400 mm diameter DCI pipe. The raw water gravity main is designed to convey the year 2040 demand.

5.3 PROJECT IMPROVEMENTS

The future water supply system should therefore consist of the following main elements:

Construction of weir intake at Lolaa River, Raw water collection sump and raw water intake, Raw water Gravity main Raw Water treatment facilities consisting of, rapid mix, coagulation/flocculation, rapid sand

filtration, disinfection and clear water reservoir. Construction of elevated clear water tank for backwashing and treatment plant compound

and nearby villages demand, Clear water pumping station, for backwashing Clear water Gravity main, Clear water reservoirs Standby generator house at treatment plant site, Access road construction which also benefits the rural population situated between the intake

and Robe town Operators Building, Store and workshop, administration building, Guard houses, and Distribution network systems.

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5.3.1 Intake Structures

General The intake structure is broad crested weir with suction pipe intake and it is designed to accommodate the year 2040 demand. The salient data of the intake structure is as shown below.

Description Unit Qty.Maximum Velocity m/s 0.08Maximum day demand (Year 2040) m³/day 17,950Required Abstraction with 7% abstraction loss m³/day 19,207

l/s 222.3Safety Factor Ls 1.7Design Abstraction of 1.7 times required m³/s 0.378

Opening (space b/n bars) cm 5.6

Bar width (dia) cm 2.4

Width of crest (inlet) m 0.50Effective area per 0.5m m2 0.28

Area over crest (grated crest) m² 4.72Length of opening m 13.00

As it has been mentioned in the previous chapters that the intake proposed is broad crusted weir with the capacity to impound water adequate to augment the minimum flow. The overall design of the intake structure is to enable raw water abstraction during the minimum flow. The estimated stream flow data is as shown in Chapter Four. The minimum flow occurs in November and December. The minimum estimated flow in these months is much higher than the maximum day demand. Thus the weir is designed without the requirement to impound water for the two month maximum day consumption. The intake weir is sized to accommodate maximum flow conditions. Accordingly, the weir structure has to be designed for flow depth of 1 m over the weir crest. In line to the above mentioned conditions the weir dimension is as indicated below.

Weir dimensions

Weir Crest Level masl 2794.3Top width m 1.50Height m 2.80Bottom width m 3.20Foundation height m 1.10Length of Crest m 22.00Opening length m 0.50Maximum Flood Level masl 2794.78Flow width at weir axis m 22Weir length m 22 Upstream ApproachWidth m 13.2Length m 2Downstream ApronWidth m 13.2Length m 3

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Diversion channel: Guides trapped water at the top of the weir to intake pipe line that conveys water to the aerator.

Shape RectangularWidth 0.50 mFloor slope 0.5%

Max Flow in channel= 800 m3/hr = 0.187 m3/s

Velocity,

Flow, Q= VA A= Q/V

Slope, s for preventing settling= 0.50% Roughness coefficient, n= 0.013

Hydraulic radius, R = A/P = WD/(W+2D) W=width of rectangular channelD=Flow depth

Take width of channel, W= 0.50 m Assume, D= 0.70 x W

R= 0.15 m V= 1.00 m/s A= 0.22 m2

Calculated W= 0.56 m Calculated D= 0.39 m

Groove for gratings= 0.15 m Free board= 0.35 m

Total Depth= 0.89 m Upper edge Invert Level= 2,793.41 masl Lower edge Invert Level= 2,793.40 masl

For minimum flow, @ 2015 2030 2040 Q= 0.050 0.143 0.222 m3/s A= 0.05 0.14 0.22 m2

D= 0.10 0.29 0.44 m Minimum water level= 2,793.50 2,793.69 2,793.85 masl

Diversion pipe: Connecting inlet channel at weir with inlet chamber of aerator.

Case 1: As OPEN CHANNEL FLOW Manning Coefficient 0.013 0.018Velocity Range 0.75 -3 m/s

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Case 1: As OPEN CHANNEL FLOW (Continued

FROM TODiversion Pipe Line Flow Diversion Channel Inlet of AeratorGround Level 2,794.30 2,785.95Invert Level 2,793.85 2,791.21Length (M) 527Slope 1 in 200 (0.50%)Peak Flow Rate - Qr (m3/S) 0.2223Computed Pipe Dia. (Mm 467Proposed Pipe Dia. (Mm) 500Proposed Pipeline Details - UltimateFull Bore ConditionQ (m3/S) 0.27V (m/S) 1.36Computed Angle of Flow In Radians 4.12Calculated Proportional Discharge 0.89Proportional Discharge (Qr/Q) 0.83Actual Velocity (m/s) 1.54Velocity Check OKDEPTH OF FLOW (Mm) 367Proportional Depth Of Flow (%) 73Desired Gradient 838HGL 2,791.58 masl

Case 2 As Pressure flow (full flow)

Design Year= 2030 2040 2015  Unit Design Flow= 0.143 0.222 0.050 m3/sMin WL in outlet/ diversion Chamber= 2,793.50 2,793.50 2,793.50 maslPipe Diameter= 0.40 0.40 0.40 mLength= 527.00 527.00 527.00 mSpecific loss= 0.0042 0.0096 0.0006 m/mVelocity= 1.15 1.78 0.40 m/sLoss in pipe= 2.24 5.05 0.31 mOutlet loss= 0.034 0.081 0.004 mBend 90 degree= 4 4 4 NOBend 45 degree= 3 3 3 NOLoss in 90 degrees= 0.108 0.259 0.013 mLoss in 45 degrees= 0.081 0.194 0.010 mInlet loss= 0.067 0.162 0.008 mTotal Loss= 2.53 5.74 0.35 mAlow Free head= 3.77 1.83 5.49 mMaximum WL in Inlet Chamberl= 2,787.21 2,785.93 2,787.66 masl

Diversion pipe is designed as pressure Flow and DN 400mm pipe shall be used

5.3.2 Aerator, Raw Water Gravity Main and Header Tank

Cascade Aerator for removal of Iron and volatile organic constituents is provided nearby the intake. from the aerator the raw water shall be gravitated to Raw Water Header Tank located in the proposed treatment plant compound. Sizing of the aerator the raw water gravity pipe line is done as indicated hereunder. The aerator is designed to serve the maximum demand of year

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2040. It is Shall be located upstream of TP at geographical coordinate of UTM 601800, 779662 & 2786masl

Description Unit Amount

Flow m³/day 19,207MWL masl 2785.93

AeratorSteps 4Step height m 0.5Step Width m 0.8Total steps width m 4.0Length m 6.0Water depth m 0.15Volume m³ 3.6

Sharp crested weir shall be provided at the outlet of the receiving chamber of the Aerator

q= 1.7718 Lh^(3/2)Take length of wier= 4.00 4.00 m Maximum flow, Q= 0.222 0.050 m3/s Head over weir, h= 0.10 0.04 m Weir Top level= 2,785.83 2,785.83 masl Take Free fall head= 0.50 0.50 m Water level on first step= 2,785.43 2,785.37 masl 2nd Weir Top level= 2,785.33 2,785.33 masl Floor Level of first step= 2,785.33 2,785.33 masl WL 2nd step= 2,784.93 2,784.87 masl 3nd Weir Top level= 2,784.83 2,784.83 masl Floor 2nd step= 2,784.83 2,784.83 masl WL 3rd step= 2,784.43 2,784.37 masl 4th Weir Top level= 2,784.33 2,784.33 masl Floor 3rd step= 2,784.33 2,784.33 masl WL 4th step= 2,784.07 2,783.87 masl Flow collection chamberWeir length= 1.00 1.00 m Maximum flow, Q= 0.222 0.050 m3/s Head over weir, h= 0.251 0.092 m 5th Weir Top level= 2,783.82 2,783.82 masl Fre fall head= 0.54 0.34 m WL in Collection chamber= 2,783.53 2,783.53 masl

Flow Diversion Chamber RectangularWidth= 1.60 mLength= 1.50 mDepth= 1.20 mVolume= 11.4 M3

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Retention time @ Year 2015 2020 2025 2030 2035 2040 2045  Flow (m³/day) 4287 6255 9014 12377 15731 19207 27593  m³/min 3.0 4.3 6.3 8.6 10.9 13.3 19.2  Det time (min) 3.8 2.6 1.8 1.3 1.0 0.9 0.6

Raw water gravity MainDesign Year= 2030 2040 2015Design Flow= 0.143 0.222 0.050 m3/sMax WL in outlet Chamber= 2,783.53 2,783.53 2,783.53 maslPipe Diameter= 0.40 0.40 0.40 mLength= 186.00 186.00 186.00 mSpecific loss= 0.0042 0.0096 0.0006 m/mVelocity= 1.15 1.78 0.40 m/sLoss in pipe= 0.79 1.78 0.11 mOutlet loss= 0.034 0.081 0.004 mBend 90 degree= 2.000 2.000 2.000 NOBend 45 degree= - - - NOLoss in 90 degrees= 0.054 0.129 0.006 mLoss in 45 degrees= - - - mLoss in Valve= 0.040 0.097 0.005 mInlet loss= 0.067 0.162 0.008 mTotal Loss= 0.99 2.25 0.13 mAvailable Free head= 9.86 9.10 10.50 mMaximum WL in Header at TP= 2,772.69 2,772.18 2,772.90 maslMaximum Ground Elevation at Treatment Works= 2,772.50 2,772.50 2,772.50 masl

Thus DN 400mm diameter DCI pipe shall be used which serves the year 2040 demand.

Header Tank

Header Tank at Treatment Plant To regulate flow and provide smooth flow to the TP.

  2015 2020 2025 2030 2035 2040 2045Q from Intake TP m³/day 4,287 6,255 9,014 12,377 15,731 19,207 27,593Unit Design Capacity m3/day 4,107 4,107 4,107 4,107 4,107 4,107 4,107No. of Units 2 2 3 4 4 5 7Plant Operating Hr 13 18 18 18 23 22 23Q frm intake m³/hr 330 261 376 516 655 800 1150Q to TP m³/hr 330 347 501 688 684 873 1200

These No. of Units Operate 1 1 2 2 3 4 4For hrs 23 24 24 24 24 24 24and one additional unit operates for 1 13 5 24 20 16 65Raw water tank capacity, m3 86 512 322 -29 289 449 -9594

Assuming TP will operate as per the above schedule the header tank should have 600m3 Capacity to serve the year 2040.

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Q design= 0.222 m3/sDetention time 45.0 minuteVolume= 600.0 m³Shape= CircularMaximum Water Depth= 4.40 mArea= 136.36 m2Diameter= 13.20 mGround Level= 2771.00 maslMaximum Water Level= 2772.18 maslMinimum Water Level= 2768.78 maslFloor slab= 2767.78 maslFree board= 0.60 mReservoir wall height= 5.00 mTop slab sofit level= 2772.78 masl

Connecting line TW.01: From Raw Water Tank to Rapid Mixing UnitDesign Year= 2030 2040 2015  Design Flow= 0.143 0.222 0.050 m3/s Max WL RWT= 2,772.18 2,772.18 2,772.18 masl Min WL RWT= 2,768.78 2,768.78 2,768.78 masl Pipe Diameter= 0.40 0.40 0.40 m Length= 36.00 36.00 36.00 m Specific loss= 0.0042 0.0096 0.0006 m/m Velocity= 1.15 1.78 0.40 m/s Loss in pipe= 0.15 0.34 0.02 m Outlet loss= 0.034 0.081 0.004 m Bend 90 degree= 4.000 4.000 4.000 NO Bend 45 degree= 1.000 1.000 1.000 NO Loss in 90 degrees= 0.108 0.259 0.013 m Loss in 45 degrees= 0.017 0.040 0.002 m Loss in Valve= 0.020 0.049 0.002 m Inlet loss= 0.067 0.162 0.008 m Total Loss= 0.40 0.94 0.05 mFree head= 1.00 0.59 1.45 mMaximum WL in Reciving chamber at Rapid Mixer= 2,767.38 2,767.26 2,767.28 maslMaximum Ground Elevation at Rapid mixer= 2,768.50 2,768.50 2,768.50 masl

Thus, DN 400 Pipe shall be used until Year 2040

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6. RAW WATER MAIN

6.1 Route Alignment

The raw water gravity main is divided in to two parts the first part having a length of 527m conveys the raw water from intake sump to aerator and the second part conveys raw water from aerator to raw water header tank 186 m long. The raw water pipe is 400mm DCI pipe; it is designed to convey the year 2040 demand. When conveying the maximum demand of year 2030 the velocity will be 1.15m/s while the velocity in year 2040 it increases to 1.78m/s.

The Route of the Raw Water Main is shown in Figures 6.1.

6.2 Selected Pipe Material

Protected lined Ductile Cast Iron (DCI) pipes, DN 400mm proposed for the raw water gravity main.

The external protection against corrosion for Ductile Cast Iron pipes shall be zinc and bitumen coating as per BS 4772/ISO 8179/EN545 and BS 3416/ISO 2531/EN545 Standards, respectively.

Jointing will be decided based on the approved make proposed by the Supplier.

6.3 Hydraulic Design

The normal raw water outlet level at the Intake is taken as 2281.73 m and the top water level at the inlet of Raw Water Header Tank at Treatment Works is 2276 m.

An economic analysis was carried out and the pipeline size adopted is 400 mm. The friction losses are based on Hazen Williams formula using roughness coefficient of 120 for a flow of 0.222 m³/s (17,950 m³/day), year 2040 demand. The inflow to the treatment plant is regulated using electromagnetic water meter and regulating gate valve. Thus, the electromagnetic water meter and regulating gate valve shall be installed at the entrance of the raw water chamber of the treatment plants. The detailed hydraulic calculations are presented in Appendix '1'.

6.4 Installation of Pipes

Pipes are to be joined and embedded in trenches. The pipe trench will be backfilled mostly by the excavated material. The minimum depth of cover is taken as 1.0 m above the crown of the pipe. The trench excavation for the raw water rising main varies between 1.40 to 2.00 m. Where rock is encountered, pipes will be laid on granular bed material borrowed from approved pits to minimize damage to the pipe coating and improve on drainage underneath the pipe. Where pipes are exposed at river, stream and other aerial crossings, the pipes shall be provided with additional approved protective coating.

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Provision has been made to have thrust blocks at horizontal and vertical bends to counter thrust forces of flowing water at such places. For pipes laid at steep gradients, adequate traverse supports have been provided to hold pipe in place as per details on drawings.

Where the pipe line crosses deep drainage gullies, rivers and streams, provision is made to construct appropriate crossing structures.

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  Section Length

Invert Level HGL 1

Flow, Q Dia Velovity HWC HL unit head loss m/10³

Pressure     RemarkCHAINAGE m3/day m3/s L3/s ND m/s   m m PN Material  

- - 2797.78 2797.78 19,181 0.222 222 400 1.78 120 0 0.0081 0.0 PN 10 DCILola

Intake221 221 2786.17 2795.99 19,181 0.222 222 400 1.78 120 1.79 0.0081 9.8 PN 10 DCI  523 303 2781.56 2793.53 19,181 0.222 222 400 1.78 120 2.46 0.0081 12.0 PN 10 DCI Aerator722 199 2762.59 2791.91 19,181 0.222 222 400 1.78 120 1.62 0.0081 29.3 PN 10 DCI RWT

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Figure 6.1

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7. NEW WATER TREATMENT WORKS

7.1 GENERAL

The New Water Treatment Works, capacity 12,377.0 m3/day, has been sited nearby the intake. The land for these Works shall be acquired by RWSSE.

The New Water Treatment Works, capacity 12,377 m3/day will cater for the maximum day water demand of Robe Township up to the Year 2030.

7.2 TREATMENT SYSTEM

Raw water quality analysis has been conducted (Appendix 6 Refers) as it is river water it is necessary, that to obtain potable water quality, full treatment of raw water is necessary. .

The treatment process adopted for final design is as follows: -

Aeration for removal of iron, and manganese Chemical dosing of raw water to assist in floc formation and trapping of suspended

impurities. Flocculation and clarification in upflow clarifier units Filtration using Rapid Gravity Sand Filters Disinfection by chlorination and pH correction of Treated Water

The Layout Plan and Typical Section of the Treatment Units is shown in Figures 7.1 &7.2

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Figure 7.1

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Figure 7.2

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DESIGN CRITERIA

a) General

Plant Design Capacity : 11,568 m3/d

Treated Water used forBackwashing of Filters and domestic use at site(approximately 7%) : 810 m3/d

Net treated water availablefor distribution : 12,377 m3/d

b) Aeration and Stilling Well

Retention Time : 1.0 to 2.0 minutes

Nr : 1

c) Plain SedimentationDetention time 0.5 to 3 hrsLength / Width Ratio (L/W) 4 to 6 to 1Water depth 1.5 to 2.5 mLength to depth ratio (L/D) 5 to 20 to 1Velocity 0.3 to 0.45 m/minSurface loading 20 80 m³/m²/day

d) Coagulation - Sedimentation

d-1 Rapid Mixing / Flow MeasurementType HydraulicPoint of Application Downstream of FlowFlow Measurement Parshall Flume Equation Q = 2.27 W ha2/3

W is width 0.46ha Water depth

Chemicals

(i) Aluminium Sulphate

(ii) Soda Ash

a) Rapid Mixing / Flow Measurement

Type : Parshall flume/ Hydraulic

Point of Application : in the Parshall Flume at a point where the jump had occurred Measurement Weir

Mixing Head : 0.5 metres

b) Flocculation coagulation and sedimentation

Type : Upflow Sludge Blanket Clarifier

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Maximum Velocity at Inlet : 0.6 m/s

Maximum Velocity at Outlet : 0.2 m/s

Detention Time : 15 - 30 minutes

Velocity Gradient : 20 - 100 s-1

GT Value : 10,000 - 100,000

c) Filtration

Type : Conventional - Rapid Gravity Sand Filters

Rate of Filtration : 5 m3/m2/hr

Rate of Backwash Water(with water alone) : 50 m3/m2/hr

Backwash Time : 10 minutes

Rate of Filtration Control : Manually controlled valve

d) Disinfection and pH Correct

Disinfection by either Hypochlorite Powder

Form : Fine Granular Material

Storage : 30 days

Dosing Method : Gravity Solution Feeders

Dosing Rate : 2.0 to 5.0 mg/l

or Chlorine Gas

pH Correction by Soda Ash

e) Clear Water (Retention) Tank

Retention Time : 30 minutes

f) Chemical Storage

(i) Aluminium Sulphate Al2(SO4)3, 18H20Form : LumpsStorage : 30 daysDosing Method : Gravity Solution FeedersDosing Rate : Average 40 mg/l

(ii) Soda AshForm : PowderStorage : 30 daysDosing Method : Gravity Solution FeedersDosing Rate : Average 40 mg/l

1 month (30 days) storage for all chemicals used on Site.

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g) Mechanical Equipment

(i) Air Scour for New FiltersNumber : 2 (1 duty, 1 standby)Capacity : Allowing the availability of 1.5 m3 of free air/min/m2 of Filter Bed

(ii) Standby GeneratorNumber : 1Capacity :

(iii) Pumps(All Pumps Positive Suction Centrifugal Pumps)

a) Backwash PumpsNumber : 2 (1 duty, 1 standby)Flow Rate : 300 m3/hr (50 minutes pumping)Dynamic Head : 26 mElectric Motor : 22 kW

b) Re-circulation PumpsNumber : 2 (1 duty, 1 standby)Flow Rate : 167 m3/hr (12 hr pumping)Dynamic Head : 9.0 mElectric Motor : 4 kW

(iv) Instrumentation Equipment forFlow Measurement, etc.a) Incoming Raw Waterb) Treated Water from New Treatment Worksc) Pumped Supply to elevated Tankd) Re-circulated Backwash Watere) Alarm System for overflow from Stilling Well, Filters etc.

V-Notch or triangular:Q = 13265 tan(θ/2)h2.47

Where Q = flow (m3 s-1)θ= notch angle or angle of triangular weirh = head (m)

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7.3 TREATMENT WORKS UNITS

7.5.1. Aeration Unit

Cascade Aeration Unit is provided as part of the treatment plant unit trains. The aeration unit has inlet and outlet part. The outlet part serves as a stilling well from which the aerated raw water conveyed to the raw water header tank via 400mm DCI pipe. An electromagnetic water meter shall be installed at the outlet of the raw water gravity main to the raw water header tank inlet. The stilling well is also provided with an overflow weir and scour arrangement. For detail Chapter five refers.From the aerator unit, the raw water flows by gravity into the raw water header tank from which it flows to the rapid mix in this case to the Parshall Flume, which is used as a hydraulic mixer, and flow-measuring unit in case of the failure of the water meter. The inlet channel and the cascade of the Aerator are designed to:

1. Facilitate the measurement of the incoming raw water, hence the requirement of tranquil flow in the inlet channel. Measurement of incoming raw water is done using bulk raw water meter. In addition, a calibrated steel measuring scale is provided fixed to the Channel just upstream of the weir. Incase of failure of the measuring equipment, this scale can be used to take head measurement reading, which can then be read against the corresponding discharge on the discharge versus head chart calibrated for the full width weir.

2. Allow maximum air water contact for oxidation of iron and volatile organic compound (VOC) for dosing of the raw water and the rapid mixing of the raw water with Chemical Solutions. This is done by creating turbulence downstream of the weir which occurs due to the fall of the raw water as it flows over the cascade steps. In addition to the cascade steps, round river gravel lairs in the floor of the cascade to enhance maximum air water contact.

The aerated raw water then flows to the Parshall Flume where rapid mixing takes place.

Details are shown in Figure 7.3.

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Figure 7.3

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7.5.2. Chemical Mixing and Dosing Building

It is proposed that the chemical storage and mixing building be constructed next to the inlet channel (Rapid mix). It allows for centralised dosing of chemicals to assist flocculation and sedimentation. This building will store chemicals for daily use, the main storage for chemicals shall be provided at main store. The proposed storage shall allow 3 months storage capacity for Alum, Soda Ash and polyelectrolyte. The chemical storage and mixing building is designed to allow for dosing by Alum, Soda Ash and chlorine solution.

a) Alum Mixing Tanks:

Three mixing tanks are provided, each with a capacity to hold enough solution for 8 hours of dosing. This allows adequate time for another mixing tank to be prepared for the next shift of dosing while one is in operation. It also ensures that the mixing tank is not used for extended periods of time, thereby preventing excessive settling of the chemicals in the solution and accumulation of sludge solution in the tank. Having more than two tanks ensures continuity in production of the plant in the event of failure of a tank's mixing equipment or closure of a tank for maintenance. Providing 4 tanks (one for soda ash) allows for repairs to be carried out without a disruption in the performance of the treatment works.

Design Calculations: unitAssumed solution strength, St % 5Assumed Dosage Quantity, d mg/l 40Design Year 2040Gross Water Demand , Q m3/day 19,207   m3/hr 800  m3/s 0.222

l/s 222Storage:

Weight of required Alum = Qd Kg/d 768

Period of storage required months 3

Hence storage required tones 69.1

Dimensions of one 50 Kg bag of alum m 0.70x0.35X0.175Volume of one 50 Kg bag m3 0.043

Hence storage requirement for each tone = m3/ton 0.86

Storage space required for Alum m3 59

Mixing Tanks:

Quantity of Alum solution required = QdSt l/s 0.17784

Daily Solution requirement m3/d 15.4

Dead storage allowance % 10

No. of Tanks to be provided 3

  m3 5.63, say 5.1

Depth of each tank m 1.65

Hence for each tank, m 1.758, say 1.8m 1.758, say 1.8

Wall thickness m 0.2Total Length of Alum mixing units m 6.2

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b) Soda Ash Mixing Tanks:

Two mixing tanks are proposed, each with a capacity to hold enough solution for 12 hours of dosing. This allows for better operation in that a tank for alum and a tank for soda ash can be prepared together and then used for a 12 hour shift, hence keeping a uniform cycle of mixing tank preparation and use for both alum and soda ash. A 12 hour cycle also ensures adequate time for another mixing tank to be prepared for the next shift of dosing while one is in operation. It also ensures that the mixing tank is not used for extended periods, hence preventing excessive settling of the chemicals in the solution and accumulation of sludge in the tank. Having more than two tanks also ensures continuity in production of the plant in the event of failure of a tank's mixing equipment or closure of a tank for maintenance. Providing 2 tanks allows for repairs to be carried out without a disruption in the performance of the treatment works

Design Calculations: Unit amount

Assumed solution strength, St % 5

Assumed Dosage Quantity, d mg/l 15

Gross Water Demand for supply area (2039), Q m3/day 19,207

  m3/hr 800

  m3/s 0.222

l/s 222

Storage:

Weight of required Soda Ash = Qd Kg/d 288

Period of storage required months 3

Hence storage required tones 25.9

Assuming the volume of one 50 Kg bag m3 0.043

Hence storage requirement for each tone m3/ton 0.86

Storage space required for Soda Ash   m3 22

      Mixing Tanks:

Quantity of Soda Ash solution required = QdSt l/s 0.06669

Daily Solution requirement m3 5.8

Dead storage allowance % 10

No. of Tanks to be provided 2

Volume of each tank m3 3.17, say 4.2

Depth of each tank = m 1.61, say 1.6

Hence for each tank, L = m 1.61, take 1.8

W = m 1.61, take 1.8Total Length of Soda Ash mixing units m 4.20 

Provide a mixing building as follows:

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Design Calculations: Unit amount

Plan Dimensions:Total Length, L = m 10.6Total Width, W = m  6.9

HEIGHT OF PROPOSED CHEMICAL BUILDING:

Height chemical store m 3.0

Taking elevation of floor slab of mixing channel (above floor level) m 3.2 

Height of mixing chamber= m 2.05Base slab of chamber= m 0.2Taking depth for dosing seat above chemical store roof slab m 0.8 Depth of mixing tanks (for dead storage) & freeboard) m 1.65+0.40    m 2.050 Free space between tank to ceiling m 1.35 Hence ceiling height of mixing building m 4.40 Height of new Chemical mixing and dosing building (high above floor level) m 7.60

For dosing purposes, provisions have been made to allow for flexibility in the system, i.e. dosing can be done in the conventional manner, using alum and soda ash as well as by the use of polyelectrolyte. This has been done so as to ensure that in the event of failure to obtain polyelectrolyte (which are not manufactured locally); dosing may be carried out in the more conventional manner using chemicals which are locally available without interrupting the production at the Treatment Works.

Dosing of Alum and Soda Ash is carried out just upstream of the point where hydraulic jump starts in the Parshall Flume. This point is clearly indicated in the drawing of the Parshall Flume. The turbulence created by the hydraulic jump helps in the mixing of the chemical solutions with the raw water. Alum and Soda Ash are obtained in solid form. These chemicals are then put into mixing tanks where they are dissolved in water to form a solution of the required strength to treat the incoming raw water.

The rapid mix has been designed for estimated flow of year 2040. Thus, it is provided with flow splitting chamber with two outlet pipes one outlet meant for future use, i.e. the treatment plant proposed to be built for year 2040 demand.

There are three mixing tanks measuring 1600mm (L) x 1600mm (B) x 1650mm (D) for Alum and two mixing tanks measuring 1600mm (L) x 1600mm (B) x 1600mm (D) for Soda Ash. The chemicals are manually loaded into the tanks and mixing is carried out by electrically driven mixers. These mixers are provided with manual overrides. Gravity dosing is provided for regulating flow of mixed chemicals to the dosing point at the Inlet Channel. Alum and Soda Ash solutions of the required strength are conveyed to the dosing point by

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pipes laid in a concrete duct from the chemical mixing tanks which are housed in the chemical mixing room.

For dosing with polyelectrolyte, a unit with an injector pump is provided. This unit analyses the incoming raw water, automatically assesses the quality of the raw water and then injects the appropriate amount of chemicals directly into the raw water mains by means of an injector pump. The injected water then flows into the Stilling Well, then to the Inlet Channel and over the Weir where the fall of the water induces rapid efficient mixing of the raw water and the polyelectrolyte solution. The mixing is further enhanced by the motion of the water round the baffle walls.

Chlorine unit amount

Assumed solution strength, St = % 5

Assumed Dosage Quantity, d = mg/l 5Gross Water Demand , Q = m3/day 19,207

  m3/hr 800

  m3/s 0.222

l/s 222

Storage:Recommended Breakpoint chlorination = ppm 5

mg/l 5.0

Kg/m3 0.005

Average dosing rate required = Kg/day 96.0

Period of storage required = months 3

Hence storage required = tones 8.64

Assuming storage volume required per ton = m3/ton 0.86Storage space required for Chlorine = m3 7.43

Storage for Alum m3 59

Storage for Soda Ash m3 22

Storage for Chlorine m3 7.43

Total m3 89

Available space Length= m 10.60

Width= m 6.90

Height= m 1.50

m3 110

The details of this Building are shown in Tender drawings.

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7.5.3. Rapid Mix

The raw water from the intake will be gravitated to the aerator, from the aerator it will flow to the Parshall Flume, which is used as rapid mixer. Chemicals will be applied just upstream of the jump at the end of section B, Figure 7.4 Refers. The hydraulic rapid mixing process will be done in the part of the Parshall Flume where hydraulic jump has occurred. After the rapid mix the water will flow to the treatment plant. Thus, maximum day flow of 12,377 m3/day will be conveyed to the Upflow Sludge Blanket Clarifiers. For hydraulic jump to occur the Parshall Flume needs to be sized based on the following table.

Throat Width Free flow capacity (m3/day)

W A B C D E F G Min Max(mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm) (m3/day) (m3/day)

150 620 600 390 400 600 300 600 122 9,550300 1,370 1,340 600 850 900 600 900 274 39,500460 1,450 1,420 750 1,030 900 600 900 367 60,200610 1,530 1,500 900 1,210 900 600 900 1,030 81,100910 1,680 1,650 1,200 1,570 900 600 900 1,500 123,000

1,220 1,830 1790 1,520 1,940 900 600 910 3,190 166,0001,520 1,860 1,940 1,830 2,150 900 600 910 3,920 210,000

                   

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Year Flow m3/day Flow m3/s Width Depth (ha) m Depth (hb) m Critical depth (Yc) m

  Max Avg Max Avg m Max Avg Max Avg Max Avg

2015 4,287 3,897 0.050 0.045 0.3 0.175 0.164 0.122 0.115 0.141 0.1322020 6,255 5,686 0.072 0.066 0.3 0.225 0.211 0.157 0.148 0.181 0.1702025 9,014 8,194 0.104 0.095 0.3 0.287 0.269 0.201 0.188 0.231 0.2172030 12,377 11,252 0.143 0.130 0.3 0.354 0.333 0.248 0.233 0.285 0.2682035 15,731 14,301 0.182 0.166 0.3 0.416 0.390 0.291 0.273 0.335 0.3142040 19,207 17,461 0.222 0.202 0.3 0.475 0.446 0.332 0.312 0.383 0.3592045 27,593 25,084 0.319 0.290 0.3 0.605 0.567 0.423 0.397 0.487 0.457

Figure 7.4: Parshall Flume Plan & Section

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W A A1 C C1 F G K N300 1,370 1,340 600 850 600 900 80 150

Level @ Throat = 2766.78 maslMaximum WL after flume= 2767.11 maslMin WL after flume= 2766.90 masl

Inlet Chamber

Width 2.20 mLength 1.30 mDepth 1 2.23 mDepth 2 1.00 m

FLOW Collecting and splitting chambers

Collection Chamber

The coagulant injected water will be combined in a chamber located downstream of the Parshall Flume.

Design Year 2030 2040 2015 Unit Flow 12377 19207 4287 m³/dayDetention time 0.5 0.5 0.5 minVolume 4.6 7.2 1.6 m³Selected size 7.2 7.2 7.2 m³

Width 2.00 2.00 2.00 mLength 2.20 2.20 2.20 mDepth 1.71 1.71 1.71 m

Splitting Chambers

The ultimate design flow shall be divided in to three independent lines before it is conveyed to the respective clarifiers.

Design Year 2030 2040 2015

Flow 12377 19207 4287 m³/dayFlow per line 4126 4126 4126 m³/dayNumber of lines 3 5 2

Flow per line when one is not working 6,189 4,802 4,287 m³/dayDesign Flow per line 6,189 6,189 6,189 m³/dayFlow Splitting Weir Rectangular weirq=1.7718* Lh^(3/2)Take length of weir= 0.70 0.70 0.70 m Flow, Q= 0.072 0.072 0.048 m3/s Head over weir, h= 0.149 0.149 0.114 m Weir Top level= 2,766.96 2,766.96 2,766.78 masl Fix weir level @= 2,766.78 2,766.78 2,766.78 masl Water level in Splitting chambers= 2,766.88 2,766.88 2,766.88 masl Actual flow, Qact= 0.048 0.074 0.025 m3/s Head over weir, Hact= 0.114 0.153 0.074 m Water level before weir= 2,767.03 2,767.20 2,766.90 masl Available Free fall head= 0.15 0.32 0.02 m

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7.5.4. Flocculation

Basically flocculation shall be carried in the Upflow Sludge Blanket Clarifiers at large. It is worth mentioning that, flocculation process will start in the channels and pipes conveying the coagulant dosed water from the hydraulic rapid mixer to the clarifiers and in the bottom section of the clarifiers.

In line to this the piping system and appurtenance work have been designed to fit the flocculation requirement.

Thus the Main Design Parameters are:

1. Detention time - 15 to 30 min provided to ensure adequate period for flocc formation and growth; this time includes the detention time spent in the lower 0.5 to 1 m of the clarifier bottom

2. Flow velocities - Ranging from 0.8m/s at the entry (when living the mixer) to 0.5m/s at about 1 m above the bottom of the clarifier, this is for prevention of breakage of floccs

3. Velocity Gradient - Tapering velocity gradient (G) from 100/s to 10/s to encourage efficient formation of flocs.

At least two separate lines of clarifiers are to be provided so that one may be shut down for routine maintenance and cleaning without considerably affecting the quantity of production at the treatment works. Accordingly two separate lines are provided to convey chemical dosed and mixed water to the clarifiers. Thus the channels and pipes system that conveys the chemical dosed water to the clarifiers has been designed as indicated hereunder.

Description Unit Quantity Design year 2030Design Capacity of the Plant m3/day 12,3771No. Channels No. 1Design Flow, Q m3/day 12,377

m3/hr 516m3/s 0.143

Gravitational Force, g m/s2 9.81Density of water Kg/m3 998.2Manning Coefficient (n) 0.013Dynamic viscosity, kg/m.s 0.00101Detention time, t minutes 3 - 6Maximum Entry Velocity m/s 0.8Maximum Exit Velocity m/s 0.5Velocity Gradient, G s-1 10 - 100

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Design Calculations and Checks: Chamber length m 1.00Depth of Flow, H m 1.30Velocity m/s 0.65Width m 1.00Area m² 1.30Volume of chamber m³ 1.30Flow Per Chamber m³/s 0.072Detention time, t min 0.3Wetted Perimeter m 3.60Hydraulic Radius (R=A/P) m 0.36Maximum free fall m 0.15Velocity v= (1/n*(R0.66667*S1/2), Q/Ac m/s 0.06Desired G at 1st Section = /s 70Number of bends or baffles 1Head loss, h = v1

2/2g , free fall m 0.148Power, P = Qpgh W 104.0Applied G at Channel =(P/u V)0.5 /s 281

Pipe from splitting chamber to Tee for second phase SBC.01 SBC.02 SBC.03Flow to in pipe segment 6402 6402 6402Max Flow in segment 0.0741 0.0741 0.0741Pipe Diameter 0.35 0.35 0.35specific loss 0.00240 0.00240 0.00240Pipe Length 6.0 5.0 6.0Velocity in Pipe 0.78 0.78 0.78 Loss in pipe=- m 0.02 0.02 0.02Power, P = Qpgh W 16.2 15.5 16.2Volume m³ 0.6 0.5 0.6Applied G =(P/u V)0.5 /s 167 178 167 

Pipe from splitting chamber to inlet pipe SBC.01 SBC.02 SBC.03Flow to a Clarifier 4126 4126 4126Max Flow to a Clarifier m³/s 0.0478 0.0478 0.0478Pipe Diameter m 0.35 0.35 0.35specific loss m/m 0.00107 0.00107 0.00107Pipe Length m 23.0 31 34Velocity in Pipe m/s 0.50 0.50 0.50 Total Loss= 0.040 0.048 0.052Power, P = Qpgh W 18.6 22.6 24.1Volume m³ 2.2 3.0 3.3Applied G =(P/u V)0.5 /s 91 87 85

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Design Calculations and Checks continued Distribution pipe to Clarifiers

Flow per clarifiers m³/s 0.0478 0.0478 0.0478Pipe diameter m 0.40 0.40 0.40specific loss m/m 0.00056 0.00056 0.00056Pipe Length m 7.50 7.50 7.50Velocity in Pipe m/s 0.38 0.38 0.38Head loss m 0.016 0.016 0.016Power, P = Qpgh W 7.4 7.4 7.4Volume m³ 0.9 0.9 0.9Applied G =(P/u V)0.5 /s 88 88 88Detention time s 19.7 19.7 19.7

In Clarifier @ Depth m 4.84 4.84 4.84Width m 7.92 7.92 7.92Area m² 62.7 62.7 62.7Velocity m/s 0.0008 0.0008 0.0008

m/hr 2.74 2.74 2.74Volume m³ 154.40 154.40 154.40Q m³/s 0.048 0.048 0.048Specific Gravity of flocs (Ss) m³ 1.05 1.05 1.05Porosity of blanket () 0.9999998 0.9999998 0.9999998Depth of blanket (h) m 1.80 1.80 1.80G =(g/u (Ss-1)(1-)h(V/Q))0.5 /s 24 24 24Detention time s 3233 3233 3233Gt 76757 76757 76757

Provide:

Diameter 350 mm main pipe m 6.0 5.0 6.0Diameter 300 mm main pipe 23.0 31.0 34.0Diameter 400 mm inlet pipe m 7.50 7.50 7.50

Total loss m 0.056 0.064 0.067Take free head of m 0.660 0.660 0.660Maximum Water level in USB masl 2,766.16 2,766.16 2,766.15

Connecting line TW.02 Rapid Mixing Unit to Upflow Sludge Blanket ClarifiersLine Name TW.02-1 TW.02-2 TW.02-3

Design Year= 2030 2030 2030Design Flow= 0.048 0.048 0.048 m3/s

Max WL in Collection Chamber= 2,766.88 2,766.88 2,766.88 masl

Segment 1Pipe Diameter= 0.35 0.35 0.35 m

Length= 6.00 5.00 6.00 mSpecific loss= 0.0011 0.0011 0.0011 m/m

Velocity= 0.50 0.50 0.50 m/sLoss in pipe= 0.01 0.01 0.01 m

Outlet loss= 0.006 0.006 0.006 mTee= 1 1 1 NO

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Design Calculations and Checks continued

Connecting line TW.02 Rapid Mixing Unit to Upflow Sludge Blanket ClarifiersBend 45 degree= - - - NO

Loss in Tee= 0.006 0.006 0.006 mLoss in 45 degrees= - - - m

Loss in Valve= 0.004 0.004 0.004 mInlet loss= - - - m

Loss in Segment 1= 0.02 0.02 0.02 m  Thus, DN 350 Pipe shall be used

Segment 2Pipe Diameter= 0.35 0.35 0.35 m

Length= 23.00 31.00 34.00 mSpecific loss= 0.0011 0.0011 0.0011 m/m

Velocity= 0.50 0.50 0.50 m/sLoss in pipe= 0.02 0.03 0.04 m

Reducer= 0.006 0.006 0.006 mBend 90 degree= 1.000 1.000 1.000 NOBend 45 degree= - - - NO

Loss in 90 degrees= 0.005 0.005 0.005 mLoss in 45 degrees= - - - m

Loss in Valve= 0.004 0.004 0.004 mInlet loss= - - - m

Loss in Segment 1= 0.04 0.05 0.05 m  Thus, DN 350 Pipe shall be used 

Segment 3Pipe Diameter= 0.40 0.40 0.40 m

Length= 7.50 7.50 7.50 mSpecific loss= 0.0006 0.0006 0.0006 m/m

Velocity= 0.38 0.38 0.38 m/sLoss in pipe= 0.00 0.00 0.00 m

Outlet loss= - - - mBend 90 degree= - - - NOBend 45 degree= 1.000 1.000 1.000 NO

Loss in 90 degrees= - - - mLoss in 45 degrees= 0.002 0.002 0.002 m

Loss in Valve= 0.002 0.002 0.002 mInlet loss= 0.007 0.007 0.007 m

Loss in Segment 2= 0.016 0.016 0.016 m  Thus, DN 400 Pipe shall be used

Total Loss= 0.08 0.09 0.09 mFree head= 0.65 0.64 0.64 m

Maximum WL in UFSB= 2,766.15 2,766.15 2,766.15 maslMean Ground Elevation

UFSB= 2,764.50 2,764.5 2,764.50 masl

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The chemical dosed raw water will be conveyed to the clarifiers via two channels. From the two channels the water will be conveyed by two ND 400mm DCI pipe which are connected to the outlet of the two channels furthermore, from these main pipes the water will be distributed by ND 350mm DCI pipes to the two group clarifiers.

Upflow Sludge Blanket Clarifiers (USB)

Upflow Sludge Blanket Clarifiers (USB) has been adapted for the new treatment plant. Sludge blanket clarifiers incorporate both flocculation and sedimentation in one unit. Chemically dosed water enters a central delay/distribution chamber where mixing and initial floc formation occurs. Flow is then distributed across the bottom of the clarifier through distribution arms. Launders collect clarified water at the top of the clarifier.

1. Inlet to each Clarifier will be via Ductile Cast Iron pipe and will be controlled by valve. This will also allow for isolating each of the Clarifiers for maintenance purposes.

2. A space will be left above the sludge blanket layer for future installation of tube settlers

3. Sludge draw-off hooper will be provided to periodically draw sludge by gravity.4. Access to each of the basins will be provided by side walkways with hand railing.5. Decanting into a channel will be over a series of V-notches which can be adjusted to

ensure uniform flow over the width of the basin.

Main Design Parameters:

1. Detention time - 1 hour of detention time has been provided to ensure adequate period for settling

2. Up flow rate - 60 m³/day-m²

3. Up flow Velocities - 2 m/hr

4. Maximum width/length of Clarifier -

10 m

5. Min width at bottom 1 m by 1 m6. Slope of hooper- 1.4:17 Space for tube settlers 1m

Table 7.5 Design Data for Upflow Sludge Blanket ClarifierDescription Unit Quantity Design year 2030

Design Flow, Q  

m3/day 12,377m3/hr 12,377m3/s 516

Gravitational Force, g m/s2 0.143Density of water Kg/m3 1000Upflow rate, vs m/hr 1.67 – 2.79Detention time, t hr 1 - 2Maximum Entry Velocity m/s 0.3 - 0.6Maximum Exit Velocity m/s 0.4Max Weir loading rate m³/hr-m 7.08Additional Volume for sludge accumulation

% of volume available for settling 20

slope range (V:H) % 120 -200Length to Width ratio = L/W 1:1

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Table 7.6 Design Calculations and Checks:Description Unit Quantity Remark Up flow rate (vs) m/hr 2.30Total Surface Area req'd = Q/vs m2 224.2

 No. of Sedimentation Clarifiers to be provided No. 3 1 rows

Hence area required per Sedimentation Clarifier  m2 74.7Taking:      

Width, W m 8.7Length, L m 8.7

L/W 1 ok

Detention time, t hrs 1

Required Volume of Clarifier m3 172

Taking: Square hooper bottom m 1Hooper slope V:H 1.4

Depth to sludge blanket top level m 5.32

Maximum sludge blanket depth m 2.5

Concentrated sludge depth @ hooper bottom m 1

Blanket level  Stable blankets starts @ Settling Velocity m/hr 6.0Area (Q/vs) m² 28.7Side width m 5.35

Height from bottom m 3.05

Min settling velocity flocs m/hr 2.74Area (Q/vs) m² 62.7Side width m 7.92Height from bottom m 4.84

 Depth of blanket (0.9 to 2.7) m 1.80

Side sludge concentrator cone top level m 4.8

Height of cone m 1.2

base of cone m 0.6

Space for future installation of tube m 0.9

Supporting beam depth m 0.35

Collector trough m 0.25

Free board m 0.30

Water depth above sludge blanket m 1.50

Total water depth m 6.82

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Table 7.6 Design Calculations and Checks continued:

Volume of top blanket m3 199.4

Volume above m3 112.2

Total volume of clarifier  m3 311.6

New Detention Time hr 1.81 Ok!New Overflow Rate m/hr 2.30 Ok!Inlet pipesFlow per-line m³/s 0.050

Providing steel pipe with diameter m 0.40

Velocity m/s 0.39

Flow rate per-clarifier m³/s 0.048

Provide inlet steel pipe with diameter m 0.40

Velocity m/s 0.38

Outlet pipesWeir loading rate m³/m-hr 7.00

Required length of weir per clarifier m 24.6

Providing two troughs per clarifier, available weir length m 34.4

New Weir loading rate m³/m-hr 5.0

  m³/m-day 120 Ok!Trough spacing m c/c 4.3

q= for V-notch of 60 degree 1.45*h^(2.47) maximum flow, Q m3/s 0.001Head over weir, h m 0.06Weir Top level masl 2,766.10Take Free fall head at weir m 0.11Water level in collecting trough masl 2,766.05TroughsMaximum flow per trough m³/s 0.024

Velocity, = Flow, Q= V*AArea = Q/VSlope, s for preventing settling = 0.10%Roughness coefficient, n= 0.013Hydraulic radius, R = A/P = WD/(W+2D), W=width of rectangular channel, D=Flow depthTake width of trough, W m 0.25 Assume, D= W 0.75 R= m 0.08 V= m/s 0.43 A= m2 0.06 Calculated W= m 0.27 Calculated D= m 0.20 Total Length o channel= m 8.00 Wall height= m 0.36 Wall thickness= m 0.20 Head loss in channel s= m 0.008

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Table 7.6 Design Calculations and Checks continued:

WL at outlet in the trough= masl 2,766.05 Floor level of trough masl 2,765.84Weir at outlet to collecting channelWeir typeq= 1.77177877* Lh^(3/2)Take length of weir= m 0.27maximum flow, Q= m³/s 0.024Head over weir, h= m 0.135Weir Top level= masl 2,765.91Take Free fall head at weir= m 0.29Water level in collecting channel= masl 2,765.76

Connecting line TW.03 Connects UFSBclarifier with Filter inletSegment 1 Segment 2 Segment 3

Design Flow= 0.048 0.096 0.048max Start HGL= 2,765.76 2,765.65 2,765.43min Start HGL= 2,765.76 2,765.65 2,765.43Pipe Diameter= 0.25 0.35 0.25Length= 10.00 16.00 10.00Specific loss= 0.0055 0.0038 0.0055Velocity= 0.98 1.00 0.98Loss in pipe= 0.05 0.06 0.05Outlet loss= 0.025 - -Bend 90 degree= 1.000 1.000 2.000Bend 45 degree= - - -Loss in 90 degrees= 0.020 0.020 0.039Loss in 45 degrees= - - -Loss in Valve= 0.015 0.061 0.015Inlet loss= - - 0.049Tee T/T= 0.077 0.025Total Loss= 0.11 0.22 0.18Head at Seg end= 2,765.65 2,765.43 2,765.24Start ground level= 2,763.50 2,765.50 2,765.50End ground level= 2,765.50 2,765.50 2,765.50

Take Free head of = 1.71Maximum Water level in the filter = 2,763.53

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Provide:No. of Clarifiers 3

Length of each Clarifier m 8.70

Width of each Clarifier m 8.60

Max Clarifier Height m 7.12

Height to Rim of hooper m 5.32

Hieght above rim m 1.80

Wall Thickness m 0.25

Base width m 1.00

Inclined Length m 6.54

Space b/n Clarifiers m 0

Space b/n Rows m 3

Total Length of all Clarifiers, L m 26.9

Total Width of Clarifiers, W m 9.1

Maximum Water Level masl 2766.16

Maximum depth m 6.84

Clarifier floor level masl 2759.32

Ground Level masl 2761.58

Check: Effect when one basin is out of service:Operation at 100% of Capacity, Q m³/hr 258

New Surface Area of Flow, vn = (n-1)LW = m2 74.8

Detention Time = (n-1)LWH/Q = hrs 1.2 ok! Operation at of Capacity 75%

Qtot - Flow in the plant m³/hr 387

Number unit operating 2

Flow per line m³/hr 193

Volume of unit m³ 312

New Detention Time = hrs 1.6 ok! Overflow Rate provided m/hr 2.58 ok!

Details shown in Tender drawings.

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7.5.5. Filters, Filter Gallery and Control Room

general 1. Entry to each filter will be controlled by a penstock to isolate/regulate flow.2. Flow into filters to be in such a way as to utilise the whole surface area for uniform filtration.3. Discharge from each filter into a common water channel.4. Level in clear water channel to such so as to ensure minimum of 100mm of water over filter

bed retained before back wash commences.5. Backwashing of filters to be by combination of air and water to economise on use of treated

water. Details provided under backwashing of filters.6. Backwash water to be discharged into a pond for reuse for treatment.7. Pipework arrangement to provide for complete drainage of water from a filter during

maintenance/repair works8. A filter gallery overlooking all filters and controls for valves, etc, will be designed for ease

of operation of filters

Design Parameters:

Design year: 2,030

 Description Unit Quantity Required production m3/day 12,377 Design Flow, Q m3/day 12,377  m3/hr 516  m3/s 0.143

Surface Loading m3/m2/hr 4-6

Allowed Filter Bed expansion % 40

Design Calculations and Checks:

1. No.of Filters = 4arranged in one row

The number of filters are such that if one is not operated for maintenance purposes, the otherscan be overloaded without affecting the output of the treatment works.

Take width of each filter bed = 4.3 m

Q per filter = 171.91 m3/hr(backwashing 1 filter-most Critical)

2. Filtration rate = 5.9 m3/m2/hr

3. Area required per filter = 29.14 m2

4. Length of each filter bed = 6.8 m

5. Filtration rate when all filters are in operation = 4.41 m3/m2/hr

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Provide:No.of Filters = 4Width per Filter bed = = 4.3 mLength per Filter bed = = 6.8 mBack Wash Collection channel = 0.6 mTotal Width of filtration unit, W = 18.7 mTotal Length of filtration unit, L = 8.25 m

Planimetric area of filter beds alone = 116.96 m2

Planimetric area of filter gallery (planimetric area+71.2% for piping, channels and walkways) = 200.20 m2

Total length of filter gallery = 18.7 mTotal width of filter gallery = 4.45 m       

6. The filter media will consist of:

   sand    

   

   

Gravel 4    

Gravel 3    

Gravel 2    

Gravel 1    

Layer   1 2 3 4 TotalDepth (mm)   100 75 75 50 300Passing square mesh 38mm 20mm 12m 5mm  

Retained   15.5mm 9.5 4.5 2.5  

Top sand layer 600mm, Effective size 0.6 mm Uniformity coefficient 1.5

Media selectionMedia selected Sandeffective size, d = 0.0006 mSpecific gravity, Sg = 2.65Uniformity coefficient = 1.5Porosity ratio, e = 0.4Media depth = 0.60 m

Head loss through media

Velocity, v = 5.9 m/hr= 0.0016389 m/s

Temperature = 20 degree C

Density of water, r = 998.2 kg/m3

Dynamic Viscosity, = 1.00E-03N.s/m2 (kg/m.s)

shape factor, = 1

Kinematic viscosity, n = 1.00E-06 m2/s

Reynolds number, Nr = dvr /

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= 0.8467764

Friction coefficient, f =150(1-e)/Nr +1.75

= 108.0

Head loss in media, hl =f/ee3L/d)

(v2/g)= 0.240 m

Loss at inlet = 0.04 mTerminal head loss = 2.50 mHead loss in under drain= = 0.036 mTotal head above media= = 2.70 m

Total loss up to manifold= = 2.816 m

7. A system of laterals and collection channel to be provided under the filter media to collect filtered water. The same laterals to be used for backwashing by water8. A separate air main system to be provided to agitate the filter media before backwashing by water. This will ensure less quantity of water being used for backwashing

Maximum Water level 2,763.53 m above top of sandFree board     0.45 mSand 0.6 mGravel 0.3 mUnder drain slab 0.15 mManifold (concrete) 0.75 mMaximum water depth abov media 2.70 mHeight of filter bed 4.95 m

Sand top level 2,760.83 masl

7.5.6. Filter Backwashing Unit

The Backwashing of filters will be done by a combination of water and air to ensure economy in usage of treated water. For this purposes, arrangements will be provided to use backwash by gravity from an elevated tank within the site and air compressors provided in the pump house.

ELEVATED WATER TANK DESIGN:

General:Treated water will be pumped from the Clear water tank to an elevated tank to backwash filters by gravity. This elevated tank will also have additional capacity to cater for "domestic" demand at the treatment works site, domestic usage includes:

1. Domestic consumption by operators who are provided shelter on site.2. Chemical mixing.3. Wash room/Toilet flushing.4. Tea making.5. Cleansing of filter walls and flushing of sedimentation tanks and flocculation basins.

Considerations taken into account for design include:1. A backwashing period of at least 10min per filter to ensure adequate time for an efficient wash to be carried out.

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2. The Pipework and storage required is based on backwashing by water alone to allow for non-interruption in the operation of the treatment plant incase of breakage in service from mechanical plant (compressors).

Design Parameters:

Design Calculations:

Filter bed dimensions = = 4.3 x6.4 mArea of filter bed to be washed = = 29.24 m2

Volume of water required for backwashing = 24.37 m3/minNo. of filters to be backwashed at one given time = 1Hence, Volume required to backwash filters = 243.7 m3

Allowance for "domestic" usage on site & Safety 30% = 73.10 m3

Hence required volume of EWT = 316.8 m3

Take Volume of Standard Reservoir = 300 m3

Provide a 300 m³ capacity elevated Concrete tank. The height of the tower to ensure supply bygravity to backwash filters.

Diameter = 8.20Area = 52.81 m²Depth = 5.68 mFree Board = 0.41 mTotal Heght = 6.09 mSloping bottom heigt = 0.74 mBottom dia = 6.00 mSlope 0.67

1.100 mBottom Volume = 30.00 m3

Top Volume = 270.00 m3

Top Height = 5.11 mTotal height = 6.26 m

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Back wash rate = 50 m3/m2/hrPeriod of Backwashing = 10 min

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Determination of Maximum Water level in Back wash water tankLocationX = 601985Y = 779606Z (Ground) = 2771.50 masl

Back Wash LineFilter Media Top level = 2760.83 maslX = 602076Y = 779626Z (Ground) = 2762.70 maslLoss in under drain system = 2.58 mQ = 0.41 m3/sBack wash line diameter = 0.40 mLength in filter galery = 24.00 mLength out side galery = 100.00 mTotal L = 124.00 mSpecific loss= = 0.0292 m/m Velocity= = 3.25 m/s Loss in pipe= = 3.62 m Outlet loss= = 0.270 m Bend 90 degree= = 6.000 NO Bend Tee degree= = 3.000 NO Loss in 90 degrees= = 1.294 m Loss in Tees= = 1.941 m Loss in Valve= = 0.162 m Inlet loss= = 0.539 m Loss in backwash piping = 7.83 mTotal Loss during Back washing = 10.40 m Trough top level = 2765.05 maslWater depth above trough = 0.050 mMaximum water level above trough = 2765.10 maslMin water Level in Back wash water tank = 2775.51 masl

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Mixing water pipe line.01Soda Ash mixing tank top level = 2773.99 maslMixing Tank volume = 5.18 m3

Tank filling time = 15.00 minQ = 0.006 m3/spipe diameter = 0.100 mLength = 72.00 mSpecific loss= = 0.0095 m/m Velocity= = 0.74 m/s Loss in pipe= = 0.68 m Outlet loss= = 0.014 m Bend 90 degree= = 6.000 NO Bend Tee degree= = 3.000 NO Loss in 90 degrees= = 0.067 m Loss in Tees= = 0.101 m Loss in Valve= = 0.008 m Inlet loss= = 0.028 m Total loss = 0.90 mFree head at mixing tank = 2.85 m Min water Level in Back wash water tank = 2777.74 masl

Mixing water pipe line.02Chlorine Mixing Tank top level = 2262.85 maslMixing Tank volume = 2.31 m3

Tank filling time = 15.00 minQ = 0.003 m3/spipe diameter = 0.050 mLength = 154.00 mSpecific loss= = 0.0623 m/m Velocity= = 1.32 m/s Loss in pipe= = 9.60 m Outlet loss= = 0.045 m Bend 90 degree= = 6.000 NO Bend Tee degree= = 4.000 NO Loss in 90 degrees= = 0.214 m Loss in Tees= = 0.427 m Loss in Valve= = 0.027 m Inlet loss= = 0.089 m Total loss = 10.40 mFree head at mixing tank = 3.00 m Min water Level in Back wash water tank = 2276.25 masl

Minimum Water level in BWT = 2777.74 maslTake Water Depth of = 5.11 m Maximum Water level = 2,782.86 maslFloor level = 2,777.00 masl

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b. BACK WASH WATER PUMPING STATION DESIGNOperation Hour per day = 4 hrPumping rate for operation = 0.0208 m3/spipe diameter = 0.150 mLength = 125.00 mSpecific loss= = 0.0142 m/m Velocity= = 1.19 m/s Loss in pipe= = 1.78 m Outlet loss= = 0.036 m Bend 90 degree= = 2.000 NO Bend Tee degree= = 2.000 NO Loss in 90 degrees= = 0.058 m Loss in Tees= = 0.173 m Loss in Valve= = 0.022 m Inlet loss= = 0.072 m

Total loss = 2.14 mFree head at BWT = 5.00 m Pump center line level = 2760.50 masl Maximum Water level = 2782.86 masl Static head difference = 22.36 m Allow NPSH = 3.00 m Pump head = 32.50 m Use pump withPumping rate = 21 l/spump Head = 35.0 m

c. AIR COMPRESSORS AND AIR MAIN DESIGN:

General:

Agitation by air scour will be done by blowing air through the filter media. Air compressors be housed in the pump house used for this purpose. The size of the air compressor is governed by the rate of discharge of air required during backwashing and the head loss of the fluid while being transmitted from the compressor to the filter bed.

Under the proposals for the treatment works, all filters will be designed to be backwashed by a centralised water and air system.

Assumptions:

i. The compressors are to be designed for the worst scenario.ii. Air main size to be designed for each set of filters.

Main Design Parameters:

1. Air requirement -0.9 - 1.5 m³ of free air/min/m² of filter bed provided for air scour (ensures efficient air scour)

2. Average time for air scour - 2 minutes for satisfactory agitation.

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Design:Volume of air required for efficient air scour, Va

m3 of free air/min/m2 of filter bed 0.9 - 1.5

Standard Density of air

(piping Handbook (5th ed) by SABIN CROCKER pg 3-157)

lb/ft3 (*note - units left in imperial form so as to use formulas provided which are meant to be used in imperial units

0.07638

Design Calculations:Proposed Filters:Estimated Pipe Length from proposed pump house to the proposed filters, L 80 m

262.47ft (1m = 3.28084 ft)

Filter bed Dimensions 4.3 x 6.8 m

Area of filter bed, A 29.24 m2

Volume of air required, Q = VaA 43.860 m3/min

1548.903ft3/min (1m3 = 35.3147ft3)

0.731 m3/s

Head loss Calculation:

Expressing head-loss in terms of pressure loss, using HARRIS Formula for compressed air:

Pressure drop, P = LQ2/(2390pcd5.31)

Where: P = Pressure drop (lb/in2)pc = density of actual fluid at flow conditions (lb/ft3) 119 lb/ft3

Q = flow rate (ft3/min)d = diameter of pipe (in)L = Pipe Length (ft)

80mm diameter main

Pipe diameter, d 80 mm3.150 in (1 in = 25.4mm)

Head loss, P 5.00539 lb/in2

34.52272

KN/m2 (1lb/in2 = 6.897112576 KN/m2)

0.34523bars (1KN/m2 = 0.01bars)

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100mm diameter main

Pipe diameter, d 100 mm3.937 in (1 in = 25.4mm)

Head loss, P 1.53054 lb/in2

10.55633

KN/m2 (1lb/in2 = 6.897112576 KN/m2)

0.10556bars (1KN/m2 = 0.01bars)

Summary:

Q (m3/s)

Diameter80mm 100mm

P (bars) P (bars)0.731 0.34523 0.10556

Provide: 1 Air Compressor capable of discharging air with the following specifications:

Q = or > 0.731 m3/sP = or > 0.34523 bars

Under-drainage SystemA pipe grid system has been adapted as under-drainage system. This system contains the manifold and perforated laterals. The two primary function of under-drainage system are:

(1) to collect filtered water and to send it on its way to a clear water reservoir, and2) to uniformly distribute air and wash water during scouring and back washing.

The under-drains are sized for up flow requirement. As a design guide the following range values are used.

RecommendedRatio of area of orifice to area of bed served: 0.0015 0.005 0.003Ratio of area of lateral to area of orifice served: 2 4 3Ratio of area of manifold to area of lateral served: 1.5 3 2.1 Diameter of orifices: 0.6 2 cm

Spacing of orifices: 7.5 30cm c/c 20

Spacing of laterals: 7.5 30cm c/c 20

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Design Calculations:

Width per Filter bed = 4.3 mLength per Filter bed = 6.8 mArea of Bed 29.24 m²Area of orfice 0.08772 m²Area of laterals 0.26316 m²Spacing of laterals 0.25 mNumber of laterals 27

Area per lateral 0.00974667 m²Diameter of lateral 0.111 mUse lateral of DN 100 mm

Area of manifold 0.4453 m²Diameter of manifold 0.753 mWidth 0.60 mDepth 0.74 m

Spacing of orifice 0.2 mLength of lateral 4.2 mNumber of orifices per lateral 21

Total Number of orifices 567

Area of an orifice 0.00015471 m²diameter of orifice 0.014 mUse orifice diameter of 10 mmTwo openings at 60 degree angle

Check

No of orifice per lateral 42Area of an orifice 0.000079Total area of orifice 0.089064Area of a lateral 0.007854Total area of laterals 0.212058Area of Manifold 0.445321Ratio of area of orifice to area of bed served: 0.0030 OK!Ratio of area of lateral to area of orifice served: 2.4 OK!Ratio of area of manifold to area of lateral served: 2.1 OK!

Head Losses

During FiltrationQ max 0.0477524 Orifice

Diameter 0.01q =Q/(number of orifices) 4.211E-05Velocity 0.54hl 0.029

 Lateral

Diameter 0.1q =Q/(number of Laterals) 0.00177Velocity 0.23hl 0.005

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 Manifold

Width 0.60

Depth 0.74

Area 0.44532076

Velocity 0.11

hl 0.001 

Total Loss 0.036

During Back Washing  24.37 m³/minQ max 0.41 m³/s Orfice

Diameter 0.01

q =Q/(number of orfices) 0.00035812

Velocity 4.56

hl 2.119 Lateral

Diameter 0.1q =Q/(number of Laterals) 0.01504Velocity 1.92hl 0.374

 Manifold

Width 0.60Depth 0.74Area 0.44532076Velocity 0.91hl 0.085

 

Total Loss 2.578  

Trough top level 2765.05Water Depth over trough, h in mm

Discharge per meter length of weir, q (l/s) 0.0567 h^(3/2)Trough length per filter, L 20 m Q 406.1 l/s q 20.3 l/s h 50.4 mm

0.0504 m Maximum water level above trough 2,765.10 masl

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Connecting line TW.04 Connects Filter with post chlorination unit

Segment 1 Segment 2Segment

3Segment

4Design Flow= 0.048 0.048 0.096 0.143 m3/smax Start HGL= 2,760.83 2,760.82 2,760.78 2,760.58 maslmin Start HGL= 2,760.83 2,760.82 2,760.78 2,760.58 mPipe Diameter= 0.40 0.30 0.30 0.40 mLength= 3.00 6.00 5.00 22.00 mSpecific loss= 0.0006 0.0023 0.0081 0.0042 m/mVelocity= 0.38 0.68 1.36 1.15 m/sLoss in pipe= 0.00 0.01 0.04 0.09 mOutlet loss= 0.004 - - - NOBend 90 degree= - - 1.000 2.000 NOBend 45 degree= - - - - mLoss in 90 degrees= - - 0.038 0.054 mLoss in 45 degrees= - - - - mLoss in Valve= 0.002 0.007 0.028 0.020 mInlet loss= - - - 0.067 mTee T/T= 0.004 0.024 0.095 0.067 mTotal Loss= 0.01 0.04 0.20 0.30 mHead at Seg end= 2,760.82 2,760.78 2,760.58 2,760.27 maslStart ground level= 2,761.84 2,761.84 2,761.84 2,761.84 maslEnd ground level= 2,761.84 2,761.84 2,761.84 2,760.80 masl

Total loss in Filtered water collection pipe= 0.56 mTake Free fall of 1.19 mMaximum Water level in receiving chamber at chlorination point 2,759.08 masl

Design Year 2030 2040 2015Flow 12377 19207 4287 m³/dayDetention time 0.1 0.28 0.5 minVolume 0.9 3.8 1.6 m³Selected size 3.8 3.8 3.8 m³

Width 1.20 1.20 1.20 mLength 1.20 1.20 1.20 mDepth 1.57 1.57 1.57 m

Design Year 2030 2040 2015Flow 12377 19207 4287 m³/dayFlow per line 12377 19207 4287 m³/dayNumber of lines 1 1 1Flow per line when one is not working 12,377 19,207 4,287 m³/dayDesign Flow per line 19,207 19,207 19,207 m³/dayFlow Splitting Weir Rectangular weir

q= 1.7718 Lh^(3/2)Take length of weir= 0.60 0.60 0.60 m

Flow, Q= 0.222 0.143 0.050 m3/sHead over weir, h= 0.188 0.140 0.069 m

Weir Top level= 2,758.90 2,758.90 2,758.90 maslMax WL in receiving chamber= 2,759.08 2,759.04 2,758.97 masl

Take Free fall head= 0.50 0.45 0.38 mWater level after chlorination weir= 2,758.58 2,758.58 2,758.58 masl

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7.5.7. Chlorine Mixing and Chlorine Dosing Room

A few alternatives were considered for disinfection of treated water, i.e. Ozonization, Ultra-Violet Light; On-Site Generation of Hypochlorite Solution; Solutions prepared from Hypochlorite Powder and Gas Chlorination.

Ozonisation: Ozone can be generated by passing thoroughly filtered and dried air between plates with a high electric voltage. This method has been used very effectively in Europe. Ozone is particularly effective removing viruses.

Ozone works rapidly and efficiently and does not remain in the water for more than about 30 minutes as the ozone reverts to oxygen. Therefore there are no secondary tastes and odours from ozonization. However the fact that ozone is quickly converted back to oxygen means that the method has no residual effect in the water which would guard against contamination in the distribution network. Furthermore the cost of the equipment required is higher than that of equivalent chlorinators and requires a high level of operation and maintenance skill, especially the air-filtering and drying apparatus.

Ultra-Violet Light: This method is used at a few small installations. The method involves applying a given intensity of ultra-violet radiation for a specific period of time through a thin film of water. The water to be sterilized must be clear of soluble iron and other substances that absorb UV light and the equipment must be checked regularly to ensure the lamps are kept clean at all times to prevent the loss of intensity over time.

UV disinfection has the advantage that no by-products are formed in the water. However, this advantage results in the disadvantage that the effectiveness of the disinfection cannot be determined by measuring a residual level as is the case with normal chlorination methods. In addition, UV disinfection has no remnant effect and can therefore only be used in distribution networks that are very small and well maintained otherwise it must be supplemented by a disinfectant with a remnant effect such as chlorination, which would reduce the advantage offered by UV.

On-Site Generation of Hypochlorite Solution: In this method brine is passed through an electrolysis apparatus where it is subjected to a D.C. current. The brine is then broken down into sodium hypochlorite, with hydrogen gas as a by-product. The sodium hypochlorite is then conveyed to the chlorination point and dosed into the treated water while the hydrogen gas is safely vented into the atmosphere. Capital cost for installation and subsequent maintenance are too high. Existing disinfection system is by using Hypochlorite Solutions.

Thus, disinfection by Hypochlorite Solution has been allowed for as described hereunder: -

7.5.6.1 Chlorine Mixing Room

General:1. Adequate exhaust fans will be provided at appropriate locations to ensure circulation of

air.2. Epoxy tiling/coating to be provided to mixing tanks and flooring.3. Corrosion free fittings and natural lighting to be ensured.4. Motorised mixers will be provided for each mixing tank.5. Plastic or other suitable pipes to be used for dosing by chemical solution. All piping to

be accessible for cleaning, etc.6. All sludge from mixing tanks to be discharged to pits.

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Treated water from the treatment works will be disinfected and pH value corrected before being stored in the clear water tank whose Capacity will ensure adequate time for chlorine contact and storage for supply to the reticulation network.

It is proposed that the chlorine dosing building be a two storey structure having:

1. A ground floor will be used for storing hypochloride powder and Soda Ash2. An upper floor will be used to house mixing tanks and dosers for chlorination and pH

correction by soda ash.

Design Calculations:

 Chlorine (by solution):

Available chlorine, ClA 65 %

Maximum Dosage Quantity,d 4 ppm4 mg/l

0.004 Kg/m3

Gross Water Demand for supply area (80.24 km2), Q 12,377 m3/day

  516 m3/hr

  0.143 m3/s143 l/s

Storage: (1 weeks storage to be provided at chlorine mixing and dosing room, the rest of the chlorine will be stored at the chemical storage and mixing building)

Ground floor dimensions of proposed chlorination room 7.5 m x5m

Upper floor dimensions of proposed chlorination room 7.5 m x5m

Area available per floor   37.50 m2                    Amount of free chlorine required = Qd 49.5 Kg/d of free Cl2

Amount of hypoclorite required, A = Qd/ClA 76.2 Kg/d

of hypochlorite

Period of storage provided 7 days

Hence storage required 0.5 tones

Chemical packaging 25 Kg drums

No.of drums to be stored 21 drums

Area required per drum 0.6 x 0.6 = 0.36

Area required for storage (assuming double stacking) 4 m2

ok! storage space adequate

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Provide storage room on upper: Floor Length 6 m

Width 3.7 m

Room available on upper floor for: mixing tanks and dosers Length 6 m

Width 6 m

Depth 3m (min floor height)

Mixing Tanks:

Strength of Chlorine solution 2% available Cl2

Chlorine requirement, ClR : (2/0.65) per 98 l of water 3.1 Kg per 98 l of water

Hence solution required = A/ClR 2408l/d of solution

No.of shifts per day for chlorine tank usage 1 shifts/day

Hence required tank volume 2.41 m3

Allowance for dead storage 10 %

Provide Two chlorine tanks each of volume 2.6 m3

Provide two chlorine mixing tanks:each measuring Depth 1.1 m Take D= 1.1

Length 1.6 m L= 1.6Width 1.6 m W= 1.6

Total dimensions of chlorine dosing: Length 3.1 munits Width 1.6 m

Depth 1.1 m

              Soda Ash             

Soda ash dosing is provided for the purpose of pH correction

Assumed solution stregnth, St 5 %

Assumed Dosage Quantity,d 7.5 mg/l

Gross Water Demand for supply area (2027), Q 12,377 m3/day

  516 m3/hr

  0.143 m3/s143 l/s

Storage: Provided at chemical building

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Mixing Tanks:

Quantity of Alum solution required = QdSt 0.021489 l/s

Daily Solution requirement 1.9 m3

Dead storage allowance 10 %

No. of Tanks to be provided 1

Volume of each tank 2.04 m3 say 2 m3

Depth of each tank = 1.14 m say 1.2 m

Provide two chlorine mixing tanks: Length 1.4 meach measuring Width 1.5 m

Depth 1.4 m

Total dimensions of chlorine dosing: Length 1.4 munits Width 1.5 m

Depth 1.4 m

Hence total dimensions of mixing : Length 2.6 m

ok! available length = 6m

tanks and dosing units Width 2.6 mok! available width = 6m

   Depth 1.4 m

ok! available floor height = 3m    

7.5.8. Clear Water Tank

Clear Water Tank Design Sizing of Clear Water Tank:

General:

1. Tank divided into equal halves to allow for maintenance.2. Circulation provided by baffle walls to avoid stagnation of treated water.3. Ventilation and separate access provided.4. All outflow for distribution from this new tank. A sampling point provided to record residual

chlorine before distribution.

Filtered water, after chlorination (for disinfection) and soda ash (for pH correction) will be retained in a clear water tank for a minimum retention time of 30minutes to allow for contact time. However, the clear water tank is a combination of a contact tank and a storage reservoir, 2500m3 capacity, for the distribution system. Hence, more than adequate contact time is provided.

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Design:Design Year 2,030

Maximum day demand 12,377 m3/dayMaximum hour factor 1.7

Maximum hour demand 21,042 m3/day

Water required for Daily chemical dilution and feed 0.20% of MDD 25 m3

Filter back wash 317 m3

Balancing for distribution 25.40% of MDD 3,144 m3

Total 28.28% of MDD 3,500 m3

Reserve volume, 15% of total 525 m3

Total Volume 4,030 m3

Existing reservoir in distribution system 450 m3

New reservoir in distribution system 1000 m3

Total in Distribution 1450 m3

Clear water Tank at TP 2,580 m3

Recommended 2500 m3

Provide Tank with dimensions:Length 25.0 mWidth 25.0 mwater Depth 4.25 mFree board 0.55 mContact time 300 Minutes; ok!

Details of this Tank are shown in tender drawings

7.5.9. Pump House Design Sizing of Pump House

General:

The proposed Pump House will be located adjacent to the clear water tank and it will house the following:

1. Two number centrifugal pumps (1 duty, 1 standby) to pump water to the elevated tank within the treatment works site.

2. Two compressors (1 duty, 1 standby) to provide air scour for backwashing the filters.

The Proposed pump house will have one floor, at the same level as the clear water tank floor. A floor mounted switchgear control panel and all the units, pumps and compressors panel would be installed on this floor.

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Design Parameters:Maximum Plinth dimensions taken = 2x1 m Number of units for (2 pumps & 2 Compressors) = 4Design Calculations:

Area Required for plinths = 8 m2

Provide floor space of area = 40 m2

Provide:Length = 9 mWidth = 5 m

Hence Provide a Pump House with floor measuring 9.0m x 5.0m

Details are shown in tender drawings.

7.5.10. Building Works

There are six buildings spread over the Treatment Works Site. These include the following: -

Chemical Dosing and Mixing Building Filter Gallery and Control Room Pump House Generator / Switch room. Chlorine Mixing Room Operator dwelling house, Administration room Meter Room and Guardroom.

Majority of buildings are single or two-room structures, with the exception of Chemical Mixing and Dosing Building. The design and location of the buildings is generally determined by their functional requirements.

The Architectural Designs of the buildings has been limited to harmonising the visual appearance of various buildings externally, and meeting the functional requirements internally. This has been achieved by appropriate choice of materials and fittings.

Externally, the buildings are finished and dressed stone walls and coloured concrete roof tiles. Stone is the cheapest building blocks available, and requires practically no maintenance. Precast concrete louver blocks have been provided to enhance natural ventilation in buildings where chemicals are used for treatment of water.

Concrete roofing tiles are readily available, hardwearing, and although marginally more expensive than corrugated iron roofing sheets, the elegance of concrete tile roof in comparison with corrugated sheet roof, justifies the choice.

Windows are steel casement, painted with anti-corrosive paint in buildings where chemicals are used. Metal louvred doors have been specified in a number of buildings to fulfill dual functions of providing adequate ventilation as well as security in buildings where expensive

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switchgear and electrical control panels will be installed. Timber doors are provided in other buildings.

Acrelin floor tiles have been specified in buildings where chemicals are used extensively. These include Chemical Mixing and Dosing and Chlorine Mixing Buildings. Hardened cement screed and grano finish used in other buildings, with PVC tiles in offices.Granola Internally, walls are generally finished with plaster and paint, except in staff rest rooms where glazed tiles will be provided. Ceilings throughout will be chipboard and painted.

7.5.11. Electrical Works

7.5.10.1General

The following report is a brief outline of the various services included for the Electrical Works at the Scheme Design Stage. The detail design work is presented in the Electro-mechanical Detail Design report.

7.5.10.2Regulations and Standards

Design is carried out in accordance with the following documents: -

(i) The current edition of the Regulations for the Electrical Equipment of Buildings issued by the Institution of Electrical Engineers of Great Britain.

(ii) The Ethiopian Electric Power Corporation (EEPCO).(iii) Relevant British Standard Specification and Codes of Practice published by the British

Institution (hereinafter referred to as B.S. and C.P. respectively).(iv) Regulations of the Federal Democratic Republic of Ethiopia.(v) Interior lighting design is carried out in accordance with the Lighting Industry Federation

Limited and the Electricity Council of Great Britain.(vi) Telephone connection requirements as required by Ethiopian Telecommunication

corporation.

7.5.10.3Incoming Electricity Supply

The power supply to the Treatment Works shall be derived from the National Power Grid System at 11 kV from an existing overhead power line to the old intake.

At the plot boundary, EEPCO will erect their pole mounted transformer (100 kVA). The incoming service cables shall be four single core and the size shall be decided by EEPCO. The incoming service cables will be connected by EEPCO to the main switchboard located within the Generator / Switch Room.

7.5.10.4Standby Generator Set

100 kVA generator set is housed in the generator room adjacent to the switch room for the essential loads during failure of supply from EEPCO.

7.5.10.5Main Switchboard

The main switchboard is cubicle type, floor mounted housed in the Switch Room adjacent to Generator Room. The busbars are split into essential and non-essential supplies i.e. EEPCO and Generator Supplies.

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In the event of a normal (EEPCO) power supply failure, the automatic change-over contactors in the main switchboard will break the connections of the normal (EEPCO) incoming mains supply and make the connections to the diesel generating plant. When the normal (EEPCO) supply is restored the reverse action will take place. The generator will also operate if there is loss of one or more phases on the normal (EEPCO) supply cable.

7.5.10.6Telephone Incoming Services

The incoming service cable will be provided by Ethiopian Telecommunication Corporation (ETC). The Contractor will provide manholes and ducts from the plot boundary to the main door front (MDF) at the Chemical Mixing & Dosing Building. The service cable of ETC will run via manholes and ducts upto the MDF. The Client will apply to ETC for telephones and pay to Telkom direct.

7.5.10.7Electrical Distribution

All the buildings at the Treatment Works are supplied by underground cables from the Main Switchboard housed in the Switch Room. The underground cables (PVCSWAPVC) will be having copper conductors of 600/1000 volts grade to B.S. 6346. Termination of cables will be carried out by means of brass compression type glands of the correct size which will secure the cable inner sheath and ensure effective electrical continuity between the cable armouring wires and the metal enclosure on which the cable is terminated.

7.5.10.8Lighting and Power Installation

Wiring for lighting and power installation in buildings will be carried in black rigid super high impact heavy gauge Class 'A' PVC conduit (non-metallic conduits and accessories). The Contractor will supply, install, connect, test and commission the lighting fittings and electrical accessories as shown on the drawings and set out in the schedule.

7.5.10.9Lightning Protection

Lightning protection is provided for the following buildings: -

(a) Generator / Switch Room(b) Chemical Mixing / Dosing Building(c) Chlorination Room(d) Administration room(e) Operator dwelling room(f) Pump House

The lightning protection will be carried out in accordance with British Standard / C.P. 326 1965 / Ministry of Urban Development and Infrastructure, Technical Instruction No. 58.

7.5.10.10 Security Lighting

125 watt MBF/U post top lanterns mounted on 5.0 metres columns are provided for security lighting. Control of security lighting will be automatic by photocell with a manual over-ride switch fixed on the panel of the Main Switchboard.

7.5.10.11 Control Cables / Marshalling Boxes

Control cables are provided under this Contract including marshalling boxes. The control cables will be used to indicate on the remote indicator panel, the water levels in the clear water tank and elevated backwash tank.

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Control of pumps for backwash water lagoon, clear water tank and elevated backwash tank will be carried out by means of electrodes. The electrodes in the tank will be stainless steel of 6 mm diameter and shall be suspended from top using special electrode holders.

7.5.10.12 Pump House

Essential and non-essential control panels for the pumps in the pump house are connected from the essential and non-essential bus bars of the Main Switchboard. Both control panels for pumps in the Pump House are connected on the normal (EEPCO) supply. In the event of EEPCO power supply failure, the change-over supply from the EEPCO to the diesel generating plant will take place at the main switchboard and the essential control panel in the pump house will be connected to the generator supply. Provision is allowed in the control panels for pumps to switch 'ON' a pump or move on the non-essential control panel if the pumps are not in use at the essential control panel. The operator must check the load available on the generator before switching 'ON' pump on non-essential control panel.

7.5.10.13 Testing and Commissioning

After installation, each part of the system will be tested in accordance with the relevant B.S. and I.E.E. Standards and the requirements of the EEPCO. In addition to these tests, the whole of the installation shall be subjected to complete functional tests to the satisfaction of the Engineer/Client.

7.5.12. Site Works

7.5.10.14 Roads

Access road to the Treatment and intake will be constructed. It will allow easy access as well as maneuvering of heavy vehicles which will be used to deliver and off load chemicals into the Chemical Storage Building.

Access road within the treatment plant compound will be constructed. It is designed to provide easy access to the Chemical Mixing & Dosing Building, Upflow Sludge Blanket Clarifiers, Filter Gallery, Generator Switch Room, Pump House, Clear Water Tank. A car park outside the environs of the Chemical Mixing & Dosing Building will be provided and the road around this area will be paved using concrete. The access road will have gravel paved surface. Ramps are also be constructed from the road edges to the building floors of the Pump House, Generator Switch Room and Chlorine Mixing Room. These will ease the transportation of heavy machinery into the Buildings as well as the off loading of chemicals in the Chlorine Mixing Room.

7.5.11.1 Fencing and Gates

Chain-link fence will be erected around the perimeter of the Treatment Works Site. Cidar (tid) hedge will be planted inside the chain-link fence. The entire Treatment Works Site will be grassed and landscaped with approved plants.

A 6m wide gate with two 915mm wide pedestrian gates on either side will be constructed for access at the New Treatment Works Site. A metal signboard will also be erected outside the main gate, bearing the name of the ROBE Water Supply & Sewerage Service, Korke Treatment Units.

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7.5.11.2 Footpaths

Footpaths will be constructed to allow access to each of the existing and new units. Strategic lengths of the footpath will be covered to enable operators get from one end of the Treatment Works Site to the other (including full access to all units) without getting wet during rains.

7.5.11.3 Storm Water Drainage

Storm water drainage will be provided all around the Treatment Works Site in the form of Invert Block Drains (IBDs) with or without one or two courses. These drains have been designed to channel all the storm water run off from the Treatment Site and drain it along the drainage of the access road and to Huluka river.

7.5.11.4 Sewerage and Domestic Waste Disposal

Septic TanksThe septic tank is recommended for housing units in the treatment plant compound. The design for a septic tank is based on the per capita demand for house connection users which is 60l/c/d. The liquid part from the septic tank is directed to drainage ditches. It is recommended to have one septic tank to serve the manager, operator and the common wash room allocated in the treatment plant compound. In this context it is assumed that 15 persons will use the sanitary facility of the treatment plant compound.

Volume of the septic tank for 15 persons use = V = Q*P = 60*50 = 3000 l = 3.0 m3.

Minimum depth of liquid (d) = 1.2 meter,Freeboard = 0.30 meter Surface area = 3.0 m3/1.20 m = 2.5 m2 Take length to width ratio = 1 : 2.5

Therefore; = 2.5 meter= 1.0 meter= 1.20 meter

Total depth of the tank including freeboard = 1.50 m.

The design of drainage ditches is determined using the following formula:

L = P*Q/2*D*I

where;L = trench length (m)P = number of usersQ = waste water flow (l/c/d)D = effective depth of trench (m)I = design infiltration rate (l/m2/day)

Effective depth of trench (D) is taken as 1.5 m as the soil treatment plant area is silty sand, infiltration rate for effluent from septic tank is taken as 15 l/ m2/day.

L = 15*60/2*1*15 = 30 m.

Therefore use three drainage ditches each having 10 m length.

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A septic tank capacity 3.0 m3 will be constructed. This tank will be linked to the managers dwelling, operators dwelling, administration building and wash room.

7.5.11.5 Domestic Use

The Elevated RC backwash reservoir will be used for storage of domestic and gardening requirements of the treatment plant compound.

The domestic usage on site catered for by the domestic water supply main includes: -

Domestic consumption by Operators Chemical mixing Urinals/Toilet flushing Tea making Cleansing of filter walls to remove any scum during / after the backwash operation Site irrigation

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8. DISTRIBUTION SYSTEM AND STORAGE RESERVOIRS

8.1 EXISTING DISTRIBUTION SYSTEM

The total area currently within the boundaries of Robe Municipality is about 80.24 km2. Out of the total area, about 15.25 km2 is open space and environmental aspect such as forest land, urban agriculture, future expansion, etc. area the remaining 64.99 km2 is used for different purposes such as residential, commercial, etc. The existing distribution system covers mostly the central part of the area. The additional coverage under the new system is assumed to adress all areas within the new master plan boundary of the town.

The existing system consists of three types of pipe material, namely Ductile Cast Iron (DCI), Galvanized Mild Steel (GMS) and unPlasticised Polyvinyl Chloride (uPVC), ranging in diameter from 50 mm to 300 mm with a total length of 39.5 km.

The distribution system is about twenty-eight years old and is anticipated that most of the pipes to be in bad condition. Accordingly, all of the existing System above ND 100mm, has been incorporated in the Proposed System.

8.2 PROPOSED DISTRIBUTION SYSTEM

The distribution System will be supplied from the clear water tank 2,500m3, located at the treatment plant site. At the outskirt of the town toward Goba town, at a higher elevation new 1000m3 reservoir will be constructed. The existing three masonry reservoirs will supply lower elevation areas. The elevated reservoir in the treatment plant compound which is meant for backwashing and compound supply will also supply the nearby villages.

8.3 DISTRIBUTION SYSTEM DESIGN CRITERIA

8.3.1. Water Demand

The water demand patterns for year 2030 and 2040 are as given in the Feasibility Study Report. Domestic demand is distributed to the nodes according to the land use and population density.

Institutional and industrial demands are distributed to the respective nodes depending on the location of the existing institutions and the Town Development Plan. Non Revenue Water is distributed to each node proportionally to the nodal demands.

8.3.2. Pipelines

Alignment The main distribution pipeline will follow the existing or/and planned roads while

observing hydraulic efficiency and economy.

Depth Depth of pipe trench shall be limited in order to provide easy maintenance and avoid

excessive earth pressure while maintaining sufficient protection against live load due to traffic. - Pipes laid in trenches shall have a minimum cover of 0.8 m- Pipes laid under carriageway or road verges shall have a minimum cover of 1.2 m- Maximum cover to crown of uPVC pipes shall not exceed 3.0 m- Ductile Cast Iron pipes to be used at road crossings

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8.3.1.1 Transmission Pipes

The transmission pipes are sized for year 2030 maximum day demand which is 1.1 times the average day demand.

8.3.1.2 Distribution Network Pipes

The distribution network pipes are designed for the peak hour demand of year 2030, which is 1.7 times the maximum day demand upto year 2017 and 1.5 times the maximum day demand thereafter. The peak hour factor in a day used is 1.7 up to year 2017. From Year 2017 onwards a peak factor of 1.5 has been used Chapter 3, Table 3.8. Velocity in the distribution net work varies between 0.3m/s to 2m/s.

8.3.1.3 Pressure in Pipelines

The minimum residual nodal pressure on average day demand shall be 10 m head.

The minimum residual nodal pressure on peak hour demand shall be 5 m head

In majority of the cases, the maximum pressure in the distribution network shall be 90 m head.

8.3.1.4 Friction Factors

To compute the friction loss in the pipelines, the following Hazen Williams coefficients shall be used.

Table 8.I Hazen Williams Coefficients

Pipe Status Pipe Type

uPVC Steel DCI

New Pipe 130 130 130

10 years old 130 110 110

20 years old 130 100 100

8.3.1.5 Selection of Pipe Material and Type

The selection of pipe material will depend upon the nature of the ground in which pipes are to be laid, over burden soil pressure, surge, type of traffic load and the cost of the pipe. When a pipe is found technically suitable for particular case the economical pipe materials available for choice are:

Ductile Cast Iron Pipe (DCI) for pipes with DN 300 mm and above

uPVC for pipes with DN 50 to 300 mm

GS for pipes DN 50 mm to 100 mm diameter.

The physical characteristics of the pipes must suit the actual service conditions in the water supply system such as pressure, external load, soil condition and the topography.

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8.3.3. Accessories

8.3.3.1 Valves

i) Air Release Valve

Location: Double air valves shall be provided at all high points with respect to the pipe profile. Additional single air valves are to be provided wherever the rising grade reduces.

Size: Air release valves shall be compatible in size, type and pressure ratings with the system. Therefore, double orifice kinetic type DN 80 mm shall be installed on mains of diameters DN 250 mm to DN 400 mm. DN 50 single orifice air valves shall be installed in pipelines of smaller diameters.

ii) Washout Valve

Location and Spacing: Wash out valves shall be provided so that the water in the respective pipeline section can be drained out in 3 to 4 hours.

Size: On pipe lines from DN 250 mm to DN 400 mm, the wash out valve shall be of DN 80 or DN 100 mm; on smaller pipelines a minimum of DN 50 mm wash out valve shall be installed. The wash out valves shall be compatible in size, type and pressure ratings to the system.

iii) Isolating Valve

Spacing: Isolating valve shall be provided along the pipe profile to isolate a portion of the system during repairs. These valves on mains will be installed at intervals as required; their spacing being dictated by factors such as washout requirements, connections to consumers and connections to other mains. In normal conditions isolating valves shall be installed at maximum distances of 500 m.

Number: The number of isolating valves to be installed in an adequately looped grid at intersections of arteries and service or consumers mains is n-1, where n is the number of branches at the intersection.

Location: At interconnecting pipes, bypass pipe connections, hydrant connections, washouts and air vents.

Type and Size: Proposed type of isolating valve is gate valve compatible in size, type and pressure ratings with the system.

iv) Pressure Reducing Valve

Pressure reducing valve shall be provided along the pipe profile to reduce the pressure and maintain it within allowable limits.

8.3.3.2 Fittings

Pipeline fittings (bends, tees, reducers etc.) shall be:

Appropriate for the pipeline configuration,

Similar in size and class to the pipelines,

The same design strength as that of the Ductile Cast Iron pipes.

8.3.3.3 Fire Hydrants

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Spacing: In CBD area fire hydrants shall be installed with a maximum spacing of 150m. In other areas the fire hydrants shall be located on road junctions.

Pressure: A minimum pressure of 15 m shall be available at the node with which the hydrant will be connected.

Type and size: Underground hydrant DN 80 with two hose connection arrangement type C.

Minimum diameter of the pipe section shall be DN 80.

Notwithstanding the above, shall be agreed by the Employer that the number of fire hydrants should be limited to avoid misuse and wastage.

8.3.4. Pipeline Appurtenant Structures

8.3.4.1 Valve Chamber

Concrete / Masonry Valve Chambers shall be provided for each valve location for protection and to provide easy access.

8.3.4.2 Trench Depth

In areas where the pipe is subjected to vehicular traffic, the minimum depth of cover to be provided is 1.2 m above top of pipe;

In other areas the minimum depth of cover above top of pipe is 0.8 m; and

If the above depths cannot be obtained, due to the natural ground profiles, concrete encasement for pipes will be considered.

8.3.4.3 Thrust Blocks

Whenever the pipeline changes direction horizontally or vertically or changes size, concrete thrust blocks shall be provided to resist the thrust force in the piping system.

8.3.4.4 Pipe Support

Concrete supports for pipes shall be provided whenever the pipe is laid above ground surface and also in situations where foundation formations are not good. Lateral transverse anchors shall be provided for conditions where pipe is laid in steep slopes.

8.3.4.5 Road and River/Ditch Crossings

Whenever pipeline crosses gravel, asphalted or concrete roads and river/ditch crossing, Ductile Cast Iron pipes or structures which will protect the pipe shall be provided. For heavy traffic road crossings, concrete encasements shall be considered.

8.4 CLEAR WATER GRAVITY MAIN

8.4.1. Route Alignment

The clear water gravity main is proposed to transmit treated water to the distribution network and the reservoirs used as break pressure tank r located at the old treatment plant compound to feed the distribution sub-mains that feed area at lower elevations.

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8.4.2. Selected Pipe Material

Protected lined Ductile Cast Iron pipes, or equivalent approved are proposed to be used for the clear water gravity main.

The external protection against corrosion for Ductile Cast Iron pipes shall be as per DIN/180 Standards.

Jointing will be decided based on the approved make proposed by the Supplier.

8.4.3. Hydraulic Design

The clear water gravity main is designed for ultimate capacity to transmit a flow of 222.8 l/s. The outlet level of outlet pipe in Clear Water Reservoir is fixed at 2667 masl. The gravity main has been analyzed with the Distribution system as line (GWM-01 to GRSR). Hazen Williams’s equation is used to calculate the friction losses by taking a Hazen Williams Coefficient (HWC) of 120. The economic pipe size is 400 mm and 400 mm NP 10 and has a length of 9.392km.

The detail Hydraulic calculations are presented along with the Distribution system analysis in Appendix '1'.

8.4.4. Installation of Pipes

Pipes are to be joined and embedded in trenches. The pipe trench will be backfilled mostly by the excavated material. The minimum depth of cover is taken as 0.8 m above the crown of the pipe. Where rock is encountered pipes will be laid on granular bed material borrowed from approved pits to minimize damage to the pipe coating and improve on drainage underneath the pipe.

The Route of the Gravity Water Main is shown in Figure 8.1.

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Figure 8.1

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8.5 DISTRIBUTION SYSTEM

The arrangement of the distribution system has ten subsystems which are connected with the Clear Water Tank located at the treatment plant compound and the Service Reservoir located at the out skirt of the town toward Goba side named as GRSR. The subsystems are Goba Road Main, Western main, Goba Road Branch, Eastern Main, Central, Addis Ababa Road Branch, Western branch, Eastern Branch, Eastern Sub-branch, and Administration Branch mainly in the Administrative area. The lower elevation areas that are located mainly the eastern out skirt of the town and will be connected to the existing reservoirs.

Accordingly, to systematize the distribution system, for ease of identification of subsystems, Six Supply subsystems are created.

8.5.1. Goba Road Main Subsystem (GBR-Main-1-3)

This sub system comprises about 2.228km pipe length and it connects all other sub-systems except the eastern sub-system. This subsystem will be supplied from the Gravity water main from the Goba Road Service reservoir (GRSR) located at 2574 masl.

8.5.2. Western Main Subsystem (West-Main-1 to West-Main-13)

This subsystem supplies areas in the western side of the town it encompasses about 9.262 km² in area. It will be supplied from the GBR-03 subsystem. The Altitude in this subsystem ranges from 2442 masl to 2542 masl.

8.5.3. Goba Road Branch Subsystem (GBR-BR-1-to ADM-BR-3)

This subsystem will be laid along the main road to Goba and branch road located in the eastern side of the main road it service approximately 13.07 km² in area. The subsystem is connected to the Goba Road water main at J-34 and runs to junction J-75. The Altitude in this subsystem ranges from 2552 to 2490 m.

8.5.4. Eastern Main Subsystem (East-Main-1 TO East-BR-2)

The subsystem is approximately 1.902 km² in area and comprises the new development area toward Goba side. This subsystem is connected to the gravity water main at J-43. The Altitude in this Zone ranges from 24919 to 2569 masl.

8.5.5. Eastern Main Subsystem (East-Main-2 TO AAR-BR-10)

The subsystem extends from the southern to the northern part of the town it has a total length of 14.4km. The Altitude in this pipeline system ranges from 2410 to 2549 masl.

8.5.6. Western Branch Subsystem (wst-br-1-2 TO wst-BR-6)

The subsystem is connected to the GBR-BR-7 at Junction, J-19 it has a total length of 4.7km. The Altitude in this pipeline system ranges from 2495 to 2519 masl.

8.5.7. Eastern Main Subsystem (East-Main-6 TO East-SBR-5)

The subsystem extends from the southern to the central part of the town it has a total length of 10.0km. The Altitude in this pipeline system ranges from 2451 to 2510 masl.

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8.5.8. Eastern Main Subsystem (East-Main-9 TO East-Main-16)

The subsystem extends from the Junction, j-62to junction J-71 it has a total length of 12.9km. The Altitude in this pipeline system ranges from 2415 to 2478 masl. It covers most of the eastern side of the town including newly included rural villages.

8.5.9. Addis Ababa Road Subsystem (AAR-BR-1TO AAR-BR-4)

The subsystem extends from the Junction, J-13 to junction J-54 it has a total length of 2.91km. The Altitude in this pipeline system ranges from 2466to 2472 masl. It covers Meda Wolabu University Area.

8.5.10. Addis Ababa Road Subsystem (AAR-BR-7 TO AAR-BR-4)

The subsystem is connected to WST-Main-13 subsystem at J-14 and runs from west to east supplying areas in the northern outskirt of the town joining with EST main-13 at junction J-70 making a loop connection. The Altitude of this pipeline ranges from 2442 to 2424 masl.

8.6 STORAGE RESERVOIRS

Filtered water, after chlorination (for disinfection) and soda ash (for pH correction) will be retained in a clear water tank for a minimum retention time of 30 minutes to allow for contact time. However, the clear water tank is a combination of a contact tank and a storage reservoir, 2500m3 capacity, for the distribution system. The contact time under this condition will be 300minutes which is more than adequate.

Design:Design Year 2,030

Maximum day demand 12,377 m3/dayMaximum hour factor 1.7

Maximum hour demand 21,042 m3/day

Water required for Daily chemical dilution and feed 0.20% of MDD 25 m3

Filter back wash 317 m3

Balancing for distribution 25.40% of MDD 3,144 m3

Total 28.28% of MDD 3,500 m3

Reserve volume, 15% of total 525 m3

Total Volume 4,030 m3

Existing reservoir in distribution system 450 m3

New reservoir in distribution system 1000 m3

Total in Distribution 1450 m3

Clear water Tank at TP 2,580 m3

Recommended 2500 m3

Provide Tank with dimensions:Length 25.0 mWidth 25.0 mwater Depth 4.25 mFree board 0.55 mContact time 300 Minutes; ok!

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8.6.1. Goba Road Service Reservoir (GRSR)

Goba Road Service Reservoir is located at the outskirt of the town toward Goba side upart from storing i also serves as a break pressure tank to keep the pipelines within 10 bar.. Accordingly, the existing reservoir and a new one nearby it, with 1000m³ capacity have been proposed to serve the subsystems, mentioned above.

8.6.2. Bulk Meters

Bulk meters shall be installed at the boundaries of Supply subsystems and at major junctions. 3 Bulk meters ranging in diameter of 400 mm are proposed in the new Distribution system. Their locations, size, and other descriptions indicated in Table 8.I.

Table 8.I Location of Proposed Bulk Meters

Line Junction X Y Z RemarkRWGM TPL 601,999 779,634 2764 Inlet to Treatment PlantGWM TPL 602,160 779,610 2,750 Outlet CWTGWM-2 GBR-SR 610,130 780,300 2573 GBR-SR outlet

8.7 Network Analysis

8.7.1. General

The existing Distribution System of the town has been studied in line with the towns Development Plan and the projected water demands.

Pipelines have been sized for year 2030 peak hour demand (222.3l/s) and are checked for the average day condition.

The service area elevation ranges from 1,990 to 2240 masl. The criteria adopted is to supply all areas from the clear water tank and break pressure tanks by gravity. The layout of the Distribution System is shown in Figure 8.2 on page 8-11.

8.7.2. System Simulation

The Distribution System is simulated using a hydraulic modeling software WaterCAD Version 6.5. The simulation was carried out for extended period by taking into consideration the hourly demand variation pattern on maximum and average day. The Distribution system is skeletonized and represented with the primary Distribution lines.

8.7.2.1 Nodal Demand

Domestic Demand, Commercial Demand, Institutional Demand and Industrial Demand, including a percentage for the unaccounted for water, are distributed to the Nodes, The Nodal Demands which were prepared and agreed during the Feasibility Study Phase are used for the original Municipality area, refer the Feasibility Design Report. For areas included recently, additional Nodes have been created and the respective demands allocated. The summarized Nodal Demands are presented in Table A1, Appendix '3'.

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8.7.2.2 Pipe Roughness

The hydraulic model (WaterCAd) uses the Hazen Williams Equation for calculations. Thus, the Hazen Williams Coefficients (HWC) are chosen for the pipes according to the material and age, refer Appendix '3', Table A3.

8.7.2.3 Computations

Two simulations were carried out, one for maximum day in which the peak hour exists and one for average day.

On average day, the hourly factors were multiplied by a global factor of 1.0. From this analysis the maximum pressure that can be developed in the system has been determined.

On maximum day the hourly factors were multiplied by global factor of 1.1. The peak hour demand is expected to occur during the maximum day on hour 8:00 at which the hourly factor is 1.7, & 1.5.

8.7.2.4 Sizing of Pipelines

The calculation of the peak hour demand case commenced with the actual diameters of existing pipelines and assumed diameters for new pipelines. Critical pipeline sections with excessive head losses were identified. If the pipeline is an existing line then a parallel line is introduced, if the pipeline is new then the diameter is increased until the minimum supply pressure (5 m), in any part of the system is achieved.

8.8 RESULTS AND CONCLUSION

After performing the hydraulic calculations, the final results for each scenario are presented under pipe result and node result along with the inputs and out puts in Appendix '1', Table A4 to A9.

Final results have shown that about 9.27 km of existing pipelines are found to be in good condition and are proposed to be used in parallel with the newly proposed lines. The remaining existing pipelines to be phased out.

Table 8.II Summary of Distribution Lines PN 10 pipes

Nominal Diameter (mm)

Length (m)Proposed Existing

uPVC Fe uPVC DCI50 5,06880 5,068

100 5,068 -

150 25,574 6192200 25,109 504 198250 15,283 1002 300 25,080 1374 400   10,306  

106,250 10,306 9,072 198 

Total 125.83km  

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Relevant Parameters of the hydraulic model as well as modifications of the Distribution System are shown on the Layout Drawing, Figure 8.2. The information includes: -

- Locations of pipelines- Pipe material and diameter- Pipe and node numbers- Proposed Reservoirs and Break Pressure Tanks sites

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Figure 8.2

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9. ENVIRONMENTAL IMPACTS OF THE SCHEME

9.1 IMPACTS DURING THE CONSTRUCTION PERIOD

The principal impacts during the construction stage are:

Waste discharges and refuse resulting from the establishment of the Contractor’s workers camp

Noise and dust resulting from the construction activity Spillage of lubricants, fuel, paint, other chemicals and scrap metal Soil erosion due to digging of trenches Off-take of woody bio-mass by the workforce Water use conflict with requirements of household and farmers Interruption to the existing water supply system

The impact of waste discharges and refuse disposal can be limited by the imposition of appropriate restrictions on the Contractor and having suitable clauses included in the Contract specifications.

Noise and dust are a short-term and localized problem. The impact of noise pollution can best be limited by the imposition of maximum noise levels on the Contractor and by the restriction of working hours, particularly with respect to locally recognized days of rest.

A waste management plan should be produced showing how waste oils, lubricants, other chemicals and scrap metal would be removed to a waste management facility where they could be recycled, incinerated, decontaminated and/or decomposed safely. If no such facility is available, the Contractor should propose and demonstrate an environmentally safe system of hazardous waste disposal.

Non-hazardous waste should be compacted and entrenched at an approved landfill sited over impermeable sub-soil, well away from a drainage course.

The Contractor should account for the quantities of hazardous (potentially polluting) materials (explosives, acid, paint, and solvents) brought to the site. Either they are used (and seen to be used) or removed.

Disturbed top soil should be preserved and restored and adequate precautions should be taken to prevent soil erosion.

Some interruptions to the existing water supply system are inevitable especially when house connections are remade. However, under present conditions frequent interruptions already occur and this should not be viewed as a significant problem.

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9.2 LONGTERM IMPACT

The improvement of the Robe town water supply would have obvious positive benefit on the quality of life and health of the public. Besides, the construction of access road to the proposed intake area has great advantage to the communities along the pipeline route and nearby areas. The construction of access road has also negative impact such as erosion and gulley formation if it is not properly designed but, this is easily prevented through appropriate design construction. For this appropriate design and specification has been produced.

Clearly, an increase in the volume of water supplied will generate a proportional increase in the volume of wastewater produced. To avoid any potential health hazards, it is essential that adequate means be provided for the safe disposal of all wastewater. This issue has been addressed in the Feasibility Study Report.

In order to mitigate negative pollution of the environment due to the waste generated during the treatment of the raw water appropriate treatment facility has been provided. If the components of the scheme are adequately maintained and design parameters are adhered to there should be no requirement for mitigation.

There is an extensively wide catchments area that brings a lot of tributaries for Lola River. All the rivers in this area start from Senete Plateau with bimodal rainfall and substantially brings a big discharge to the river almost constantly throughout the year.

The proposed water source is Lola river which has an estimated catchment area of 26 km2 at the proposed intake site and at upstream of the proposed intake it has three major tributaries among which Adoda is one.

Although the present situation and the past experience indicates that the Lola river catchment hasn't experienced draught, uncontrolled land use and deforestation of the catchment could negatively affect the river flow. With this context, dry period flow decrease and pollution of Lola river can be a problem if land use is not controlled around the catchment and along the river at upstream of the proposed intake. Measures that should be considered include:

Uncontrolled land use and deforestation of the catchment area and along the river should be prevented.

No refuse dumps or landfill sites should be permitted upstream of the intake area

Livestock farming should be prohibited upstream and nearby the raw water intake area and such installations or facilities fenced off

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10. PROJECT COSTS

10.1 Cost Estimates

The estimated costs for the Robe town Water Supply Project is assessed on the basis of tender rates from recent Contracts in Ethiopia and latest budget quotations for pipes, fittings, valves and equipment obtained from manufacturers, and local / overseas suppliers.

The costs have been estimated as total costs inclusive of Government duties and taxes. The estimated costs for the various Project components are presented in Table 10.II on pages 10-3 to 10-6 and summarised below:

Table 10.I Summary of Project cost Item No Description Amount in ETB1 CIVIL WORKS1.1 General Item and Preliminaries 2,574,500.001.2 Weir Intake and Aerator unit 1,271,227.431.3 Raw Water Gravity Main 347,074.031.4 Treatment Plant Works 23,604,914.931.5 Administration building, dwelling, workshop, etc 4,217,516.321.6 Access Road along the gravity main 16,631,138.421.7 Break Pressure Tank/Reservoir 1000m3 2,474,563.111.8 Treated Water Gravity Main 1,901,563.971.9 Distribution Mains 12,870,905.951.10 Secondary Lines 1,974,552.741.11 Public Fountains 199,038.00

Civil works sub-total 68,066,994.90VAT 15% 10,210,049.23

Civil Works Total 78,277,044.132 Power Supply 5,505,992

SUPPLIESSupply of Pipes, Fittings and Valves 62,783,885.22

3 Electro-mechanical Works 22,916,618.76

4 Sub Total estimated project cost 169,483,540.115 Capacity Building 2.5% item no. 4 847,417.707 Physical contingency 7.5% item no. 4 12,711,265.518 Price contingency 7.5% item no. 4 12,711,265.519 Total Project cost 195,753,488.83

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10.2 Criteria for Costing

The criteria used in the derivation of the costs is given below:

10.2.1 General

All prices are as applicable in October 2009. Allowance for price escalation during the contract period has been made by adding 10% of costs for the various project components to the total estimated costs. The costs derived are inclusive of Preliminary and General.

10.2.2 Pipeline Costs

Quotations were received from overseas and local suppliers of ductile iron and steel pipes respectively. Quotations were also received for locally manufactured uPVC pipes.

10.2.3 Supply of Pipes & Fittings

The current exchange rates have been used in the case of imported pipes and applied to c.i.f. prices quoted. To the c.i.f. prices, allowance has been made for all incidental financial costs, Contractors profits and overheads.

10.2.4 Civil and Construction Works

This includes costs for excavation, laying, jointing, testing and backfilling for both pipes and fittings, and construction of chambers, road crossings etc.

10.2.5 Pumping Plant, Compressors Costs

The costs include the supply, delivery and installation of the pumpsets, compressors, associated pipework, fittings, valves, electrical switchgear, cables etc.

10.2.6 Treatment Works Costs

The costs are based on unit rates derived from existing contracts of similar nature and magnitude under construction in the country. The figures are based on conventional water treatment works incorporating coagulation, clarification, rapid gravity filtration and chlorination.

10.2.7 Storage Reservoir Costs

The costs are based on reinforced concrete storage reservoirs. Recent costs for various capacities of similar reservoirs were studied, and unit rates derived.

10.2.8 EEPCO Power Line Connection and road Crossings

Actual budgetary costs were obtained from the parastatal bodies.

10.2.9 Total Gross Costs

The total gross cost excluding duties and taxes is arrived at after pricing actual Bills of Quantities, allowing 5% for Physical Contingencies and 5% for price contingencies.

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Table 10.II Project Costs Supply of pipes and fittings

 BILL NO.  DESCRIPTION

Amount

ETB

SP-01 GRWM From LOLA INTAKE To RWT 1,709,437.46

SP-02

TREATED WATER GRAVITY MAIN FROM CLEAR WATER TANK @ NEW TREATMENT PLANT TO NEW RESERVOIR TOWARD GOBA SIDE 18,833,491.53

SP-03GRAVITY WATER MAINGOBA ROAD RESERVOIRJUNCTION, J-43

1,039,875.09

SP-04 GBR-MAIN-1, 2 &3FromGM-2 @ JUNCTION J-43ToJUNCTION, J-1 1,041,187.44

SP-05

LINE-WST-MAIN-01 TO LINE; WST-MAIN-13GBR-MAIN-03 @ JUNCTION J-1JUNCTION J-14 4,350,887.14

SP-06GBR-BR-5 TO AAR-BR-12GBR-MAIN-02 @ JUNCTION J-16JUNCTION J-77

5,523,589.55

SP-07 WST-BR-1 TO WST-BR-6CBR-BR-7 @ JUNCTION J-19JUNCTION J-31 1,200,168.39

SP-08 GBR-BR-1 TO ADM-BR-3GBR-Main-1 @ JUNCTION J-34JUNCTION J-75 3,091,427.63

SP-09 EST-MAIN-1 & EST-BR-2GM-2 @ JUNCTION J-43JUNCTION, J-46 1,963,601.53

SP-10EST-MAIN-2 TO AAR-BR-11EST-MAIN-1 @ JUNCTION J-44JUNCTION J-76

3,807,407.31

SP-11 EST-MAIN-6 TO EST-SBR-5EST-MAIN-5 @ JUNCTION J-50JUNCTION J-59 2,626,976.06

SP-12 EST-MAIN-9 TO EST-MAIN-16EST-MAIN-8 @ JUNCTION J-62JUNCTION J-71 3,652,686.11

SP-13 GBR-SBR-1 & GBR-SBR-2GBR-BR-4 @ JUNCTION J-38JUNCTION J-50 236,368.80

SP-14

CNT-SBR-1, CNT-SBR-2 & CNT-SBR-3CNT-MAIN-1 @ JUNCTION J-20JUNCTION J-51 572,132.99

SP-15 EST-SBR-4EST-BR-4 @ JUNCTION, J-52JUNCTION, J-57 253,069.02

SP-16AAR-BR-1, TO AAR-BR-5WST-Main-12 @ JUNCTION J-13JUNCTION J-54

908,622.56

SP-17 ADM-BR-4FromAAR-BR-3 @ JUNCTION J-73ToJUNCTION J-74 164,851.88

SP-18

AAR-BR-7 TO AAR-BR-10FromWST-MAIN-13 @ JUNCTION J-14ToJUNCTION J-70 865,717.28

SP-19 DISTRIBUTION - Secondary Lines 2,753,185.03

  Bill Total Exclusive of Duties and Taxes 54,594,682.80

  Estimate of Duties Payable (by Category)

  Sub-Total Duties

  Total Inclusive Duties 54,594,682.80

  Estimate of V.A.T. Payable (by Category)

 

This should be based on Tax Status on various goods and services provided by the VAT Department - Inland Revenue Authority

8,189,202.42

   

  Sub-Total Taxes 8,189,202.42

  Total Inclusive of Duties and Taxes 62,783,885.22

ARMA Engineering PLC 3

Page 100: Robe-Detail Design Report

ROBE TOWN WATER SUPPLY PROJECT - FINAL DETAIL DESIGN REPORT CHAPTER 10

Table 10.II Project Costs for civil works   SUMMARY OF BILLS

 ROBE WATER SOURCE DEVELOPMENT AND TREATMENT

WORKS

    Amount

BILL NO. DESCRIPTION ETB

BILL NO.A01 Preliminaries and General 2,574,500.00

BILL NO.A02 Intake Weir 1,026,932.58

BILL NO.A03 Cascade Aerator 244,294.85

BILL NO.A04 Raw Water Gravity Main 01:- From Intake to Aerator 236,797.31

BILL NO.A05 Raw Water Gravity Main 02:- From Aerator to Header Tank 110,276.72

BILL NO.A06 Header Tank 910,322.24

BILL NO.A07 Chemical Building & Rapid Mixer 2,008,786.87

BILL NO.A08 Clarifiers 1,726,832.43

BILL NO.A09 Rapid Sand Filters 5,405,279.99

BILL NO.A10 Chlorination Building 1,086,704.18

BILL NO.A11 Clear Water Tank 3,253,140.68

BILL NO.A12 Pump & Compressor House 514,232.59

BILL NO.A13 Generator House 590,186.09

BILL NO.A14 Back Wash Water Tank 995,707.02

BILL NO.A15 Back Wash Water Detention Tank 800,842.99

BILL NO.A16 Sludge Drying Beds 2,745,113.43

BILL NO.A17 Treatment Plant Site and Pipe work 3,567,766.42

BILL NO.A18 Administration Building 2,207,061.52

BILL NO.A19 Workshop & Store 863,264.31

BILL NO.A20 Managers Dwelling 623,969.13

BILL NO.A21 Guard House 216,611.36

BILL NO.A22 Toilet & Shower 306,610.00

BILL NO.A23 Access and Maintenance Road Along Gravity Main 16,631,138.42

CW-01TREATED WATER GRAVITY MAIN FROM CLEAR WATER

TANK @ NEW TREATMENT PLANT TO NEW RESERVOIR TOWARD GOBA SIDE

1,901,563.97

CW-02GRAVITY WATER MAINGOBA ROAD

RESERVOIRJUNCTION, J-43 62,426.13

CW-03GBR-MAIN-1, 2 &3FromGM-2 @ JUNCTION J-43ToJUNCTION,

J-1 322,358.59

CW-04

LINE-WST-MAIN-01 TO LINE; WST-MAIN-13GBR-MAIN-03 @ JUNCTION J-1JUNCTION J-14 1,275,322.87

CW-05GBR-BR-5 TO AAR-BR-12GBR-MAIN-02 @ JUNCTION J-

16JUNCTION J-77 1,615,810.00

CW-06WST-BR-1 TO WST-BR-6CBR-BR-7 @ JUNCTION J-

19JUNCTION J-31 687,299.43

CW-07GBR-BR-1 TO ADM-BR-3GBR-Main-1 @ JUNCTION J-

34JUNCTION J-75 1,465,008.21

CW-08EST-MAIN-1 & EST-BR-2GM-2 @ JUNCTION J-43JUNCTION,

J-46 790,185.11

ARMA Engineering PLC 4

Page 101: Robe-Detail Design Report

ROBE TOWN WATER SUPPLY PROJECT - FINAL DETAIL DESIGN REPORT CHAPTER 10

Table 10.II Project Costs for civil works continued

 BILL NO.  DESCRIPTION

Amount

ETB

CW-09EST-MAIN-2 TO AAR-BR-11EST-MAIN-1 @ JUNCTION J-44JUNCTION J-76 1,843,899.54

CW-10EST-MAIN-6 TO EST-SBR-5EST-MAIN-5 @ JUNCTION J-50JUNCTION J-59 1,260,710.75

CW-11EST-MAIN-9 TO EST-MAIN-16EST-MAIN-8 @ JUNCTION J-62JUNCTION J-71 1,591,296.13

CW-12GBR-SBR-1 & GBR-SBR-2GBR-BR-4 @ JUNCTION J-38JUNCTION J-50 264,240.66

CW-13CNT-SBR-1, CNT-SBR-2 & CNT-SBR-3CNT-MAIN-1 @ JUNCTION J-20JUNCTION J-51 347,809.46

CW-14 EST-SBR-4EST-BR-4 @ JUNCTION, J-52JUNCTION, J-57 137,387.79

CW-15AAR-BR-1, TO AAR-BR-5WST-Main-12 @ JUNCTION J-13JUNCTION J-54 511,619.51

CW-16 ADM-BR-4FromAAR-BR-3 @ JUNCTION J-73ToJUNCTION J-74 150,152.22

CW-17AAR-BR-7 TO AAR-BR-10FromWST-MAIN-13 @ JUNCTION J-14ToJUNCTION J-70 545,379.53

CW-18 DISTRIBUTION LINES - Secondary Lines:- 1,974,552.74

BILL No. A24 DISTRIBUTION - PUBLIC FOUNTAINS 6 Nos 199,038.00BILL No. A25 GOBA ROAD 1000m3 RESERVOIR 2,474,563.11

   

  (A) TOTAL OF BILLS 68,066,994.90  (B) VAT @15% x (A) 10,210,049.23  (C - TOTAL (A) + (B) 78,277,044.13  (D) CONTINGENCIES @15% x (C 11,741,556.62  GRAND TOTAL (C + D) 90,018,600.75

ARMA Engineering PLC 5

Page 102: Robe-Detail Design Report

ROBE TOWN WATER SUPPLY PROJECT - FINAL DETAIL DESIGN REPORT CHAPTER 10

Table 10.II Project Costs for Electromechanical works

  SUMMARY OF BILLS

       AmountBILL NO. DESCRIPTION ETB

EM-001 General 1,656,445.31

EM-002 Intake 321,324.29

EM-003 Header Tank & Aerator 839,163.74

EM-004 Rapid Mixer and Chem. Dosing Unit 831,554.90

EM-005 Upflow Clarifier 1,896,270.73

EM-006 Rapid Sand Filter and Gallery 7,766,889.06

EM-007 Clear Water Tank 810,346.79

EM-008 Clear Water Pumping Station 1,988,211.20

EM-009 Backwash Water Tank 913,464.26

EM-010 Compound Work 1,523,009.92

EM-011 Break Pressure Tang/Balancing Reservoir (1 x 500 m³) 1,380,814.37

EM-015 Treatment Plant Electrical     19,927,494.57

  Bill Total Exclusive of Duties and Taxes 1,656,445.31

        Estimate of Duties Payable (by Category)        Sub-Total Duties …………………………..     Total Inclusive Duties …………………………..        Estimate of V.A.T. Payable (by Category) 2,989,124.19

 

This should be based on Tax Status on various goods and services provided by the VAT Department - Inland Revenue Authority

     Sub-Total Taxes 22,916,618.76        Total Inclusive of Duties and Taxes 22,916,618.76

   

ARMA Engineering PLC 6