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HÁRVESTING RAINWATER
SEMI-ARID AFRICA
ManuaL No. 3Rock Catchment Damwith se[f-c[osing Watertap.
Erik Nissen-Petersen~ Dr Michael Lee.Nairobi~1990
217—8879 L
Harvesting Rainwater in Semi—arid Africa consists of 6 Xanuals:
Manual No. 1. Water Tanks with Guttering and Hand-pump.
Manual No. 2. Small Earth Dam built by Animal Traction.
Manual No. 3. Rock Catchment Dam with self—closing Watertap.
Manual No. 4. Shallow Wells with Bucketlift.
Manual No. 5. Sub—surface and Sand—storage Dams.
Manual No. 6. Spring Protections.
Each I4anual deals with siting criteria, standard designs and bills ofquantities in a simple text and drawings.
The Manuals are based on practical experience gained by building some700 water structures for rainwater harvesting in semi—arid Kenya overthe last 14 years.
Copyright
Permission is hereby given for reproduction of this material, in wholeor part, for educational, scientific, or development related purposes,except those involving commercial sale or services, provided that fullcitation of the source is given.
Reproduction for commercial purposes may not take place without priorpermission from:
ASAL Rainwater HarvestingP. O. Box 14333NAIROBIKenya
—
LIBRARYI INTERNATIONAL REFERENCECEN1RE FOR COMMUNITY WATER SUP~LYAND 3A~1TATV)N(IRC)P.O. Bo~93!~0, 2509 AD The HagueTt~l.(070) 814911 ext. 141/142
~ÑLO:~ ~
(i)
ACKNOWLEDGMENT
The authors of these manuals are qrateful for the qrants given byDanida which made possible the compiling and publishing of theirexperience with rainwater harvesting for self—help groups in semi—aridareas of Africa.
Much gratitude is also due to the Ministry of Agriculture in Kenya,which together with Danida afforded the opportunity of developing low—technology and labour—intensive methods of harvesting rainwater andthereby enabling people and livestock in a semi-arid region of thecountry to have access to a steady water supply.
Thanks are also due to the local inhabitants with and for whom thesetechniques were developed and implemented. Their understandableskepticism in starting up these demanding activities gave the processa sound and realistic foundation on which to build.
Personal thanks are very much due to:
Preben Enhard of Mutomo Soil and Water Conservation Project for hisconsiderable support.
Jan Nissen—Petersen for assisting in drawing more than half of theniany drawings.
Kim Nissen—Petersen for the many proof—readings and useful comments.
Erik Nissen—Petersen and Xichael Lee
(11)
CONTENTS
PAGE
SURVEYORSMANUALON ROCK CATCHMENTDAMS 1
1. Introduction 12. Siting and Selection Considerations 13. Deciding on the Size of Dam to Build 44. Calculating the Required Catchment Area 55. Designing the Dam 76. Dam Wall Volume Calculations 87. Standard Designs 118. Materials, Labour and Transport Requirements 139. Bills of Quantities and Costing 16
10. Site Preparations 1711. Setting Up the Templates 1812. Preparing the Foundations 2013. Bringing Materials and the Contractor to the Site 2014. Maintaining and Improving Water Quality 21
CONTRACTORSMANUALON ROCKCATCHMENTDAM 23
1. Preparing the Foundations 242. Installing the Draw—off Pipe 253. Constructing the Dam Wall 264. Plastering the Dam Wall 275. Laying Out and Building Masonry Gutters 286. Constructing the Draw—off Pipe and Tapping Station 307. Quality Control and Maintenance 32
CONTRACTORSMANUALON SELF-CLOSING WATERTAP 34
1. Self—closing Water Tap 352. Materials and Cost 363. Making the Self—Closing Water Tap 374. Installing the Water Tap 39S. Making a Fixed Spanner for the Caretaker 40
SURVEYORSMANUAL
ON
ROCK CATCHNENTDANS
1. Introduction
The masonry gravity dam is a vertical wall constructed around theouter edge of a depression or hollow in a rock—surface to capture andretain water running off the rocky surface. Rock surfaces have thesame efficient run—off production as iron—sheet rooftops without thecost to the user therefore local people in ASAL regions have taken agreat liking to these water harvesting systems. This is particularlytrue where the materials are provided by an outside agency or thegovernment and the people supply all the manual labour for sitepreparation and system construction.
Hasonry gravity walls can be built in all lengths and sizes dependingon the shape of the site where they are built and the size of thereservoir they will hold. There is no standard design for thereservoir as with tanks but there is a standard design for the wallitself and the method by which it is built. A set of techniques areexplained that can be used •to build a single wall, or a dam withseveral sections each of a different height or length. Gravity wallshave been built that there are 2 metres high and 10 metres long and 6metres high and 60 metres long. Reservoirs have been created thatcontain 20,000 litres and ones that contain 4 million litres, allusing the same construction design, methods and materials althoughobviously in different sizes and quantities and with differentcatchment areas.
The maximum size of the reservoir is ultimately determined by the sizeof the catchment and the expected rainfall depth in a season or year.This determines the amount of supply, but it can also be limited bythe shape of the site where the dam can be built and the amount oflabour the self-help group can, or want to supply. This last factordepends on their water demand and their size, organisation andexisting time commitments. A brief discussion of these points isgiven here.
2. Siting and Selection Considerations
Finding a Site
Masonry gravity dams are constructed on rock outcrops either in rockytop slope areas or ìn the lowlands where inselbergs are found(sometimes called tors or whalebacks).
To site them, features to look for are hollows, depressions or gullieswhere the rock dips either looking down the slope, across the slope orboth. These dips can then be converted into a water—holding reservoirby constructing a single gravity wall dam, or several sections of wallin a V-shaped or U—shaped dam.
1
Sometimes the dips are filled with soil. If trees and shrubs growthere this is good because it means there will be a deep dip which canbe excavated and store plenty of water.
The rock above the dip should preferably be wide and slope like afunnel towards the dip so that water will drain there. However,straight slopes or rounded hills are suitable catchments becausesimple stone and mortar raised gutters can be built out from the endsof the gravity dam sloping up and across the rock. They catch run-offwater from the rock surface and bring it down to the dam. Where therock outcrop is a steep—sided, flat—topped hill with the dam built atthe base of the cliff these gutters can still be used. In this casethey can be built around the top of the rock, bringing water to apoint above the dam and letting it flow over the cliff and fall intothe reservoir.
Positioning the Dam Wall
When such a site has been found in the field the best position tobuild the dam must be decided upon. Looking down the slope of therock, the best site is the outer edge of a dip, where the angle of therock face is near the horizontal before it steepens again.
By having a horizontal base, reinforcement of the dam is not requiredbecause the weight of the dam can withstand the pressure of the storedwater. With no reinforcement the construction and the design becomessimple. The dam wall must be built on a rock sloping down towardsthe reservoir because the weight of the wall can push it down the rockface and cause its destruction. Make sure the foundations are builton almost flat rock surfaces or ones sloping slightly backwards to thereservoir. The foundation must be a clean, hard rock surface and notsoil or loose rock.
r r/ l / l
/ l l/ l
/ l/ l /
/ l // l
/ , l/ /
, i /
jj!/ j ,~// / 200
SuitQbIe slopes ~,..7977UnsuitabIe slope
Slopes of rock tloor
2
Because these dips in the rocks come in a variety of slopes and sizes,the size and shape of the dam wall varies too. The number of separatesections in the dam will depend on the shape and the curve of the lipor ledge on which the dams foundations are laid.
Generally, for a cross—slope depression forming a small valley in therock surface, a single wall can be built across the dip that isdeepest in the middle and tapers to both ends when it joins the valleysides.
For a funnel shaped depression like a small basin, a V—shaped dam willbe built with the point at the front of the depression with twotapering arms back to the two sides of the funnel.
Forthehigh
a continuous slope where the dip is downslope stretching acrosscomplete width of the slope a U—shaped dam will be built with afront—wall and two tapering side walls.
3
3. Deciding on tbe Size of Dam to Build
In deciding how big to build a dam several things need to beconsidered;
a. the water demand of the self—help builders and usersb. the amount of labour the self—help group can supplyc. the size of the catchment area and the rainfalld. the volume of the reservoir created by the dam.
A11 these have to meet somewhere in the middle for an effective,appropriate water harvesting system.
The best size of self—help group for the construction of a masonrygravity dam is about 60 families so that each family can supply oneadult member to the workforce for three or four days per week duringthe construction.
There is a limit to the number of work days a self—help group can beexpected to provide in a given season. This depends on the length ofthe dry season and the commitments of the self-help group to otheractivities. Generally, at the most a self—help group can be expectedto work for 9 months or 180 work days a year. During the rainy seasonthe construction site will be mostly underwater as the partiallyfinished dam retains water. Some dams have been built too big for thecatchment area and never filled completely. For that reason it isnecessary to build in stages. The first stage should be a maximum of2.5 metres. The dam can be raised to 3.5 metres in the next dryseason should the catchment area prove big enough. Should the usergroup need more water and be willing to continue with construction,then the dam wall can be raised another 1.0 metre.
If a dam is built in stages, the designer should not build thefoundations of the larger dam in the first season and then add theadditional sections using the larger dam design. Instead, a small damshould be built using the templates for a dam of this size. As thedam is built higher both the thickness and the height is built up.
To help fill the dam, gutters can be built to harvest from as large acatchment area as possible, preferably the whole rock.
2nd
lst phi
3nd pr
4
Water Demand
To calculate the water demand for a group of people is simple.
Formula:
No. of families x litres per family per day in dry season = demand.
Example:
60 families x 60 litres per family per day x 180 days dry season
= 648,00 litres
The amount of water that needs to be stored at the end of the rainyseason is therefore 648,000 litres (648 cubic metres) to satisfydemand it is wise to include losses to evaporation of about 33%.
The minimum size of the dam reservoir can then be determined as:
Formula: demand + 33% in evaporation losses
Example:648,000 litres + (648,000 litres x 33) = 861,840 litres (862 cu.m.)
1 00 r
4. Calculating the Required Catchment Area
If the catchment area is all rock outcrop with little soil cover, itis possible to calculate the size of the area that will supply thisvolume if the seasonal rainfall is known.
Formula for calculating run—off:
Rainfall mm x run-off coefficient x catchment area sq.m. = run—off volume
The run—off coefficient is the proportion of rainfall that will becomerun—off and for all rock surfaces is 0.9. With small catchment areasit is generally true that the catchment is all rock and the 0.9 run—off coefficient can be used. As dams and catchment areas get bigger,the soil covered area increases and the coefficient 0.7 must be used.
Marking Out the Catchrnent Area
To calculate the area draining to the proposed dam site estimate wherethe ends of the dam will be situated. From these points, walk orclimb up the slope along the steepest line, marking your route withchalk until you reach a point where the slope is going away from youand you are going downhill again. If that is done for both ends ofthe dam, the area between the chalk lines drains to the dam—site.
The area used in the calculation is the plan area, that is the areayou would see if you looked down from right above. If the slopeangles are less than about 15 degrees then the surface area is closeto the plan area. As the slope increases, the plan area becomes lessthan the surface area by increasing amounts.
5
Since the length of an average step is about 0.60 m (60 cm) followingexamples on measuring catchment areas by walking can be shown:
a. easy walk on a square rock sloping only a little, lengthsmeasuring 140 steps x 75 steps = (140 steps x length of step0.60 m) x (75 steps x length of step 0.60 m) = 129 sq.m.
b. difficult walk on a square rock sloping much, lengths measuring140 steps x 75 steps = (140 steps x length 0.60 m x 0.75) x (75steps x length 0.60 m x 0.75) = 97 sq.m.
c. climping on a square rock sloping very much, lengths measuring140 steps x 75 steps = (140 steps x 0.60 m x 0.5) x (75 steps x0.60 m x 0.5) = 65 sq.m.
Example of calculating run-off volume:
Rainfall 300 mm x run—off coefficient 0.7 catchment area 97 sq.m
= 20,370 litres (20 cu.m.)
Enlarging a catchment area.
The catchment area of a dam can be enlarged by building stone guttersaround the rock. Such gutters will collect run—off which otherwisewould have bypassed the dam reservoir. Stone gutters are build offlat stones sat in mortar. Start building the gutters from the endsof the dam wall and let them surround as much rock surface as possibleby building them with a gradient sloping 3 cm upwards per 100 cm.this is best measured by using a gutter—level 100 cm long with 2 legs,the one being 3 cm shorter than the other (see contractors manual).
If the rock outcrop is a rounded inselberg and the dam built on oneside, the gutters can circle round so that most of the outcrop can bemade to drain to the site. Where the dam is situated at the base of asheer cliff, the measurers can climb to the top, mark a point directlyabove the dam site and mark out gutters going off either side acrossthe more shallow hill top. This is the catchment area and the watercollected can be made to drain straight down the cliff.
—.
.-
6
Having marked out the area, measured it, and multiplied the surfacearea by the factor of its steepness the size can be compared againstthe size of the catchment needed. This will indicate whether thegutters are needed or if the catchment is too small. If it is toosmall it may still be worth going ahead with the construction if thereare no alternative sites nearby. If the area is bigger than thatrequired this is fine because then a bigger reservoir can be built andthe demand will stand a greater chance of being exceeded by the supplyalmost every year.
5. Designing the Dat
Having worked out the demand and the supply potential of the catchmentit is necessary to work out exactly where to put the dam, how big itmust be and how much water the reservoir it creates will hold. Withrooftop tanks these things are easy because the shape is standard andthe volume can be calculated knowing a few simple measurements. Withmasonry gravity dams, the shape of the reservoir is not standard andis uneven. To work out volume speedily and without using highlytechnical methods involves approximating the complicated slopes byconvenient standard shapes and taking a few simple field measurements.
The method should be simple enough to take measurements in the fieldand work out the approximate volumes on paper with a pocketcalculator. As an example of the methods to be adopted we use thesingle—wall gravity dam. To design multiple wall dams requires moreexperience which will be gained from designing and building some ofthe less complex dams first.
The Single Gravity Dam
The shape of the reservoir can be approximated as shown below.
7
To calculate the volume of the reservoir, the following dimensions are
required:
a. the proposed height of the dam at its deepest point (h).
b. the length of the crest of the dam on either side of the deepest
point (Xa and Xb)
c. the length from the top of the proposed dam wall at the highestpoint back along the horizontal to the rock surface (L). Thismarks the surface of the water when the dam is full.
With these dimensions the volume of the reservoir can be found
considering the two sides A and B separately;
Formula: Volume A = h x Xa x L + Volume B = h x Xb x L = Volume
Example:4 4
A = h 2.5 m x Xa 6.0 m x L 34.om + B = h 2.5 m x Xb 8.0 x L 34.0 m4 4
6. Dam Wall Volume Calculations
= 297.5 cu.m.
by
There are two shapes that the gravity wall sections can have, giventhe standard design of the wall. They depend on the depth at eitherend of the section and are illustrated as Section 1 and 2 below.
Section 1 is the shape of each half of a straight, single—wall dam.However, in some situations, a V—shaped, or U—shaped dam needs to bebuilt to take advantage of a particular hollow. In this case, the dammay be made up of separate parts that look like Section 1 and scmelike section 2. (see page 10)
8
Franrneasurerientwe know the heightsand lengthsof the secticin. We also know because ofthe standard designthe width of the crestand the base. The crest is always 0.3 m nomatter what the dam height. However, the basewidth varies according to the height asshown in the relatic*iship below.
6~h~gti~
5
4
3
2
00 1 2 3 4m.bcise
height 0.7 1.0 1.5
base 0.3 0.45 0.7
crest 0.3 0.3 0.3
2.0 2.5 3.0 3.5 4.0 4.5 5.0
1.1 1.4 1.8 2.1 2.5 2.8 3.2
0.3 0.3 0.3 0.3 0.3 0.3 0.3
This graph, which gives us the base for eachheight allows us to calculatethe volurries ofthe dam wa].ls.
For Sectic*~ 1, the volurne is equalto ha].f a rectangularblock plus a quarter of arectangularblock for each of the t~halvesof the dain wall called A and B.
The voluirie of a dam wall thereforecc~sistsof half block + quarterblock for both sides
of a dam wall.
Forimila for calculatingvoltine of dain wall:
Volume A + volume B = voluine of wall.
VoluineAandBformulasaresiiiiilar:(hxxxo.3)x(hxxx(base-0.3)=volume2 4
F~amp1e:
Volume A = (h 2.5m x Xa 6.Om x 0.3) + (h 2.5 x Xa 6.Om x (1.4 - 0.3) = 6.375 cu.m.2 4
VolumeB= (h2.5nixxb8.OmxO.3) + (h2.5mxXb8.Omx (1.4-0.3) =8.5cu.m.2 4
Volume A 6,375 cu.m. + volume B 8,5 cu.m. = 14,875 cu.m. voltmie of dam wall. say 15 cu.rn
,,
-
- —
1111711 1— —
250-~-
~Sliding factor
~14ObaseOverturning i~ctor
—~
9
Thn~i1afor calculatingvoliiæ of 4 a~plasterœcrestand frcnt wall:
Area to be plasteredx 0.04 m thicknessof plaster= volume
Example: (AreaAh2.5xXaG.0) + (keaBh2.5xXb8.0) +2 2
(Crest 6.0 + 8.0 x 0.3) x 0.04 m plaster= volume
A 7.5 sq.m.+ B 10.0 sq.m. + crest4.2 sq.m. x 0.04 = 0.87 cu.m. plaster= say0.9 cu.m.
For secticn 2, the volume is equal to a block with the averageof the two heightsha and
hb plus half a block with the averageof the t~heightsha andhb.
Secticn2 thereforecctisistsof block + half block.
Fbrninla fœ block: (ha + hb) x Xa x 0.3 = volume of block2
Fbrriilafœhalfblock: (ha+hb)xXax(Baseb-Basec-0.6) = volumeofhalfblock2 2
2
(Secticn 2 is not includedin the examplesshown on the following pages)
10
StandardDesigns
Drow-pf
Lay-out ptan1:100
Longttudtnot section1 75
2.50
~jI
Cross section25
11
Standard Designs
o 30
L~Q~o~
O 45
Tapping station
Lay-out planV200
1200
4-4Cross sectìon
1 50
Rock
12
7. Materia].s, labour aM transportrequircments
The requireiientsof materials, labcur aM transportare calculatedas follows:
a. Voline of structure.
First calculatethe total voltine of the structureto be build by findir~the volinesof the varicius parts of the structureand thereafteradding it all together. Theresult will be th~ total voline measuredin cubicmetres (cu.m.).
b. Type and weight of materials.
When the total volume of the structurevariouscccin-ientsof that volume can be
Weight per 1 cubic metre (cu.m.) material.
Water 1 cu.m. weigbs 1000 kg = 1.00 tccneCeinent 1 cu.m. weigbs 1350 kg = 1.35 tc*meSand 1 cu.m. weigbs 1600 kg = 1.60 tccneStcnes 1 cu.m. weighs 2200 kg = 2.20 tccne
1 cu.m. Stcce-iiiasccry weighs 2850 kg = 2.85
stcces75% 1650 kg = 1.65ixrtar 1:4 25%ceinent 200 kg = 0.2sand 800kg=O.8water 200kg0.2
hasbeenfound, tbe typeaM weigbt of the
estiinatedby using the following formula:
Cccvertedmeasurcments.
1 tccne = apprax. 5 drums of water.1 tccne = 20 bags of cenent.1 tccne = apprax. 8 wheelbarrows of sand.1 tccne = apprax. 8 wheelbarrows of stcces.
tccne aM cccsists of:
tccne = 14 wheelbarrow of stcces
tccne = 4 bags of cementtccne = 7 wheelbarrows of saMtccne = 1 drum of water
lcu.m. ~rtar, 1:3withnilweigbs2400kg =2.4tccneaMcccsistsof:
cement 500 kg = 0.5 tccne = 10 bags of cementsaM 1600 kg = 1.6 tccne = 13 wheelbarrows of sandwater 300kg=0.3tccne=11/2drumofwater
1 cu.m. ~rtar, 1:4 weighs
ceiiìentsandwater
2200 kg = 2.2 tccne and consists of:
400kg=O.4tccne= 8bagsofcement1600 kg = 1.6 tccne = 13 wheelbarrows of sand200kg=0.2tccne= ldrumofwater
13
requireiænts= tc*mes = Œtlvertedmeasurements.
Yor plastering: Multiply volume with requirementsfor 1 cu.m. n~rtar1:3 w±thnil.
Voliiie of plaster x 1 cu.m. requirements= tcmnes= atvertediæasurements
O.9cu.m.xceinento.Sotccnes=O.5tccnesx2o= lObagsofcement
Fbr stcnegutters: 1 cu.m. n~rtar,
Required1et~thx Requirementsper
Eiample:
200 m guttersx cement 4.0 kg per
200 m guttersx sand 16.0 kg per
200 m guttersx stcces90.0 kg per
200mguttersxwater 2.Okgper
Thtal requ±rementsof materials
1.5 tctmes x 8 = 12 wheelbarrowsof sand
O.3tctmesx 5= 2drun~ofwater
d
1:4, g±ves100 metresof stcce gutters.
1 m = kg = tccnes = cccvertedineasuraænts
~ter the requirementscn the bills of quantities
Eiaiçle:
Fbr walls: Multiply voluiæ with requirementsfor 1 cu.m. of stccemascnry.
Voluæ of wall x 1 cu.m.
15.0 cu.m. x
15.0 cu.m. x
15.0 cu.m. x
15.0
cement 0.20
stcces1.65
sand 0.80
tcmne= 3.Otcnnesx20= 60bagsofcaænt
tcnne=24.8tccnesx8=l98wheelbarrowsofstcne
tccne = 12.0 tctmesx 8 = 96 wheelbarrows of sand
cu.m. x water 0.20 tcnne= 3.0 tcnnesx 5 = 15 drums of water
0.9 cu.m. x sand 1.60
0.9 cu.m. x water 0.30
tcmnes=
tcnnes=
lm= 800 kg= 0.8 tc*mes= l6bagsofcement
1 m = 3200 kg = 3.2 tccnes= 26 wheelbarrows/sand
1 m = 18000 kg = 18.0 tccnes= 144 wheelbarrowsfstcnes
lm= 400kg= 0.4 tcnnes= 2druinsofwater
Caænt 4.3 tcnnes = 86 bags of cement
Stcces 42.6 tc*mes = 343 wheelbarrows of stcces
SaM 16.7 tcnnes = 134 wheelbarrowsof sand
Water 3.7 tc*mes = 19 drums of water
67.3 tccnes
14
\
Labour requirements:
On experienceit is known that cne skilled artisanwith the help of 15 self-help labourerscan prepare the site, carrymaterial, in±xm~rtaraM btiild 0.8 cubicmetre of stcnemascnryper day. The estimatefor labour requirementsis thereforeas follows:
Thrmula for wall: Volume cu.m. = skilled days required. Unskilled days = x 150.8 cu.m. per day -
~mp1e: Volume 15 cu.m. = 19 days of skilled labour. UÏiskilled days 2850.8 cu.m. per day
Forimila for stcnegutters: m of gutters= skilled days. Unskilleddays = x 1515m
Example: 200 m of gutters= 14 skilled days and 210 unskilled days15
&iter the requirementscc the Bil1s of ~antities
Transportrequirementsof material
Transportaticcof materia1sis divided into t~categories:
a. Transportof lœa1rnaterials,such as sand, stcnesand water, wi11 be transportedtothe site by the self-helpgroupsusing oxen-donkeyandhand carts given to then bythe project. The number of loads to be transportedand the d±stancesinvolveddependson local conditicnsaM cannot be estimatedhere.
b. Transportof purchasedmaterials, e.g. cement, reinforcenentwire aM tenplatesisestimatedaccord±ngto tcnnage,distanceaM ccst per kxn.
Formula: Thnnes x return distance (kin) x Shs. per kin.
Example: 5 tcnnesx return distance86 kni x Shs. 6/50 per kni = Shs 2,795/00
&kter the requirementscc the bills of quantities
15
Bi11 of Quantity fcr ite~ to be deliveredfree of tharge
Unskilled labour: 495 labour days . x
Sand: 16.7 tcnnes (= 134 wheelbarrows) x
Stcces: 42.6 tcnnes (= 343 wheelbarrows) x
Water: 3.7 tcnnes (= 19 drums) x
Transport:63 tcnnes (= 126 cart loads) x Shs = Shs
Thtal value of self-help Shs
CkaM total œstaM value of project Shs
8. R~11~of QUantitiesand Cœting.
Two bills of quantitiesare needed,becauseabouthalf the itans will be deliveredby thedccor/ministry aM the otherhalf will be deliveredfree of charge by the ccnamityccccerned. Since the ccinmunity is supposedto ccctributeaboutha1f the œst of theproject, avalueof their inpit hasto be calculated.
Eiaiçle.
Bills of QUantitiesfor itai~ to be deliveredby the dcrsx/rriiriistzy.
Skilled labour: 1 ccctractorfor 33 days x Shs = Shs
Caænt4.3 tonnes= 86 bags x Shs = Shs
G.I.piping,r:9ometres/6=lslengths xShs =Shs
Polythenesheetingfor curing: 20 metres x Shs = Shs
Thansportof ccntractoraM materials8 tctmesx... km x Shs = Shs
Thtal œst Shs
I~the self-helpgroup
Shs = Shs
Shs = Shs
Shs = Shs
Shs = Shs
16
9. Site Preparations
Having decided on the layout of the dam wall sections and shape of thedam and having calculated the size of dam that can be built in onework season the construction site can be prepared. As indicated inthe previous section, if a large dam is to be built, but in stagesthen the site should be prepared for the smaller dam (2.5 m firststage) first (with the templates for the height of the smaller stage).In future work seasons the dam can be built upwards and outward. Ifthe base of the dam is built according to larger templates a lot ofeffort is needed to create even a low structure and this effort willbe wasted if the future work plans are abandoned.
Preparing the site involves the following step3:
a. clearing a track to the site from the nearest road and sources ofbuilding materials
b. clearing a flat area near the site for the construction camp andfor stockpiling materials
c. setting up the templates and builders lines marking out thesections of the gravity wall
d. preparing the foundation of the rock ready for building
e. training a storekeeper who will be responsible for looking after
materials delivered to the site
f. local sources of sand, ballast and water can be located andtransported to the site by the self—help group by donkey cart,wheelbarrow or basket, or by jerrycan. If this is not possible,materials can be brought by tractor and trailer.
The templates are made in the workshop using the measurementsdiscussed earlier. As explained there are two templates for eachcorner of the dam wall and there can be intermediate templates.
lst pl
2nd ph
3nd
17
Clearing a Track and the Construction Camp:
a. The self—help group should be issued with tools on loan such asmachetes, hoes and axes with which they can clear a track wideenough for a tractor with trailer. They should avoid fellinglarge trees to prevent the need for stump removal, and should notcross deep gullies or steep slopes.
b. At the end of the track, as close to the construction site aspossible, the self—help group should clear a large enough areafor vehicles to park and turn, for materials to be piled and forthe self—help group to sit and rest and for meetings.
c. At the dam site, the self—help group should excavate any soilcontained where the reservoir will be and sweep and clear soilfrom the catchment area where relevant. If there is a lot ofsoil it should be carried to the foot of the rock outcrop andbuilt into a semi—circular earth dam to catch water and provide alivestock watering point.
10. Setting Up the Templates
a. The templates should be placed upright at the corners of the dam,at the deepest point of the single wall and can be supported bysmall stones and mortar. In the sketch this is shown for adouble-walled dam.
b. The sites for the templates should have already been marked inthe site assessment but can be double—checked. Having confirmedthis then the templates should be positioned at right angles tothe line of the wall section they mark the position of. Amasons square can be used to sight along to the other templateat the end of the dam.
4~2timber
// t40
End of walt of~stone masonry
SEEN FROM ABOVE
Setting-up temp[cites
18
c. The end of the dam should be fixed with a small cement ledge 30cm wide to which the builders lines can be attached and whichmark the point the dam will be built to.
Use a hose pipe filled with water to measure that the top of thetemplates are in a horizontal level, and to locate the ends ofthe dam wall on the rock.
d. Four builders lines should be fixed from the ledge to thetemplate (and between templates) to show the form of the masonrywall along its length.
e. The two top lines should pass inside the template frame and betied around the top corners of the frame. The bottom or sidelines must also pass inside the template and can be tied aroundthe sides of the frame.
f. Once the templates and dam ends are definitely level and thelines fixed the templates can be anchored in the upright byapplying mortar and stones to their base.
g. As a double check, the lengths of the section crests should bemeasured again and compared to the earlier measurements. Ifthere is any difference, the materials calculations should bemade again to ensure the correct amount of materials aredelivered.
19
11. Preparing the Foundations
Once the builders lines have been strung, the foundation of the damwalls can be traced exactly. The self—help group need to follow thesesteps to ready the rock surface as a foundation for the dam wall;
a. Remove all dirt and loose rock fragments inside these lines whichwill form the foundation of the dam wall.
b. Thereafter, chisel this area so that it has a rough enoughsurface to ensure proper bonding with the dam wall to be buildupon it. Any hollow sound from the rock indicates a fracture orhollow space underneath. The rock must be chiseled away untilthe sound of solid rock is heard on striking with the hammer.
12. Bringing Materials and the Contractor to the Site
a. On clearing the reservoir area of soil, many stones will beunearthed. These should be piled separately at the edge of thesite near the foundations for use in the dam fill. If the rockoutcrop is granite and has been folded and fractured, then itwill be possible to lever off large flat slabs of stones 3—10 cmthick like large roofing slates. these can be prized off for usein facing the outside of the dam and for the gutters.
b. Cement should be brought by tractor and trailer and the bagscarefully counted and guarded by a trained storekeeper from thelocal community. A careful account of each bag used inconstruction should be kept to make sure none goes missing.
c. The contractor and staff bring their tools and the first load ofcement with them to the site and the Inspector will hand over thedetailed instructions for construction to them.
20
13. Maintaining aud Improving Water Quality
Water Quality
To be able to obtain unpolluted water from a rock catchment, it isimportant to keep the catchment area and the reservoir clean and tidy.This is best is done by the following methods;
a. Fence off the entire rock formation on which the rock catchmentis situated by planting a live fence of thorny bushes along itssides and/or around its entire foothill. Recommended plantsinclude;. Fig Cactus (Prickly Pear) which also provide fruit,Sisal which provide poles for roofing, and any local thornyplants which deter livestock, wild animals and people fromentering the area.
b. Keep the catchment area clean by removing all soil, vegetation orother loose debris from it. If necessary, sweep the catchmentarea once or twice a year.
c. Just before the onset of the rainy season, it is recommended thatthe dam be emptied and cleaned thoroughly of silt and algae.
d. Dig a ditch at the tapping station to lead waste water away fromthe tapping point. The ditch can end up in a pit where bananas,sugar cane or fruit trees can benefit from the waste water.
e. To avoid mosquito breeding which promotes the spread of malaria,Tilapia fish can be brought to the site and introduced to thereservoir. Besides eating mosquito larvae and algae, the fishmake good sport and a protein rich food in the dry seasons wheneggs and vegetables are scarce. Fish excrement pollutes areservoir less than if the reservoir had no fish and organismswere allowed to breed unchecked.
21
Water Quantity
Evaporation in ASAL regions can result in two metres of water beinglost from a reservoir in a year. For a single dry season in thetropics, this will be more than one metre which amounts to between 25%and 50% of the volume of most masonry gravity dam reservoirs.
Where a rock catchment dam cannot supply sufficient water, eitherbecause it is too small, has too many consumers, or each consumerdraws too much then the reservoir can be roofed to reduce evaporationby up to half.
In our experience, the most effective low—cost roof is made bybuilding pillars of concrete blocks within the reservoir spaced 3 to 4metres apart. Trunks cut from nearby trees are then tied onto the topof the pillars with galvernized wire. Sisal poles are then tiedacross these trunks with rope. Although roofs are expensive to build,it is often cheaper to roof a reservoir to conserve water than it isto extend the dam wall another metre to compensate for the evaporationlost.
Roof ing.
22
CONT~ACT0RSMANUAL ON ROCK CATCØMENT DAN
CONTENT S
PAGE
CONTRACTORSMANUALON ROCK CATCHMENTDAN 23
1. Preparing the Foundation 24
2. Installing the Draw—off Pipe 25
3. Constructing the Dam wall 26
4. Plastering the Dam Wall 27
5. Laying Out and Building Masonry Gutters 27
6. Constructing the Draw—off Pipe and Tapping Station 30
7. Quality Control and Maintenance 32
•CONTRACTORSMANUALON SELF-CLOSING WATERTAP 34
1. Self—closing Water Tap 35
2. Materials and Cost 36
3. Naking the self-closing Water tap 37
4. Installing the Water Tap 39
5. Naking a Fixed Spanner for the Caretaker 40
23
The design of the rock catchment dam will be made by the Inspector.The Inspector will also set up the templates and ensure the necessarysite preparation has been carried out by the community group. TheInspector will decide how much material is needed for the constructionand supply the sufficient cement, rock ballast, sand and water for thej ob.
1. Preparing the Foundations
Once the builders lines have been strung, the foundation of the damwalls can be traced exactly. The artisans need to follow these stepsto ready the rock surface as a foundation for the dam wall.
a. Remove all dirt and loose rock fragments inside these lines whichwill form the foundation of the dam wall.
b. Thereafter, chisel this area so that it has a rough enoughsurface to ensure proper bonding with the dam wall to be builtupon it. Any hollow sound from the rock indicates a fracture orhollow space underneath. The rock must be chiseled away untilthe sound of solid rock is heard on striking with the hammer.
® 3cm f mort 1:3
______p
c. Having prepared the foundation, to create a proper bonding forthe gravity dam which is very important, clean the chiseledsurface with water. Then sprinkle a thin layer of dry cementonto the still inoist rock surface.
d. Within the same hour, compact a 3 cm thick layer of mortar (1cement: 3 sand) onto that cement—sprinkled surface. This layerof mortar is left with a rough surface. to allow good bonding forthe next stage of construction.
24
2. Installing the Draw—off Pipe
a. Place a draw—off pipe, 3 metres long and made of 3.8 cm (1.5)galvanized iron pipe with threads at both ends, at the lowestpoint of the planned dam wall and attach it with mortar (1:3)onto a clean surface of the rock.
b. The draw—off pipe should slope in order to avoid air bubbles thancan block the passage of water in the pipe.
c. When a rock catchment dam is situated on a rock shelf or in avalley, the floor of the reservoir will be higher than the bottomof the dam wall. In this instance water will flow downwards bygravity without the need of syphon. The draw—off pipe should,therefore, slope down towards the dam wall and the plannedtapping station at the foot of the rock.
Gravitv flow / Upwards/ sloping/ : reservoir
3m•of 1 1/2G.l.pipe
d. With some rock catchment dams, part of the reservoir is situatedin a depression lower than the bottom of the dam wall, andtherefore water must be drawn through a syphon system. In thiscase therefore the draw—off pipe must slope down away from thedam into the reservoir so that the syphon is outside thereservoir. This prevents the inconvenience of opening the pluginside a filled reservoir.
Siphon flow Downwardssloping
SEope of draw-offpipe.
25
3. Constructing the Dam Wall
a. Carefully clean large flat stones (previously prized off therock) with water and set them in mortar (1:4), exactly along theinner side of the two buílders lines marking each side of thewall. Tap the stones with a mason hammer to ensure a firmconnection with the mortar. The stones must not touch eachother. Mortar must be in between them. Support the stones inplace with small sticks until the mortar is hard enough to holdthem securely. Build both inner and outer walls up to a heightof about 50 cm.
STONE MASONRYClean stones sat inmortarl ~
3cm.mortar t3.Dry cement or~wet rock. -Glearock~
b. When these inner and outer walls have cured for a day or twounder polythene sheet, fill in the space between them with cleanstones and mortar (1:4). A11 the stones must have mortar betweenthem. Re—use any mortar that has fallen outside the wall andonto the rock immediately. Keep all mortar under shade and useit before it is one hour old. Compact the stones and mortartogether by pushing down with a stick. When this section of thewall is filled in, leave it with a very rough surface, withstones sticking up so as to achieve a good bonding with the nextsection of wall.
fJLL-IN COREForevery SOcm ~llfilI-in clean StOneSin mortar 1:4andcompact welt. -~
—
c. The inner and outer walls are now extended again by 50 cm to 100cm with flat stones set in mortar (1:4). When these walls areset firm, fill in the space between them with stones and mortar(1:4) as previously described in b. The dam walls should beextended like this until the top of the dam is reached as shownby the templates and builders lines
d. During the building process and for three weeks afterwards, thestone masonry wall must be kept damp under polythene sheeting forproper curing. When this is complete, remove the templates andstore them for use elsewhere.
Build wall in cipprox.5Ocm high courses.
26
4. Plastering the Dam Wall
d. Moisten the inner side of the wall facing the reservoir withwater. Throw a layer of plaster (1:3) onto the wall until itreaches a thi-ckness of 2 to 3 cm. Smooth the plaster off to aneven and equal surface with a wooden float.
e. Within the same day, press a water—tight coat of cement mixedwith water (called Nil) onto the still moist plaster with asquare steel trowel.
f. Keep the plastered dam wall damp and covered with polythenesheeting for three weeks in order to obtain a strong, waterproofdam.
a. Some skilled artisans can build a wall so water—tight that noplaster is needed at all. However, at most dams, the inner wallfacing the reservoir should be plastered.
b. Chisel the stone masonry wall to a smooth, clean surface free ofloose chippings and wash any dust away with water. In
-particular, thoroughly clean the corner between the inner walland the rock floor with chisels and water.
c. Moisten the clean corner with water. Press compact mortarinto it. This plaster should extend 10 cm up the wall andout onto the rock floor. Smooth the mortar with a woodenuntil a 45 degree bank of plaster is created.
3).Plaster 3cmthick, 1:3.
4). Nl L,cementslurry. pressedonto freshmortar.
(1:3)10 cm
float
PLASTERINO
1).Clean corner properly.2) Fill corner with
mortar 1 :3.
27
5. Laying Out and Building Masonry Gutters
The catchment area draining into the reservoir created by the dam canbe increased by constructing gutters out from the ends of the dam wallthat catch run—off running down the rock and leads it into thereservoir. Without the gutters it would run—off either side of thedam. On circular rock outcrops, water can even be brought round fromthe other side of the rock. On steep, flat—topped rock outcrops,gutters can collect the water draining off the flat top and let it rundown the cliff directly above the site of the dam.
a. The gutters can be laid out using a channel layout frame, alsocalled a gutter level, and a sprit level. Notice that one leg is3 cm shorter than the other leg.
100~, ~ .,i —
~ç=~nTflI ~0_~~3cm slope per lOOcm
Gu tter- level
b. Place the longest leg of the layout frame where the end of thedam wall meets the rock. Place a spirit level on the top of thelayout frame. Move the short leg of the frame up or down therock surface, pivoting around the other leg, until the bubble inthe spirit level shows it is horizontal. Mark the point wherethe short leg is with chalk or a sharp stone. This point isexactly 3 cm higher than the end of the dam over a distance of100 cm.
c. Repeat this exercise•moving the long leg to where the short legused to be and finding the next point 3 cm higher with the shortleg, marking it again. This marking continues from each end ofthe dam wall until the edges of the rock outcrop is reached, thelines cross somewhere around the back of a circular outcrop, orwhen you are sure that you have a large enough catchment area.For a given dam size, the larger the catchnent the better becausethe reservoir should then fill most years. It is better tooverdesign the catchment area than undersign the storage volume.
28
d. Starting at e,ither end of the dam wall, clean flat stones about30 cm high with water. Set them in mortar (1:4) along the linesmarked out by the layout frame. The smoother side of the stonesshould be facing upslope so that water passes by them freely.Fill in the space between these flat stones with mortar andsmaller flat stones tö make the gutter wall a uniform height.The flat stones should be angled slightly downslope. Supportthem in this position with a line of smaller round stones alsoset in mortar. Brush all the joints and mortar surfaces with awet brush so that all the joints are smooth and closed and run—off water can flow smoothly into the reservoir with no leaks.
e. Keep the newly built gutters damp under polythene sheeting for aweek or two depending on the weather.
GUT TERS
Guttering.
29
6. Constructing the Draw—Off Pipe and Tapping Station
a. Although some people may prefer to fetch water directly from thereservoir, they should be encouraged to collect their water froma tapping point for reasons of hygiene.
b. When water has to be drawn by gravity from a reservoir situatedat a lower level than the dam wall, as in the example shown inour diagrams, the piping system must be equipped with a syphondevìce and a tapping point located at1a level lower than thefloor of the reservoir. Attach the syphon, which consists of a70 cm length of 3.75 cm (1.5) galvanized iron piping (GI),vertically to the draw—off pipe with a (GI) pipe tee as shown.Close the upper end of the syphon with a removable plug.
c. From the syphon tee, reduce the piping from 3.8 cm (1.5) GI to2.5 cm (1) GI down to the tapping point which is usuallysituated at the foot of the rock outcrop on which the dam isbuilt. Lay this piping on the rock so that it bends to fit itsprofile. Support the GI pìpe etery 100 cm with a large stonelaid in mortar which should also cover the pipe and secure it tothe stone.
Tcipping
Draw-oft piping
30
d. Build the ta~ping station of stones or blocks under a shady tree.Divide the 2.5 cm GI pipe with tees to feed three water taps.Build the tapping station so there is room for three jerrycans tostand under the three taps at the same time.
e. In the reservoir, reduce the draw—off pipe in the dam wall from3.8 cm (1.5) to 2.5 cm (1) and extend it down to the deepestpoint in the reservoir. Connect a perforated PVC pipe, 100 cmlong to the 2.5 cm GI pipe with a horizontal non—return valve.Build a box of filter blocks (made of a mixture of cement andsmall stones) around the PvC pipe but with the lid of the non—return valve just outside the box.
0.40 ~O40020 .Q:-?sìt~ 122
01.5 ~ry1~ t?O _______9j9~
0.30 ~ ______ _______________ _____
//~/%~/)/)//)/~///,2~ //////////////, ~777
1.20
f. Remember that all the joints in the syphon pipe system must bescrewed together properly, otherwise air will enter the pipingand prevent the system from working.
g. Normally, the syphon system begins working by itself as soon asthe reservoir is filled with water and a water tap is opened atthe tapping station. However, if it does not begin working,unscrew the removable plug in the syphon pipe and let out any airwhich might be blocking the flow. If the reservoir is notcompletely full, then close the water tap and screw the plug andfill up the syphon pipe with water. In both cases, re—screw theplug with sealing material so that it cannot let in air.
Fìlter blocks
t \~1O0
~~~PerforatedPvc pipe
Non-return vatve
31
7. Quality Control and Maintenance
If the instructions given are not followed closely then the dam maynot prove water—tight and the take—off system will not function. Themost important are as follows;
a. If the foundations are not prepared properly, then the dam willleak and the reservoir will rapidly empty. The rock surface mustbe cleared, washed and chiseled and a good base of cementapplied.
b. The packing of mortar and ballast within the dam should be tight,with stones and mortar pushed in hard and the stones wettedbeforehand. A piece of wood should be used to poke the mortar inbetween the stones to fill all the airholes. If this is not doneeffectively, the dam could leak.
c. The facing of the wall needs to be formed of flat stones boundwith mortar. There should be no gaps, and an even finish.
d. The draw—off pipe must be at the lowest point in the reservoir toallow as much water as possible to be drained out through it. Ifsediment is washed into the dam it should be cleaned out if thedam dries up so that the filter box is not buried and draw—offprevented.
e. The syphon point, if fitted, should be at the highest point ofthe draw—off pipe and filter box because otherwise water may notleave the dam.
It is important that all the above requirements are satisfied. Ifthere are problems, then these questions and answers should help spotand solve them;
Does water leak from the base of the dam?
If it does this is probably due to a poor seal between the damfoundations and the rock. If the inside of the dam has not beenplastered the corner between the rock surface and the dam wall must becleaned thoroughly and plastered.
32
Does water leak from the face of the dam?
If it does there is a weak spot in the wall where the facing, and/orthe fill have not been properly constructed. If the dam is to beenlarged with the building of another stage, thís fault can be ignoredbecause building the dam upward and outward will provide an effectiveseal. If it is not to be enlarged, then once the water level hasdropped below the leak, the facing should be chiseled away within alarge radius of the leaking area and a layer of plaster added withwater—proofing.
Does water flow over part of the dam wall outside the spillover whenthe reservoir overfills?
If it does, the crest of the dam is not level all the way round.Using the hosepipe the top should be leveled with mortar and smallstones. This prevents concentrated overflow and erosion formingdownslope.
Does the dam fail to fill up over most years even though your designcalculations say it should?
If so, check your volumetric calculations again to see if you have notoverdesigned your storage. If they are correct, check along thegutters for breaks or leaks and if possible, extend the gutters tocatch run—off from a large area.
Is the plaster lining the dam cracked and flaking?
If so, the curing was not carried out properly, or else the plasterand waterproofing mixtures were incorrect. If the dam does not leak,then the plaster can be left. Otherwise, a second coat can be applied(with the first remoted in the worst places) and cured properly.
Are their wet patches or marshy ground alongside the draw—off pipe tothe tap station?
If so, there is a leakage in the pipe which wastes water and mayeffect the syphon action by leaking air into the pipe. Eachconnection should be checked and properly sealed.
.
33
CONTRACTORS MANUAL ON SELF-CLOSING WATER TAP
CONTENTS
PAGE
CONTRACTORS MANUAL ON SELF-CLOSING WATER TAP 34
1. Self—closing Water Tap 35
2. Materials and Cost 36
3. Making the Self—closing Water Tap 37
4. Installing the Water Tap 39
5. Making a Fixed Spanner for the Caretaker 40
34
1. Self-Closing Water Tap
Below is a drawing of a self—closing water tap. Fitting a tap such asthis to draw—off pipe from a rock—catchment, spring protection, tankor sand—dam will provide a major saving in water use in ASALenvironments. Rural people will often leave taps running andunattended, wasting large quantities of water. The sight of runningwater gives the impression of unlimited supply and just as people inmore humid regions leave a tap running when washing hands or doingdishes, ASAL rural people will do -the same.
By having a tap that turns itself off by the downward force of thewater and the weight of the handle once the upward pressure on the taphead is released by the user this problem is successfully solved. Inaddition, the use of a rubber ball valve is a robust design withlittle maintenance requirements and has few moving parts that can bebroken or worn down.
The tools needed for manufacturing the tap include;
1 engineering vice1 pipe wrench1 flat file1 bench drilling machine (hand or power driven)1 4mm drill bit1 19 mm drill bit1 28 mm drill bit1 hacksaw1 hammer
The total cost of the tap, not including labour is$7.0. -
approximately US
35
2. Materials and Cost
The materials required to manufacture a self—closing tap are
illustrated in sequence and include;
a. Reducing bush, galvanized iron
(G.I.), 1.5 to 3/4
b. Elbow pipe, G.I. 1.5
c. Rubber ball with 2mm diametre
d. 75 mm length of 8 mm diametreiron bar
e. Reducing bush, G.I., 1.5 to3/4
f. Nipple, G.I., 3/4
g. Round 2 nail
h. 4 cm length of 1 G.I. pipewìth one thread
ei. Socket, G.I., 1 to 1/2
g
h
ab
c
d
36
3. Making the Se],f—Closing Water Tap
The valve
a. Wind athread1.5 to
few rounds of sealing tape clockwise around one end of a3/4 G.I. nipple and screw it into a reduction bush of3/4 G.I.
b. Cut two 5 mm wide and 20 mm long slot in the nipple with a 4 mmdrill bit and file.
c. Drill a seat for a 22 mm rubber ball in the joint of the nippleand reduction bush using firstly a 19 mm drill bit, and then a 28mm drill bit.
d. Removefile.
most of the thread on the free end of the nipple with a
e. Cut a 75 mm long piece of 8 mm diametre round4 mm hole through it at 20 mm from one end.at the opposite end to a thickness of about 3
iron bar.reduce 30mm with a
Drill amm of itfile.
f. Drill a 2 mm hole through the centre of a 22 mm rubber ball. Fitthe thinned-down end of the iron bar (the pin) through this holeand bend the end of the pin over the rubber ball on the other-OEIIIcII~~-
g. Test the water—tightness of this valve with water. If it leaks,then the seat in the reduction bush needs to be re—drilled to geta more even, better seat.
side.
37
The Eandle
a. Cut a 40 mm long piece of 1 G.I. pipe with thread at one end.
b. Drill a 4 mm hole through the G.I. pipe at 13 mm from its
unthreaded end.
c. Wind a few rounds of sealing tap clockwise around the threadsthe 1 G.I. pipe and screw it into a reducing socket of 11/2 G.I.
_
Assembly of the Water Tap
a. Place the rubber ball with its attached pin onto the seat ofvalve with the hole in the pin poìnting towards the slits innipple.
b. Place the handle over the nipple so that the hole in the handleis in line with the hole in the pin and slits.
c. Put a 2 round nail through these holes and slits and bendend of the nail sharply and firmly against the outside ofhandle.
d. Test this valve again for water—tightness and perfectfunctioning. When the handle is pushed upwards it will lift therubber ball off its seat thereby allowing water to flow. Whenthe handle is released it will drop under the force of the waterand through gravity until the rubber ball rests in its seatcausing the water flow to stop.
onto
thethe
thethe
38
e. Wind sealing ,tape around the threads of the free end of thereduction bush and screw it into a G.I. 1.5 elbow.
f. Wind sealing tape over the reads of a G.I. reducing bush of 1.5to 3/4 G.I. and screw it into the other end of the 1.5 elbow.
OEUVERV
g. The self—closing water tap is now ready
3/4 pipeline from the water source.
4. Installing the Water Tap
to be fitted onto the
a. Train three people living near the water point to which the tapsare fitted on how the self—closing taps function. They will bethe caretakers of the tap station.
b. Fix the water tap to the draw—off pipe or feeder pipe leading offthe water reservoir.
c. The caretakers should be trained in replacing the self—closingwater taps if there are any problems. They can do this with afixed spanner (see below). If the tap should stop working theyshould remove it and fit a spare tap which they are given withthe spanner.
d. The caretakers can get the faulty tap replaced by another tap bythe manufacturers.
39
5. Naking a Tixed Spanner for the Caretaker
The inaterials needed to make a fixed spanner include;
30 cin of flat iron, 30 mm x 6 inm22 cm of flat iron, 25 mm x 6 mm
Total Cost of Fixed Spanner
The fixed spanner is the tool the caretaker will use to takethe tap off the pipe if there are any probleins.
a. Cut a 22 cm long piece of flat iron 25 mm x 6 inm. Slit the ironbar at 5 places correspondingto the six sides of the hexagonalreducing bush of 1.5 to 3/4 used to connect the tap to thepipe. Bend it tightly around this shape. Weld the iron bar ateach of the slits and at the join between the two ends.
b. Cut a 300 min length of flat iron 30 niin x 6 min andit onto the hexagonal spanner end as a handle.
weld one end of
144 l
T ~i Cutsj 25
~=6300mm
Fixed Spanner for Watertap
.
l 220mm44 i44 144 ~44 44
l l l l l
40
1I
I!
4 ~
