CHAPTER-IV Rain Water Harvesting 4.1 Estelarshodhganga.inflibnet.ac.in/bitstream/10603/29904/4/chapter 4.pdf · Rainwater harvesting potential and effective harvesting of water by

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CHAPTER-I V

Rain Water Harvesting

4.1 General: Rain water is the main source of fresh water which is available

annually through the hydrological cycle. The principle of water harvesting is

collection and storage of the rainwater when and where it falls. Major portion

of available rainwater goes unutilized in the Himalayan region mainly due to its

distribution pattern and topography of the area. About 80% of annual rainfall

occurs in three months during monsoon. The only option is to harvest this

rainwater and to store it for lean season. In the areas where slopes are steeper,

overland flow gets flushed of very swiftly resulting in non-availability of water

in peak water stress period even through the average rainfall is very high. In

such areas efforts should be made to harvest maximum rainwater, possible by

constructing suitable water harvesting structures to artificially recharge the

ground water and store water for domestic use by constructing roof water

harvesting structures and water harvesting structures. Integration of Remote

Sensing and Geographical Information System (GIS) techniques provides

reliable, accurate and updated database to identify suitable sites for water

harvesting such as farm ponds, ground water recharge zones, check dams,

percolation tanks, nala bundh and shaugel pond etc. The population of the

Dabka watershed is completely dependent on spring water for their daily needs.

The increased population pressure and declining trends of spring discharge has

caused severe water shortage in the area. For the optimum use of the available

water resources in the catchment, it is necessary for conservation of the water

resources in the area.

The area, Dabka watershed comprises fifteen villages out of which, seven

villages namely Bansi, Ghughukhan, Sigri, Saur, Dola, Baghni, Jalna have been

found to face severe water scarcity during water stress periods of the year.

Beside these villages some parts of other villages and grazing lands located at

comparatively head ward region of the area have been found to suffer from this

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issue. Therefore, to make the availability of water throughout the year for

domestic, animal husbandry and local agricultural use, an attempt has been

made to conserve water thorough rainwater harvesting methods. In this regard

an attempt has been made by conducting pilot studies in few selective villages,

to assess the conservation of water.

Irrigation is very essential for the survival of agricultural crops in rainfed areas

where slopes are steep and dry. The excess rainwater has to be conserved or

stored in different storage structures, which can be used later. Water harvesting

systems have largely focused on the technology of roof top in catchment areas.

Usually the roof is made of tiles (roof stones), iron or asbestos sheets. It is

connected by gutters and down pipes to one or more storage containers ranging

from simple ponds to large cement tanks.

4.2 Methodology for Rainwater Harvesting:-Site selection for water

harvesting structure, the technical guidelines of Integrated Mission for

Sustainable Development (IMSD), prepared by National Remote Sensing

Centre (NRSC), Indian National Committee of Hydrology (INCOH) are used

in the present study. On the basis of structure, lithological, geomorphological,

socio-economical conditions, check dams and shaugel pond are proposed in the

study area.

For the site selection of Check dams lower order streams up to third order (Fig.

4.2) with medium slopes are taken. Check dams are proposed where water table

fluctuations are very high. The slope of the region was considered flat to

gentle, so that the maximum quantity of water could be stored.

Farm ponds can be proposed within individual farms. The main aim for the

construction of Farm ponds is, i) to provide water storage for life saving

irrigation in a limited area, ii) to provide drinking water for livestock and

human beings in arid areas, iii) to serve as water storage for providing critical

irrigation to a limited number of fruit plants for establishment purpose.

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Nala bundhs and percolation tanks are structures constructed across nallah or

streams for checking velocity of runoff, increasing water percolation etc. Nala

bundhs are less expensive which is smaller in dimension and constructed

usually by local material. The percolation tanks are large and more expensive.

The main aim for construction of Nala bundhs and Percolation tanks are i) to

impound surface runoff coming from the catchment and to facilitate percolation

of stored water into the strata to raise the groundwater level and ii) to hold the

site flow.

4.3 Site selection for harvesting:-The area under investigation comprises of

very rugged topography which includes hillocks with steep slopes, escarpments

with cliffs and long narrow ridges. Apart from the area comprises of tightly

folded and faulted rock terrain with closely spaced fractures and shears. The

available formation exhibits their respective attitudes vary in different

directions. Hence, the configuration of formations in the area is found to be

dominantly manifested with the fracture porosity and bedding planes in

different directions. However, the intensity of the distortion of such directions

is found increasing towards the main thrusts. So, construction of recharge wells

may not feed recharge to the right desired directions. The area receives an

annual average rainfall of the order of 172.8 cm (Table 3.2). The monsoons are

found to contribute the major portions of the rainfall. The socio economical

condition of the inhabitants is observed to be based on the subsistence

agro-economy of the area, animal husbandry etc. Thus, the inhabitants are

forced to lead a difficult life. Therefore, keeping in consideration the geology,

topography and social economic conditions of the inhabitants an attempt has

been made to propose the construction of selective water harvesting structures

in the Dabka watershed so that their living condition could be improved

(Fig. 4.2).

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Three types of structures may be recommended for the area

(i) Shaugel ponds

(ii) Check dams

(iii) Farm ponds

(i) Shaugel Ponds: - Shaugel ponds for rainwater harvesting and overland

flow interception have been proposed in the area. The different feasible locations

are Taliya (1 no.), Dhanak (1 no.), Jalna (2 nos.), Chhara (1 no.), Salba (1 no.),

Sigri (1 no.), Ghughukhan (1 no.), Saur (3 nos.), Banshi (4 nos.), Baghni (5 nos.)

are proposed (Fig.4.2). The shape of such ponds is governed by lithology, slope

and structures of the bed rock. The area in general comprises of hard rock terrain

in upper reaches with slopes in the range of more than 200 with dominance of

fracture porosity will be introduced with such ponds of trench shape. Cube or

cuboid shaped ponds will suit to the parts of the area having slopes in the range of

10-200 and considerable unconsolidated regolith cover. Whereas the bowel shaped

ponds are best suited in the areas having gentler slopes in the range of 0-100, with

thick cover of unconsolidated regolith. The construction of Shaugel pond (Fig.

4.1) is efficiently low cost and easy to maintain. To stop infiltration of water thin

plastic lining is used with clay covering. It is calculated that for a pond having

2.50 m width, 1 m height and 2 m length, about 16 m2 plastic sheets would be

required. For maintenance point of view it is very easy and low cost effective.

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Fig. 4.1: A sample of Shaugel pond

(ii) Check Dams: -The proposed sites selected for construction of Check dams

(Fig. 4.2) on the comparatively higher reaches will arrest the part of the

sediment load being shifted from their still respective higher reaches and

overland flow during rainy spells thus diffusing the potential of the sliding

material and diffuse runoff to minimize its erosional impact farther down

slopes. Such check dams are to be constructed by dry stone masonry work. The

arrested regolith will behave like aquifer skeleton and will absorb part of the

rainwater or overland flow. The interception of rainfall or overland flow in this

way would definitely lead to prolonged seepage of water down slopes which

otherwise has flushed out spontaneously in absence of such structures. The

construction of such Check dams will be cost effective and will help in

maintaining sustainable flow in respective nallahs for longer periods after an

event of rainfall. Whereas proposed sites for such structures on the perennial

nallahs of the area have to be constructed in accordance with the design by

engineers so as to ensure optimum availability of water all the year round.

Check Dams are proposed at Baghni (1 no.), Bansi (1 no.), Saur (3 nos.), Sigri

(1 no.), Ghughukhan (1 no.), Jalna (3 nos.) and Taliya (1 no.).

(iii) Farm pond: - Farm pounds are purposed at farms in the catchment. Farm

ponds are proposed at Baghni (4 nos.), Bansi (2 no.), Saur (6 nos.), Jalna

(2 nos.), Devipura (1 no.) to support horticulture, floriculture and seasonal

vegetable farming in the area (Fig. 4.2).

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Fig. 4.2: Proposed locations for water harvesting structures in Dabka watershed

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4.4 Roof top rain water harvesting:-Domestic rain water harvesting or Roof

top rain water harvesting is the technique through which rain water is captured

from roof catchments (Fig. 4.3) and stored in tanks, ground water aquifers. It

consists of conservation of roof top rain water and to increase ground water

storage by artificial recharge. It requires connecting the outlet pipe from roof

top to divert collected water to existing tanks, wells, ground water aquifers etc.

4.4.1 Component of Roof Top Rain Water Harvesting:

(Rainwater Harvesting and conservation manual, 2002)

The system comprises the following basic components:-

i) Catchment area/roof: surface upon which rain falls.

ii) Gutters: transport channels from catchment surface to storage.

iii) Cisterns or storage tanks: where collected rain water is stored.

iv) Conveying: the delivery system for treated rain water, either by gravity or

pumps.

v) Water Treatment: filters and equipment and additives to settle, filter and

purify.

Fig. 4.3: Sample of roof top rain water harvesting for hilly area

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4.4.2 Methodology for Roof top rainwater harvesting:-Roof top rain water

harvesting methodology has been taken from manual of Consultancy Services

Organization, Central Public Work Department, New Delhi. For this pilot

project seven sample village namely- Sigri, Bansi, Ghughukhan, Saur, Dola,

Baghni, Jalna were selected. A few houses are selected to calculate the

Rainwater harvesting potential and effective harvesting of water by following

the Central Public Work Department, New Delhi manual. To compute runoff

coefficient of corrugated metal sheets coefficient is taken (Table 4.1). For

calculating Effective rainwater harvesting potential the average annual rainfall

172.8cm is taken. The calculated availability of rainwater through roof top is

compared with the calculated values (Table 4.2). The amount of rain fall which

could be harvested in different villages is given in (Table 4.3 to Table 4.9).

4.4.3 Sample calculation for effectively harvested water from total

rainfall (Bansi village)

The total amount of water i.e. received in the form of rainfall over an

area is called the rainwater endowment of that area. Out of this the

amount that can be effectively harvested is called the rainwater harvesting

potential.

Rain water harvesting potential = Rain fall (mm) X collection Efficiency

Annual rain fall of the area = 1728 mm = 1.728 m

Height of the rainfall = 1.728 m

Area of Roof Catchment = 40 sq m

Vol. of rain fall over the plot = Area plot X height of rain fall

Rain water endowment of that area = 40 Sqm X 1.728 m = 69.12 cum

= 69,120 liters

Considering roof catchment is having Corrugated metal sheet, so

coefficient for roof surface can be taken as 0.80 (Table 4.1)

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Another constant coefficient for evaporation, spillage and first flush wastage

can be considered as 0.80 (for all situations).

Effectively harvested water = Rain Water endowment of that area

(A) X 0.80 X Surface efficient

= 69,120 X 0.80 X 0.80

= 44236.8 liters

The rain water falling over an area cannot be completely harvested

because of evaporation, spillage etc. First spell of rain is flushed out,

evaporation and spillage cannot calculate factors like run off coefficient

as shown various types of roof and land surfaces etc. (Table 4.1). So, a

constant co-efficient of 0.80 may be assumed for all situations. This is

because of the first spell of rain carries with larger amount of pollutants

from the air and catchment surface area.

Table 4.1- Runoff co-efficient of various surfaces

(Source - Rainwater harvesting and conservation manual, 2002)

1. Roof catchment Co-efficient

1.1 Tiles 0.8-0.9

1.2 Corrugated metal sheets 0.7-0.9

2. Ground surface covering

2.1 Untreated ground catchments

2.1.1 Soil on slope less than 10% 0.0-0.3

2.2.2 Rocky 0.2-0.5

2.1.3 Business area

2.1.3.1 Down town 0.70-0.95

2.1.3.2 Neighborhood 0.50-0.70

2.2 Residential complexes in urban area

2.2.1 Single family 0.30-0.56

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2.2.2 Multiunit, detached 0.40-0.60

2.2.3 Multiunit, attached 0.60-0.75

2.3 Residential complexes in Suburban area apartments 0.50-0.70

2.4 Industrial

2.4.1 Light 0.50-0.70

2.4.2 Heavy 0.60-0.90

2.5 Parks, cemeteries 0.10-0.25

2.6 Play grounds 0.20-0.35

2.7 Railroad yard 0.20-0.35

2.8 Unimproved land areas 0.10-0.30

2.9 Asphaltic or concrete pavement 0.70-0.95

2.10 Brick pavement 0.70-0.85

2.11 Lawns, sandy soil having slopes 0.50-0.10

2.11.1 Flat 2% 0.05-0.10

2.11.2 Average 2 to 7% 0.10-0.15

2.11.3 Steep 7% 0.15-0.20

2.12 Lawns, clayey soil having slopes

2.12.1 Flat 2% 0.13-0.17

2.12.2 Average 2 to 7% 0.18-0.22

2.12.3 Steep 7% 0.25-0.35

2.13 General Driveways and walls 0.15-0.30

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Table 4.2 Availability of Rainwater through Roof Top Rain water Harvesting

Rainfall (mm) 100 200 300 400 500 600 800 1000 1200 1400 1600 1800 2000

Roof top area (Sqm) Harvested water from Roof Top (cum)

20 1.6 3.2 4.8 6.4 8.0 9.6 12.8 16.0 19.2 22.4 25.6 28.8 32.0

30 2.4 4.8 7.2 9.6 12.0 14.4 19.2 24.0 28.8 33.6 38.4 43.2 48.0

40 3.2 6.4 9.6 12.8 16.0 19.2 25.6 32.0 38.4 44.8 51.2 57.6 64.0

50 4.0 8.0 12.0 16.0 20.0 24.0 32.0 40.0 48.0 56.0 64.0 72.0 80.0

60 4.8 9.6 14.4 19.2 24.0 28.8 38.4 48.0 57.6 67.2 76.8 86.4 96.0

70 5.6 11.2 16.8 22.4 28.0 33.6 44.8 56.0 67.2 78.4 89.6 100.8 112.0

80 6.4 12.8 19.2 25.6 32.0 38.4 51.2 64.0 76.8 89.6 102.4 115.2 128.0

90 7.2 14.4 21.6 28.8 36.0 43.2 57.6 72.0 86.4 100.8 115.2 129.6 144.0

100 8.0 16.0 24.0 32.0 40.0 48.0 64.0 80.0 96.0 112.0 128.0 144.0 160.0

150 12.0 24.0 36.0 48.0 60.0 72.0 96.0 120.0 144.0 168.0 192.0 216.0 240.0

200 16.0 32.0 48.0 64.0 80.0 96.0 128.0 160.0 192.0 224.0 256.0 288.0 320.0

250 20.0 40.0 60.0 80.0 100.0 120.0 160.0 200.0 240.0 280.0 320.0 360.0 400.0

300 24.0 48.0 72.0 96.0 120.0 144.0 192.0 240.0 288.0 336.0 384.0 432.0 480.0

400 32.0 64.0 96.0 128.0 160.0 192.0 256.0 320.0 384.0 448.0 512.0 576.0 640.0

500 40.0 80.0 120.0 160.0 200.0 240.0 320.0 400.0 480.0 560.0 640.0 720.0 800.0

1000 80.0 160.0 240.0 320.0 400.0 480.0 640.0 800.0 960.0 1120.0 1280.0 1440.0 1600.0

2000 160.0 320.0 480.0 640.0 800.0 960.0 1280.0 1600.0 1920.0 2240.0 2560.0 2880.0 3200.0

3000 240.0 480.0 720.0 960.0 1200.0 1440.0 1920.0 2400.0 2880.0 3360.0 3840.0 4320.0 4800.0

Source: Rainwater harvesting and conservation manual, 2002.

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Table 4.3: Roof top rain water harvesting in Bansi village

Total No of house 50

No. of houses Length of one the roof (m)

Breadth of the one roof (m)

Surface area of the roof ( m2)

Rain fall in year 2002 (m)

Rain water harvesting potential (cubic mt)

Effective harvesting water (lit)

3 5 8 120.0 1.728 207.36 132710.4

3 8 7 168.0 1.728 290.304 185794.56

3 8.5 4.5 114.8 1.728 198.288 126904.32

1 6.5 9 58.5 1.728 101.088 64696.32

4 8 9 288.0 1.728 497.664 318504.96

4 3.5 6.5 91.0 1.728 157.248 100638.72

5 8.5 5.5 233.8 1.728 403.92 258508.8

3 4.5 8 108.0 1.728 186.624 119439.36

5 9.4 5.4 253.8 1.728 438.5664 280682.496

5 7.3 4.8 175.2 1.728 302.7456 193757.184

6 10 8 480.0 1.728 829.44 530841.6

2 7.5 4 60.0 1.728 103.68 66355.2

2 6.7 8.5 113.9 1.728 196.8192 125964.288

3 5.2 8.7 135.7 1.728 234.52416 150095.4624

1 5 3 15.0 1.728 25.92 16588.8

50 103.6 99.9 2415.6 4174.19136 2671482.47

Source: Census data and Field survey.

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Table 4.4: Roof top rain water harvesting in Ghughukhan village

Total No of houses 22

Length of one the roof (m)



Average annual rain fall



2 10.5 5.5 115.5 1.728 199.584 127733.76

3 4.5 8 108 1.728 186.624 119439.36

1 9.4 5.4 50.76 1.728 87.71328 56136.4992

3 7.3 4.8 105.12 1.728 181.64736 116254.3104

4 12 16 768 1.728 1327.104 849346.56

2 7.5 4 60 1.728 103.68 66355.2

4 6.7 8.5 227.8 1.728 393.6384 251928.576

2 5.2 8.7 90.48 1.728 156.34944 100063.6416

1 5 3 15 1.728 25.92 16588.8

22 68.1 63.9 1540.66 2662.26048 1703846.707


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Table 4.5: Roof top rain water harvesting in Sigri village

Total No of house

15





Rain fall in (mt cube)



3 9.4 5.4 152.28 1.728 263.13984 454.7056435 291011.6119

3 7.3 4.8 105.12 1.728 181.64736 313.8866381 200887.4484

2 12 16 384 1.728 663.552 1146.617856 733835.4278

2 7.5 4 60 1.728 103.68 179.15904 114661.7856

2 6.7 8.5 113.9 1.728 196.8192 340.1035776 217666.2897

2 5.2 8.7 90.48 1.728 156.34944 270.1718323 172909.9727

1 5 3 15 1.728 25.92 44.78976 28665.4464

15 53.1 50.4 920.78 1591.10784 2749.434348 1759637.982 Source: Census data and Field survey.

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Table 4.6: Roof top rain water harvesting in Saur village

Total No of houses

70





Rain water harvesting potential(cubic mt)


5 5 8 200.0 1.728 345.6 221184 4 8 7 224.0 1.728 387.072 247726.08 5 8.5 4.5 191.3 1.728 330.48 211507.2 1 6.5 9 58.5 1.728 101.088 64696.32 3 12 9 324.0 1.728 559.872 358318.08 4 3.5 6.5 91.0 1.728 157.248 100638.72 3 10.5 5.5 173.3 1.728 299.376 191600.64 3 4.5 8 108.0 1.728 186.624 119439.36 4 9.4 5.4 203.0 1.728 350.85312 224545.9968 2 7.3 4.8 70.1 1.728 121.09824 77502.8736 4 10 15.3 612.0 1.728 1057.536 676823.04 2 7.5 4 60.0 1.728 103.68 66355.2 1 6.7 8.3 55.6 1.728 96.09408 61500.2112 3 5.2 8.7 135.7 1.728 234.52416 150095.4624 6 5 3 90.0 1.728 155.52 99532.8 3 7.3 4.8 105.1 1.728 181.64736 116254.3104 2 11.5 14.2 326.6 1.728 564.3648 361193.472 2 7.5 4 60.0 1.728 103.68 66355.2 2 6.7 8.9 119.3 1.728 206.08128 131892.0192 2 5.2 8.7 90.5 1.728 156.34944 100063.6416 1 5 3 15.0 1.728 25.92 16588.8 2 9.4 5.4 101.5 1.728 175.42656 112272.9984 3 7.3 4.4 96.4 1.728 166.51008 106566.4512 3 12 16 576.0 1.728 995.328 637009.92 70 181.5 176.4 4086.8 7061.97312 4519662.797 Source: Census data and Field survey.

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Table 4.7: Roof top rain water harvesting in Dola village


No. of houses Length of one the roof (m)






3 5 8 120.0 1.728 207.36 132710.4

2 8 7 112.0 1.728 193.536 123863.04

1 3.5 4.5 15.8 1.728 27.216 17418.24

2 6.5 6.3 81.9 1.728 141.5232 90574.848

3 7 6.5 136.5 1.728 235.872 150958.08

2 3.5 6.5 45.5 1.728 78.624 50319.36

2 5.5 5.6 61.6 1.728 106.4448 68124.672

15 39 44.4 573.3 990.576 633968.64


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Table 4.8: Roof top rain water harvesting in Baghani village


No. of houses







2 5.2 4.7 48.9 1.728 84.46464 54057.3696 2 5 4.3 43.0 1.728 74.304 47554.56

3 6.5 4.5 87.8 1.728 151.632 97044.48

1 6.5 7 45.5 1.728 78.624 50319.36

2 6 4 48.0 1.728 82.944 53084.16

10 29.2 24.5 273.1 471.96864 302059.9296 Source: Census data and Field survey.

Table 4.9: Roof top rain water harvesting in Jalna village


No. of houses







1 5 8 40.0 1.728 69.12 44236.8

2 7 6.5 91.0 1.728 157.248 100638.72

2 8 4.5 72.0 1.728 124.416 79626.24

3 6.5 5 97.5 1.728 168.48 107827.2

2 6 7.5 90.0 1.728 155.52 99532.8

10 32.5 31.5 390.5 674.784 431861.76


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A common practice is to use average coefficients for various types of areas and

assumed that the coefficients will be constant throughout the duration of the

storm.

The approximate volume of water available for harvesting with respect to roof

top area and annual rain fall has been shown in (Table 4.2) for designing the

Rain Water Harvesting Structures.

Table 4.10: Village wise analysis for Roof Top Rain water Harvesting

Village name

No. of houses

Population in 2001 (NIC, Nainital) data )



Per day total water availability (lit)

No. of persons that could be provided water at the rate of 40 lit/day

Bansi 50 798 4174.19136 2671482.47 7319.130056 183

Ghughukhan 22 400 2662.26048 1703846.707 4668.07317 117

Sigri 15 172 2749.434348 1759637.982 4820.925979 121

Saur 70 1367 7061.97312 4519662.797 12382.6378 310

Dola 15 211 990.576 633968.64 1736.900384 43

Baghni 10 396 471.96864 302059.9296 827.561451 21

Jalna 10 700 674.784 431861.76 1183.182904 30

Total 192 4044 18785.18795 12022520.29 32938.41174 823 Source: National Information Centre (NIC) and Census data, Nainital

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4.5 Observation and discussion:

In the upper reached water scarcity problem has been observed. To reduce the

water scarcity problem three rainwater harvesting structures Shaugel pond,

Check dam and Farm ponds are proposed at different locations by taking

consideration of geology, geomorphology, geomorphology, socio-economic

conditions. It is observed that constructions of Shaugel pond are low cost

effective and easy to maintain. Check dams are proposed to harvest rainwater

for local people and for recharge the ground water. At some places form ponds

are also proposed in the individual farm to support farms horticulture,

floriculture and seasonal vegetable farming.

Careful perusal roof top rainwater harvesting of the available rain water, for

harvesting in the seven pilot villages indicate that the area has immense

potential for harvesting rain water in Dabka watershed. It is calculated that 15

houses of Bansi, 22 houses of Ghughukhan, 15 houses of Sigri, 70 houses of

Saur, 15 houses of Dola, 10 houses of Baghni and 30 houses of Jalna, can

harvest 32938.411 lits water per day (Table 4.10). In which 823 (Table 4.10)

person at the rate of 40 lit/day from the seven selected villages can be fed

throughout the year.

In area which is facing acute shortage of water, such water harvesting and

spring water conservation measures could be of immense help to the

community.

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Documents

CHAPTER-IV Rain Water Harvesting 4.1 Estelarshodhganga.inflibnet.ac.in/bitstream/10603/29904/4/chapter 4.pdf · Rainwater harvesting potential and effective harvesting of water by