RAIN WATER HARVESTING

Source: A Water Harvesting Manual For Urban Areas Harvesting System Broadly rainwater can be harvested for two purposes- Storing rainwater for ready use in containers above or below ground  Charged into the soil for withdrawal later (groundwater recharging)                                                                                              Source: A Water Harvesting Manual For Urban Areas

There are two main techniques of rain water harvestings. RAIN WATER HARVESTING TECHNIQUES : There are two main techniques of rain water harvestings. Storage of rainwater on surface for future use. Recharge to ground water. The storage of rain water on surface is a traditional techniques and structures used were underground tanks, ponds, check dams, weirs etc

Recharge to ground water is a new concept of rain water harvesting and the structures generally used are :- Pits :- Recharge pits are constructed for recharging the shallow aquifer. These are constructed 1 to 2 m, wide and to 3 m. deep which are back filled with boulders, gravels, coarse sand.

Trenches:- These are constructed when the permeable stram is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter materials. Dug wells:- Existing dug wells may be utilised as recharge structure and water should pass through filter media before putting into dug well.

Hand pumps :- The existing hand pumps may be used for recharging the shallow/deep aquifers, if the availability of water is limited. Water should pass through filter media before diverting it into hand pumps. Recharge wells :- Recharge wells of 100 to 300 mm. diameter are generally constructed for recharging the deeper aquifers and water is passed through filter media to avoid choking of recharge wells.

Recharge Shafts :- For recharging the shallow aquifer which are located below clayey surface, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m. deep are constructed and back filled with boulders, gravels & coarse sand. Lateral shafts with bore wells :- For recharging the upper as well as deeper aquifers lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long depending upon availability of water with one or two bore wells are constructed. The lateral shafts is back filled with boulders, gravels & coarse sand.

Spreading techniques:- Spreading techniques:- When permeable strata starts from top then this technique is used. Spread the water in streams by making check dams, bunds, cement plugs, gabion structures or a percolation pond may be constructed.

Reasons of Shortage of Water Population increase Industrialization Urbanization (a) Increase in per capita utilization (b) Less peculation area Decrease in surface area of Lakes. Deforestation 1

What is the solution ? Rain water is the ultimate source of fresh water Potential of rain to meet water demand is tremendous Rain water harvesting helps to overcome water scarcity To conserve ground water the aquifers must be recharged with rain water Rain water harvesting is the ultimate answer

Why Rain water be harvested To conserve & augment the storage of ground water To reduce water table depletion To improve the quality of ground water To arrest sea water intrusion in coastal areas To avoid flood & water stagnation in urban areas 4

Therefore rain water harvesting is - It is the activity of direct collection of rain water Rain water can be stored for direct use or can be recharged into the ground water aquifer 5

Rain Water Harvesting….. Rain Water Harvesting RWH- process of collecting, conveying & storing water from rainfall in an area – for beneficial use. Storage – in tanks, reservoirs, underground storage- groundwater Hydrological Cycle

Rain Water Harvesting……. RWH - yield copious amounts of water. For an average rainfall of 1,000mm, approximately four million liters of rainwater can be collected in a year in an acre of land (4,047 m2), post-evaporation. As RWH - neither energy-intensive nor labour -intensive It can be a cost-effective alternative to other water-accruing methods. With the water table falling rapidly, & concrete surfaces and landfill dumps taking the place of water bodies, RWH is the most reliable solution for augmenting groundwater level to attain self-sufficiency

RWH – Methodologies Roof Rain Water Harvesting Land based Rain Water Harvesting Watershed based Rain Water harvesting For Urban & Industrial Environment – Roof & Land based RWH may be used in Public, Private, Office & Industrial buildings Pavements, Lawns, Gardens & other open spaces

Rain Water Harvesting– Advantages 1.Provides self-sufficiency to water supply 2.Reduces the cost for pumping of ground water 3.Provides high quality water, soft and low in minerals 4.Improves the quality of ground water through dilution when recharged 5.Reduces soil erosion & flooding in urban areas 6.The rooftop rain water harvesting is less expensive & easy to construct, operate and maintain 7. In desert, RWH only relief 8. In saline or coastal areas & Islands, rain water provides good quality water

Appropriate Technology Water conservation and groundwater recharge techniques Water harvesting cum supplementary irrigation techniques

The roof catchment are selectively cleaner when compared to the ground level catchment Losses from roof catchment are minimum Built & Maintained by local communities No Chemical contamination & only required filtration Available at door step with least cost 16

Rain water harvesting system- The typical roof top rain water harvesting system comprises of – or components - Roof catchment Gutters Down pipe & first flushing pipe Filter Unit Storage Tank 17

Roof catchment The roof of the house is used as the catchment for collecting rain water. The style construction and material of the roof effect its suitability as a catchment, Roofs made of corrugated iron sheet , asbestos sheet, Tiles or Concrete can be utilized for harvesting the rain water 18

Gutters Gutters are channels fixed to the edges of roof all around to collect & transport the rainwater from the roof. Gutters can be made in semi-circular and rectangular shape with cement pipe, plain galvanized iron sheet, PVC pipes, bamboos etc. Use of locally available material reduce the overall cost of the system. 19

Down Pipe It is the pipe which carries the rainwater from the gutters to the filter & storage tank. Down pipe is joined with the gutters at one end & the other end is connected to the filter unit of the storage tank. PVC or GI pipe of 50mm to 75mm (2 to”) are commonly used for down pipe. Bamboo can be also used wherever available and possible 20

First Flush Pipe Debris, dust & dirt collect on the roof during non rainy periods when the first rain arrive. A first flush system arrangement is made to avoid the entering unwanted material into the Filter media & storage tank. This is a simple manually operated arrangement or semi-automatic system with a valve below the ‘T’ junction 21

Filter Unit The filter unit is a container or chamber filled with filter media such as coarse sand, charcoal, coconut fiber, pebbles & gravels to remove the debris & dirt from water that enters the tank. The filter unit is placed over the storage tank or separately. It may be of Ferro cement filter unit, Aluminum, Cement rings or Plastic bucket etc. 22

Storage Tank It is used to store the water that is collected from the roof through filter. For small scale water storage plastic buckets, jerry cans, clay or cement jars, ceramic jars, drums may be used. For larger quantities of water, the system will require a bigger tank with cylindrical or rectangular or square in shape constructed with Ferro cement or cement rings or plain cement concrete or reinforced cement concrete or brick or stone etc. The storage tank is provided with a cover on the top to avoid the contamination of water from external sources. The storage tank is provided with pipe fixtures at appropriate places to draw the water to clean the tank & to dispose of extra water. A provision for keeping the vessel to collect. the water is to be made. 23

Size of Storage Tank Based on No. of person in the House hold Per capita water requirement No. of days for which water is required 24

Water available from Roof Annual rainfall (in mm) x roof area (in sq. m) x co-efficient of run off for roof co-efficient of run off - GI sheet 0.9 Asbestos 0.8 Tiled 0.75 Plaster on bricks/ Concrete 0.7 25

How the problem can be minimized By providing pipe water system with source (electric based) (a) Surface water (b) Deep tube wells Recharging strata through rainwater harvesting methods (No. of villages of lower range concentration can be decreased) Storing rain water for drinking purpose (a) In areas where electricity problem is more (b) In areas where concentration is more (c) In areas where dependable source is not available 36

Advantages of groundwater: There is more ground water than surface water Ground water is less expensive and economic resource. Ground water is sustainable and reliable source of water supply. Ground water is relatively less vulnerable to pollution Ground water is usually of high bacteriological purity. Ground water is free of pathogenic organisms.

Ground water needs little treatment before use. Ground water has no turbidity and colour. Ground water has distinct health advantage as art alternative for lower sanitary quality surface water. Ground water is usually universally available. Ground water resource can be instantly developed and used.There is no conveyance losses in ground water based supplies. Ground water has low vulnerability to drought. Ground water is key to life in arid and semi-arid regions. Ground water is source of dry weather flow in rivers and streams.