this small video shows the benefits of rainwater harvesting in urban areas.(source: youtube.com)

• 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

therefore ,we have seen the great benefits of rainwater harvesting.


 Why Rain water be harvested????????????

To conserve & augment the storage of ground water

• To reduce water depletion
• To improve the quality of ground water
• To arrest sea water intrusion in coastal areas
• To avoid flood & water stagnation in urban areas

 A video which shows the benefits of rainwater harvesting(source: youtube.com)

A small animation video to show rainwater harvesting system.(source : youtube.com)

Ancient techniques for rainwater harvesting

Talab/ Bandhis
Talabs were reservoirs. They could be natural, such as the ponds (pokhariyan) at Tikamgarh in the Bundelkhand region or could be man-made, such as the lakes in Udaipur. A reservoir area of less than five bighas was called a talai; a medium sized lake was called a bandhi or talab; bigger lakes were called sagar or samand. The pokhariyan served the purpose of irrigation and drinking. When the water in these reservoirs dried up, the pond beds were used for cultivation. 

Johads Johads, in Rajasthan,  were small earthen check dams built to capture and conserve rainwater, thus  improving percolation and recharging ground water

Baoris / Bers
Baoris or bers were community  wells, found in Rajasthan, that were used mainly for drinking. Most of them are  very old and were built by banjaras for their drinking water needs. They  could hold water for a long time because of almost negligible water  evaporation.

 

Jhalaras
Jhalaras were man-made tanks, found in  Rajasthan and Gujarat, essentially meant for community use and for religious  rites but not for drinking. Often rectangular in shape, jhalaras have  steps on three or four sides. They were ground water bodies which were built to  ensure easy and regular supply of water to the surrounding areas.

Water Temples or ‘Step Wells’
Another most unique example for  harvesting rainwater and providing water for drinking purpose in arid parts of  our country was the step well.

Step wells are also  called water temples of India. The idea to construct step wells  was initiated due to the need to ensure  water supply during the period of drought. Some of the step wells were dug very  close to tanks to get drinking water    throughout   the year. Step wells  are also called Vav, Vavadi, Bawdi, Bawri,  Baoli, and Bavadi   and can be found  in Gujarat and Rajasthan.

Adalaj-Vav is a  very popular step-well i.e. about 20 kms from Ahmdabad. It is made in the form  of a temple that ends into a well. The well is about six storeys below ground  level. Picture 6 illustrates the depth of the well. Agrasen ki baoli is one of them which situates in Delhi.

RAIN WATER HARVESTING TECHNIQUES

There are two main techniques of rain water harvestings-

1. Storage of rainwater on surface for future use.
2. 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 :- When permeable strata starts from top then this technique is used. Spread the water in streams/Nalas by
  making check dams, nala bunds, cement plugs, gabion structures or a percolation pond may be constructed.

Reasons of Shortage of Water

• Population increase
• Industrialization
• Urbanization  
• Increase in per capita utilization
• Less peculation area
• In places where rain fed/ irrigation based crops are cultivated through ground water
• Decrease in surface area of Lakes, talab, tanks etc.

     Deforestation
     (i) Less precipitation
     (ii) Absence of Barriers
        (a) Rain drops checked by leaves of tree
        (b) Water slowly descends through twigs & trunk
        (c) Humus – acts as reservoir
        (d) Tiny creatures – helps percolation

Do you know--------

1 hectare of forest-6-7 Lac ton of water(after filtering) top layer can hold 1.2 Lac tons of water.