Rain Water Harvesting
Rain water harvesting generally means collection of rain water. Its special meaning is a technique of recharging of underground water. In this technique water is made to go underground after collecting rain water locally, without polluting the same. With this, water during the time of scarcity local domestic demand can be met.
Now the question arises – After all why do we need water harvesting? Three main reasons are responsible for this –
- Scarcity of surface water
- Growing dependence on underground water
- Increasing urbanization
Total amount of rain water recovered in an area is called ‘rain water reserve’. Effective management of rain water reserve is called ‘potential water harvesting’.
Think for a while the area of the roof of your house is 100 square metres and the ‘average rainfall’ of this area is 60 cms. Suppose the water on the roof has neither flowed, percolated nor evaporated then there will be 60 cms high water on the roof.
Volume of water
= Area of the roof x Amount of annual rainfall
= 100 x 60 cms = 100 x 0.6 metres = 60 cubic metres
In other words, a family can collect 60,000 litre water in a year. All water related needs of this family can be met with this. On an average a person needs 10 litre water for drinking daily. If your family consists of 6 members, then you need 6x10x365 = 21900 litres water. Remaining (60,000 – 21,900) = 38,100 litre water can be used in dry weather when there is a scarcity of water.
The tradition of water harvesting is very old in India. But the utility of water harvesting has never been felt so much as it is today.
Even today the people living in the areas of water scarcity try to do their domestic work by adopting old methods. Deepening and dredging of wells, tanks and ponds are included in these methods.
Water harvesting in the small channels (locally known as bawli) is an important traditional method in the areas of water scarcity.
Now we can be in a better and secure situation by adopting new technique of water harvesting.
Think for a while. If the people living in 5,87,000 village engage themselves for harvesting rain water of their 2000 lakh hectare area, there will be lot of water available for use. On an average a village comes under the radius of 37,500 lakh cubic metre rain water reserve.
By this calculation we come to know that there is great potential of rain water harvesting.
Methods of Rain Water Harvesting
We can adopt different methods for rain water harvesting according to need, available facilities and environmental conditions. The following methods are worth mentioning –
1. Construction of potholes – We can harvest water in small ditches constructed in those areas where there is not much underground water. These ditches may be constructed 1-2 metre wide and 2-3 metres deep. Their shape could be anything. These ditches are filled with roubles and sand. Rainwater can easily percolate through these.
2. Construction of trenches – In the lower regions where porous rocks are found after making trenches of 0.5 to 1 metre width, 1 to 1.5 metre depth and 10 to 15 metre length, these are filled with roubles. These trenches should be made parallel to the slope of the land.
3. Use of wells – The wells which have become dry and are not being used at present can be used for water harvesting.
4. Hand-pump – Stored rainwater can be made underground with the help of filter by running hand-pumps in the areas of lack of underground water.
Bibliography : NIOS – Geography