A broken down school in Givha, Saharsa district, Bihar, destroyed in the floods after the Kusaha breached in 2008Posted on 29 Mar, 2010 12:18 PM
When the foundation stone for the Kosi embankment was laid on January 14, 1955, near Nirmali in Saharsa district in Bihar, euphoric people shouted, Aadhi roti khayenge, Kosi bandh banayenge (we will eat only half a chapati but we will surely build the embankment), writes the prolific engineer and activist Dinesh Mishra in his book, “ Trapped! Between the Devil and the Deep Waters.” No one really paid any attention to the protests and the fears of the people who would live with these embankments and what would happen to their lives.
To measure how fast water percolates into the soil, you need to measure the time it takes for a specific amount of water to soak into a specific area of soil. The easiest way to do this is to get a length of cylindrical pipe that is sharp enough to push (or hammer) into the soil at one end. Mark it with two lines – one is the line to which you insert it into the soil, and the other is the line to which you fill the water.
You can measure slope by making use of gravity. Find a protractor for measuring angles. Attach a straw across the straight edge of the protractor.
The first project was conducted by the BAIF Development Research Foundation in the Hassan District of Karnataka. They created a linked network of 350 farm ponds covering 700 hectares of the watershed.
The ideal farm pond should be dug into the ground in a naturally low-lying area. Some of the soil that is removed can be used to construct an earthen berm around the pond, which should be planted with trees and grasses for stability. The shade and wind protection provided by the raised mound and vegetation will reduce evaporative losses.
Where conditions are favorable, it is better to recharge the groundwater than to create surface ponds for storage. This approach minimizes evaporative losses, and often improves water quality. Recharge structures can be anything from a small pit simply dug into the soil, to a borewell converted for recharge. Recharge structures are useful in sloping landscapes where the water would not otherwise have time to sink into the ground before running off.
Where possible, it is much more cost effective to restore existing tanks, than to build new tanks. Restoration can involve silt removal to increase the storage capacity of the tank and reduce evaporative loss. The silt can be used to restore the earthen bund, and any remaining silt can be applied to nearby farmland. The outflow structure can also be improved.
If the intention is to develop a tank by holding back a large amount of water, then the dam must be carefully designed (with the assistance of experienced local people or engineers).
In addition to controlling gully erosion, check dams also serve to slow the movement of water, allowing increased percolation into the soil. Just above a check dam is a good place to put in a percolation structure. Silt that builds up behind the dam creates good farmland, which can be planted after the rains while it retains moisture. The following series of pictures show one farmer’s success with building a percolation tank just upstream of a series of check-dams.