Varanashi Sand and Plastic Barrage
“Katta” a kind of barrage is a temporary water storage structure being built across seasonal rivers and streams every year during tail end of rainy season. The stored water is used for irrigation. This is practiced by the farmers of Coastal and Malnad area for hundreds of years. The introduction of pump-sets, bore wells and increased labour cost has reduced the numbers drastically.
Dr. Varanashi Krishna Moorthy of Varanashi Research Foundation for the first time in 2002-03 summer built 35 meter long “Katta” across Seere river using Sand bag and UV stabilized “silpaulin” sheets. It stored water to a length of 1.5 KM. He shared the information and in the subsequent year three more Katta’s came across same river and another four elsewhere. The technology was further simplified in subsequent years and now only sand and plastic sheets are being used.
The construction involves following steps.
Choose the narrowest site with strong bunds in the stream / river. A rocky bedded area is most suitable.
In case of sand bed, dig a trench across the river till soil level is reached either manually or by machine.
Insert 250 GSM plastic sheet. Building a mud bund with good quality soil and then inserting the plastic sheet in the front is still better. Fold and Keep a little extra sheet of plastic well below the bed level, cover with sand and keep stones over it. This process of making the river bed seepage proof has to be done in summer. In case of rocky bed no such work is necessary.
At the tail end of rainy season as the flow thins down open the sand bed and unfold the plastic and build the barrage just behind plastic sheet line using sand bag to the desired height but not more than three meters. For a barrage of three meter height, the wall thickness should be two meters. Incase plenty of sand is available, excavators could be used to heap up the sand. In this case bottom width should be six meters.
Introduce extra plastic of 125 or 250 gsm in the front and secure up to the top.
As the water gets blocked, a sloppy side flow provision has to be built with sand bag and plastic sheet lining. In case of expected higher flow, in un-seasonal rainy areas, a permanent structure using locally available material is desirable at the overflow opening.
As the rainy season starts the top plastic sheet need to be removed. The bottom sheet is folded and secured as explained earlier and will last for many years, where as a good quality top sheet can last 2-3 seasons. Instead cheap quality recycled thick plastic sheet could be also used at the top. But exposed area needs to be protected with material like coconut frond.
Varanashi model of Sand and Plastic structure could be built across from small stream to any big river at minimal cost. It is getting popular.
This kind of barrage if serially built at distances of 0.5 to 2.0 km across seasonal streams and rivers, water scarcity could be greatly reduced.
Read the article by well known water harvesting expert Shree Padre.
Kattagalu Anushodhanegalu Mattu Varanashi Madari.