Check Dams: A practical alternative to our large dam fetish
Check Dams are boulder dams or rock check dams. The purpose of check dams is to retain water up stream, so that the water percolates into the ground and recharges the ground water table. As concerns arise around large dams and environment, check dams are proving their worth over and over. Check Dams built on seasonal rivers, stop rain water discharging into the sea or going waste and provide natural fresh water bodies for local use as well as strengthening ecosystems. Check dams also serve to trap sediment and pollutants, strengthen local bio-diversity and help improve the overall quality of the water.
Check dam design: No complex engineering design or supervision is involved in check dam design. Check Dams can have a width of 5 feet and the height should not be more than 5 feet at any point from the river bed. That means the check dam will follow the contour of the river bed. The side slopes of a rock check dam can be 1 vertical to 1.5 horizontal. The objective is not to create a reservoir and exceed banks or submerge adjacent land, but to provide a point for the water to slow and permeate through the ground and replenish increasingly threatened water tables.
That means the bottom of the dam should be around 20 feet wide, sloping upwards at 1:1.5 to get a width of 5 feet on the top.
The foundation should be concrete, say around 1 feet high. (Where river bed is hard murrum or rock foundation avoided). Lay boulders, the heavier ones below and fill the voids with stone chips. Cement mortar 1: 6 can be used upto a height of 2.5 feet after which 1:8 mortar is fine. The voids between boulders need to packed with stone chips and low strength mortar.
Alternatively, check dams have also been created from logs, discarded truck tires and even sandbags. Virtually anything that can be stacked to block water which is sturdy enough to not drift or decay and does not leach harmful chemicals can be used to create a check dam.
Once the dam is built, secure all open faces with wire mesh, anchored to the foundation or ground for added durability.
The purpose of the dam is just to impede the flow of water and create a small reservoir to serve local needs and environment. What ever water remains trapped on the river bed, will recharge the ground water level. In case of flash flood, check dams provide slight resistance to the flow of water without actually stopping it. The flood passes over the dam, like regular water. If the flood is very heavy part of the dam may give way. So maintain it. My experience does not cause flooding of the banks. Dam stays well if maintained and the costs of maintenance are low.
Such Check Dams can be build every 3 or 5 km along seasonal water courses and will go a long way toward improving year round water availability in our country, which is predicted to have severe water scarcity in another decade or two. Studies have shown that the ground water table rises sufficiently after 2 seasonal entrapments.
It is also cost effective. In the cost of one major hydro electric project, or two, we could build check dams on most seasonal streams and make a significant dent in the problem of water availability.
Being labour intensive, check dam construction provides productive work for neighborhood and results in restoration of water table and strengthening of eco-diversity that lead to further sources of income. Check dams increase the availability of water for agriculture – an important factor for better yields in a country and world where food production is also an important objective.
Large dams entrap large amounts of water which percolates into the ground and makes the soil water logged and less fertile. Their large size results in trapping of heat and changes local climates. Not so with check dams.
Check dams are a cheap method to conserve water, rejuvenate falling water tables, support the ecology and fight the ever present threat of drought. In an increasingly polluted and water insecure world, check dams are a quick and effective way of reversing the clock.