Over the last half century, human population has expanded considerably in India. This has resulted in much shortage of fresh water for human needs. Water is basic to life and the resulting shortage severely compromises quality of life in the country.
While this shortage of fresh water persists, a huge proportion of fresh water that falls as rain in the country during monsoon months collects in rivers and is lost to oceans. One way to reduce this loss is construction of dams. However, large dams take time to build, cost a lot, pose dangers and are disruptive of ecology, river life and human habitations. Another way to collect excess monsoon water that gathers in rivers is through side streams that lead to lakes and ponds situated near or far from the river. In some parts of the country where they have done this, as in Karnataka, India’s Bangalkot district (see report 1) it has wiped out water shortages. However this effort was through impromptu barrages constructed by people. There is a need to repeat this all over India in a more systematic manner.
The L-Bend barrage as described here can assist in collecting excess water in monsoon months from rivers in lakes and ponds spread across the country. The L-Bend is a low cost solution, can be constructed rapidly along with the associated side streams with help of earth moving equipment. It preserves river and surrounding ecology and fish life and improves human habitations. It has the potential to add value through blue water farming.
When water is collected in lakes and ponds, some of it is lost through evaporation but much of it is used directly or percolates into ground where it serves to increase ground water level. The majority of fresh water used in India by humans is sub-soil water drawn through bore wells or traditional wells. Presently the water table has been falling in most areas but when a lake or pond is constructed nearby, the water table rises. Because of the presence of Himalayan Mountains in the North of the sub-continent much of the evaporated water from lakes and rivers also returns as rain.
The L-Bend consists of two walls in the shape of an L as shown in figure. The shorter side blocks the mouth of a side stream from the river to a lake. It is constructed at a height of the average river level during monsoon months. Whenever the river level exceeds height of this sidewall, water from the river flows into the stream that leads to a lake or multiple lakes and ponds. The longer side of the l-bend is kept at the level of the riverbank on the side on which the stream is constructed. It spans one third or less of the river width so it never completely blocks river flow. Average of river level during monsoon months can be determined from data of past several years to fix the height of the shorter section of the L- bend
Rivers continue to collect water during their course from tributaries and seasonal streams that develop during monsoons. Therefore, it is necessary to construct such L-Bend fed lakes all along the course of the river. The lake may be close or at some distance from the river depending on the topography of surrounding land. Existing ponds and lakes that fill up in monsoons may be enlarged if connected to an L-Bend Stream or alternatively entirely new lakes developed.
Precise dimensions and details are not given here but can be easily worked out by engineers from the discipline once the concept is understood. If more clarifications are needed from this author, a reader may enquire by posting a query as a comment to this note.