Many places in the world are prone to facing floods frequently. Bihar, Assam, and many other parts of Northern, Central and Southern India are quite prone to flooding during Monsoon.
Bihar is specially ravaged almost every year but still no permanent solution has been found.
When one faces the challenges of flood, one is not only dealing with untold miseries it causes but all the valuable rain water goes to waste as it ultimately flows into the ocean.
Building dams to control the flood is a common thought and practice but it is expensive, time consuming and requires submerging a vast area of arable land permanently.
Constructing dams make it possible to generate some hydro-electricity but for that the terrain must have appropriate geography. Simple mud embankments and levees do not fit the bill for hydro power. In addition, there are some ecological problems with it too. The much celebrated Farakka dam on the Ganges has not been as successful as it was originally hoped. This barrage, in addition to causing silting, and slow migration of the much prized Hilsa fish away from India has become a cause of tension regarding water rights with Bangladesh.
One possible way to control floods can be letting the rain water run through a plurality of pipes or boreholes into the ground.
In the USA, this technique is known as recharging the aquifers and is practiced in New Jersey, Texas, and other states. The water is pumped out during need and is pumped back in when it becomes available during rains. Luckily, the aquifers in the states are not too deep, around 100-200 feet only. In India, one has to probably go deeper as suggested in the case of the Ganges below. In India one can dig a 900' deep borehole at a total cost (labor, materials, casing, electrical pump and all the piping) of less than Rs. 150,000.
Fortunately, there was a study conducted and report issued in 2013. It was called "Master Plan for Artificial Recharge of Ground Water in India with Monsoon Runoff" by the Ministry of Water Resources. It was not indicated in this report that this can also help Flood Control. Unfortunately, as far as I know, this report has been collecting dust since then.
The technologies of sinking boreholes are well established and the cost of boreholes is much cheaper than building a dam. It uses very little land and does not interfere with navigation and agricultural practices.
The geological studies indicate that the ground underneath the Ganges in Patna-Jehanabad area up to 1200 feet (330 meters) deep consists of various porous layers of coarse, medium and fine sands. These sand layers are interspersed with impervious clay layers such that only sand layers are available 10 meters below the first clay layer and then after 60 meters or so. There is another clay layer of 10 meters that is followed by 220 meters of sandy layer. So at least in Patna (and there is no reason why the Ganges in UP, etc., and other rivers of India have stratas similar to that found in Patna) one can channel the flood water underneath the Ganges.
In case of Patna, assuming the sand porosity of only 40%, there is ample space underneath the Ganges to divert 40 to 60% of the river flow for a period of 1- 2 months underneath.
A geological survey extending to depths beyond 300 meters may reveal additional space underneath the surface for storage. The Geological Society of India (GSI) can undertake a study of such potential. Instead of indirect methods of survey, I think it would be better to use a rather direct technique such as by analysing samples from actual core sampling of the rivers (beds) that flood Bihar and other states.
The stored flood but sweet water then can be pumped out in times of needs for general and agricultural use.
Rabindra K. Sinha, Leander, Texas, USA