Artificial flood & water scarcity in urban areas

Jatindra Nath Mahanta

(A probable solution to the twin problem of artificial floods and water scarcity in urban areas in Assam given by this writer seems tangible and worthy of consideration by those at the helm of affairs. He can be reached at mahantajn12@gmail.com)

The urban areas today have become concrete jungles. The underground water body does not get recharged through the natural process of rainwater permeating through the permeable soil strata to the aquifer level located at around 15-20 metres below ground level. The rain water gets drained out through the city drains and during heavy rains, the city suffers from artificial flood situation till the surplus water gets completely drained out. Gradually, the UG-water level gets depleted and the city's ring well, tube well or bore wells go dry.

As a concerned citizen, a probable solution to the problem of artificial flood and water scarcity in Guwahati is suggested for consideration of the authorities of GMC, GMDA and GDD. The suggested solution is 'Rain Water Harvesting through Recharge Shaft'. The scheme is simple, cost-effective and effectiveness of the scheme is readily measurable. It is the most efficient and cost-effective rainwater harvesting technique to recharge unconfined aquifer overlain (covered on top) by poorly permeable strata. Recharge shafts may be dug manually or by mechanical means. These are to be located at the city's drain beds at suitable intervals. The diameter of the shafts may be between 0.5 m and 2.5 m depending on the size of the drains where the shafts are dug. The shafts should penetrate the top impermeable strata and end in a depth of 10 to 15 m reaching the more permeable strata leading to aquifer. This will force the rainwater to flow directly downward to the aquifer level where it will spread around. If sufficient numbers of such recharge shafts are dug on the beds of the city's drains, the surplus rain water, which does not get drained out due to inadequate drainage capacity, will rush down the recharge shafts. It would solve the problem of artificial floods and additionally raise the ground water level helping the city to fight severe water scarcity. The city's tube wells and bore wells will start spewing out water once again. The shafts may be left unlined or may be lined with RCC rings (as in a ring well) and it should be backfilled initially with boulders followed by gravels and coarse sand. The dirty storm water will filter down the shafts to meet the underground water body. The backfilled materials will prevent the ingress of impermeable clay from the surface and save the shaft from choking. GI pipes may also be used as shafts.

This suggestion may be tried on an experimental basis, say, in the drains along R.G. Baruah Road. About 300 shafts (150 on each side) of 0.5 to 1 m diameter and 12 to 15 m deep may be bored on the 3-km-long stretch along R.G. Baruah Road and then backfilled with boulder, gravel and coarse sand. The effectiveness can be observed during a heavy downpour. It would cost less than Rs. 10 crore. In order to increase the downward flow rate of the rainwater, back filling may be avoided. In that case, the shaft will need to be lined with RCC rings and provided with a strong metal cover (grating) with a fine mesh steel wire netting placed on top to prevent ingress of solid materials and clay from the surface.

If the experiment proves successful then it can be extended to cover the entire city drains, including the Bharalu, Basistha and Bahini rivers. Smaller 6-inch diameter GI pipe shafts can also be inserted on the edges of the roads in order to augment the process with quicker evacuation of the surface water and thereby eliminating flooding of the roads. In these narrow shafts back filling should be avoided and strong steel wire netting-cover should be used.

Rainwater harvesting through recharge shaft is a proven method of harvesting rainwater covering wide area. If it is found effective for Guwahati, the city's perennial problem will get solved. The other equally important gains will be availability of huge quantity of ground water solving the acute water scarcity problem in Guwahati. The scheme can be extended to other towns of Assam where the same problems are making the lives of millions miserable.

GMC, GMDA and GDD can carry out the experiment even if it is considered to be remotely feasible since the cost is negligible compared to hundreds of crores spent so far and untold miseries suffered by the citizens. If successful, it would be a great achievement of the departments concerned and a huge gift to the victims of artificial floods and water scarcity. If the experiment does not work, it will be another failed but honest attempt to mitigate the miseries of the citizens. Expert opinion of agencies involved with rain water harvesting schemes and Central Ground Water Board may also be sought.

(Help taken from Google information on Rainwater harvesting)