|Call for radical changes in drainage concept|
GUWAHATI, July 19 – The Senior Engineers’ Forum of Greater Guwahati has called for radical changes in the drainage concept for the city.
In its meeting held here recently, all its members were of the opinion that there is an urgent need for radical changes or modifications in preparation and implementation of the plans and schemes which are mostly based on the 1971 Drainage Master Plan of the city.
The basic concept of the said master plan was to divert the storm water coming from the Khasi-Jayantia Hills of Meghalaya to the Deepor Beel, resection of the existing natural drainage channels to accommodate the storm run-off from the influenced areas of the city, introduction of trunk and secondary drains within the city with connection to the natural drainage channels, retention of existing beels and providing control devices with pumping at the outfalls at the Brahmaputra.
The above re-sectioning parameters were determined on the basis of pre-1970 data, like paved area, sparse human settlement in the hills, land use within the city etc., and on analysis of rainfall data for the past 50 years prior to the seventies of the last century.
Now, after a lapse of four decades, the pre-1970 conditions no longer exist. Rainfall pattern, intensity and duration have been drastically changed – may be due to global warming and the El Nino effect. The hills are now degraded with extensive cutting and full of human settlements. Paved areas had been increased due to massive construction of high rise buildings and other developments including concrete roads.
The areas of the existing beels have been reduced by large scale encroachments and development. It is very unlikely that the haphazard, or, unauthorised developments in the plains as well as in the hill areas would be undone in future and the degradation reversed.
Therefore, a fresh look at the drainage concept as well as the future schemes proposed for the city on the basis of the master plan is required immediately.
It is in this context, the forum felt that if there is no limitation of funds as has been claimed by the officials very often, the entire city will have to be completely redeveloped by raising the general ground level of the city by a few metres.
Simultaneously, all of its infrastructure and utilities are to be reconstructed in a phased manner, starting from the drainage outfall areas and proceeding towards higher region to completely prevent occurrence of artificial floods even if that requires flattening of a few existing hills and hillocks and massive temporary relief and rehabilitation.
However, to reduce the severity of the problem, the existing natural drainage channels, after removal of their encroachments, may be developed as retention-cum-drainage channels covering the entire available width and by providing physical boundaries and deep beds to the maximum possible extent.
Wherever large areas are available by the side of the channels, retention ponds may be constructed to retain excess storm run-off temporarily till the water level is lowered by massive pumping at its outfall similar to the dam operation methodology.
Since encroachments on the existing beels are also being removed, the beels may be developed as retention reservoirs by deepening them and protecting their boundaries with permanent structures.
Of course, massive pumping arrangements commensurate with the excess run-off are to be provided at all the outfalls.
The above measures are in addition to other works that would be required for area drainage and maintenance, the Forum said.