River Research Institute, West Bengal, Calcutta.
The control of a flashy river by storage reservoirs is likely to affect the regime of the lower reaches of the river and create post-construction problems of bed deformation in these reaches. The reduction of peak discharge by means of storage dams in the upper catchment reduces the dominant discharge in the lower reach which adjusts itself to this reduced dominant discharge. This deformation of the bed in these reaches may ultimately prove to be a potential source of danger since a sudden flood of higher intensity, exceeding the dominant discharge after routing through the reservoir, may cause flooding even though the controlled peack discharge may be lower than the one which passed down the river in the uncontrolled period without much damage. Due attention should, therefore, be paid to the consumptive as well as non-consumptive uses of the river water, and a balance should be struck between the two for preservation of the river regime.
The River Damodar in the south-eastern part of the Indian Union is a typical flashy river and was at one time notorious for its floods and widespread devastation. Embankments were put up from very early times for protection against inundation due to high flood level but these have not been able to solve the flood problem permanently as a gradual raising of the river bed has taken place and occasional flood-ings and damage have occurred from abnormal floods. In 1946, a memorandum for the unified development of the Damodar Valley took shape and four multipurpose reservoirs have since been constructed at different places in the upper valley in the rivers Damodar, Barakar and Konar and have been controlling the flood flow for the last few years. The problem of bed deformation of the Damodar and Rupnarayan, through which the flood waters of the Damodar Spill, under post-dam condition has been discussed in the paper.
