EFFECT OF INCREASED DREDGING LENGTH OF THE GORAI RIVER OFF-TAKE ON LEAN SEASON FLOW OF THE GORAI RIVER IN BANGLADESH

摘要

The Gorai River off-taking from the Ganges River, is the main source of fresh water supply to the Southwest Region of Bangladesh. It is observed that, since 1989 the off-take of the Gorai fully dries up during the critical dry periods (January ― May) and completely cuts off the supply of fresh water. This has caused a serious socio-ecological problem with negative environmental impact on the Southwest Region. Several past attempts of excavating the Gorai mouth have failed to produce hardly any benefit due to lack of adequate knowledge of the off-take mechanism. For the first time a mathematical model aided three-year pilot dredging programme has been carried out for providing data and experience in devising a long-term sustainable dredging design and strategy. During the dredging, decision on the long-section, cross-section, and alignments of dredging were supported by several scenario simulations by numerical modelling of the hydraulic performance in terms of flow diversion from the Ganges, backfilling rate and erosion processes. Results with hydraulic interpretation of the corresponding simulations have been assessed to minimise the dredging effort by keeping track of the cut-off date for the dredging ensuring required flow diversion from the Ganges and to take decisions on a sustainable approach towards deciding on dredging strategy.