ASSESSMENT OF FLOOD MITIGATION MEASURE FOR MITHI RIVER ? A CASE STUDY

Mumbai city which has an area of 437sq km with a population of 12 million came to an abrupt halt because of the unprecedented rainfall of 944mm during the 24 hours starting on 26th July 2005; with 380mm occurring in just 3 hours between 14:30 to 17:30 and hourly rainfall exceeding 126 mm/hr. This particular event is considered to be an extra-ordinary event. Numerical model study using one dimensional mathematical model HEC-RAS is carried out to simulate unsteady flow in Mithi river with the existing conditions and with the telescopic channelization as suggested by MMRDA for 100 years return period and 6 hours storm duration. The appropriate boundary conditions at the upstream, downstream and the internal boundaries were applied. The results indicated that due to the channelization, the average reduction in the water level is of the order of 20 % to25 % and the increase in the conveyance capacity of Mithi River causing rapid flushing of floods, is found to vary from 23% to 340% which is quite significant compared to existing conditions at various locations along the river. Thus the telescopic channelization is found to be effective for mitigating floods