Hydrological modeling of Goranchatbari storm water drainage system using storm water management model

Abstract

Throughout history urban floods have been one of the most severe naturalcatastrophes, which brought about loss of lives and huge economic losses inaddition to the influence on community activities and adverse effects on theenvironment. We have witnessed enormous flood events almost all over theworld, even in the early years of 21st century. The cruel lesson learnt is that wehave not coped well with floods in many over populated mega cities like Dhaka.

Stormwater modeling has a major role in preventing issues such as flash floods and urban water-quality problems. However, in-detail modeling of large urban areas is time-consuming as it typically involves model calibration based on highly detailed input data. Stormwater models of a lowered spatial resolution would thus appear valuable if only their ability to provide realistic results could be proved.

An urban inundation model, combining a storm sewer model SWMM and operations of Goranchatbari pumping station, has been developed to simulate inundation in urban areas due to storm water and outlet pumping station. The movement of water in the studied Goranchatbari watershed is characterized by two components, namely, the storm water flow component and the inundation component.SWMM is employed to solve the storm water flow component and to provide the flow hydrographs for surface runoff exceeding the capacity of the storm water. Drainage by pumping stations at outlets of the storm water system has also been taken into consideration.

Rainfall frequency analysis of30 yr, 50yr and 100yr return periodswere conducted for Dhaka BMD and BWDB stations. The effect of rainfall due to climate change was incorporated in this SWMM drainage model to generate future scenarios of study area. The combined study is suitable for analysis of inundation on urban areas due to overflow of storm water and flooding caused by Climate Change. The parameters of the Goranchatbari model were calibrated by pumping water level and velocity verified for discrete storms with some internal khals system.The simulated SWMM model also validated with World Bank study inundation map prepared for actual event 2004. Simulated results applied to establish inundation maps to find out the flooded regions of study area due to waterlogging with different return periods.

Simulated SWMM Model and inundation maps showed that the major drainage takes place at several locations of study area like Kalshi, Mirpur-10, Shewrapara and Kazipara which covering a huge study area from Mirpur-10 to Uttara with BauniaKhal to DigunKhal at retention pond. These area variations modify the features of both urban hydrology and hydraulics, and change the distribution of drainage network. It may lead to dual adverse effects in one specific region like Shewrapara, Kazipara which will risk of flooding on extreme rainfall. Therefore, finding appropriate solutions for these problems has been being a great challenge for the urban city like Dhaka.