Development of an Innovative Dynamical Approach for Flood Reduction in a Large City in Eastern India.

A large City of 600 000 inhabitants in India is frequently suffering from large flooding events occurring especially during the monsoon season. This City is composed of 2 main drains that release wastewater and stormwater to the nearby river. During the monsoon season, the outlets of the drains are closed because of the high levels of the river (maximum flow up to 40 000 m3/s). The main objective of the project is to provide the best solution to reduce the flood damages. The common approach in India is to apply the rational method to redesign the drain for a given return period considering free flow conditions.

In this project, a new dynamical approach has been developed in order to take into account the special local conditions. More precisely, to gain the understanding of existing conditions and to analyze potential solutions, PCSWMM that is a dynamic hydrology/hydraulic model was used to simulate the various conditions under single and long term events. In addition, a precise local rainfall analysis has been carried out with the development of the local IDF curves (based on the 1 hour data) and the statistical analysis of the monsoon season.

Using this approach, it clearly appeared that the optimal scenario was not to redesign entirely the main drains but to use a combination of solutions, including the drain design, the improvement of the regulation rules to close the gates, use of the existing canal as additional outlet for the drains, the use of the existing low land areas within the City and the update of the pumping stations.