DEVELOPMENT OF A COUPLED NUMERICAL AND MULTI-OBJECTIVE OPTIMIZATION MODEL TO REHABILITATE URBAN STORMWATER DRAINAGE SYSTEMS - CASE STUDY: EASTERN

Nowadays, \ design/rehabilitation of \ urban \ stormwater \ drainage systems has become a challenging issue due to more frequent severe floods in urbanized areas. These severe floods may cause significantly crucial social problems as well as financial damages. Also, regarding considerable advance in soft computing, optimization \ frameworks can \ provide a valuable \ computational \ tool for storm management. In the present study, using NSDE (Non-dominated Sorting Differential Evolution) \ algorithm and EPA-SWMM (Environmental Protection Agency - Stormwater Management Model) software, a coupled numerical and multi objective optimization model was developed to rehabilitate eastern part of Tehran metropolis drainage system. Not only is this part of Tehran Stormwater Drainage System (TSDS) the biggest drainage network of TSDS, but also its eastern part is dealing with a significant lack of capacity. In this direction, different mitigating strategies including combinations of relief tunnels and/or storage units were evaluated and optimal rehabilitation strategies were suggested according to minimizing conflicting objective functions of costs and flooding. For this purpose, formerly suggested rehabilitation solutions introduced by Mahab Ghodss consulting engineering company have been evaluated and extra relief tunnels considered to enhance their performance in relation to reduce volume of flooding in the network. Therefore, the total number of four different layouts of rehabilitation strategies have been assumed in order to rehabilitate eastern part of TSDS. Results have revealed considerable reduction of costs with respect to previous rehabilitation proposals for the study area stating the desirable performance of proposed coupled numerical and optimization framework of the present study. Moreover, regarding application of storage units in upstream of the network, although these units reduced rehabilitation costs significantly compared to other strategy by reducing length of required relief tunnels, relief tunnels slightly outperformed than upstream storage units in relation to the flood volume reduction. It seems possible to enhance the performance of storage units by relocating them.