Evaluatiopn of Strategies for Modifying Urban Storm Water Drainage System Using Risk-based Criteria

Appropriate modification of existing urban storm water drainage networks may help reduce network inundation and flood-borne pollution risks. It will, therefore, be necessary to analyze the risks associated with water quantity and quality during urban flooding before any reconstruction strategies can be identified that are adaptable to, or compatible with, urban sustainable development strategies. In this paper, three network modification strategies are evaluated against the three criteria of network inundation at different sections, flood pollution risks, and modification plan costs. The modification strategies evaluated include the conventional approach of increasing conduit dimensions as well as the two novels swale and bio-retention systems. The strategies are then prioritised using a Multi-Criteria Decision Analysis (MCDA) method. The application of the proposed methodology is illustrated in the case study of urban storm water drainage systems in the Golestan City in Tehran Province for which a hydrological and hydraulic simulation model has been developed using the SWMM software. The results show that the swale system is the best strategy with an approximate cost of 20 billion Rials (almost US$ 6 million). Compared to the existing system in operation, the proposed system will be capable of reducing 59% of the quantitative risk of flooding (inundation) and 26% of the water quality risk (pollution loads).