Evaluation of urban storm water network in Hyderabad city using SWMM

Abstract

Management of the quantity and quality of storm water runoff from urban areas is a complex task which has become an increasingly important environmental issue for urban communities. Together with economic and social issues, this increased awareness of the impacts of urban drainage systems has resulted in a need for system managers to obtain information regarding the drainage system response to varying climatic conditions. In an ideal situation, storm water systems would be designed and analyzed with catchment modeling systems which fully replicated the important processes involved with the generation and transmission of storm water. This ideal situation, however, requires catchment modeling systems, generally mathematical in form, to be developed that include all potential and feasibility. Effective urban storm water management is highly dependent on appropriate consideration of the spatial variability of urban watershed characteristics. This realization has prompted increasing use of physically based urban watershed models such as the Environmental Protection Agency (EPA) storm-water management model (SWMM) (Huber et al. 1983). The use of spatially distributed, physically based models enhances the ability to simulate the dynamic runoff response of urbanizing catchments. The available historical hydrological data, which is suitable for urban hydrological studies, have been evaluated in the Hyderabad city. No flood inundation maps, short terms rainfall and water level data is available for the study area. However historical hourly rainfall within study area at Hyderabad station (maintained by IMD) has been collected and analyzed. The hourly rainfall computed for 2, 5, 10, and 25 years return periods using Extreme Value Type 1 distribution and developed the IDF formula. During the project period five tipping bucket rain gauges and one automatic water levels recorder have been installed in the study area. The storm water drainage network details were collected and GIS database has been prepared. Using thematic layers of DEM delineated the 15 sub-catchments and drainage network. Using these thematic layers, the study area has been schematized using 15 nodes and 13 links in the EP-SWMM model. Based on measured rainfall and water level data in the study area, the EP-SWMM model performance has been evaluated in terms of stage computation in the study area. The average runoff coefficient found in the study area is 0.863. After successful testing of the model, the design storm for 2, 5 10 and 25 years return periods have been considered as input into the model and found that the present storm water drainage network is not sufficient to drain two-year return period storm. The data monitored in the basin may act as benchmark dataset for further research and to explore other flood mitigation measures in the study area.