Site selection for rainwater harvesting reservoirs in urban areas using the SWMM model (case study: Tehran's first district)

Iran’s location on Earth’s dry belt, and the consequent low precipitation, temporal and spatial changes in precipitation, have placed immense importance to the planning and management of water resources in the country. Thus, modeling can be viewed as one of the methods to investigate flood potential due to land use change. The aim of this study is to determine sites for water harvesting reservoirs for urban landscape applications in Tehran’s first district using the SWMM model; in order to efficiently use water resources, in addition to mitigating damage caused by runoff accumulation downstream and increased pollution. The SWMM model was used to simulate precipitation-runoff. After running the model, 2 events were used to calibrate the model and one event was employed to evaluate the model to confirm its validity and efficiency. The Nash-Sutcliffe coefficient was used to measure efficiency, producing values greater than 0.5 for all three events which confirmed the accuracy of our model. In the next step, factors influencing the possible site of reservoirs were determined using satellite images and GIS software capabilities, which indicated “proximity of the site of accumulation to site of consumption”, “significant volume of runoff”, “site’s suitability for construction”, and “ownership by the city’s municipality” as primary factors. “Distance from raw water supply network”, “existence of a reservoir”, “history of flooding”, “water supply limitations”, and “future development needs” were determined as secondary factors. The results revealed 23 suitable point for runoff storage reservoirs in Tehran’s first district for landscape applications in such a manner that in precipitation events with return periods of two and five years, 3892 and 4880 m3 of runoff pass through the 23 proposed sites. The results point to the district’s potential for development of water harvesting systems which can reduce pressure on subterranean water resources and address some of the challenges faced in the maintenance and extension of urban landscapes through use of unconventional sources of water.