Analysis and Economical Justification of the Construction of Earth Dam to Urban Runoff Management in Other to Use in Green Spaces

Runoff management in developing urban areas and susceptible to flood, is a major concern in urban management. Runoff harvesting methods, can reduce the risk of flooding, furthermore, these methods are useful for non-potable purposes. Region 22 is one of the most important centers of population of Tehran that urban development is growing, rapidly. Impermeable surfaces increases and proximity this urban basin, with two catchment, Kan and Vrdyj, Has provided the conditions for floods. In this study, according to the specific topography of  region 22, has been suggested the construction of earth dam for harvesting  part of the basin runoff and use it for irrigation part of urban green spaces in this area. Finally, in order to justify this project, has been economic analysis in the previous (current situation) and after runoff harvesting (after construction of earth dam). According to the results, the best place for construction of earth dam, was detected in behind the hills of Chitgar park, Based on, Water Supply Requirementsfor irrigation of‌ Forest Park of Cheetgar, Khargoosh dare and Nation Garden of Herbology, that these are located near the proposed earth dam site, Volume of the proposed earth dam, was estimated, at about 9.775.000 Cubic meters. The runoff harvesting system, can provide Water Requirements 49.7% of the total area of ​​green space in this area, also, it can  control, flood peak flow, 100-yr or more in. Finally analysis of the benefits and costs indicated, cost in current condition is 1.55 time (4.011.892.840 Rial in year) more after runoff harvesting.