Reduce flood In Urban Basins Using LID- BMPs IN SWMM Model And Selecting The Best Option With AHP- TOPSIS(Case Study: Golestan Area In Semnan)

With passing the time and progress of civilization, access to sufficient and high quality water resources in order to provide the needs of human societies, is very important. With increasing impenetrable surfaces in urban areas and its resulting flood hazards, the new prespective of management methods of LID- BMPS has been considered in order to use surface runoff, decreasing peak discharge and preventing flood in urban areas on developed or developing parts. In this research, the effect of correction of channel dimensions, reservoir design for flood control and provision of required water for the green area and the use of LID facilities including implementation 100% of Permeable pavement for Sidewalks area and rain barrels in two conditions (using 100% of the surface of the roof) and (using 50% of the surface of the roof) on decreasing peak discharge and the volume of flooding 12 subbasing in the study area of Golestan settlement in Semnan city was evaluated using SWMM model. Finally, by using AHP- TOPSIS methods, rain barrels (using 50% of the surface of the roof) with about 81% reduction of peak discharge flood for the return period of deasining 5 year and 78% reduction of peak discharge flood for the return period of deasining 10 year have been allocated themselves the first and the last rank of correction of channel dimensions.