Application of EPASWMM model to simulate incoming floods into urban areas of rural hydrological catchments by using mathematical relations,Case Study: Paydari Town of Mashhad

Different models have been designed to simulate incoming floods into urban areas from rural areas, one of the models is the EPASWMM. Mashhad urban watershed with 8 inde-pendent subbasins and area of 2,472 hectares, located in south of Mashhad city . Study area is the residential area of Mashhad Paydari township (Area= 95.6 ha) that located below the M2, M3 and M4 subbasins. Due to high peak flood events in M2, M3 and M4 subbasins, the capacity of urban transmission channels in the Paydari township is’nt suf-ficient and after every rain, a lot of runoff enters the residential areas. The purpose of this research is evaluate the efficiency of EPASWMM model in simulating runoff. The study area was divided into 12 hydrological units (OUT1 to OUT12) and after determine of input parameters of the model, the runoff gathering network in the form of nodes-channels was introduced into the model. Four rainfall events were used to evaluate and calibrate the model with (NS), (RMSE) and (R2) coefficients. In the calibration section of the model, the value of the (NS) coefficient for discharge in the first and third events was 0.94 and 0.92 respectively and for runoff height, 0.9 and 0.86, respectively and indicates simulation accuracy of EPASWMM model in both parameters. The results of the model evaluation section for the second and fourth events shows that the NS and R2 coefficients for three parameters of discharge, height and runoff were from 0.78 to 0.9 and 0.73 to 0.89 and indicates a large correlation between observational and simulated data. Flood reduction scenarios in hydrological units have been investigated according to the simulation results.