The Comparison and Analysis on Optimal Status of Best Management Practice (BMP) Mixed Technique to Reduce Urban Flood Discharge in Tehran District 4

Abstract

Nowadays, damages caused by flood are deemed as one of the important concerns for urban management. This study aims to analyze effects of coefficient of runoff to urban flood using one of the Best Management Practice (BMP) hybrid techniques with respect to change in use of urban lands and development in urban administration to reduce urban flood discharge. District 4 is one of 22 municipal districts in Tehran city as the east water basin with over 61.4km 2 . In this investigation, runoff coefficient was calculated by means of Geographic Information System (GIS) to determine rise of this coefficient in hydrological computations using of Storm Water Management Model (SWMM) techniques to adjust urban flood. Similarly, the level of effect was evaluated for four parameters of gradient (slope), roughness coefficient, Curve Number (CN), and impermeability on change of use. With respect to results of sensitivity analysis of peak discharge, this system has the maximum sensitivity in terms of parameter of impermeability percent due to change of use so that following to 10% increase in impermeability, the output discharge of hydrograph runoff was increased 15% and due to 10% reduction in impermeability level, output discharge of hydrograph runoff was decreased 19%. Curve Number (CN) has highest sensitivity after parameter of impermeability percent and following to 10% increase in CN parameter, the output discharge of hydrograph runoff was increased 15% while by 10% reduction in roughness coefficient, output discharge of hydrograph runoff was reduced 8%. After implementation of model with the given mixed scenario through comparing of discharge in 10year return period, it was characterized that the maximum reduction rates occurred in output No 2 (26.8%) and output No 7 (54.3%).