assessment of watershed management activities on time of concentration and curve number using hec-hms model (case study: kan watershed, tehran)

assessment of watershed management activities is one of the main subjects for future planning of practical projects and natural resources management. due to the lack of any tool for assessment of watershed processes in many cases, distributed hydrological models can be useful. the purpose of this study was evaluation of watershed management activities in kan watershed by hec-hms (hydrologic modeling system). for this purpose, first by considering observed events, hec-hms model was optimized and calibrated. then, for evaluating the effects of check dams on time of concentration, it was calculated before and after of check dam's construction by use of field observations and vegetation cover improvement was also estimated after the project. these parameters were imported to hec-hms to find out the effects of watershed practices and then flooding condition was simulated. for assessment purposes, peak discharge and flood volume were calculated for “before” and “after” construction conditions. results showed that check dams as mechanical measures had low effect on time of concentration while biological practices lead to decrease in curve number with an average value of 3.1. this effects result in decrease of peak flow and flood volume meanly 21% and 11%, respectively.