Investigating the Possibility of Using Surface Runoff in Mashhad

Declining pervious areas is one of the most important effects of land use changes and replacing natural watersheds with urban zones. This phenomenon increases the surface runoff and the possibility of urban floods. In recent years, the unprecedented expansion of urbanized areas of Mashhad City has caused an increase in runoff potential. Since, on the other hand, there is a serious lack of water resources for the city, a comprehensive study on urban surface runoff and methods of managing the runoff has become a serious necessity in Mashhad. In this study, after sub-basin delineation, based on the available data, first the rainfall-runoff process for a number of urban and natural sun-basins was calibrated using HEC-HMS rainfall-runoff model. Then, the volume of surface runoff was computed for the whole city of Mashhad. Finally, management methods of surface runoff especially in terms of runoff storage were considered both technically and economically. The results showed that despite the high volume of produced runoff, runoff management merely based on storage is not reasonable due to spatial restrictions. In other words, the cost ratio for storing and using each cubic meter of runoff is very high and economically not feasible. Consequently, the main approach in runoff storage in Mashhad needs to focus on utilizing the potential of existing lakes and reservoirs. In addition, the other important approach should be based on storing the water released from Golestan Dam located 5 km of the southwest of Mashhad.