Investigation Flooding Potential in The Kashafrud watershed, Mashhad The Method SCS and GIS

Kashafrud Watershed Area is the part of the Great Plains Gharehghom in the northeastern province of Khorasan Razavi with area of 8996 square kilometers and considered the main drain Mashhad plain. to determine flooding potential of Kashafrud watershed used of modified SCS Method, the GIS system according to classification of map watershed and Tamab grade 4 in the digital elevation model, mapping the distribution of precipitation, precipitation losses and land use. Meteorological data, including precipitation statistics and rainstorms (28 stations) related to the period received of the relevant organizations and reviewed. After calibration data based on a common time base for 25 years (1989-1988 to2013-2012) and remove of suspicious data, in some cases rebuild the lengthening period. Layers of information is used such as maps: weather stations location, topography, land use, soil, vegetation, Political divisions of province and divisions watershed of Tamab. receiving DEM and making any necessary modifications basin boundary and physiographic characteristics calculated such as area, perimeter, height, slope, time of concentration. value of CN calculated by using the land use map and soil hydrology groups performed. Analysis Storm determined by using the software SMADA and standard distribution function (Pearson type 3) and value of of rainfall and storm return periods of 2 to 100 years. After calculation of weighted average height of the runoff in each subwatershed (sub 86), to determine the flood zones watershed, estimates maximum flooding (Qmax) caused by rainfall effective and drawn flooding potential map of watershed. Of the total area of watershed is, 68.25% of the normal flooding potential, 25.5% of of critical and is 6.25%.supercritical flooding potential. Cities Chenaran and Mashhad are flooding potential than other cities. From a total of 658 villages and population center recognized in watershed, 78% of the villages due to their placement in plain areas and low-slope are in the zone of potential flooding normal, 17% of the villages in the area with the potential flooding of critical and 5% of the villages due to the inclusion in the Highlands and steep with the potential flooding zone supercritical.