Mehdi Ghasemizade - Graduate student of Tarbiat Modares University, Department of Water
Kourosh Mohammadi - Professor of Tarbiat Modares University, Department of Irrigation
Monire Biyabanaki - Post-graduate student of Isfahan university of Technology, Department of Water Engineering
Saied Morid - Professor of Tarbiat Modares University, Department of Water Resources

Since Iran is located in an arid region and its annual average precipitation is about one third of the average precipitation in the world, the necessity of applying and building structures which can prevent loss of water in high-precipitated years is a must. What that is of great importance is the correct estimation of peak and volume of floods entering these structures, as a result of heavy rainfalls. Unfortunately, most of the basins which their runoffs have not yet been brought under control are the ones that either lack of sufficient data or are unguaged basins. Consequently, a variety of methods which each has its own advantages and disadvantages is suggested for use in unguaged basins. Although these methods are of great help in such situations, nevertheless, they cannot be applied without prior calibration. Because the basin under study in this research lacks of measured hydrometric data, a gauging watershed which not only is similar to our watershed in terms of vegetation, geology and physiographic but also close to the unguaged basin has been chosen for calibration. To better simulate the under study basin, ArcGis and HECGeoHMS were applied to determine the physiographic features and input parameters of HEC-HMS for both basins. We also used method of average variability and method of consecutive blocks to determine the rainfall temporal pattern to get results closer to reality. Results indicate that for return periods of 2, 5, 10, 25, 50 and 100 years the peak flow will be 16.4, 35.4, 51.5, 72.8, 91, 110 m3/s and the volume of flood for the above return periods are 4.68, 10.5, 14.52, 20.68, 25.6 and 30.82 MCM, respectively.

Peak flow, Return periods, Rainfall Temporal pattern, Unit hydrograph