چكيده لاتين :
In this study, a part of the floods water volumes of Ghara-Chay basin located in Hamadan province was investigated using excess rainfall determination. In this regard, digital elevation model, rainfall gradient and isohyetal map of the basin were prepared using the maximum daily rainfall of the meteorological stations of the region for different return periods. Then, based on the soil infiltrations and satellite images, the soil hydrological groups and land use maps were produced. Finally, by overlaying the prepared maps, the curve number maps were developed. The depths of direct runoff from the storm generations were computed using the SCS method. The overland flow plan of each storm was developed by conversion and combination of all the information maps in the GIS. A classification consisting 7 runoffs category which was included the runoff depth less than 20 mm to higher than 120 mm was considered. The difference between the classes was 20 mm. Frequency of each class was calculated from 25 to 200 year return periods. The results confirmed a high relationship between the digital elevation model and the runoff depth maps. They showed that the overland flow decreases from high lands toward plain of the basin that is exactly coherent with the long term flow coefficient of the basin. An exponential decreasing trend was identified between the runoff depth and the area of each class. In exception of the class which was less than 20 mm, the area of each class was directly related to return periods from 200 to 25 years. In the class less than 20 mm, the inverse relationship between the surface and return periods showed that the runoffs with an area about 50% of the total area of basin, are the normal runoffs that occur frequently, but in the rest of the classes, which flow depth increase, non-flooding flows play a major role.
