Runoff simulation and investigation the effect of land use changes on surface water quantity using remote sensing data and Hec-Hms model (Case study: Halil Rud basin)

Runoff evaluation in ungauged basins, like most of basins in Iran, is imperative for   sustainable management of water resources. Changes in land uses were related to different hydrological responses. This paper discusses the hydrological impacts of land use changes on the Halil-Rud Basin during the past two decades_. Firstly, the land use map of the Halil Rud basin was prepared using Landsat satellite images in seven classes. Results reveal that from 1993 to 2013, a 1.99% increase in arid land is the strongest change in land use. By integrating the land use map and the soil map of the area, the curve number map of the basin was prepared. In order to ensure the accuracy of the curve number map, the flood hydrograph of the mentioned years was determined using the precipitation-runoff model of HEC-HMS and compared with observed hydrographs. The accuracy of 85% of the results showed that it can be reliable according to the exactness and precision of the curve number calculated by GIS and RS data in basins with limited or lake of data. The comparison of the flood hydrograph from the precipitation-runoff model from a specific precipitation (1993) showed that during the years 1993 to 2013, the peak flood discharge was about 106.1m3/s and the runoff volume increased about 7.5 million cubic meters. The results of this study indicate that the continuation of the degradation process in land use of the area towards the arid state will lead to decreased infiltration, with a degradation of maximum soil water contents, less winter recharge rates to aquifers, and increased run off and debated risks of floods.