Evaluation of runoff curve number method by Remote Sensing and HEC_HMS model (Case study: Birjand Mansourabad watershed)

The runoff curve number method is a simple, widely used and efficient procedure for determining the expected amount of runoff from rainfall. In this study, runoff curve number map of Birjand Mansourabad watershed was prepared by geographic information system (GIS) data and Landsat ETM+ satellite images based on the factors of hydrologic soil group, land use and land cover. The land cover map was determined using Normalized Difference Vegetation Index (NDVI) and VI Index and classified to three groups: good, fair and poor. The watershed land use map was produced by Landsat satellite data and hydrologic soil group map was produced using field survey, watershed soil, slope, geology and land use maps. The combination of these maps in GIS and using SCS table, runoff curve number and soil surface store Coefficient maps was obtained. To assess the accuracy of each curve number map, runoff peak discharges computed by HEC_HMS model were compared to measured amounts. 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.