Preparing Curve Number Map of Run-off and Investigating its Precision Using Hydrological Model (Case Study: Navdar Catchment)

Curve Number (CN) is one of the required parameters for runoff calculation using SCS method. Considering spatial variability of factors affecting this parameter, different values of CN is expected within different parts across a catchment. The present research aims to map CN in Navdar catchment, Kermanshah province, Iran. Therefore, modern technologies such as geographical information system (GIS) and remote sensing (RS) have been used. First, land use map of the study area was determined based on Landsat satellite images (TM) using ERDAS software package. Then ground coverage density was determined based on Normalized Difference Vegetation Index (NDVI). The map of soil hydrological groups was prepared in GIS environment based on the available soil map in the study area. Finally, CN map was prepared based on SCS table and the maps of land-use, ground coverage density, and soil hydrological group. Average curve number under intermediate humidity conditions in the study area was calculated as 78. Simultaneously, CN in the catchment was determined as 76 by the analysis of recorded runoff events using HEC-HMS model. Results of this study indicate that the accuracy of calculated curve number via RS and GIS technique is high, so the obtained curve numbers using RS and GIS method across this catchment are reliable. Based on the determined curve number in the catchment (78), it can be concluded that this catchment has high potentials in terms of runoff generation.