Application of GIS-based Curve Number Method for Runoff Estimation in Agricultural-Forest Watershed, Thailand

The objective of this study was to apply the GIS-based hydrologic model for simulating runoff in the Upper Lam Ta Kong watershed, an agricultural-forest watershed, Nakhon Ratchasima province, Thailand. The Soil Conservation Service Curve Number (SCS-CN) method integrated with a Geographic Information System (GIS) was used to simulate the event-based runoff. Model calibration and validation were performed by comparing observed and simulated results at the M.43A and M.89 stations during the monsoon season of year 2011 and 2012, respectively. The runoff model calibration showed that the coefficient of efficiency (E) was 0.74 and coefficient of determination (R2) was 0.83 at the M.43A while E was 0.73 and R2 was 0.78 at the M.89 station. The results of the runoff model validation showed that the E was 0.66 and R2 was 0.75 at the M.43A while E was 0.73 and R2 was 0.87 at the M.89 station. This indicated that the GIS-based curve number method could be applied with satisfactory accuracy to runoff estimation in the study area. This model was also able to estimate varying runoff over the watershed spatially.