Investigating of the Effect of Land Use Changes on Daily River Discharge Using the HEC-HMS Model (Case study: Ajerloo Watershed, West Azerbaijan Province)

Precise estimation of discharge is a key step in planning and optimal management of water resources. One of the effective factors in changing the rivers flow regime is basin-wide land use changes. In this study, the effects of land use changes on Ajerloo river flow regime were investigated using the HEC-HMS hydrological model. To detect the changes of land use in this watershed, we used some satllite images of the MSS Landsat and LISS III (IRS-1C satellite) for the years 1975-2008. After applying various corrections and different analyses and random sampling of land use units, classification for each image was done using maximum likelihood algorithm. For the both series of images (according to Kappa coefficients 0.76 and 0.78 for the MSS and LISS III, respectively) the bands of green and red as well as NDVI index were selected as the best combination band. Then the accuracy of the produced maps was evaluated. The results showed that during 33 years, the area of rangelands had decreased by 37.65 % whereas the areas of agriculture and bare lands had increased by 57.27% and 37.65, respectively. For this purpose, after providing the land use map for the years 1975 and 2008 and combining them with the Hydrological soil groups map in GIS, the HEC-HMS hydrological model was calibrated and validated using the curve number and SCS unit hydrograph of the basin based on rainfall-runoff observations. The results of the model calibration (after optimization the curve number and the lag time basin parameters) showed that the land use changes in the mentioned time period had increased the peak discharge about 29.7 cubic meters per second (86.8%) as well as the runoff volume 18.8 million cubic meters (12.7%).