Abstract: (84 Views)
Introduction and Objective: In recent decades, land use changes have been identified as one of the most influential factors affecting the hydrological behavior and flood generation in watersheds. These changes are mainly driven by population growth, agricultural expansion, urban development, and the degradation of natural vegetation, all of which alter soil infiltration capacity, reduce water storage potential, and increase surface runoff. In many mountainous watersheds of Iran—particularly in Ardabil Province—these transformations have led to a rise in flash flood events, soil degradation, and threats to critical infrastructure. Due to its unique topographic conditions and increasing anthropogenic interventions in the downstream areas, the Atashgah watershed is especially vulnerable and requires a detailed assessment of the impacts of land use change on its hydrological response.
This study aims to investigate the effects of land use management scenarios on flood characteristics—particularly peak discharge and the shape of the flood hydrograph—in the Atashgah watershed using the semi-distributed SCS model in the WMS environment. The research also seeks to analyze the spatial and temporal impacts of proposed land use policies on hydrological parameters and simulate watershed responses under different return periods.
Materials and Methods: Initially, land use maps for the baseline year 2011 were prepared using satellite imagery, Digital Elevation Model (DEM) data, and field observations. Based on slope analysis and soil capability, four management scenarios were developed, each incorporating different levels of change in rangeland coverage, dryland and irrigated agriculture, and barren lands. Climatic data were collected from 11 surrounding weather stations and used to determine design rainfall values for return periods of 2, 5, 10, 25, 50, and 100 years. The design rainfall was calculated using the CumFreq software. The SCS rainfall–runoff model was calibrated in the WMS environment, and three observed rainfall–runoff events were used for validation. Key parameters, including Curve Number (CN), Initial Abstraction (Ia), and Time of Concentration, were computed for each scenario. The model outputs—peak discharge and flood hydrographs—were then extracted for final analysis.
Results: The results showed that implementing the management scenarios led to a decrease in CN and an increase in Ia. These changes directly resulted in reduced peak discharges and modifications in the shape of the flood hydrograph. Scenario 4, which combined optimized land use redistribution based on slope and soil infiltration capacity, produced the most significant reduction in peak discharge across all return periods, with a maximum decrease of 22.95% compared to the baseline condition. Spatial analysis revealed that areas with lower slopes and elevations experienced the highest degree of land use change, which in turn had a considerable impact on the watershed's flood response. Furthermore, the spatial distribution of runoff improved, and a delay in the time to peak was observed in some scenarios. These findings suggest that even moderate land cover modifications, when properly designed, can significantly reduce flood vulnerability.
Conclusion: The SCS model implemented in the WMS environment proves to be an effective tool for evaluating the hydrological impacts of land use changes at the watershed scale. The findings emphasize that land use management policies, if based on detailed topographic analysis, soil characteristics, and infiltration capacity, can greatly mitigate flood risk and enhance environmental resilience. It is therefore recommended that natural resources and watershed management authorities utilize the outcomes of such studies for planning and executing adaptive management scenarios in high-risk watersheds. Future studies should consider integrating land use change scenarios with climate change projections to provide a more comprehensive understanding of watershed behavior under compound threats.
This study aims to investigate the effects of land use management scenarios on flood characteristics—particularly peak discharge and the shape of the flood hydrograph—in the Atashgah watershed using the semi-distributed SCS model in the WMS environment. The research also seeks to analyze the spatial and temporal impacts of proposed land use policies on hydrological parameters and simulate watershed responses under different return periods.
Materials and Methods: Initially, land use maps for the baseline year 2011 were prepared using satellite imagery, Digital Elevation Model (DEM) data, and field observations. Based on slope analysis and soil capability, four management scenarios were developed, each incorporating different levels of change in rangeland coverage, dryland and irrigated agriculture, and barren lands. Climatic data were collected from 11 surrounding weather stations and used to determine design rainfall values for return periods of 2, 5, 10, 25, 50, and 100 years. The design rainfall was calculated using the CumFreq software. The SCS rainfall–runoff model was calibrated in the WMS environment, and three observed rainfall–runoff events were used for validation. Key parameters, including Curve Number (CN), Initial Abstraction (Ia), and Time of Concentration, were computed for each scenario. The model outputs—peak discharge and flood hydrographs—were then extracted for final analysis.
Results: The results showed that implementing the management scenarios led to a decrease in CN and an increase in Ia. These changes directly resulted in reduced peak discharges and modifications in the shape of the flood hydrograph. Scenario 4, which combined optimized land use redistribution based on slope and soil infiltration capacity, produced the most significant reduction in peak discharge across all return periods, with a maximum decrease of 22.95% compared to the baseline condition. Spatial analysis revealed that areas with lower slopes and elevations experienced the highest degree of land use change, which in turn had a considerable impact on the watershed's flood response. Furthermore, the spatial distribution of runoff improved, and a delay in the time to peak was observed in some scenarios. These findings suggest that even moderate land cover modifications, when properly designed, can significantly reduce flood vulnerability.
Conclusion: The SCS model implemented in the WMS environment proves to be an effective tool for evaluating the hydrological impacts of land use changes at the watershed scale. The findings emphasize that land use management policies, if based on detailed topographic analysis, soil characteristics, and infiltration capacity, can greatly mitigate flood risk and enhance environmental resilience. It is therefore recommended that natural resources and watershed management authorities utilize the outcomes of such studies for planning and executing adaptive management scenarios in high-risk watersheds. Future studies should consider integrating land use change scenarios with climate change projections to provide a more comprehensive understanding of watershed behavior under compound threats.
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