Modeling hydrologic responses to land management scenarios for the Chi River Sub-basin Part II, Northeast Thailand

The Chi River Sub-basin Part II, in Northeast (NE) Thailand, experiences many anthropogenic activities due to the agricultural expansion and intensification, forest deterioration, and a high demand for resource utilization. Land use/land cover change (LULCC) associated with land management, agricultural and conservation practices within the basin can significantly affect hydrologic responses. Like other basins in NE Thailand, the Chi River Sub-basin Part II-comprising more than 60 % of agricultural lands-is characterized by severe floods, droughts, and sedimentation, which directly affect human well-being. Therefore, the objective of this study was to investigate the influences of land management and conservation practices on discharge and sediment yield, and then to develop appropriate management solutions, which could provide alternatives to the current watershed management practices. Three management scenarios-current land use with conservation practices, land use planning (LUP) based on Watershed Classification (WSC), and WSC with conservation practices-were modeled with the Soil and Water Assessment Tool (SWAT), and the results were compared to the existing conditions. The findings indicated that LULCC and conservation practices-conserving the remaining forest, reforestation, applying strip cropping to agricultural land, and channel stabilization by plant cover and engineered constructions-had a little effect on discharge, but greatly influenced the sediment yield. Current land use with the addition of conservation practices resulted in a slight decrease in both total discharge and sediment yield. WSC resulted in a small decrease in discharge, but a dramatic increase in sedimentation. Lastly, WSC together with conservation practices resulted in a slight decrease in discharge and a small increase in sedimentation. These results informed that land management that adopts conservation practices has a strong effect on discharge and sediment yield. A decreased in forest cover when applied WSC resulted in a slight decrease in discharge, but much higher sediment yield. When conservation practices were applied, sediment yield was found to be significantly decreased. Therefore, watershed management should consider LUP, vegetation cover measures, and channel improvements to sustain the Chi River Sub-basin Part II.