Streamflow and Sediment Yield Analysis for Evaluating Best Management Practices under Changing Climate

Abstract

Streamflow and sediment yield are the important aspects in river systems. Assessing the consequences of anthropogenic changes is important for optimal management of land and water resources in the basins. Soil erosion is a major environmental issue that has a harmful effects on crop yields, the quality of water, aquatic ecosystems, and river morphology. When soil erosion flows into reservoirs and rivers from croplands, it generates a variety of contaminants and causes a variety of water pollution issues. So, it is necessary to analyse the streamflow and sediment transport in the river basins to identify the critical source areas and to evaluate the Best Management Practices. In the present research work, Nagavali and Vamsadhara basins are considered as study area. These two east flowing medium-sized basins in Peninsular India are prone to frequent flooding due to heavy rainfall in the monsoon season and tropical cyclones formed by low-pressure depressions in the Bay of Bengal (BoB) during pre- and post-monsoon seasons. Based on the proposed objectives of the research work, a detailed methodology for the research is developed. With the developed methodology, work has been carried out in three modules. In the first module, SWAT model calibration and validation, water balance components, spatial distribution of precipitation, streamflow, groundwater flow, evapotranspiration and sediment yield over Nagavali and Vamsadhara basins is analysed using Indian Meteorological Data. The critical sediment source areas are identified for both river basins. The obtained statistics over the Nagavali and Vamsadhara basins range from very good to satisfactory, indicating the SWAT model’s acceptance. From the water balance analysis evapotranspiration is the dominant process, accounting for 63% of the average annual rainfall over the basins. From the sub-basin average annual sediment yield analysis, 26.5% of Nagavali and 49% of Vamsadhara basin area are falls under high erosion. In the second module, the effect of climate change on streamflow and sediment yield is carried out using downscaled bias corrected GCMs under SSP245, SSP370 and SSP585 scenarios for three-time frames, historical (1975–2014), near future (2022–2060), and far future (2061 2100). Selection of climate models is carried out to identify the Wet and Dry models based on the changes in average annual precipitation (ΔP) and average temperature (ΔT) across the Nagavali and Vamsadhara watersheds between the model’s historic data (1975–2015) and the projected future data (2022–2100). The implications of climate change on precipitation, streamflow and sediment yield is performed. The spatial distribution of precipitation, steamflow vi and sediment is performed under Cold-Wet and Warm-Dry models. From future projections, the increase in mean annual precipitation (ΔP) and mean temperature (ΔT) are expected to vary across different scenarios. The climate models provide divergent future scenarios for the Nagavali and Vamsadhara basins. The ACCESS-CM2 model predicts a Warm-Dry future, while the EC-Earth3 model predicts a Cold-Wet future. In the near and far future, the percentage change in precipitation for these watersheds will range from 5.35 to 35.1% and −1.57 to 8.48% under the Cold-Wet and Dry-Warm models, respectively. This indicates that there will be an increase in streamflow and sediment yield for these watersheds. In the third module, four individual (i.e, filter strips, sedimentation ponds, contour farming and contour stone bunding) and four combined BMP scenarios are evaluated for effectiveness to reduction of sediment yield and streamflow at critical sub-basins. From the results, Filter strips with a width of 10 meters demonstrated notable efficiency in reducing sediment yield. Particularly, filter strips contributed to a substantial 73% reduction in sediment yield without influencing streamflow in the critical sub basins across both basins. It is concluded that 10 meter-wide filter strips exhibited the most efficient reduction in sediment yield under individual BMP scenarios, followed by filter strips of 6 meters, contour stone bunding, 3-meter-wide filter strips, sedimentation ponds, and contour farming. Similar results are observed in BMPs efficacy under future climate change scenarios. Sedimentation ponds produce more efficient reduction in streamflow followed by contour farming and contour stone bunding under individual BMP scenarios. Moreover, the combination of BMPs resulted in a substantial decrease in sediment yield by 37% and 72%, coupled with a reduction in streamflow by 16.50% and 54% over the Nagavali and Vamsadhara basins, respectively. This combined BMP approach proved to be highly effective in reducing sediment and streamflow at critical sub-basin and basin levels. Under future climate change scenarios, the combined BMPs from BMP1 to BMP4 yielded the higher reductions in sediment yield surpassing individual BMP impacts. By mitigating soil erosion and improving water management, this research will contribute to sustaining soil fertility and agricultural productivity. This is particularly crucial for the livelihoods of communities in the river basins, where agriculture is a primary occupation. Methodology developed in this research work can be easily extended for other river basins for controlling sediment yield.