Distributed Model of Hydrological and Sediment Transport Process in Mekong River Basin

Abstract

Soil erosion and sediment transport have been modeled at several spatial and temporal scales, yet few models have been reported for large river basins (e.g., drainage areas > 100,000 km 2 ). In this study, we propose a process-based distributed model for assessment of sediment transport at a large basin scale. A distributed hydrological model was coupled with a process-based distributed sediment transport model describing soil erosion and sedimentary processes at hillslope units and channels. The model was tested in Mekong River Basin (795,000 km 2 ). The simulation over 10 years showed good agreement with the observed suspended sediment load in the basin. The average Nash-Sutcliffe efficiency (NSE) and average correlation coefficient (r) between the simulated and observed suspended sediment loads were 0.60 and 0.78 respectively. Sensitivity analysis indicated that the suspended sediment load is sensitive to soil detachability over land (Kf) in the Mekong River Basin. Overall, the results suggest that the present model can be used to understand and simulate erosion and sediment transport in large river basins such as Mekong River Basin.

Estimation of Soil Erosion and Sediment Yield in the Lancang–Mekong River Using the Modified Revised Universal Soil Loss Equation and GIS Techniques

“…The dams located in the central and south parts of upper Mekong River basin are relatively less risky than those in the north part, because soil erosion in those areas have low and moderate erosion levels. Previous studies [10,53,79] obtained results that coincide with our research for the analysis of soil erosion impact on dams in the upper Mekong River basin. Meanwhile, soil erosion in the lower Mekong River basin, especially from the Khorat Plateau (Thailand) to the Mekong Delta, can also generate sedimentation problems due to the high occurrences of soil loss.…”

“…Our results are in the range near the mean values of the previous research. The spatial pattern of soil erosion occurrence in the north part of upper Mekong River basin is generally consistent with the findings of [10,49,50,53,79], but some spatial soil erosion results differ in other areas, especially in the lower part of Mekong River. Furthermore, we presumed that the different results can be attributed to the computation of the R factor (the main factor in soil erosion) which is influenced by differences in rainfall data.…”

“…Digital elevation model images with a 1 km resolution were downloaded from the US Geological Survey (https://earthexplorer.usgs.gov). Past researchers applied high-resolution DEM images for soil erosion determination because of these images' good accuracy and reliability [6,10,16,20,[49][50][51]53,60,62,73,[76][77][78][79]. The calculation of the LS factor can be based on the RUSLE principle by using the GIS software as explained in References [20,73,78,[80][81][82].…”

“…The river as the research object had many data limitations, and accessing input data to develop research on soil erosion, sediment yield capacity and sediment transport was difficult. This study attempted to utilize previous research on soil erosion in the Lancang-Mekong River basin [10,49,50,53,79], as no other evidence and information exist on how much the soil erosion rate has changed in this basin. The average soil erosion in the previous research ranges from 1400 to 8500 t/km 2 /y.…”

“…Meanwhile, the results of descriptive statics in the RULSE model clearly showed that the LS factor is the most influential factor for soil erosion and sediment yield in the Lancang-Mekong River basin, especially in the upper Mekong River. Most studies on soil erosion and sedimentation claim that the geographical features of the Lancang-Mekong River basin, such as its steep slopes and the slope length of its hills and mountains, are affected directly by the occurrence of soil erosion in specific areas, and these sediments are transformed when transported along the river [10,32,35,41,47,[49][50][51][52][53]79]. Consequently, the mitigation measures currently used to reduce soil erosion need to further consider solutions related with the LS factor such as the implementation of check dams and the application of vegetation cover.…”