Understanding of the distribution patterns of sediment erosion, concentration and transport in river basins is critically important as sediment plays a major role in river basin hydrophysical and ecological processes. In this study, we proposed an integrated framework for the assessment of sediment dynamics, including soil erosion (SE), suspended sediment load (SSL) and suspended sediment concentration (SSC), and applied this framework to the Mekong River Basin. The Revised Universal Soil Loss Equation (RUSLE) model was adopted with a geographic information system to assess SE and was coupled with a sediment accumulation and a routing scheme to simulate SSL. This framework also analyzed Landsat imagery captured between 1987 and 2000 together with ground observations to interpolate spatio-temporal patterns of SSC. The simulated SSL results from 1987 to 2000 showed the relative root mean square error of 41% and coefficient of determination (R(2)) of 0.89. The polynomial relationship of the near infrared exoatmospheric reflectance and the band 4 wavelength (760-900nm) to the observed SSC at 9 sites demonstrated the good agreement (overall relative RMSE=5.2%, R(2)=0.87). The result found that the severe SE occurs in the upper (China and Lao PDR) and lower (western part of Vietnam) regions. The SSC in the rainy season (June-November) showed increasing and decreasing trends longitudinally in the upper (China and Lao PDR) and lower regions (Cambodia), respectively, while the longitudinal profile of SSL showed a fluctuating trend along the river in the early rainy season. Overall, the results described the unique spatio-temporal patterns of SE, SSL and SSC in the Mekong River Basin. Thus, the proposed integrated framework is useful for elucidating complex process of sediment generation and transport in the land and river systems of large river basins.
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.
This paper evaluates the potential impact of climate change and dams on suspended sediment (SS) dynamics in the Mekong River Basin (MRB). To this end, a distributed process-based sediment transport model was used to examine the potential impact of future climate and dams on suspended sediment dynamics changes in the MRB. Climate scenarios from two GCMs outputs together with effects of 3 existing, 5 under construction and 11 planned dams were considered in the scenario analysis. The simulation results show that the reductions in annual suspended sediment load (SSL) are likely to range from a 20 to 33%, 41 to 62%, and 71 to 81% for existing, under construction, and planned dams respectively in case of no climate change for baseline scenario (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000). Moreover, the reductions on sediment concentration (SSC) are even greater (23% to 78%) due to the potential impact of dams. In contrast, the SSL and SSC shows 40% to 92% increase in the near future (2041-2050) and 28% to 90% in the far future (2090)(2091)(2092)(2093)(2094)(2095)(2096)(2097)(2098)(2099). As the projected climate change impact of sediment varies remarkably between the different climate models, the uncertainty should be taken into account in sediment management. Overall, the changes in SSL and SSC can have a great implication for planned reservoirs and related sediment management.
Sediment transport models in river basins have been developed over the years for various temporal and spatial scales. However, yet few models have been reported for small-scale catchment and still under investigation by many researchers. In this paper, a distributed model based on process was presented for evaluating transportation of sediment in a small catchment scale. The integration of distributed hydrological and sediment model was developed for simulate the soil erosion and sedimentation processes in the catchment area located at Universiti Pertahanan Nasional Malaysia (UPNM). The finding prevailed that the simulation of suspended sediment load over a period of four years gave a good significant result with an average Nash–Sutcliffe Efficiency (NSE) and a Correlation Coefficient (r) were of 0.60 and 0.78, respectively. Moreover, sensitivity analysis revealed that the suspended sediment load in the UPNM catchment was influenced by soil detachability over land (Kf). Overall, the outputs from the present model can be taken as input to predict the soil erosion and sedimentation processes in a small-scale catchment, especially in Malaysia such as in the UPNM.
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