Magnitude and factors influencing soil loss and sedimentation in the Mun River Basin, Thailand

Abstract

Previous studies have shown potentially high soil loss in the Mun River Basin, the largest sub-basin of the Lower Mekong Region in Thailand, due to its rapid land cover changes, agricultural practices, and soil erodibility properties. This study aims to estimate the soil loss and sedimentation rates in the Mun River Basin using the analysis of long-term sediment loading data from the Royal Irrigation Department (RID), GIS-based Revised Universal Soil Loss Equation (RUSLE) approximation, and sediment core analyses. This study found that a high loss (>12.5 ton ha−1 yr−1) and RID sediment loading rate were predominant in the upper basin. The support practice was most sensitive to the loss, but during extreme rainfall events (El Niño Southern Oscillation), the role of rainfall intensity was more pronounced. Therefore, mechanical measures should be adopted in combination with the soil–water conservation practices to mitigate the effects in eroding agricultural areas. Sediment core analyses revealed that the highest sediment deposition rate was up to 5.2 cm yr−1 in the middle part of the Mun River Basin, primarily due to the floodplain lowland characteristics and repeated flooding events. Several factors influenced the sediment deposition rate: installation of dams or check dams, waterway maintenance, upstream land cover, water plant outgrowth, and flooding. The RID sediment loading also suggests that sediment mass transfer to the Mekong River was highly contributed from the lower basin, where the sediment from the upper part was either trapped by the dams or deposited within the channel.