No abstract

The Bhumibol Dam on Ping River, Thailand, was constructed in 1964 to provide water for irrigation, hydroelectric power generation, flood mitigation, fisheries, and saltwater intrusion control to the Great Chao Phraya River basin. Many studies, carried out near the basin outlet, have suggested that the dam impounds significant sediment, resulting in shoreline retreat of the Chao Phraya Delta. In this study, the impact of damming on the sediment regime is analyzed through the sediment variation along the Ping River. The results show that the Ping River drains a mountainous region, with sediment mainly transported in suspension in the upper and middle reaches. By contrast, sediment is mostly transported as bedload in the lower basin. Variation of long-term total sediment flux data suggests that, while the Bhumibol Dam does effectively trap sediment, there was only a 5% reduction in sediment supply to the Chao Phraya River system because of sediment additions downstream.

The Wang River is one of the major tributaries of the Chao Phraya River (CPR) system in Thailand as the key riverine sediment source supplying the Chao Phraya Delta that has experienced severe shoreline retreat in the past six decades. Historical and observed river flow and sediment data measured during 1929–2019 were used to assess the variation in total sediment load along the Wang River and evaluate the effects of three major dam constructions on sediment supplied from the Wang River to the CPR. Results indicated that sediment loads increased toward downstream. Variation in long-term total sediment load (TSL) along the river suggested that construction of the Kiew Lom Dam in 1972 did not cause a reduction in sediment yield in the Wang River Basin because it impounded less than 20% of the average annual runoff, while the Mae Chang and Kiew Koh Ma Dams caused downstream sediment reduction. These three dams are located in the upper and middle river basins, and their effects on sediment load in the Wang River are ameliorated by additional sediment supplied from the lower basin. Results confirmed that construction of these three major dams in the Wang River did not greatly impact sediment supply from the Wang River to the CPR system. The dam site and sediment load variation along the river are the primary factors controlling the impact of the dam construction.