Did the Construction of the Bhumibol Dam Cause a Dramatic Reduction in Sediment Supply to the Chao Phraya River?

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.

Effects of Dam Construction in the Wang River on Sediment Regimes in the Chao Phraya River Basin

“…Details of river discharge and suspended sediment data at each station are summarized in Table 1. Since bedload data are not available, the total sediment load in the Wang River system was analyzed using the sediment rating curves and bed to suspended sediment ratios from the river survey data described in Namsai et al [5]. Long-term trends of streamflow and sediment data along the Wang River were studied using a non-parametric statistical method, the Mann-Kendall (MK) test [52,53], that has been broadly used to identify significance of trends in hydro-meteorological time series with skewness and missing data [4,5,40,[54][55][56][57][58].…”

“…Depth-integrated samples in vertical were collected at the center of each increment by lowering the device to reach the river bed then immediately raising to the surface to collect water sample at about 90% of the sampler volume [60]. Water samples were sent to the soil laboratory to analyze sediment concentration described in Namsai et al [5]. The SSL (Q s ) at each river section was estimated from the product between the suspended sediment concentration and the corresponding discharge (Q w ).…”

“…To determine sediment grain size distribution, each dried sample was sieved and weighed using a standard test method of soil particle-size analysis (ASTM D422). Bedload transport rate (Q b ) was then estimated, as described in Namsai et al [5,[62][63][64]. In this study, bed materials were collected at the left, middle, and right locations of a river cross-section.…”

“…During the past several decades, changes in riverine sediment flux have been reported due to human activities such as deforestation, damming, water diversion, and sand mining [1][2][3][4][5]. Modification of riverine transport patterns directly affects sediment load carried to coastal oceans.…”

“…Many studies have suggested that construction of major dams in the CPR tributaries (the Bhumibol and Sirikit Dams in the Ping and Nan Rivers, respectively) has caused a 75-85% reduction in sediment yield to the Chao Phraya Delta and is responsible for delta shoreline recession [44][45][46][47]. Recently, Namsai et al [5] reported that construction of the Bhumibol Dam caused only about a 5% reduction in sediment supplied from the Ping tributary to the CPR. The Wang River is one of four major CPR tributaries that supplies water and sediment to the Chao Phraya Delta.…”