Abstract In this paper, we provide a holistic view of the hydro-sedimentological regimes of the Chao Phraya River (CPR) Basin, the fifth largest basin in Southeast Asia. Our analysis of daily discharge and sediment data from 42 major gauge stations showed high seasonal variation in the suspended sediment discharge (Qs), with the maximum discharge occurring in October on an inter-annual average. At Nakhon Sawan, the river discharges 304x104 tons of sediment every year, 60% of which is transported in the peak flooding months (September to November). The peak sediment discharge in October is dramatically attenuated at a station 150 km downstream from Nakhon Sawan, mainly due to discharge diversion to irrigation canals, distributaries, and branches, as well as seasonal flooding over the Central Plain. Sediment yield (SY) calculated at major stations showed spatial variability across the basin, generally decreasing in a downstream direction (i.e. as drainage area increases) (R2=0.55). Some stations in the upper basin’s watersheds showed SY as high as >700 tons/km2/yr, which is comparable to upstream catchments of other large rivers with high sediment production. Two significant sediment sinks were identified in this study: the Bhumibol and Sirikit dams (each on Ping and Nan Rivers) - which trap ∼236x104 tons of sediment each year (∼90% trapping rate) - as well as the floodplain of the CPR which stores 176 x104 tons annually along the 150 km downstream reach from Nakhon Sawan (∼60% of Qs at Nakhon Sawan). By extrapolating the floodplain sediment budget, we estimate that around 300x104 tons/yr of suspended sediment can be stored downstream of Nakhon Sawan (to the Gulf); comparable to the total annual storage of the two mega dams upstream. Although these dams have been previously reported to cause substantial sediment starvation in the CPR Delta, this study is the first to recognize the important role of lowland storage on the CPR’s basin’s sediment discharge to the Gulf of Thailand, and how it contributes a similar degree of threat to the shrinking delta.

中文翻译：

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泰国湄南河源汇沉积物通量和收支：基于国家数据集的多尺度分析

摘要 在本文中，我们提供了东南亚第五大盆地湄南河 (CPR) 盆地的水文沉积状况的整体视图。我们对来自 42 个主要测量站的每日排放和沉积物数据的分析表明，悬浮泥沙排放量 (Qs) 的季节性变化很大，以年际平均值计算，最大排放量发生在 10 月份。在那空沙旺，这条河每年排放 304x104 吨泥沙，其中 60% 是在洪水高峰期（9 月至 11 月）运输的。那空沙旺下游 150 公里处的一个站点 10 月的高峰泥沙排放量急剧减弱，这主要是由于排放到灌溉渠、支流和分支的分流，以及中原地区的季节性洪水。在主要站点计算的沉积物产量 (SY) 显示整个盆地的空间变异性，通常在下游方向下降（即随着流域面积增加）（R2=0.55）。上游流域的一些站点显示SY高达>700吨/平方公里/年，与其他产沙量高的大河流上游集水区相当。本研究确定了两个重要的沉积物汇：Bhumibol 和 Sirikit 大坝（分别位于 Ping 河和 Nan 河上）——每年可捕获约 236x104 吨的沉积物（约 90% 的捕获率）——以及 CPR 的洪泛区沿着 Nakhon Sawan 下游 150 公里（约 60% Nakhon Sawan 的 Qs）存储 176 x104 吨。通过外推漫滩沉积物收支，我们估计大约 300x104 吨/年的悬浮沉积物可以储存在 Nakhon Sawan 的下游（到海湾）；与上游两座大型水坝的年总蓄水量相当。尽管之前有报道称这些大坝会导致 CPR 三角洲大量沉积物匮乏，但这项研究首次认识到低地蓄水对 CPR 盆地向泰国湾排放沉积物的重要作用，以及它如何促成类似程度的对不断缩小的三角洲的威胁。