The Mekong River basin is undergoing rapid hydroelectric development, with 7 large mainstem dams on the upper Mekong (Lancang) River in China and 133 dams planned for the Lower Mekong River basin (Laos, Cambodia, Thailand, Vietnam), 11 on the mainstem. Prior analyses have shown that all these dams built as initially proposed would trap 96% of the natural sediment load to the Mekong Delta. Such a reduction in sediment supply would compromise the sustainability of the delta itself, but there are many uncertainties in the timing and pattern of land loss. The river will first erode in-channel sediment deposits, partly compensating for upstream sediment trapping until these deposits are exhausted. Other complicating factors include basin-wide accelerated land-use change, road construction, instream sand mining, dyking- off floodplains, and changing climate, accelerated subsidence from groundwater extraction, and accelerated sea level rise. It is certain that the Mekong Delta will undergo large changes in the coming decades, changes that will threaten its very existence. However, the multiplicity of compounding drivers and lack of good data lead to large uncertainties in forecasting changes in the sediment balance on the scale of a very large network. We quantify uncertainties in available data and consider changes due to additional, poorly quantified drivers (e.g., road construction), putting these drivers in perspective with the overall sediment budget. We developed a set of most-likely scenarios and their implications for the delta’s future. Uncertainties are large, but we should not discount there are certainties about the delta’s future. If its sediment supply is nearly completely cut off (as would be the case with ‘business-as-usual’ ongoing dam construction and sediment extraction), the Delta is certainly doomed to disappear in the face of rising seas, subsidence, and coastal erosion. The uncertainty is only when and how precisely the loss will progress.
Forecasting the Cumulative Impacts of Dams on the Mekong Delta: Certainties and Uncertainties.
SCHMITT, RAFAEL JAN PABLO;
2016-01-01
Abstract
The Mekong River basin is undergoing rapid hydroelectric development, with 7 large mainstem dams on the upper Mekong (Lancang) River in China and 133 dams planned for the Lower Mekong River basin (Laos, Cambodia, Thailand, Vietnam), 11 on the mainstem. Prior analyses have shown that all these dams built as initially proposed would trap 96% of the natural sediment load to the Mekong Delta. Such a reduction in sediment supply would compromise the sustainability of the delta itself, but there are many uncertainties in the timing and pattern of land loss. The river will first erode in-channel sediment deposits, partly compensating for upstream sediment trapping until these deposits are exhausted. Other complicating factors include basin-wide accelerated land-use change, road construction, instream sand mining, dyking- off floodplains, and changing climate, accelerated subsidence from groundwater extraction, and accelerated sea level rise. It is certain that the Mekong Delta will undergo large changes in the coming decades, changes that will threaten its very existence. However, the multiplicity of compounding drivers and lack of good data lead to large uncertainties in forecasting changes in the sediment balance on the scale of a very large network. We quantify uncertainties in available data and consider changes due to additional, poorly quantified drivers (e.g., road construction), putting these drivers in perspective with the overall sediment budget. We developed a set of most-likely scenarios and their implications for the delta’s future. Uncertainties are large, but we should not discount there are certainties about the delta’s future. If its sediment supply is nearly completely cut off (as would be the case with ‘business-as-usual’ ongoing dam construction and sediment extraction), the Delta is certainly doomed to disappear in the face of rising seas, subsidence, and coastal erosion. The uncertainty is only when and how precisely the loss will progress.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
