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Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam
Citation:
Minderhoud, P., G. Erkens, V. Pham, V. Bui, L. Erban, H. Kooi, AND E. Stouthamer. Impacts of 25 years of groundwater extraction on subsidence in the Mekong delta, Vietnam. Environmental Research Letters. IOP Publishing LIMITED, Bristol, Uk, 12(6):064006, (2017).
Impact/Purpose:
Groundwater extraction is a major contributor to land subsidence in deltas throughout the world. Pumping-induced subsidence increases vulnerability to flooding, storm surge and salinization, threatening many aspects of economic, social and environmental well-being for large populations that commonly live in deltas. In the Mekong Delta, subsidence has been estimated using ground- and satellite-based observations, and its relation to pumping examined for specific locations and time-averaged period. Here we use 3D numerical modeling or groundwater flow and sediment compaction to quantify time-varying rates and spatial patterns of pumping-induced subsidence delta-wide. Results may guide groundwater management efforts in the Mekong Delta.
Description:
Many major river deltas in the world are subsiding and consequently become increasingly vulnerable to flooding and storm surges, salinization and permanent inundation. For the Mekong Delta, annual subsidence rates up to several centimetres have been reported. Excessive groundwater extraction is suggested as the main driver. As groundwater levels drop, subsidence is induced through aquifer compaction. Over the past 25 years, groundwater exploitation has increased dramatically, transforming the delta from an almost undisturbed hydrogeological state to a situation with increasing aquifer depletion. Yet the exact contribution of groundwater exploitation to subsidence in the Mekong delta has remained unknown. In this study we deployed a delta-wide modelling approach, comprising a 3D hydrogeological model with an integrated subsidence module. This provides a quantitative spatially-explicit assessment of groundwater extraction-induced subsidence for the entire Mekong delta since the start of widespread overexploitation of the groundwater reserves. We find that subsidence related to groundwater extraction has gradually increased in the past decades with highest sinking rates at present. During the past 25 years, the delta sank on average ~18 cm as a consequence of groundwater withdrawal. Current average subsidence rates due to groundwater extraction in our best estimate model amount to 1.1 cm yr−1, with areas subsiding over 2.5 cm yr−1, outpacing global sea level rise almost by an order of magnitude. Given the increasing trends in groundwater demand in the delta, the current rates are likely to increase in the near future.
