Abstract
Abstract. Land subsidence rates of ~ 1–4 cm yr−1 are measured in the low-lying Vietnamese Mekong Delta. These relatively high subsidence rates are attributed to groundwater extraction, which has increased drastically over the past decades due to growing domestic, agricultural and industrial demands. As a result, hydraulic heads in aquifers are dropping, on average 0.3–0.7 m yr−1. There is an urgent need to go from measurements to predictions in order to test possible future groundwater management scenarios and to reduce the increase of flood risk, salt water intrusion and, on the longer term, prevent the delta from drowning. In this study, we aim to assess the subsidence potential of the multi-aquifer subsurface of the Mekong delta due to groundwater extraction. The first step is to gain a thorough understanding of the complex sedimentary architecture of the heterogeneous subsurface. Combined with the related geotechnical properties, the subsurface build-up determines the subsidence potential. Here, we present our approach to develop a 3-D geo-hydrological model based on lithological borehole data, geophysical sedimentary properties, palaeogeography and conceptual models of delta evolution.
Highlights
The Vietnamese Mekong delta is experiencing strong intensifications of agricultural and aquaculture practices and cities in the delta are growing fast (Renaud and Kuenzer, 2012)
Groundwater extraction is hypothesized to be a main driver of subsidence, but the contribution of other possible human-induced drivers, like loading by buildings and infrastructure and drainage have not been quantified yet
The development of a new lithological model of the Mekong delta based on subsurface data and incorporating palaeogeographical and delta evolutional insights is the first step towards resolving the subsidence balance
Summary
The Vietnamese Mekong delta is experiencing strong intensifications of agricultural and aquaculture practices and cities in the delta are growing fast (Renaud and Kuenzer, 2012). Aquifer drawdown occurs at rates of 0.3–0.7 m yr−1 (Wagner et al, 2012) Such declines in hydraulic head can trigger high compaction in the drained subsurface sediments, causing land subsidence at the surface J. Minderhoud et al.: Land subsidence of the multi-aquifer subsurface, Mekong Delta tem (e.g. groundwater extraction causing consolidation). In this paper we present our approach to develop a new 3-D subsurface model, which enables groundwater and subsidence modelling, based on thorough analysis of the complex multi-aquifer subsurface This model can be used to create meaningful predictions and evaluate (ground)water management scenarios for policy-makers
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