Impact of groundwater extraction on subsidence in the Mekong delta (Vietnam)

The Vietnamese Mekong Delta, the third largest delta in the world, is facing land subsidence rates of 1–4.7 cm/yr-1. These relatively high subsidence rates are largely attributed to groundwater extraction, which has drastically increased over the past decades due to growing domestic, agricultural and industrial demands. Hydraulic heads in the aquifers drop on average 0.3–0.7 m/yr-1, potentially accelerating subsidence. With over 50% of the delta surface elevated less than 1 meter above sea level, subsidence increases flood risk and salinization in river channels. InSAR techniques are now widely used to establish subsidence rates, but for the Mekong Delta the spatial coverage is limited to the build-up environment, and data is only available for the period 2006-2010. Using a 3D geohydrological model, we were able to model groundwater extraction induced subsidence in both the urban and rural part of the Mekong Delta and could establish the onset of this subsidence in the delta.
We present subsidence calculations and compare rates and spatial patterns with measured INSAR data. The calculated spatial subsidence patterns correlate with measurements, however, fail to explain total measured subsidence. This suggests groundwater extraction to be a major driver, yet also other drivers seem to contribute to total subsidence.