Project: Rise and Fall

Rise and Fall: strategies for the subsiding and urbanising Mekong Delta (Vietnam) facing increasing salt water intrusion

This research programme aims to enhance the capabilities of individuals and organisations to develop sustainable strategies for dealing with groundwater extraction, land subsidence and salt water intrusion in the increasingly urbanising Mekong Delta (Vietnam). This programme consists of the following 4 projects.

  1. Subsurface characterization and subsidence
    To understand, quantify and predict subsidence in the Mekong Delta and to determine the impact of subsidence on current and future saltwater intrusion under different delta management scenarios.
  2. Fresh and saline groundwater dynamics
    To quantify the dynamic behavior of fresh and saline groundwater in response to surface water dynamics and urbanization induced changes of the hydrogeological system.
  3. Salt intrusion and flood risks in estuarine channel networks
    To understand and predict the changes in flooding statistics and salt intrusion in surface and groundwater, both as a function of different management strategies.
  4. Governance strategies for sustainable management
    To develop governance strategies together with public and private stakeholders to deal with groundwater extraction, subsidence and salt-water intrusion in delta areas and their economic and potential ecological damage. This project integrates the results of the PhD studies and implements these results into policy and management.

Delta: Mekong delta, Vietnam

Future Deltas theme: Understanding Drivers

Funding: NWO-Urbanizing Deltas of the World

Duration: 2014-2019

Researchers: P.S.J. Minderhoud MSc, dr. E. Stouthamer, dr. G. Erkens, prof. dr. H. Middelkoop, H. Pham Van MSc, dr. ir. G. Oude Essink, dr. B.T. Vuong, prof. dr. F. van Geer, S . Eslami Arab MSc, dr. M. van der Vegt, prof. dr. P. Hoekstra, dr. N.H. Trung (Can Tho University, Vietnam), dr. C. Dieperink (UU), H. Otter (Deltares)

The subsiding Mekong delta: impact of groundwater extraction

Mekong Delta

3D hydrogeological modelling revealed subsidence due to groundwater extraction in the Vietnamese Mekong delta. Subsidence rates greatly exceed global sea level rise. Our next step is come up with much needed projections of future subsidence, highly relevant to develop effective policy strategies to curtail subsidence. Deltas should be regarded as full dynamic systems in which both the biophysical and the anthropogenic aspects are integrated.

Delta-wide 3D models to address other groundwater related issues

Deltas should be regarded as full dynamic systems in which both the biophysical and the anthropogenic aspects are integrated. By creating a delta wide 3D model in which we can simulate groundwater flow and the impact of groundwater extraction, we take an important step towards determining the impacts of water exploitation in the Mekong delta and quantifying the amount of pumping-induced subsidence.

Our approach paves the road to work towards solutions dealing with this important issue which is faced in many deltaic areas. Furthermore, the use of complex, delta-wide 3D models also opens the door to address other groundwater related issues, for example salinization.'

Mekong Delta

The Vietnamese Mekong Delta, the third largest delta in the world, is facing land subsidence rates of 1–4.7 cm/yr-1 (Erban et al., 2014). 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, causing aquifer-system compaction. With over 50% of the delta surface elevated less than 1 meter above sea level, this poses a real threat to its inhabitants, enhancing flood risk and salinization.

Modelling groundwater extraction induced subsidence

To determine the contribution of groundwater extraction induced subsidence to total subsidence in the Mekong delta, we built a 3D numerical groundwater flow model. This model simulates hydraulic heads over the past 25 years based on the groundwater exploitation history. Subsequently, we calculate corresponding aquifer-system compaction using a coupled land subsidence module (SUB-CR), which includes a direct, elastic component and a secondary, viscous component (i.e. creep). Where InSAR is limited to the build-up environment, our approach enables modelling groundwater extraction induced subsidence in both the urban and rural part of the Mekong Delta.

Even though not all measured subsidence is explained by the model, the calculated spatial subsidence patterns largely correlate with the measurements. This identifies groundwater extraction as a major subsidence driver, yet also other drivers like phreatic water level lowering and loading by infrastructure seem to contribute to the total subsidence balance. Furthermore we found that delta-wide pumping-induced subsidence initiated around two decades ago. Since then subsidence accelerated, with present rates exceeding previous measured values.