Rise and Fall – Strategies for the subsiding and urbanising Mekong Delta (Vietnam) – Facing increasing salt water intrusion
Project page: http://rf.ctu.edu.vn/en/
1.1 Background and rationale
River deltas represent both valuable as well as vulnerable coastal systems that are difficult to manage due to their dynamic nature (Syvitski et al., 2009). In particular in Southeast Asia, major metropolitan areas are located in large river deltas that face a range of problems. Urbanisation and population growth in these areas will increase dramatically in the coming decades. Consequently, land use changes from agricultural to urban occur and the demand for clean drinking water increases.
Contemporaneously, sea-level rise, causing increased salt-water intrusion and flood risk, is predicted. Together, these developments will cause significant changes in the hydrological system, in particular a significant drop of groundwater level and quality. This leads to 1. accelerating land subsidence (present subsidence already outranges absolute sea-level rise in many deltas!) and 2. increasing of salt-water intrusion (Zhang et al., 2013), in both surface water and groundwater.
Typical aspects for deltas are:
- Major deltas develop by means of large distributary networks with channel bifurcations and estuaries; due to tidal effects these estuaries are perfect “gateways” for the intrusion of salt water (Zhang et al., 2013);
- Delta sedimentary systems are characterized by a non-uniform character of their deposits and, consequently a spatially non-uniform behavior of hydrological properties (such as horizontal and vertical hydraulic conductivity) which complicates the groundwater flows and the subsidence pattern;
- Urban areas in delta systems are heavily affected by the development of infrastructure such as roads and canals; this results in cities which are split into more or less isolated compartments with a lack of proper drainage (compare Jakarta); and,
- Major (flash) floods are already jeopardizing the urban communities and economic activities in these areas, such as Bangkok and Jakarta. Without adequate water management measures, urbanisation will result in shortage of clean water for public water supply and agricultural use, increased flood risk, and damage to buildings and infrastructure due to land subsidence. Currently, a blue print for accurate policy measures to cope with these problems does not exist. Often they are approached as isolated issues.
The main objective of this program is to develop a toolbox to address three interrelated problems of delta systems: the excessive extraction of groundwater, land subsidence and salt intrusion. The toolbox consists of:
- Instant access to large-scale information on bottom composition and groundwater characteristics via airborne electromagnetic monitoring.
- Developing scenarios for future development and management strategies.
- Quantifying the effects of these scenarios on salt intrusion, subsidence and flood risks using the newly developed delta-model.
- Assessing the damage caused by the resulting changes in the delta system.
- We develop a new delta-model that consists of a dynamically coupled surface water, groundwater and geo-mechanical model. This essential tool allows us to study the interrelated problems of groundwater extraction, land subsidence and salt intrusion. It will advance our generic understanding of the dynamical evolution of river deltas.
- We apply a highly innovative airborne electromagnetic remote sensing technique that allows us to obtain information on bottom composition and groundwater characteristics. The great advantage over other monitoring systems is that it provides at a large-scale in a very short time. It is there ideal to use for quick scans in data-poor environments.
- We develop a toolbox to quantify the effects of management strategies and policies on groundwater quality and level, land subsidence and flooding risks. Using this toolbox we will strengthen the knowledge basis of scientists, practitioners, coastal and river zone managers and stakeholders.