Subsidence in deltas
In many deltas across the world, subsidence is taking place. This has consequences for agriculture, nature and related water management. When cities are located within these deltas, subsidence in the urban context needs attention, as infrastructure like roads, bridges and buildings may be affected by subsidence.
In different countries and in different deltas, experiences are different. This thematic page on subsidence in deltas, we pay attention to this topic. We welcome further contributions.
Subsidence in urbanizing deltas and coastal zones
In many coastal and delta cities land subsidence exceeds absolute sea level rise up to a factor of ten. Without action, parts of Jakarta, Ho Chi Minh City, Bangkok and numerous other coastal cities will sink below sea level. Increased flood risk and other widespread impacts of land subsidence result in damage totalling billions of dollars per year. A major cause of severe land subsidence is excessive groundwater extraction due to rapid urbanization and population growth. A major rethink is needed to deal with the often ‘hidden’ but urgent threat of subsidence, as well as more guidance to support decision making.
The policy brief, entitled: 'Subsidence in urbanizing deltas and coastal zones' describes briefly the challenges and the actionable approaches to counteract subsidence. Recommendations are made on policy and governance, technology, capacity building and financing aspects. This reflects the vision of the Delta Alliance community.
Subsidence in the Vietnamese Mekong delta
The Vietnamese Mekong delta has world’s third largest delta plain, inhabited by nearly 18 million people and responsible for 50% of Vietnam’s total food production. The delta is impacted by decreased fluvial sediment supply, salinization, coastal erosion and global sea-level rise. Moreover, the annual subsidence rates up to several centimeters per year cause the Mekong delta to rapidly lose elevation. Research carried out by Mr P.S.J. Minderhoud (Utrecht University) was to understand and quantify the main natural and human-induced drivers and processes causing subsidence, and its impact on current and future surface elevation of the Vietnamese Mekong delta. Read more in article: The sinking mega-delta: Present and future subsidence of the Vietnamese Mekong delta (2019, UU).
Sinking Yangon, Myanmar
Yangon is a city in the Irrawaddy delta in Myanmar where little is known about the true extent of subsidence, while its effects can potentially harm millions of its inhabitants. The aim of the research from T. van der Horst, (TU Delft, 2017) was to assess if any subsidence is occurring, and to determine if groundwater extraction could be the cause of it. Read more here.
Subsidence in The Netherlands
The Netherlands National Research Program on Emissions from Peat Meadows (in Dutch: Nationaal Onderzoeksprogramma Broeikasgassen Veenweide; NOBV) started in 2019 and is studying the effects that measures have on emission of greenhouse gas emissions in peat meadows in the Western and Northern part of the Netherlands. As the emissions are caused by oxidation of peat, they also result in soil subsidence. In parts of the Netherlands, this process has been ongoing since the Middle Ages, resulting in total subsidence of several meters.
A methodology for measuring both emissions and subsidence is being established and monitoring sites have been set up in 5 provinces. Focus in the first year of the project was on the effect of submerged drains and pressure drains, but in coming years monitoring will be extended to other measures, such as very high groundwater levels (-20 cm), paludiculture and conversion to nature. The aim is to quantify emissions and subsidence, and to find ways to minimize both. The programme is expected to last for at least 3-5 years. Read more on the NOBV website (in Dutch).