Abstract
Land subsidence and its consequences are at an alarming level in the Southern and low-lying areas of the Mekong Delta. This chapter will discuss the situation of groundwater uses and urban development activities that caused the negative impacts of land subsidence and sea level rise in Ho Chi Minh City and the Mekong Delta region of Vietnam. The PSInSAR technique was applied for land subsidence monitoring and showed that an average subsidence rate at 15 mm/year which is 5 times greater than the effects resulting from the rise of sea level. This implies that land subsidence coupled with sea level rise have been as a major factor contributing to increasing the depth of annual flood and causing inconveniences to the daily lives of residents that suffered waterlogging of between 0.4 – 0.5m. Apart from the restriction of groundwater abstraction, rainwater harvesting – an alternative water sources – is a humanitarian engineering solution to minimize groundwater extraction which in turn to prevent from flood risks caused by land subsidence and the rise of sea level.
TopBackground And Issues
Natural Characteristics
Floods in the MD and HCMC are intricately caused by heavy rain, high tide, rain, and tide combination. Natural characteristics of research area show major factors that contribute to cause the impacts of land subsidence and SLR. The situation of tidal flood for coastal cities will be increased frequency in which floodwater depth and duration of inundation for years depend on these natural factors.
Key Terms in this Chapter
PSInSAR: (Persistent Scatterer Interferometric Synthetic Aperture Radar) : A remote sensing technique that uses radar signals from a satellite to accurately measure ground displacement. PSInSAR is an improved and more accurate analysis algorithm compared to the DInSAR (Differential Interferometric Synthetic Aperture Radar).
Groundwater overexploitation: A situation in which average withdrawal (pumping) rate is greater that recharge rate. This causes a drawdown of water table and leads to the depletion of groundwater resources.
Humanitarian Engineering: The application of engineering to improve the living conditions and well-being of marginalized people and disadvantaged communities, usually in the developing world. Humanitarian engineering typically focuses on programs that are affordable, sustainable, and based on local resources. Projects are typically community-driven and cross-disciplinary, and they focus on finding simple solutions to basic needs (such as close access to clean water; adequate heat, shelter, and sanitation; and reliable pathways to markets).
Rainwater Harvesting: The harvesting of rainwater refers to the collection of water from surfaces on which rain falls, and subsequently storing this water for later use. Rainwater harvesting can occur in multiple contexts and at a variety of scales. The collection of rainwater from the rooftops of buildings is suitable for urban areas and requires little investment or technology, as only roof gutters and storage tanks are needed to capture rainwater.
Waterlogging: A form of natural flooding when underground water rises to surface level as the result of over-irrigation simply the saturation of soil with water, either temporarily or permanently. When there is too much water in an area, the soil is unable to absorb the water as it should ordinarily.
Urbanization: The process by which a large number of people become permanently concentrated in relatively small areas, forming cities or built-up areas. This phenomenon is an emerging trend in developing countries that poses a wide range of urban environmental issues such as the contamination of water sources (bodies), groundwater depletion, air pollution, and municipal solid wastes.
Land Subsidence: A gradual settling or sudden sinking of the Earth's surface due to the removal of subsurface materials. Land subsidence occurs when the large amounts of groundwater have been withdrawn from certain types of rocks, such as fine-grained sediments. The rock compacts because the water is partly responsible for holding the ground up. When the water is withdrawn, the rocks fall in on itself. The main causes of land subsidence include aquifer-system compaction associated with groundwater withdrawals; drainage of organic soils; underground mining; natural compaction or collapse, such as with sinkholes or thawing permafrost.
Sea Level Rise: An increase in the mean level of the ocean due to melting ice and thermal expansion related to global warming and may have consequences for life on Earth. Generally, sea-level rise is a climate change phenomenon through which the ocean water volume increases, mostly as a consequence of icesheets and glaciers melting and water thermal expansion. As a consequence of sea-level rising, coastal life around the world is threatened and adaptation policies need to be developed to avoid further and faster catastrophic impacts.