Mains Marathon

• Introduce concept of subsidence and provide examples of the Subsidence of the cities.
• Analyse the several causes behind this phenomenon and propose sustainable solutions.
• Conclude suitably.

Answer

Subsidence is a geological phenomenon of land sinking due to various natural or human-induced factors. It poses a serious threat to many coastal cities around the world, as it increases their vulnerability to flooding, erosion, storm surges and sea level rise. Some examples of coastal cities that are experiencing subsidence are New York, Mumbai etc.

The causes of subsidence vary from city to city, but some common factors are:

• Groundwater extraction: This is the main cause of subsidence in many coastal cities, especially in Asia, where rapid urbanization and population growth have increased the demand for freshwater. Pumping out groundwater reduces the pore pressure and causes the soil to compact and settle.
• Natural compaction: This is the gradual settling of sedimentary layers due to their own weight (huge skyscrapers) and tectonic movements. It affects coastal areas that are built on soft and compressible soils, such as deltas and marshes.
• Oil and gas extraction: This is similar to groundwater extraction, as it lowers the pressure in the reservoirs and causes the overlying rocks to collapse. It affects coastal cities that have offshore or onshore hydrocarbon fields, such as Houston and New Orleans.
• Construction and urbanization: This is the loading of the land surface by buildings, infrastructure and landfill. It increases the stress on the underlying soil and causes it to deform. It affects coastal cities that have high-density development and poor planning, such as Jakarta and Manila.

Some possible solutions or adaptations to address subsidence are:

• Reducing groundwater extraction: This can be done by implementing water conservation measures, developing alternative sources of water supply, such as rainwater harvesting, desalination and wastewater reuse, and regulating or pricing groundwater use.
• Restoring natural ecosystems: This can be done by enhancing wetlands, mangroves and coral reefs that can buffer the impacts of waves and storms, provide habitats for biodiversity and sequester carbon. It can also involve restoring natural sediment flows that can replenish the land surface.
• Adopting engineering measures: This can be done by strengthening or elevating buildings and infrastructure, installing drainage systems and pumps, constructing seawalls and dikes, and injecting fluids or grout into the subsurface to stabilize the soil.
• Improving monitoring and governance: This can be done by using satellite data and ground-based instruments to measure subsidence rates and identify hotspots, developing risk assessment and early warning systems, raising public awareness and participation, and coordinating policies and actions among different stakeholders and sectors.
• Mitigating global warming and climate change: It will reduce the thermal expansion of oceans and reduce the speed of melting of ice and prevent further sea level rise. This will reduce the risk of flooding, erosion, and saltwater intrusion for many coastal cities that are already sinking due to natural or human-induced factors.

Subsidence is a serious challenge for many coastal cities that requires urgent attention and action. By addressing its causes and consequences, coastal cities can enhance their resilience and sustainability in the face of climate change and sea level rise.