The land subsidence is the slow settlement or sudden Earth surface sinking caused by the movement of the earth’s material into the surface. This can be brought on by human activities like digging underground water or by a natural process called soil consolidation. In India, land subsidence is now becoming a significant issue in various regions mainly the urban areas and regions that depend on groundwater extraction.
Mechanism of the Land Subsidence
The land subsidence mainly happens in that case, when the groundwater is drawn from underground mines more quickly than naturally restored.
The settling and compression of the groundwater may come from the collapse of the soil’s water-filled pore pores caused by groundwater removal. This is noticeable in those areas where the soil structure is more vulnerable to compression.
The sediments that were once supported by the water mainly started to compress diagonally as groundwater levels reduced, which caused the land to sink. The lateral compression might result from this diagonal compression. Land subsidence occurs as the soil pore water pressure is reduced, the effective stress rises and the soil consolidates.
The Seriousness of the Issue
- Global Economic Impact: Land subsidence has effects. The land subsidence caused significant losses for the nations like US, China, and the Netherlands.
- Irreversible Nature: The land sinking irreversibility is one of the most alarming features. It is difficult if not impossible, to move the ground to its original condition once it has reduced.
Major Factors Which Caused Land Subsidence
The given below are the various causes of the land subsidence.
Dissolution of limestone
The subsidence mainly caused various problems in the karst terrains where the flow of the subsurface fluids caused the limestone to break down by creating the spaces. This type of subsidence can easily produce sinkholes that are deep about a hundred meters.
Mining
The surface subsidence will be caused by the various subsurface mining methods like longwall mining, pillar extraction and any of the minimal method that holds the “caving,” like “block caving” or “sub-level caving.” The mining induced subsidence is fairly predictable in terms of the extent, appearance, and degree.
The minimal subsidence only affects the areas that are above the mined area and a margin on all sides.
Extraction of Petroleum and Natural gas
If the natural gas comes from the natural gas field then the initial pressure which can rise upto the 60 MPa will be decreased. The pressure gives support to the soil layers in the field. Ground subsidence and earthquakes may come from the compressed sediment brought on by the overburden pressure if the gas is extracted.
Earthquake
At the time of the earthquake, various factors might have contributed to the land subsidence. Because of the offset along with the fault lines, the land’s substantial section is susceptible to abrupt subsidence at the time of the earthquake.
Groundwater Related Subsidence
It is the term used to show the sinking of land brought on by groundwater extraction. As the population and water increased, pumping is becoming a more significant problem in emerging nations without enough supervision and enforcement.
80% of the significant land subsidence problems are caused due to excessive groundwater extraction, making it a worldwide problem that is becoming worse.
The changes in the groundwater levels can also have an indirect effect on the organic material decomposition. To sustain human habitation, lowlands like delta plains or coastal areas must be drained.
Faulting induced Subsidence
The earth accepts the various stresses by the faulting into the geological structure of the brittle crust or by the ductile movement into the hotter and more fluid mantle.
The subsidence may occur wherever there are flaws. The sinling into the thrust and the reversal faults can be checked by the use of the footwall.
Seasonal Effects
Various soil includes various levels of clay. Because of the extremely small particle size they are affected by the changes in the content of the soil moisture.
The dying of the season caused a decrement in the soil surface and the volume. If the building foundation is higher than the level reached by seasonal drying, it may slide and result in tapering fractures. Trees and other plants hold a major impact on the seasonal drying of the soils. The cumulative drying occurs as the tree ages over several years.
Impacts of Land Subsidence
- The cities sinking are the result of ground subsidence, rising urbanization, and the cumulative effects of climate change.
- Due to the area’s poor drainage system land subsidence takes place which may cause it to settle on the larger levels, destroying the city’s infrastructure and increasing the flooding risk.
- The experts warned that it caused the fissures to form into the foundation of the buildings and could destroy the homes and other infrastructure.
- The water management disruption and its related effects like canal, and drain gradients, increased intrusion of seawater, and higher pump power.
- Due to the reduction of the freshwater availability brought on or by an increase in saltwater intrusion from a drop in land elevation brought on by land subsidence.
- When the ground sinking stops, various environmental problems might arise.
Various solutions to reduce the land subsidence crisis:
- Slope Stabilization: By the use of techniques like retaining walls and terracing, the slopes can be stabilized and erosion-induced subsidence can be avoided.
- Vegetation Planting: By fixing soil and stopping erosion, planting tress and other vegetation which is deeply rooted helps in lowering the chance of subsidence.
- Drainage Control: Waterlogging and the compaction of the soil will be avoided by the use of efficient drainage systems, which reduce the chance of sinking into the impacted areas.
- Strengthening Foundations: The foundation building can be strengthened to improve stability and resilience by lowering the effects of the subsidence.
- Planning and Zoning: By reducing and limiting the growth into high-risk, subsidence-prone areas, strategic zoning, and planning laws can reduce the exposure to possible risks.
FAQ:
Q: What is land Subsidence?
Ans: Land subsidence is mainly termed as the downward, vertical movement of the Earth’s surface which can be brought by natural and human forces.
Q: What are the causes of the Land subsidence?
Ans: The causes of the land subsidence are as follows:
- Dissolution of the Limestone
- Mining
- Earthquake