Recently, there were reports of Land subsidence in different parts of the Chenab Valley, especially in the Ramban, Kishtwar, and Doda districts, which led to destruction of several houses.Earlier, landslides were common during rain and snowfall in the region. However, there has been frequent occurrence of land subsidence in the last 10 to 15 years.
Land Subsidence
- According to the National Oceanic and Atmospheric Administration (NOAA), Land subsidence is sinking off the ground because of underground material movement.
- It can happen for many reasons, man-made or natural, such as the removal of water, oil, or natural resources, along with mining activities. Earthquakes, soil erosion, and soil compaction are also some of the well-known causes of subsidence.
- It can happen over very large areas like whole states or provinces, or very small areas.
Causes
- Overexploitation of Underground Resources: Extraction of resources like Water, Natural gas and Oil leads to decreased pore pressure and increased effective stress, causing ground subsidence.
- Over 80% of the world’s extracted water is used for irrigation and agricultural purposes, contributing to ground subsidence.
- Extraction of Solid Minerals: Exploitation of underground solid mineral resources leads to formation of large empty space underground (goaf), which can lead to the ground sinking or subsiding.
- Mining activities, such as coal mining, can lead to the formation of goaf areas, which contribute to ground subsidence.
Load Exerted on Ground
- The construction of tall buildings and heavy infrastructure can exert significant pressure on the ground, leading to soil deformation and subsidence over time.
- Soil creep is the slow, gradual movement of soil downhill due to gravity and can contribute to ground subsidence over time.
- Soil Creeps: Continuous low load and soil creep can cause slow deformation of the foundation, contributing to ground subsidence.
Examples
- Jakarta, Indonesia: It is experiencing severe land subsidence (25 cm/year) due to excessive groundwater extraction.
- Netherlands: Land subsidence has been a major problem due to the extraction of natural gas from underground reservoirs.
Reasons for Land Subsidence in the Chenab Region
- Geological Factors: Region has the presence of soft sedimentary deposits and alluvial soils, which contributes to land subsidence.
- These materials are prone to compaction under the weight of overlying structures and the influence of external forces such as groundwater extraction.
Unplanned Constructions and Urbanization
- Urbanisation and unplanned construction in hilly regions put immense pressure on the land.
- The Himalayan foothills have witnessed rapid development, leading to land subsidence.
Hydroelectric Projects
- Construction of hydroelectric stations can alter the natural flow of water and impact the stability of the land.
- Eg: Joshimath, a popular town for tourists, faces subsidence due to its proximity to a hydroelectric station.
Poor Drainage Systems
- Inadequate drainage systems in the Chenab region can worsen land subsidence through waterlogging, increased groundwater levels, soil erosion, saltwater intrusion, and infrastructure damage.
Geological Vulnerability
- Scattered rocks in the area are covered with old landslide debris comprising boulders, gneissic rocks, and loose soil, with a low bearing capacity.
- These gneissic rocks are highly weathered and have a low cohesive value with a tendency of high pore pressure when saturated with water, especially during monsoons.