Recently, Himachal Pradesh has been in the news due to heavy rains that resulted in flash floods and landslides. This article delves into the causes of these natural disasters and possible mitigation strategies.
Understanding Landslides
A landslide refers to the movement of a mass of rock, debris, or earth down a slope. This phenomenon, known as mass wasting, happens when the downward forces (mostly gravity) exceed the strength of the earth materials constituting the slope.
Factors Leading to Landslides
Three major factors contribute to landslides: geology, morphology, and human activity. Geology refers to the material characteristics, as weak or fractured earth or rock, or layers with different strengths and stiffness can lead to a landslide. Morphology, involving the land structure, is another factor. For instance, slopes losing vegetation to fire or drought are more susceptible to landslides, since vegetation stabilizes soil. Human activities like agriculture and construction also increase landslide risks.
Areas Prone to Landslides
The entire Himalayan tract, sub-Himalayan hills/mountains in northeast India, Western Ghats, the Nilgiris in Tamil Nadu, and Konkan areas are known for their susceptibility to landslides.
Mitigation Strategies for Landslides
Preventive methods include restrictions on construction and other developmental activities, limiting agriculture to valleys and moderately sloped areas, controlling development of large settlements in high vulnerability zones, promoting large-scale afforestation programmes and constructing bunds to reduce water flow.
National Landslide Susceptibility Mapping
The Geological Survey of India (GSI) has mapped 85% of the country’s 420,000 square km landslide-prone area. This has led to division of areas into different zones based on disaster propensity. Improved early warning systems, monitoring and susceptibility zoning can decrease the damage by landslides.
Flash Floods: An Overview
Flash floods refer to sudden water level surges, usually during or after intense rainfalls. They are localized events of short duration with a high peak, with less than six hours between rainfall occurrence and peak flood.
Causes of Flash Floods
Heavy rain associated with severe weather conditions, meltwater from ice or snow flowing over ice sheets or snowfields, dam or levee breaks and mudslides can cause flash floods. Flash floods have also been recorded in areas near volcanoes following eruptions due to the melting of glaciers. The rainfall intensity, location, distribution, land use, topography, vegetation, soil type, and soil water content can determine the speed and location of flash flooding.
Mitigation Strategies for Flash Floods
To mitigate flash floods, it is recommended that people should live on slopes with firm ground rather than in valleys. In areas where ground fissures have developed, it becomes necessary to check the infiltration of rainwater and surface water. Prohibiting indiscriminate and unscientific construction works is another mitigation measure.
