Silt in rivers to urbanisation: Behind Kerala's worsening floods, Pg12

Key Highlights:

• An unexpected spell of extremely heavy rainfall in early August triggered severe flooding in several parts of Kerala, particularly in Kottayam, Pathanamthitta, and Alappuzha districts.
• The floods resulted in 26 fatalities and four missing persons, with over 27,000 individuals seeking shelter in approximately 460 relief camps.
• Key human-made factors contributing to the worsening floods include reduced carrying capacity of rivers due to siltation, decreased reservoir storage, disappearance of wetlands, and altered natural hydrology.
• A CAG report in 2021 highlighted significant fall in dam storage capacity, with Kallarkutty dam losing 47% and Anayirankal dam losing 30.92% of gross storage.
• The state government plans to desilt rivers and reservoirs, prepare an asset register for water bodies, and conduct land auditing to prevent encroachment.

Kerala Floods.jpg

Detailed Insights:

• Studies by Kerala’s irrigation department confirm that accumulated silt and sand have significantly reduced the water-holding capacity of rivers.
• The 2018 floods exacerbated the situation by depositing large amounts of sediment into river beds, further obstructing water flow.
• Rapid urbanization and changes in land use patterns have led to a drastic reduction in paddy fields, marshlands, and wetlands, which naturally absorb rainfall.
• Kerala's paddy land decreased from 7.93 lakh hectares in 1979-80 to 1.80 lakh hectares in 2023-24, while wetlands shrank from 5,950 hectares to 2,937 hectares in the same period.
• Extensive concrete roads and paved surfaces across the state act as impervious surfaces, channeling stormwater rapidly into rivers and streams, causing quick water level rises.
• The government's strategy includes urgent desiltation of rivers and dams to increase their capacity and mitigate future flood threats.
• Past sand mining in rivers, though widespread, was banned due to environmental concerns, highlighting a complex balance between resource extraction and ecological impact.

Key Concepts Involved:

• Carrying Capacity (of rivers): The maximum volume of water a river channel can hold and transport without overflowing its banks.
• Sedimentation: The natural process where eroded material like silt, sand, and clay settles and accumulates in riverbeds and reservoirs.
• Wetlands: Areas saturated with water, either permanently or seasonally, crucial for flood control, water purification, and biodiversity.
• Urbanization: The process of population shift from rural to urban areas, leading to increased concrete surfaces and altered natural landscapes.
• Impervious Surfaces: Man-made surfaces like roads and pavements that prevent water from infiltrating the ground, increasing surface runoff.