Mains Paper 3: Environment | Conservation, environmental pollution and degradation, environmental impact assessment
From UPSC perspective, the following things are important:
Prelims level: Hungry Water Effect
Mains level: Floods have been devastating in India as usual irrespective of the terrain. The newscard studies various factors which intensifies the impact of flooding events in India.
Causes of Extreme Floods
(A) Above Normal Rainfall
- The summer monsoon rainfall in Kerala from May to August this year was 2,290 mm, which was 53% above normal.
- The average rainfall during the summer monsoon period (June-September) is about 1,619 mm.
- As a result, six of the seven major reservoirs in the State had over 90% storage before August 8, well before Kerala received the unprecedented extreme rainfall events.
- Finally, the catchment areas of major reservoirs in the State received extreme rainfall never before witnessed in the State.
(B) Problem of Storage
- With over 90% storage, six of the seven major reservoirs had more than the normal storage before the extreme events could occur.
- In August 2018, the catchments upstream of the major reservoirs of upstream of the Idukki, Kakki, and Periyar experienced unprecedented extreme rainfall since 1901.
(C) Hungry Water Effect
- The capture of sediments below dams has profound impact on geomorphology of downstream river. This water released below dam level is called hungry water.
- The potential energy of the hungry water released from dams scour the river banks downstream, uprooting trees or riparian vegetation and damaging bridges and other engineering structures
- Overloaded with silt and clay from the eroding river banks, the highly turbid and viscous water clogs drainage channels.
- Subsequent discharge of water from the dam will lead to inundation and waterlogging of large areas.
(D) Sand Mining
- Years of uncontrolled sand mining have left most of the rivers in Kerala depleted or exhausted of sand and gravel.
- When the river channel has adequate supply of sand and gravel, the potential energy of the water is used to transport the mixture.
- The water does not scour the banks or turn muddy.
- The submerged areas devoid of sand and gravel in turn triggers hungry water effect until the clay in the water settles.