Flood control measures should be included in operational policy of all the reservoirs in the wake of the two floods in 2018 and 2019, an expert committee has suggested.
The panel, headed by K.P. Sudheer, Executive Vice President, Kerala State Council for Science Technology and Environment, was asked to look into the extreme heavy rainfall events and subsequent floods and landslides in the State.
The reservoirs are being operated on the policy that no spilling of water over the spillways will be permitted until the water level reaches the Full Reservoir Level. In case of floods, the policy followed till 2018 was to release flood water by following the principle that the volume of water released shall not exceed the inflow, it was noted.
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Ban on construction
The panel proposed a ban on construction in the flood ways of rivers to allow the free flow of flood water.
In flood-fringe areas, only regulated constructions may be permitted. No construction shall be allowed in the buffer zones of the rivers, which shall be marked at a distance from 50 metre to 100 metre, it suggested.
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It was the over saturation of the soil that triggered landslides during the Extreme Rain Events (ERE) in August 2018 and 2019 and the rain events were associated with the deep depression over the northwest Bay of Bengal and nearby areas, it concluded.
Landslides
Generally, steep areas with more than 33% slope are vulnerable to landslide and the majority of landslides recorded during the last two years occurred in these terrains. Idukki experienced the maximum number of landslides (977) in 2018, it was reported.
Agricultural expansion and water conservation such as terracing, blocking/diversion of storm water channels and alteration of natural vegetation pattern in steep slopes have amplified the landslide susceptibility, especially at Kavalappara, Pathar and Puthumala. Soil piping too triggered landslips, especially in north Kerala, it noted.
Rain gauges
Kerala should increase the network density of rain gauges by putting up at least 500 automatic rain gauges on priority in regions receiving high-intensity rainfall in short time periods. Half the number of instruments shall be in the highlands, it was proposed.
Considering the instability of the slopes and their vulnerability to landslips, the panel suggested preventive measures, including slope stabilisation.
Cutting and levelling of land for construction of houses in regions of slopes of more than 25% inclination and a slope length exceeding 100 metre shall not be allowed. Diversion or blocking of stream channels in the upper slopes, ponding of water in the sloping sections over a 25% slope shall not be permitted. Regional ERE and Flood forecast system using Artificial Intelligence shall be put in place to predict flash floods and to trigger an advance warning system, it suggested.