‘Regulated reservoir operation can reduce floods in the Adyar’

Anna University team’s study suggests box model approach before heavy inflow

Published - August 07, 2021 03:55 am IST - CHENNAI

Disaster management:  Peak flow in the Adyar can be kept at 49,910 cusecs during extreme weather, says the study.

Disaster management: Peak flow in the Adyar can be kept at 49,910 cusecs during extreme weather, says the study.

The northeast monsoon is just a few months away and the storage in city reservoirs that meet drinking water needs is on a steady rise. A study by the Department of Geology, Anna University, suggests that flood peaks in the Adyar can be reduced up to 38% with controlled reservoir operation and water release during extreme weather events.

The combined storage in five reservoirs has touched nearly 69% of their capacity of 11.75 tmc ft as on Friday.

About 700 cusecs of Krishna water enter the State through the Kandaleru-Poondi canal. Since July 1, nearly 2.08 tmc ft of Krishna water has been added to the storage at Poondi reservoir.

The study by the Department of Geology has come up with a box model approach that suggested that maintaining different initial water levels between 50% to 75% before receiving the heavy inflow during the monsoon and releasing water accordingly would reduce the flood peaks in the river from 13% to 38%.

L. Elango, professor, Department of Geology, said the enhanced box model was integrated with the hydrological modelling system and the HEC-river analysis system to assess the performance of the Chembarambakkam reservoir with data from the 2015 floods. “We developed a step function to improve the box model to define a target storage at the end of such weather events. This is to ensure that the reservoir would have enough water for supply after monsoon,” Prof. Elango said.

Titled “Integrated modelling of rainfall-runoff process and reservoir operation for balancing water supply and flood mitigation — a case study from Chennai”, the study was published in the Journal of Earth System of Science .

Based on the inputs such as rainfall forecast, storage in the reservoir, inflow and the evaporation of flow, the model simulated different reservoir operation scenarios to balance both the water supply and to decrease flood. P. Anandharuban, a research fellow who authored the study, said, “We worked out scenarios for discharge of surplus water on an hourly basis based on rain forecasts and inflow. It is possible to reduce the inundation area by 4.71 sq km and the storage of the reservoir can be maintained at 81.5% to provide water supply if the initial water level is maintained at 50%.”

He recalled that about 81,400 cusecs flowed in the Adyar during the 2015 floods at the Thiruneermalai confluence point. With the study’s suggestions, flood peak flow can be decreased to 49,910 cusecs during similar events.

The study suggested that additional storage capacity and an accurate inflow forecast system would help in better reservoir operations.

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