The untimely and sudden releases from the dams in Kerala should not add to a flood situation in future, says Sharad Chandra, Director of Flood Forecast Monitoring at the Central Water Commission (CWC), New Delhi. In an e-mail interview, he recommended that the reservoirs in the State be operated in a scientific manner.
What are the key lessons that the CWC’s Flood Forecast Monitoring Directorate has learnt from the massive floods that hit Kerala?
Reservoir operation may not have had much effect in attenuating the flood caused by intense unprecedented rainfall during August 2018 in Kerala. However, untimely and sudden releases from the reservoirs in Kerala should not add to any flood situation in future.
These reservoirs need to be operated in a scientific manner following rule curve/operation manual. Inflow forecasting is helpful for this purpose. However, inflow forecast may be possible only based on quantitative rainfall forecast which so far is not available in Kerala’s case. The State government/project authorities may thus be emptying/filling the reservoirs as per the rule curves/standard operating procedures (SOPs) finalised for specific projects.
The CWC is already generating experimental advisories using satellite rainfall (products of NASA), IMD rainfall forecast products (Weather Research and Forecasting (WRF), Global Forecast System (GFS)) and mathematical models (hydrodynamic and rainfall-run-off models) for all the major flood-prone basins. The CWC has also prepared an atlas for the Brahmaputra river for various return periods (the frequency with which floods return) and circulated the same to all stakeholders. The commission shares its model-based flood advisories with stakeholders through its web portal which gets updated every three hours. This can be extended to the west-flowing rivers of Kerala provided State government makes available real-time dam releases data and IMD provides quantitative precipitation forecast (QPF) for the region.
Have you done a flood risk analysis and flood management plan for the watersheds of the Periyar and Pampa rivers?
The CWC is mainly into flood forecasting. Flood risk analysis is under the domain of State government, which has to formulate its flood management plans based on that analysis. The CWC is carrying out a comprehensive study of Kerala floods to analyse the causes to help avoid such calamities in future. Vital hydro-meteorological data such as reservoir levels, inflow, outflow from the reservoirs and rainfall in the catchments as well as riverwater levels and discharges along with the danger levels of the various hydrological observation stations maintained by the Kerala Water Resources Department and the Kerala State Electricity Board are being collected for these studies.
On Kerala not having flood forecasting stations
The CWC had written to State governments to suggest locations where the CWC would set up their flood forecasting stations. States such as Haryana, Karnataka, Andhra Pradesh, Jharkhand, Tamil Nadu, Odisha etc. had proposed the locations. Accordingly, 226 flood forecasting stations have been set up on various rivers of India. However, no proposal was received from Kerala. Hence there are no flood forecasting stations in Kerala maintained by the CWC. However, the commission has set up 22 flood monitoring stations in Kerala.
The near real-time data is being entered in eSWIS (CWC website) and the hydrographs have been shared regularly online with the public. Based on the water level trend and rainfall situation, the CWC has issued daily flood situation report-cum-advisories through social media.
During the annual Relief Commissioner’s Conference held in May 2018, it was informed that the CWC will disseminate flood information through Facebook page @cwccfcr and Twitter handle @FFM_CWC. All State governments were asked to follow these social media platforms for information. Flood-related information was shared regularly through social media platforms during the 2018 floods.
Effective flood forecasting and better flood control
Kerala is situated along the Western Ghats with most of its town and cities are located on the foothills.
The State has several small intra-State rivers, almost all of them flowing west towards Arabian Sea. These rivers have very small catchment areas. The topography is such that the travel time for rainwater to reach the stream is very less (3-6 hours). Thus, the response time to issue level-based forecast for a station with respect to a base station upstream is very less.
These rivers swell up pretty quickly, and hence, no effective forecast can take place.
Early warning system for these rivers can only be issued based on rainfall-runoff mathematical modelling. For intra-State rivers of less areal spread, States generally have their own arrangement.