Prolonged high tide slack may have triggered recent unprecedented flooding in Kochi

On January 3, unlike the usual 10-15 minutes, the water remained at high levels for over two hours before receding.
| Photo Credit: File photo

A prolonged high tide slack, the phenomenon where tidal water remains stagnant without movement, may have caused the unprecedented tidal flooding in various divisions of the Kochi Corporation, 20 panchayats, and two municipalities earlier this month. 

Slack tide, typically occurring with both high and low tides, lasted unusually long during the high tide triggering one of Kochi’s worst tidal floods in recent times. On January 3, unlike the usual 10-15 minutes, the water remained at high levels for over two hours before receding.

The tidal gauge at Willingdon Island in Kochi recorded a high tide level of 1.62 metres around 3:30 a.m. on January 3, which persisted for two hours. “On December 18, the gauge at Willingdon Island recorded a maximum high tide of 1.63 metres, probably the highest in eight decades, but the water receded within the usual 10-15 minutes. However, on January 3, the relatively lower tide level caused greater havoc as the water remained above 1.50 metres for over two hours,” said C. G. Madhusoodhanan, chief executive officer of Equinoct, a Kochi-based community-sourced modelling solution provider.

The extended duration of slack tide allowed water to spread to a wider area. He said the cause of the phenomenon requires further study and that its recurrence could not be predicted. Equinoct has proposed a technology-driven dashboard for tidal flooding mitigation, impact assessment, and forecasting, modeled on its Community-Sourced Impact-Based Flood Forecast and Early Warning System (CoS-it-FloWS) designed to address river flooding.

Families in several divisions of the Corporation faced severe hardship as tidal flooding inundated homes, and overflowing drains contaminated drinking water sources and storage tanks. The situation was particularly dire in areas like Kadavanthra and Edakochi, where water levels rose unusually high. Councillors from the worst-affected divisions urged dredging of water bodies to ensure smoother water flow.

Mr. Madhusoodhanan cautioned that unscientific deep dredging could worsen flooding by increasing the flow of seawater through river mouths. He emphasised the need for a detailed bathymetry survey of the Vembanad Lake to assess silting levels. Based on the survey, hotspots should be identified for targeted and systematic dredging.

“The silt and mud from dredging should be utilised to raise the height of land and bunds across pokkali fields in the area, enhancing the resilience of Kochi’s surroundings to tidal floods. Besides, sluices and shutters should be installed to regulate the flow through channels connecting the land and the kayal,” he said.