Flood investigation findings published
The new flood defence barrier at West Kirby ‘worked as intended in breaking the energy of the waves’ when extreme tidal conditions hit the area during storms last April – and in doing so helped protect properties from potentially serious damage.
That is a headline conclusion from a Flood Investigation report conducted in the aftermath of the storm that looked at the causes and affects of localised flooding during the storm on 9th April 2024.
The report, compiled by the Lead Local Flood Authority, also looked at the effectiveness of the new 1.2m high flood wall – and the associated operational plan - during the first real severe test the flood alleviation scheme had faced since its completion.
Storm Pierrick, as named by the French meteorological service Meteofrance, coincided with high spring tides on April 9th. This combination of conditions resulted in the sea level rising to a height that easily submerged the old sea wall.
The waves hit the new flood defence at force and the water from those reflected waves was carried by the strong northwesterly wind resulting in an accumulation of water on the highway behind the wall, with the lowest points of South Parade impacted the most.
The highway drainage was initially unable to drain the water away due to a combination of tide-locking due to the height of the tide above the outfalls and issues with the highway drainage system caused by debris brought in by the water.
However, once the tide levels dropped the water drained away and the highway was almost completely clear within four hours.
Damage was caused to three residential properties and a storeroom used by a business at South Parade.
The report concluded: “All available data indicates that the April 2024 event should be classified as an extreme event and appears to have been of a greater return period than the design standard of the wall. The overtopping that occurred as a result of the conditions on the day is therefore not unexpected.
“The new defences however limited the damage that would have otherwise occurred had they not been built. The new flood wall worked as intended in breaking the energy of the waves and retaining an extreme mean sea level on the seaward side of the wall.
“Waves breaking at the flood wall will always occur, with the volume of water blown over the flood wall very much dependent on the conditions at the time of the event. All flood risk management infrastructure carries the residual risk of a flood event that exceeds the design standard, such as a flood that overtops a raised flood defence or an intense rainfall event that a drainage system cannot accommodate. The recommendations look to improve the management of the residual risk as it cannot be eliminated.”
I am grateful to the officers who have carried out this thorough review of the circumstances that led to the high-profile incident last April. What is clear is that sea levels and wave heights on that day exceeded forecasts and, combined, created a situation which tested the effectiveness of the new flood barrier to the limit.
The damage caused to other areas, including other parts of Wirral, showed the extremity of the conditions so for properties in West Kirby to be impacted in a relatively minor way is vindication of the investment the Environment Agency and Wirral Council made in the new flood alleviation scheme.
I was heartened to read the testimonies from some local residents who said that they felt safer and more protected from the event as a result of the flood wall intercepting energy from waves that would previously have travelled, unimpeded, across the promenade to their properties.
Ordinarily, the impact of the flooding in West Kirby on this occasion would not have met the threshold for a Section 19 Flood Investigation. However, given the public interest in West Kirby during and after the April 2024 event, the Lead Local Flood Authority felt a full investigation was required and their findings and recommendations are welcomed.
The report lists six recommendations, two of which have already been enacted by Wirral Council as the Coast Protection Authority. These involved a recommendation to install non-return valves within the demountable barriers, which has been done, as well as a request for the operational procedures at West Kirby to be reviewed to include an appropriate trigger point to close South Parade to traffic.
Another recommendation also already actioned was for the Environment Agency to review its forecasting model and triggers for the issue of a flood warning for West Kirby.
Decision - West Kirby Flood Investigation April 2024 | Wirral Council
