New data reveals level of rainfall when storms hit LOVE BINGO?
THE highest rainfall levels in at least 150 years marked flooding which engulfed Calderdale in February 2020.
The highest totals were recorded in the west and north east of Calderdale, according to a new report considered by flooding authorities.
Rainfall gauges recorded greatest rainfall depths over a 48-hour period during which Storm Ciara hit.
During the storm, gauges at Gorpley, Todmorden, and Ogden, Halifax, had the highest return periods of one-in150-year to one-in-200-year events, says the report, which contains very detailed data, including street by street impacts for the worst hit areas.
Two years on, Calderdale Flood Recovery and Resilience Programme Board members were considering reports into the Storm Ciara event of February 9, 2020, which struck just weeks before the first Covid-19 lockdown, and the Storm Franklin event of February 20, last year, which produced less severe flooding.
By contrast in the east of the borough, Great Wolden Edge near Ryburn registered lowest levels in the same period in February 2020, recording levels of between one-in-two-year and one-in-five-year events.
Some rainfall in the days leading up to Storm Ciara was followed by intense rain over a particularly prolonged period, with more than a month’s rain falling in West Yorkshire during an 18-hour period, said the report, which flooding authorities have to produce by law after data analysis of such events.
Rainfall rates exceeding 32 millimetres an hour were recorded in Calderdale between 11am and noon – when river levels peaked – on February 9, last year, according to Met Office data.
An estimated 695 homes and 572 businesses were internally flooded during Storm Ciara, said the report.
From Walsden to Todmorden, river and surface water cause flooding, while in Hebden Bridge “torrents” of surface water and run-off from the hillsides was largely the cause.
Flooding wrecked temporary flood defences in Mytholmroyd – work on a flood alleviation scheme was not complete at that time, a specific issue previously considered by the board which indicated the sheer volume of water would still have overtopped defences if it had been finished.
Surface water and cellar flooding hit buildings in parts of Sowerby Bridge and Halifax with problems of blocked drains, while a mixture of river flooding, canal breaches, surface water, blocked gullies, sewer overflow and hillside run-off all hit Elland.
River overtopping, canal overtopping, surface water and blocked culverts all affected Brighouse, said the report, which outlined responses before, during and after the event.
Last year’s February 20 event saw heavy rainfall from around midnight the previous day contribute to a “double peak”, morning and, more intense, in the afternoon, and rainfall levels at Ogden registering a one-in-30-year level over an 18 to 24-hour period.
There were impacts but not on the scale of two years previously, the board heard.