A ‘ONCE in a 100-year flood’ caused devastation to more than 110 properties and shut three schools, a council report has revealed.

On Sunday, May 16, a thunderstorm caused ‘extremely intense’ rainfall in Horwich and Lostock, with severe flash flooding closing roads and damaging many buildings. Residents had to be evacuated from their homes with at least one taken to hospital.

This rain and floods came without a prior weather warning due to the ‘unpredictable nature of thunderstorms’, council officials say.

A flooding investigation report published by Bolton Council has revealed the impact this had on the community, and changes that could be made to prevent this damage happening again in the future.

The report says at least 59 properties suffered ‘major flooding’, which resulted in ‘complete or substantial inundation of ground floor or basement areas’.Twenty-seven of these were commercial, including the Beehive Pub which has only recently been able to reopen again, and three schools - St Joseph’s RC High, Chorley New Road Primary, and St Mary’s RC Primary.

In Lostock Lane and Poplar Avenue, floodwater in some properties reached a depth of one metre.

The council report states the reason for the severity of the flooding as: “The rainfall was extremely intense and is estimated to have a return period of once in 100 years.

“The area where the most rain fell is largely undeveloped, and its predominant use is for agriculture.

“The very intense rainfall caused a flash flood of run-off from land, particularly from the undeveloped land to the north-west of Horwich. This run-off overwhelmed the design capacity of existing drainage infrastructure, particularly at the transitions between the rural and urban areas.

“In many cases where open watercourses enter piped underground drainage the debris screens at the inlets were quickly blocked by debris being washed into them from further upstream. This resulted in large overland flows from culvert inlets which entered property and flooded roads.”

The report also warned such floods may become more commonplace with climate change. They said measures are ‘urgently’ needed to prevent these floods, including an ‘overhaul’ of drainage systems to ensure they are not overwhelmed again.

“Unfortunately, the sources of funding to make these changes are limited,” the report added.

Horwich town councillor and Horwich and Blackrod ward councillor, David Grant, has raised concerns over the Rivington Grange development under construction at the time of the flood for not having ‘land drainage consent’ according to the report, which was heavily damaged in the floods.

He said: “While the flash flooding was very unprecedented, a large portion of Horwich, particularly around where the most severe flooding occurred, was new build developments which you would have hoped were not only capable of handling current levels of rainfall but should be capable of improving outflow of our older Victorian flood defences.

“Improvements to the flood defences are being undertaken however (and my hope) is the recommendations in the report are fully implemented to protect residents. Improved scrutiny of developers to ensure they are complying with their legal obligations should also be a priority for the local planning officers.

“While flooding on the main road may not have been prevented due to historic drainage, the flooding through people’s homes on Rivington Grange appears on my interpretation of the assessment to have been entirely of the developer’s own making, and I am sure the homeowners will have some very serious questions to ask of them.”

Recommendations have been made to the council and Environment Agency (EA) to try and prevent this happening in the future. This includes making drainage improvements on several roads to potentially increase capacity so periods of heavy rain do not result in flooding.

The EA has been recommended to put precautions in place at Nellies Clough, St Leonard’s Avenue, and Bessy Brook to reduce flood risks.

Bolton’s planning authority have been recommended to ensure more care is taken when considering applications that a ‘flood risk assessment’ should be fully incorporated into the design of the development to minimise flood risk.

Horwich Golf Club developers, Peel Investments (North) Ltd and Northstone, have also had it suggested to them that they ensure their ‘drainage infrastructure on their land is adequately maintained, operational at all times’, to reduce flood risks.