Agenda item

Objective: To understand partnership working to improve flood mitigation in the borough.

James Mogridge – Flood Risk and Planning Engineer

James Mogridge, Flood Risk and Drainage Engineer, presented his report, which highlights how Cheltenham fits into a complex national arrangement of stakeholders and flood risk management responsibilities; the importance of cross-boundary collaboration; and mitigation measures put in place since 2007 to ensure the borough is better prepared and protected.  No two rainfall events are the same, and climate change presents further challenges, but more can be done to improve resilience, with nature-based solutions such as SuDs schemes being used to slow down the flow of water through Cheltenham catchments, at the same time complementing other aspects of the climate emergency. He said the standard protection offered by some of our flood defences is expected to decrease over time, and we need to ensure that our decision-making around choosing cost-effective schemes is robust and well-informed.  

Members welcomed his report, the positive level of cooperation between the county and the borough, and the emphasis on natural solutions.

In response to questions from members of the committee, the Flood Risk and Drainage Engineer stated that:

-       the greenspace team has submitted a bid to the county council’s £100k fund for natural flood risk management at community level, for a project in one of the town’s parks;

-       providing the right level of flood risk mitigation in planning is a tough balance:  developers are currently required to  design up to and including a 1-in-100 year event, set at a national scale, plus 40% local rainfall allowance for climate change which is set by the Environment Agency, but 2007 saw two high magnitude events occur in two weeks. Developers do need to ensure exceedance events (ie events greater than 1-in-100 plus 40% climate change) are appropriately managed in their design.  Over-engineering for larger events could contribute to the problem by creating more emissions, with additional concrete, pipes and machinery.  The local 40% allowance will be reviewed  against UK climate trajectory and revised by the Environment Agency if required.

The Cabinet Member for Climate Emergency confirmed that national guidance has to be followed but noted that the heavy rainfall in September 2024 which flooded roads and one house and threatened many others in St Mark’s ward was classed as a 1-in-74 year event.  There are clearly gaps in the flood mitigation schemes shown on the map, and he will be talking to the county council about this soon. 

He went on to say that modelling is available – super Clausius-Clapeyron scaling calculates that with a 1^o  increase in global temperature since 1975, a 7% increase in moisture in the atmosphere – and therefore rainfall – is to be expected, and the projection is a 48% increase by 2050, potentially increasing annual rainfall from 900mm in 1975 to 1350mm in 2050.  It is important to keep focused on this.

In response to further questions from Members, the Flooding and Drainage Engineer said that:

-       when the surface water management plan was commissioned by the county council, it identified the highest risk areas, and the most cost-effective flood schemes that could be put in place.  Residents in areas of localised flooding should use the online flood reporting tool;

-       if highways drains are not being properly maintained and causing surface water issues, this should be raised with the highways authority. It could be that the underlying sewers are undersized and unable to cope with the level of rainfall we are seeing now.  The flood risk management team at the county council and the flood team at CBC can look further into infrastructure upgrades, taking a more natural approach if possible;

-       while recognising that there are areas of Cheltenham where heavy rainfall causes great concern to residents, CBC and GCC teams are only likely to get involved only when homes or commercial buildings are at risk of flooding.  Flooding on the highway is a nuisance and a safety concern, but this is an issue for Highways drainage teams rather than for flood risk management teams

-       regarding budget for flood management work, the team has a recurring budget, to cover maintenance of water courses and flood schemes amongst other things, and the flood alleviation reserve can also be used for schemes – although this tends to be spent on large asset repairs, an important part of flood risk mitigation work, rather than building more smaller-scale schemes to be maintained.  Any new schemes would therefore usually rely on funding such as natural flood management fund mentioned earlier.

The Cabinet Member for Climate Emergency added that CBC’s flooding and drainage team tracks and collects videos of problem areas for evidence, and he will soon be calling for an update to the 2011 surface water flooding plan.  He said there is a  network of flood wardens across the town, suggesting that if councillors knew any residents who might be able to help, they should direct them to the website, where advice is also available to residents who are concerned about the risk of flooding to their homes.

The Vice-Chair noted that some areas of Cheltenham don’t appear to have any flood wardens, and reiterated the suggestion that councillors should encourage their communities to volunteer. 

Returning to Members’ questions, the Flood and Drainage Engineer confirmed that:

-       Warden Hill is very familiar to his team, with its location and lack of natural greenspace making it susceptible to flash flooding.  A working group including borough and county councillors has been set up, and has seen some successes and SuDS schemes delivered by the Wildlife Trust, with more work to be done by Severn Trent on undersized sewers which cannot cope with flash flooding.  His team is working with the parish council and planning department on engagement regarding the planning rules around tarmacking of driveways as it is hard for planning enforcement to keep pace with the number of residents who perhaps unwittingly carry out this type of work, unaware that impermeable solutions over a certain size are not allowed. The CBC flooding team has previously worked with  Warden Hill Parish Council to deliver 1000 leaflets promoting the use of permeable solutions and greening of properties, and there are plans in place for similar engagement next year.

The Vice-Chair wondered if a flooding supplementary planning document would help. The Cabinet Member for Climate Emergency suggested that, having walked around Warden Hill recently and compared it with his own ward (St Mark’s) where some paved driveways have been replaced with grass and hedges, maybe the parish council could get some sort of rotation going, encouraging Warden Hill residents to do the same.

In response to further questions, the Flood and Drainage Engineer confirmed that:

-       regarding the impact of building houses on greenspace and where the excess surface water will go, developments such as at The Folly in St Paul’s ward have to present modelling with a consultant as part of the planning application.  This must show that any new impermeable surfaces are balanced, in that case by a pond that will hold water and release it slowly.  Even smaller developments of 1-10 houses must now use hydraulic modelling software to demonstrate drainage measures, such as attenuation tanks or ponds depending on the size of the development;  

-       following on from a written question and whether the complex relationship between different organisations works well in a crisis situation, a flood event such as that in 2007 as communication is well co-ordinated across all management authorities (emergency planners being the point of contact for CBC).  A call to the wrong authority would be quickly passed on during the event; the one-call system suggested would be useful for issues outside flood events (such as bank collapses, debris in waterways or blocked drains) incorporating a system to identify who is responsible and directing the call to the correct authority, but it is hard to say how this would be done or who would implement it at the moment;

-       regarding public perception that a lot of problems arise from floodwater running into the sewage systems, in new development on greenfield sites, surface water would not be connected to the combined network; where a site already drains to a combined sewer, all other options are considered before discharging surface water to a combined sewer as a last resort.  A lot of attenuation would be required in such instances to better what is already there;

-       regarding incidents such as the severe flooding in January 2025 which closed the A40, emergency planners and on-call officers collaborate with neighbouring districts during such events, and if one district is affected where its neighbour is not, will offer resources to help.

The Vice-Chair welcomed the very thorough scrutiny of this subject, and said it was helpful for unparished areas to hear about the grants and schemes available for flood mitigation.