The Flood Hub

The River Caldew and Willowholme flood cell is the focus of the Caldew Flood Risk Management Scheme. The area comprises the floodplains on both banks of the River Caldew, as well as the left bank of the River Eden, and includes approximately 1,700 properties at risk of flooding.

There are two main causes of flooding in this area. The risk comes from the two largest rivers: the River Caldew and the River Eden. The differing sizes and locations of the catchments feeding these two rivers means that a flood event will typically affect one watercourse more than the other.

This can be seen in the events of recent years. For example, the devastating floods in 2015 resulted in the largest ever recorded flows on the River Eden through Carlisle, resulting in widespread overtopping of the River Eden flood defences. In comparison, flows in the River Caldew during this event, whilst still very large, were not as exceptional as those on the River Eden and the River Caldew defences were not widely overtopped. Where they were overtopped was in the lower reaches of the river (adjacent to the Willowholme and Caldewgate areas of the city). This was a direct result of very high water levels on the River Eden.

 

 

The largest flows ever recorded on the River Caldew were in June 2012. The flood defences in this event performed well and extensive flooding to the city was avoided. In comparison, the flows on the River Eden at Great Corby (upstream of Carlisle) during this event were only approximately a fifth of the peak flow recorded following Storm Desmond.

Looking at both rivers, it is flooding from the River Caldew that has the potential to affect far more properties in this area of Carlisle. However, it is important to recognise that it was the River Eden which led to the flooding in 2015. Many of the properties which flooded in 2015 as a result of exceptionally high flows on the River Eden could also flood from the River Caldew, it if were to overtop its defences.

The Caldew and Willowholme flood cell also includes the lower reaches of Parham Beck and Dow Beck as well as the Little Caldew. The Little Caldew is a historic mill stream fed partially from the River Caldew (via a controlled off take upstream of Holmehead Weir) and partially from other watercourses and drainage systems that discharge into it. Under normal flow conditions, the Little Caldew flows back into the River Caldew under gravity just downstream of the The Maltings. However, during flood conditions, when high river levels on the Caldew prevent this, the EA operate a pumping station in order to maintain the discharge into the River Caldew and close the sluice at Holmehead Weir to minimise the inflows to the Little Caldew. The flooding that occurred during December 2015 and affected the downstream reach of the Little Caldew was the result of overtopping of the flood defences along the River Caldew and was not caused by the Little Caldew or it’s pumping station.

As each of these rivers affect the same connected area of floodplain, the EA need a flood scheme that addresses all these flood mechanisms. The EA would be unlikely to be able to fund a scheme which addresses the flood risk from only one of these rivers in isolation. The main reason for this is that the EA cannot claim the funding to mitigate flood risk to properties unless each potential source of flooding is taken into account.

The Caldew Flood Risk Management scheme must therefore reduce flood risk arising from high flows on both the Rivers Eden and Caldew, as well as considering other watercourses and potential sources of flooding.

A significant amount of work has been undertaken to improve the EA’s understanding of the flood risk along the River Caldew corridor through Carlisle.

This work has been necessary to help the EA understand how they can best protect the area from future flooding, and to demonstrate how government funding (such as a Flood Defence Grant in Aid) can help them effectively achieve this.

The type of work undertaken so far includes:

• Developing the EA’s understanding of flood risk in this area of Carlisle:
  • The EA have updated and improved their modelling system so that it is better able to replicate the flooding observed in 2015, as well as the high flows which occurred on the River Caldew in 2012 and 2020. Importantly, it is now better able to predict how the River Eden and River Caldew may be affected by future flooding, taking into account climate change predictions.
• Data collection:
  • The EA have continued to collect and analyse a lot of data to develop their understanding, which will continue to inform future work. This includes, topographic data, ground investigation works, environmental surveys, flood event data, a review of existing flood defences and data on buried services etc.
• Engineering advice and cost estimates:
  • The EA’s design and appraisal team have worked closely with their contractors to ensure that the options they are exploring can be delivered and are financially robust. This approach also allows for the EA’s building contractors to influence the design so that construction costs and risks can be minimised.
• Reviewing a broad range of potential options to further reduce flood risk and picking a preferred combination of options that was consistent with available funding.

There is a very clear process in place to secure government funding to deliver a new or improved flood mitigation scheme in England. This ensures that government funding for flood mitigation is invested fairly across the country. Whilst the EA were undertaking this work, the likely funding available helped inform their assessment of the most feasible option.

The most feasible option identified in the work undertaken to date was based on maximising the volume of flood water that could be passed through the city without flooding. In some locations this was to be delivered by removing additional vegetation that currently grows within the river channel. In other locations the existing flood defences would have been raised or extended.

It recently became clear that the combination of options the EA had chosen was not financially viable or technically feasible. This is partly because the level of funding the scheme qualified for was lower than initially estimated, and partly because estimated costs to deliver the scheme had increased. This resulted in a very large funding gap. Furthermore, the nature of this scheme meant that the EA were unable to adapt it to provide an increased level of protection consistent with recently revised climate change predictions.

The EA have therefore concluded that it is no longer possible to continue to invest in the leading option. 

However, new guidance on the way the EA assess flood risk and fund their flood risk management schemes has been developed and recently published. This will allow the EA to explore new opportunities to mitigate flood risk in ways that would not previously have been possible. The EA will do this by undertaking a series of feasibility assessments in the first instance.

 

The way the EA design and fund flood schemes has changed in recent years. These changes have the potential to improve the possibility of some flood risk management options which were not previously considered viable in this area of the city. As a result of this the EA have been able to secure funding to assess the feasibility of several new options. This work is expected to take 18 months.

The EA will engage with members of the public, affected landowners and third parties such as Network Rail during this period.

The feasibility study will build on the EA’s knowledge on flood risk mechanisms and mitigation options developed so far.  This includes upstream measures for managing flood risk from the River Caldew, as well complementary measures within the city. The objective of this study is to identify a preferred option, or more likely a combination of options. The options will be selected based on their economic viability and fundability as well as their ability to reduce flood risk in a robust, sustainable and acceptable manner.

The following FAQs have been provided by the EA.

What is a feasibility assessment?

• A feasibility assessment is a study which allows the EA to review whether an improvement they would like to make is possible, or not. The EA look into lots of different things when they undertake a feasibility assessment, including cost, anticipated effectiveness, land ownership, timescales and other constraints.
• The River Caldew Flood Risk Management Scheme comprises a programme of feasibility assessments which are being undertaken to explore the opportunities to reduce flood risk along the River Caldew, for the benefit of the Carlisle community.

 

Will we be given complete transparency on the possible solutions and the reasonings behind them? Will we have the opportunity to give our opinions and actually be heard, even if it means delays to the project?

• The EA are committed to ensuring that all potential options that they want to progress with are consulted on. This means that if the EA think that one or more of their solutions are viable options to reduce flood risk in this area, they will ask for feedback from residents and stakeholders as they progress with any designs.
• Whenever the EA host a consultation, they aim to work collaboratively to understand others’ views, experiences, and expertise, and to collate local knowledge. Community engagement forms a critical component of the EA’s work and by establishing a strong relationship and means of communication, they can create a shared vision for the project.

 

How do you plan on ensuring all stakeholders are kept informed throughout each stage of the process?

• The EA will keep this web page updated to include key updates about the feasibility assessments, their progress and their thinking. Newsletters will also be produced, which will be available via The Flood Hub.
• The EA will also work with local and national media and community voices, such as local councillors, to mark key announcements as appropriate. You can also follow their social media channels to stay up to date on significant milestones.

 

Is this area now at greater risk of flooding because of the flood defences constructed elsewhere in the city?

• The EA are confident that the improved flood risk management schemes delivered in the city over recent years have not increased flood risk elsewhere. The EA would not promote a scheme which increases flood risk elsewhere, and they would not have been able to secure planning permission for any scheme without being able to demonstrate this.

 

How much money have you spent in Carlisle since 2015….?

• Since 2015, the EA has invested over £30m including over £0.5m of partnership funding on measures to reduce flood risk in the City of Carlisle; this is considerably more than the £25m originally allocated. As a result, the EA have been able to reduce flood risk to over 1,500 properties, many of which were flooded in 2015. However, this work is ongoing, and the EA are committed to continue their work to manage and further reduce flood risk throughout the city.

 

What type of options are being assessed as part of the feasibility study?

• The feasibility study includes a range of options which include localised improvements to the existing defences and river channel within the city, improved flood resilience measures and upstream options to reduce the size of flood flows reaching Carlisle.

 

What is being done to minimise the risk of further flooding in the meantime?

• Over the last year the EA have cleared some in-channel vegetation along the Little Caldew and the River Eden around the Sheepmount meander, this work helps to ensure that the current flood defences continue to work as intended and provide the level of protection which avoided widespread flooding in June 2012 (still the largest recorded flood flows on the River Caldew).

 

Do you suspect any of the solutions will cause disruption to the surrounding environment? Removal of trees, changes to landscape etc?

• It is too early to comment on the specifics of any of the potential solutions at this stage. Any changes to the local landscape will be carefully considered and information about this would be included in any public consultation.

 

How long will it be before a scheme is delivered?

• The EA expect that the feasibility assessment stage will take around 18 months to complete. However, this could change depending on the outcomes of this process. The EA will update this page at regular intervals and communicate with relevant stakeholders as they make progress.

 

What effect will climate change have on flood risk in Carlisle?

• The EA know that a warming atmosphere as a result of climate change can hold more water and as a result heavy rainfall that can lead to flooding will become more likely.
• In July 2021, new guidance was released which defines how much peak flood flows are likely to increase by, as a result of climate change in different parts of the country. This was based on climate modelling that is almost a decade newer than the previous guidance.
• For the River Eden catchment (which includes the River Caldew), the new guidance predicted that climate change would have a much greater impact on the frequency and magnitude of flood flows. The EA’s best estimate is that peak river flows in the Eden catchment by the 2080’s will be 47% larger than the decade of 2020. For more information, please visit: https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances

 

Why are you not using Natural Flood Management to slow the flow and store water upstream?

• Natural Flood Management (NFM) is on option which will be investigated as part of the feasibility assessments. However, it is likely that with a catchment area the size of the River Caldew, NFM interventions would need to be very widespread to significantly reduce flood risk in the city of Carlisle.

 

Why are you not removing gravel which is accumulating in the channel?

• The River Caldew moves a lot of sand and gravel and in some locations, often where the river channel is particularly wide, this is deposited to form bars (islands or banks of gravel at the edges of the channel). These gravel bars have very little impact on the amount of flood water that can be passed through the city without overtopping the flood defences. When gravel is removed from the channel, the river soon replenishes it and recreates these natural features. A programme of frequent gravel removal from the river would therefore be both expensive and provide little benefit in terms of reducing flood risk. Despite this the EA do maintain access to the river and monitor the gravel accumulations so that it can be removed if required.

 

Why is more of the vegetation not removed from the channel?

• The River Caldew is designated as part of the River Eden Special Area of Conservation. The existing flood defences were designed to minimise the impact on the environment and to retain some vegetation within the river channel. This vegetation provides habitat for species like Otter on the banks as well as cover and shade for fish within the river. However, if the vegetation grows too much it reduces the amount of flood water that can be passed through the city before the flood defences overtop. For this reason, the EA maintain the vegetation within the channel. This is done in consultation with specialists in the environment and flood risk. The EA’s maintenance activities are undertaken outside of the bird nesting season.

 

You suggest that the guidance has been updated since the original appraisal work was undertaken. Specifically which pieces of updated guidance are being referred to as part of the feasibility studies?

• Updated Partnership Funding (PF) Calculator
  • This is the tool, or set of rules, which are used to determine the amount of government funding a flood scheme is eligible for. The term Partnership Funding refers to the principal that the amount of government investment in a scheme is determined by the benefits that the scheme delivers. These rules are applied equally to all flood risk management schemes in England to ensure government funds are invested fairly.
  • In many locations it will not be possible to fully fund a flood scheme through Flood Defence Grant-in-Aid (FDGiA) alone and additional contributions will be sought locally in the form of Partnership Funding. There are many potential sources for such funding, but it is anticipated that local stakeholders and businesses that would benefit from reduced flooding are likely to be approached. The 2020 update to the PF calculator has in many cases increased the amount of government funding that proposed flood schemes are able to secure. You can find out more here: Partnership funding for FCERM projects – GOV.UK (www.gov.uk)

• Updated appraisal guidance
  • This guidance defines the approach that must be used to appraise potential flood risk management schemes in order to secure government investment.
  • Flood and Coastal Erosion Risk Management appraisal guidance manual – Guidance – GOV.UK (www.gov.uk)

• Updated climate change guidance
  • In July 2021, new guidance was released which defines how much peak flood flows are likely to increase by, as a result of climate change in different parts of the country.
  • This was based on climate modelling that is almost a decade newer than the previous guidance. For the River Eden catchment, the new guidance predicted that climate change would have a much greater impact on the frequency and magnitude of flood flows. You can find out more here:
  • https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances
• Non-stationarity
  • This is a term used to describe changes in the frequency or magnitude of observed flood flows in the EA’s rivers. There are many factors that could cause these changes, they include changes to land use and climate change. The data shows that large floods appear to be happening more frequently on many rivers in Cumbria and this has implications for the way the EA estimate flood risk.
  • https://www.gov.uk/government/news/interim-national-guidance-non-stationary-fluvial-flood-frequency-estimation
• Residual Uncertainty Analysis
  • This is the approach the EA uses to identify, understand and manage uncertainty in flood risk management.
  • Accounting for residual uncertainty: an update to the fluvial freeboard guide – GOV.UK (www.gov.uk)

 

• Caldew Flood Risk Management Scheme Newsletter – July 2022

 

If you would like to provide any feedback on the information provided or would like to contact the Carlisle Flood Risk Management Scheme project team please use the following email address: CarlisleFRMS@environment-agency.gov.uk.