This Engagement Pack has been provided by the Environment Agency and relates to the Low Crosby Flood Risk Management Scheme. For more information on the scheme, click here.
Low Crosby has suffered from several flooding events, including Storm Desmond in 2015. As a result, the Environment Agency (EA) have been looking at options to address this risk of flooding. They have undertaken an assessment of various options and this engagement pack presents the outcome of this assessment alongside a general project update. This pack will look to explain why the embankment re-profile at Warwick Holme has been selected to be the chosen flood risk management option.
The Environment Agency are continuing to work under extraordinary circumstances during the COVID-19 pandemic. Their key priorities are: to protect the health, safety and wellbeing of their staff, public, businesses, and partners they work with. For this reason, and in line with Government guidelines, they are not consulting or engaging face-to-face until it is safe to do so, instead they have included all the relevant information in this engagement pack.
The village of Low Crosby is subject to flood risk, primarily from the River Eden, and it has suffered flooding on multiple occasions historically. The village has flooded due to high flows in the River Eden in January 2005, November 2009, December 2015 and most recently, February 2020. The flood map below and the accompanying aerial photo, show the extent of flooding caused by Storm Desmond. The last (Eastern) defence scheme for the Village was developed in 2009 and was in response to the 2005 flooding. At the time it was stated that a whole village scheme did not generate a cost benefit analysis strong enough, for the whole village, using the funding criteria.
High water levels in the River Eden during an extreme storm event causes an additional issue in that it stops the Willow Beck from discharging flows into the River Eden and therefore, causes increased water levels in the beck.
Following Storm Desmond, the Environment Agency have been working with their consultants and the Flood Action Group to identify and appraise flood risk management solutions. The first step of this process was to identify a long list of options which would reduce flood risk in Low Crosby. The outcome of this process was a shortlist that comprised three options.
This option aims to deliver small scale interventions within Low Crosby to target known vulnerable areas. This includes drainage network repairs, pumping station upgrades and installation of non-return valves at key locations to stop river water entering the drainage network. The Environment Agency have obtained approval to progress these advanced works and they are programmed for delivery this year and updates will be given via their six-weekly newsletters. The intention is to deliver these works as soon as possible. These improvements will take place in addition to either option 2 or option 3.
This option would see a raised linear defence constructed around the western side of the village. This has the aim of preventing back-flow from the River Eden up the channel of the Willow Beck, which acts as a pathway for floodwater to enter properties on Primrose Bank and the Low Crosby Village Hall. The proposed defence would be a continuation of the existing eastern village defence. The Environment Agency expect additional control structures would need to be installed on Willow Beck and a small tributary upstream of the A689 in order to manage flood risk from this source. Please refer to Fig. 3.
To download the Option 2 flood risk extent drawing PDF and view in more detail, click here.
This option focuses on the re-profiling of an existing 3km embankment on the opposite bank of the River Eden to Low Crosby, at Warwick Holme. This involves lowering existing flood embankments at Warwick Holme by spreading the material over a determined width and depth. This allows the water to flow across the farmland on the river’s natural flood plain, which will reduce the water levels on the River Eden at times of flood and will significantly reduce the risk of flooding to homes in Low Crosby. The Environment Agency have now entered into the Detailed Design phase in order to establish the most effective way to achieve the objective of lowering water levels by allowing flow onto the newly connected flood plain. Please refer to Fig. 4.
To download the Option 3 flood risk extent drawing PDF and view in more detail, click here.
Having identified the options shortlist, the Environment Agency project team have undertaken an assessment to identify the preferred way forward. This assessment and the criteria used to undertake this assessment (which consider national strategic Environment Agency objectives) are presented in the table below.
During the assessment process the Environment Agency have liaised closely with their partners, the local Flood Action Group and other members of the community for their welcomed suggestions and input.
Table 1: Shortlist options assessment.
|Criteria / Objective||Outcome(s)||Village Defence||Warwick Holme Embankment Re-profile|
|Deliver key flood risk management outcomes||Flood damages are avoided over the investment period.||Protection up to a 1 in 75 return period storm event based on current data. Refer to Appendix A for an illustration.||Protection up to a 1 in 200 return period storm event based on current data. Refer to Appendix A for an illustration.|
|Reduced flood risk to
~100 residential properties. Resilient to future impacts of climate change and reduce flood risk to local business premises where appropriate.
|The long-term resilience of critical infrastructure to flooding is not adversely affected and improved where possible.||Road and utilities infrastructure better protected.||Road and utilities infrastructure better protected.|
|Protect and enhance the environment||The natural environment
is protected and conserved or restored.
|No quantifiable improvement.||~180 hectares floodplain restored. Over 100% biodiversity net gain.|
|Water Framework Directive objectives for relevant waterbodies are achieved (full or in part).||Detriment to Willow Beck would require mitigation.||3km of river improved.|
|Scheme compliments the natural landscape and enhances it where
|New defences designed to complement landscape.||Natural landscape restored. Reinstate natural processes and facilitate land management change. Collaboration enabled between DEFRA organisations, such as Natural England.|
|Promote health and wellbeing||Positive impact on the mental health and wellbeing of residents due to reduced flood risk.||In comparison with the Warwick Holme Scheme, this option would provide some reassurance to residents albeit some flood risk would remain.||Due to the considerable reduction in flood risk, this option would significantly reduce any anxiety and provide a positive impact on mental health.|
|Delivery||Alleviating flood risk in a timely manner.||This option would have to be progressed through detailed design followed by a planning application and a potential Environmental Impact Assessment. This could take up to 24 months before construction is started.||In comparison with the Village Defence Scheme, the detailed design for this option could be undertaken within a shorter
duration and the Environment Agency could potentially progress this option via their permitted development rights. Therefore, a planning application
may not be required.
|Implement a sustainable low carbon solution||The solution balances social, environmental and economic factors over the long term.||Partial alignment to key global, national and local business strategies.||Strong alignment to key global, national and local business strategies.|
|Minimise emissions of climate change gases throughout the whole life of the scheme, including the reduction of the carbon footprint associated with flood recovery and property repair.||4,534 CO2e calculated embodied whole-life carbon.||1,186 CO2e calculated embodied whole-life carbon, as modelled by the removal of the Warwick Holme embankment. This is likely to be improved by the reprofiling of the embankment.|
The probability that events such as floods or storms will occur is often expressed as a return period. The longer the return period, the more infrequent the flood event will be. The most extreme events, for example, the 1 in 100 year, occur infrequently, i.e. have a 1% chance of occurring in any given year.
A 1 in 100 year Standard of Protection does not mean that a property is protected for the next 100 years. It means (based on current data) that the property is protected up to the worst storm that could happen within a 100 year timeframe.
Currently, the Standard of Protection communicated within this engagement pack does not include uncertainty. However, the Environment Agency will update the community once this assessment has been completed.
All Standard of Protection communicated within this engagement pack are estimates for the present day. Climate change impacts may reduce the Standard of Protection throughout time.
The Environment Agency have also uploaded section drawings showing the difference in flood levels if Option 2 or Option 3 was implemented. These drawings focus on the area of Primrose Bank because this area has the lowest land level and is susceptible to flood risk. The drawings can be found in the ‘How can the Environment Agency tackle this problem?’ section above
It should be noted that hydraulic models are mathematical tools used to represent the complex behaviour of river and floodplain flows. The mathematics that underpin how a hydraulic model represents river flows is based on various, well-tested theories that can normally be relied on to approximate reality. However, this does require judgement by the modeller on how best to build a model of a specific river and for a particular purpose.
As a result, various assumptions, approximations and simplifications have to be made to balance accuracy with practicality. It must, therefore, be recognised that while a hydraulic model is always developed using the best available real world flood data, it will never be able to perfectly replicate a real incident. Therefore, it should be used as a guide for decision making only.
Following completion of the options appraisal against the project objectives and criteria, the preferred way to reduce flood risk in the village of Low Crosby is to progress with Option 3 (i.e. re-profile the Warwick Holme embankment in order to reconnect a floodplain). As demonstrated within Table 1, this option provides numerous benefits in comparison with Option 2 (i.e. the Village Defence scheme). This option delivers multiple benefits as follows:
Please note: The FlAG’s position has always been clear that their support is for a scheme that offers all properties in the village protection against a Storm Desmond event. In the event that Option 3 cannot be delivered for whatever reason, in order to secure FlAG support for Option 2, FlAG would seek reassurance/confirmation, through the detailed design process, that the Storm Desmond standard of protection is being achieved.
Historically, many engineering solutions have been addressed to create flood protection for communities, including hard defences, dredging, river straightening and others. These have benefitted many communities but can, in some instances, serve to increase the flow of water downstream. Latterly natural flood management has looked at a number of measures such as: to create river meanders where flow can return to its natural state and spill out onto flood plains when the channel has exceeded its capacity, thus reducing the flood risk downstream.
Addressing the situation at Low Crosby, this environment creates the perfect opportunity to use the course of the river to allow this above situation to happen naturally. This allows for a process of water to dissipate energy by the slowing of water, it widens the cross sectional area channel to not only include the river but also the flood plain thus reducing the flood level. Importantly, it creates areas rich in biodiversity and can store carbon. The reconnection of floodplains also has further benefits in that unlike hard defences, less maintenance is required, which in turn reduces the carbon footprint of the scheme. In order to secure the long term flood risk management benefits the Environment Agency will need to develop an agreement with the landowner committing them to the necessary maintenance regime and preserving the required ground levels. This proposal will allow for the Environment Agency to stick to its core principles of creating better places for people and wildlife.
The preferred option currently attracts approximately £5 million of funding. This includes £250k of Department for Education Funding and £2.7 million of Government Grant in Aid Booster funding.
Although this option is the most economical, there remains a funding gap of £2 million. The Environment Agency have applied for additional funding from various sources and are confident this funding gap will be closed shortly.
In order to develop the recently identified preferred option in more detail, the Environment Agency require the approval of their Outline Business Case from the EA’s Assurance Board. This document summarises their optioneering and appraisal assessments to date. Once approval has been sought, they would be looking to start the detailed design of the preferred option.
The following timeline is a current best estimate. It should be noted that there are a number of programme uncertainties which are explained in the next section.
It should be noted that the above timescales are specifically associated with the re-profile of the embankment – with the works undertaken via our Permitted Development Rights, which removes the need for planning. If the scope of works is increased or amended (i.e. the Environment Agency are required to undertake further works at Warwick Holme), planning may be required and this could increase the programme by approximately 6 months.
A requirement of the options appraisal process is to investigate as many options as possible, including various standards of protection, so the Environment Agency can determine the option which provides the tax-payer the best value for money. This is known as the nationally preferred option.
In order to determine this, they are required to develop hydraulic models and undertake various simulations so they can then undertake further engineering, environmental and economic assessments.
The time required to undertake this process depends on the state of the model and supporting data at the start of the project.
Due to the nature of this project, there are a number of programme uncertainties:
The drawings focus on 1 Primrose Bank because it is the lowest point on the western side of the village. However, the Environment Agency acknowledge that there are areas of the village which have flooded more than the depth experienced at 1 Primrose Bank.
The Warwick Holme embankment re-profile option will prevent water entering the village from both the western and eastern flood routes for all events up to the design standard. Therefore, no flooding should be observed as a cause of the high levels within the River Eden.
By developing additional resilience measures (i.e. Option 1 – Advanced Works Package) the Environment Agency will also be helping to reduce the issues around the performance of the local drainage system that the village has historically observed.
The water level in Willow Beck during big floods like Storm Desmond is driven by the water level on the River Eden. Water seen to the north of A689 and around the Parish Hall is essentially water from the River Eden that has flown the ‘wrong’ way up Willow Beck and spread out until it has reached the level of the River Eden. There will be some water from Willow Beck itself but the main driver for the flood levels and extents is the River Eden.
By delivering a scheme which lowers the levels in the River Eden, it will prevent the Willow Beck from river-locking and will enable the Beck to discharge flows into the River Eden during extreme events. This will therefore reduce flood risk to properties from the Willow Beck.
The Environment Agency have identified a number of additional resilience measures to reduce flood risk caused by surface water drainage issues, which include:
Closing the penstock during high river levels causes the pumps to lift detritus that comes into the system from the gullies and ditches. This causes problems with running of the pumps. In addition, closing the penstock causes the village system to backfill to a level that causes concerns to residents who have French drain runs overflowing into gardens behind the existing Environment Agency flood defences.
In order to solve these issues, the Environment Agency are moving forward with changing the pumping station so it can cope with detritus and with a new sump, it can prevent the existing system backfilling and overflowing into the surrounding area before the pumps are triggered.
The Environment Agency are currently obtaining quotes to undertake the design of these works. This will be subsequently followed by construction / installation. Ownership, operation and maintenance will remain with Cumbria County Council.
The Environment Agency have recently undertaken a CCTV survey of the United Utilities network and have observed no issues. However, there may be manholes which are susceptible to river water inundation during extreme events. They have discussed with UU about how to seal these manholes covers.
They have identified issues in the highways drainage network that are currently being rectified. This includes the installation of a flap valve on the outfall to the River Eden from Green Lane, and works to improve the performance of the existing Cumbria County Council pumping station on the eastern side of the village.
The Environment Agency’s Consultants have recently undertaken a survey of the Parish Hall and have identified a number of areas where there are vulnerabilities to flooding. The survey identified 14 options to remove such vulnerabilities and provide protection for up to 600mm of flood depth. Options include flood boards, re-pointing, sealing of vulnerable points and the fitting of non-return valves. The Environment Agency have appointed a contractor to undertake the supply and installation and work will commence this summer.
Baseline model: A model used for the representation of the flood extents and depths experienced in Storm Desmond.
Breaches: Gaps created in the existing embankment to allow flood water to pass through the embankment and onto the flood plain.
CCTV Survey: A camera system which records the structural condition of the drainage network.
CO2e: Carbon Dioxide Equivalent, standard unit for measuring Carbon footprints.
Control Structure: Controls Flow
DEFRA: Department for Environment, Food and Rural Affairs
Detritus: Waste or Debris of any kind
Dredging: Removal of sediment from the river bed
EA: Environment Agency
FlAG: Flood Action Group
Flood risk management options appraisal: Evidenced based process which looks to identify the best value for money flood risk management option.
Ground Water Table: An aquifer which is below ground level which is topped up by rain and ground water.
Heads of Terms: Head of Terms is a document that sets out a summary of the intended terms of a transaction. They are generally not legally binding, but act to show the intent to complete the transaction and can act as a starting point for further negotiations between parties. (For info – EA would then develop a Partnership Agreement based on the Heads of Terms).
Optioneering: Consideration, in appropriate depth, of various options in order to identify the best option to take forward to delivery.
Non-return valves: Making sure that water does not enter the drainage network from the river. Therefore, allows water to only discharge into the river and not to back up.
Penstock: Making sure that water does not enter the drainage network from the river. Therefore, allows water to only discharge into the river and not to back up.
Permitted Development: In certain circumstances, the EA has Permitted Development rights which negates the requirement for planning.
Property Flood Resilience (PFR): Mixture of Active and Passive measures which are designed to prevent entry of water into the property up to a level of 600mm above ground level. Can include: flood boards/ doors, repointing, non-return valves on drains etc.
Re-Pointing: Re-pointing is the process of replacing mortar in the brickwork of a building/structure to prevent water entry.
Re-profiling: To change the profile of something, in this instance the existing flood embankment.
River-Locking: The point at which the height of the river level prevents entry of tributaries to flow into it.
SAC: Special Area of Conservation
SSSI: Site of Special Specific Interest
UU: United Utilities
Uncertainty / Freeboard: There are unknowns/uncertainties in the estimation of extreme water levels. The quantifying of these unknowns/uncertainties informs the additional height that it is necessary to add in order to have confidence that a flood risk management scheme will deliver the standard of protection it has been designed to deliver.