You might recall a BBC feature about a chap, Nick Lupton, who successfully built a flood wall around his home, effectively safeguarding it against the River Severn’s floods. This instance of triumph has sparked widespread interest, with many echoing the sentiment, “We need a flood wall around our home too.” Our clients, often driven by the “Build Back Better” initiative, are increasingly inquiring about such constructions, with insurers understandably wanting to rigorously scrutinise the plans for structural robustness.
We’re going to delve into the intricacies of building a flood wall, sectioned into three detailed scenarios. Our focus will be solely on the construction of these walls, setting aside other site-specific measures like drainage, for clarity and conciseness.
A poignant reminder of the significance of sturdy and well-designed walls came during Storm Babet in Woodborough, Nottinghamshire. I witnessed the failure of a garden wall, previously serving as a homeowner’s self-designed flood defence, which dramatically collapsed. This incident underscores the grave risks involved and the insurance companies’ valid concerns over potential catastrophic failures.
Obtaining the necessary consents, and structural designs, can run from thousands of pounds into tens of thousands of pounds, and therefore as always, a flood survey and risk assessment should be the first port of call to help ensure any funds are spent in the most suitable areas.
It’s paramount that any flood wall is not only robustly constructed but also complies with current regulations to prevent exacerbating flood risks elsewhere. Additionally, it’s vital to have a grasp of the site’s drainage networks prior to designing flood walls, a topic we’ve explored in a video, accessible here: Drainage Networks and Backflow Protection.
Simplifying the complexity, we’ll navigate through three primary scenarios:
- Dealing with flooding from ordinary watercourses or surface water, and where Planning Permission is not required for a wall or landscaping.
- Where flooding stems from a main river, and Planning Permission is not required for walls or landscaping.
- Cases where Planning Permission is indeed necessary.
Each scenario presents unique challenges and requirements, it is important that you’re well-informed and prepared for your flood defence project.
Is it an Ordinary Watercourse/Surface Water or Main River Flooding?
If you have assessed the site drainage, and deem a flood wall viable, a crucial step in your flood defence project is to determine the classification of the river or watercourse in question: Is it an ordinary watercourse or a main river?
This vital information is readily available online at the Main Rivers Map, and is essential for understanding the regulatory framework you’ll be working within. Ordinary watercourses fall under the jurisdiction of the Lead Local Flood Authority (LLFA), while main rivers are managed by the Environment Agency. If you are impacted by surface water, this would fall under the LLFA.
Is Planning Permission needed?
Next, assess whether your project requires planning permission. Generally, for a wall exceeding 1m in height adjacent to a vehicular highway, or over 2m high in other areas like a backyard, planning permission is typically necessary. If you are constructing a wall in the grounds of a listed building, you will require planning permission. If your house is located in a conservation area, you may require planning if dictated by an Article 4 Direction. In such instances, consulting with your local planning authority is a prudent step to ensure compliance with specific area regulations.
- First case: Dealing with flooding from ordinary watercourses or surface water, and where planning permission is not required for a wall or landscaping.
This falls under the Land Drainage Act. It should be noted that land drainage is a complex area of responsibility,
If your activity is on an ordinary watercourse you may need:
- a land drainage consent
- to follow local council or internal drainage board byelaws
As a riparian owner you have the right to:
- Protect your property from flooding but must obtain permissions from the appropriate RMAs to carry out work in and around the watercourse. Damages may be claimed against you if any development increases flood risk for others.
There are of course other areas where you may not be on an ordinary watercourse, or be a riparian owner, but of course still wish to build defences, and this same approach would apply.
Our experience in this area is that the authorities are generally open to such development, if the proposal can be shown that it will not impact on others, however we have found their approaches different across the country.
In various situations we have experienced, Lead Local Flood Authorities (LLFAs), have offered comprehensive feedback and specified certain prerequisites that must be met to their satisfaction before endorsing such proposals.
In other cases, we have experience where the Local Lead Flood Authority (LLFA) review plans and comment that, although they do not have any fundamental objections, they cannot offer an unequivocal, ‘rubber-stamped’ approval. This caution is due to the possibility that if a neighbour were to raise an objection and demonstrate that the impact of the project could be detrimental, the responsibility for any legal dispute would fall directly between the project initiator and the neighbour, not involving the council. Essentially, while the LLFA might not oppose the plans initially, they cannot guarantee immunity from potential future legal challenges from others affected by the project.
It is therefore a key consideration when designing flood walls that there isn’t a negative impact.
The key factor we have experienced is always around impacting flow path, and that an exceedance flow path should not be interrupted – for example if water flowed across your land, to re-enter a watercourse, building a wall could impact this and negatively impact other people.
This is usually a bigger consideration than displacement of flood water, which can often be managed through compensatory storage, or, in rural areas, may not impact other properties.
- Second case: Where flooding stems from a main river, and Planning Permission is not required for walls or landscaping.
If you want to build defences for a flood caused by main river flooding, there are established environmental permits and processes to follow.
You may need an environmental permit if you do an activity that could:
- pollute the air, water or land
- increase flood risk
- adversely affect land drainage
You are breaking the law if you operate without a permit when you should have one.
You may need an environmental permit for flood risk activities if you do work:
- in, under, over or near a main river (including where the river is in a culvert)
- on or near a flood defence on a main river
- in the flood plain of a main river
- on or near a sea defence
These permits were formerly known as flood defence consent (FDC).
You should check if your activity is regulated.
I have covered the areas I believe are key, but this is not fully exhaustive so please review the Environment Agency website.
You may need to apply for permission to do any of the following regulated flood risk activities:
- building or altering any permanent or temporary structure designed to contain or divert flood waters from a main river
- any activity within 8 metres of the bank of a main river, or 16 metres if it is a tidal main river
- any activity within 8 metres of any flood defence structure or culvert on a main river, or 16 metres on a tidal river
- activities carried out on the floodplain of a main river, more than 8 metres from the river bank, culvert or flood defence structure (or 16 metres if it is a tidal main river), if you do not have planning permission
Activities that do not need permission before you start work:
You do not need to get permission if you plan to do one of the excluded activities. But you must operate within the description and conditions of the exclusion.
A relevant exclusion includes:
Flood protection devices attached to buildings
You can install door boards, airbrick covers and attach other flood protection devices to buildings without a permit.
If your activity is not excluded, then you need permission before you start work.
There are 3 ways to get permission to do your work:
- register for an ‘exemption’ – you do not need a permit but you must still register your exemption with the Environment Agency.
- apply for a ‘standard rules permit’ – permits that include a set of fixed rules for common activities
- apply for a ‘bespoke permit’ – for all other flood risk activities – permits that are tailored to the risks from your activities.
Within flood risk management, the two for consideration are Exemption or Bespoke.
The relevant exemption we have identified is:
Constructing raised flood defences around a maximum of 6 adjoining properties (FRA26)
This exemption can be used, for example, to build a wall around a pair of semi-detached houses.
BUT: Before you register this exemption, you must check your activity meets all of the following conditions:
- you cannot carry out the activity within 8m of a main river
- the dimensions of the flood defences are no more than 1m high and 6m wide
- the defences are at least 20m from any building not owned by the owners of the properties
- the total area protected by the defences is no more than 150m2for each property
- the defences are to protect existing buildings
- the works are within the existing boundary of the properties
Otherwise, you are likely to need a bespoke permit, where your activities would be assessed, and you are likely to be required to show that you are not making flood risk worse elsewhere. You may be required to provide compensatory storage.
You must apply for a bespoke permit if your activities do not fit within any of the standard rules, exemptions or exclusions.
It is likely that you may be required to demonstrate that you are not exacerbating flood risk elsewhere, which may be through the use of compensatory storage.
Compensatory storage in terms of flood risk management, particularly in the UK, refers to a technique used in floodplain development to mitigate the impact of construction on flood risk. When development takes place on a floodplain, it can reduce the natural capacity of the area to store flood water, potentially increasing flood risk elsewhere.
To counteract this, compensatory storage involves creating an equivalent volume of storage for floodwater elsewhere within the same catchment area. This is achieved by excavating or lowering land levels in nearby locations to create additional space for water during flood events. The principle behind this is to ensure that any loss of flood storage due to development is compensated for by providing an equivalent volume of storage elsewhere.
- Third Case: Cases where Planning Permission is indeed necessary.
If your proposals require planning permission, it is likely that you would need to submit a Flood Risk Assessment with the planning application. This assessment should thoroughly assess the risk, and provide an understanding of whether this could increase risk for others, and if not, how this is being managed on site. It would also be vital as part of this assessment that the wall was built to the suitable height for the flood risk.
If the FRA concludes that there is no increased risk, or it can be effectively managed onsite, it must clearly detail the strategies and measures being employed for this purpose. Depending on the specific location of your project and the level of detail required by the Environment Agency and the planning department, you might also need to undertake detailed flood modelling. The requirement for such modelling is contingent upon the complexity of the flood risk in your area and the degree of examination the application will undergo by the regulatory authorities.
Beyond the flood risk, consider the environmental impact of the construction. This includes assessing potential effects on local wildlife, vegetation, and the broader ecosystem. Mitigation strategies should be outlined to minimize any negative environmental consequences.
You may need to include an Emergency Response Plan in case of flood wall failure or unexpected flooding scenarios. This plan should detail evacuation routes, communication strategies, and emergency services coordination.
Given the complexity of navigating this, and potential costs involved, it is vital to seek suitable advice early on in any project.
Caveat: I shall caveat this article on the basis that this is my experience, my understanding, and you should seek advice in your area from the EA, LLFA (via a Flood Risk Consultant), Planning Authority, or even Land Drainage Act Specialist Lawyers.