Developing a Flood Risk Site - Flood Protection Solutions

Posted 22. 10. 2020

Developing a Flood Risk Site

As seen in Self Build & Design

Flood mapping identifies vast areas of the UK to be prone to flooding from rivers, sea and surface water. One in six properties in fact.  Many areas benefit from formal lines of defence, whether its flood embankments, levees, walls, or storage ponds, with the majority of these maintained by the Environment Agency (in England). Numerous major towns and cities are located next to rivers and coastlines by virtue of their industrial past, meaning that flooding is an inevitable a risk that has to be continually managed.


London is a prime example of a city which is heavily reliant upon the vast flood defence network along the River Thames corridor to protect it. Should you look at flood mapping for this city, you would realise that several major populated areas of London are within designated flood zones. Taking note of this, it begs the question of how do so many new construction projects continually commence within the nation’s capital given the existence of this risk?


The answer to this question can be met in part by a combination of housing demand; lack of suitable sites; and, a growing population. Ultimately, it will often be decided by your local planning authority (LPA) whether a site is suitable to be developed should flood risk be consideration. The LPA are often guided by their statutory consultees, including the Environment Agency (in England) and Internal Drainage Boards (IDB’s) prior to making their final decision.


Should you be considering developing a site that is identified at flood risk, you should firstly ask the LPA for pre-development advice. This advice should then be passed onto a flood risk professional, who can offer you a realistic view as to whether the development would be viable in the LPA’s eyes. Using a flood risk professional to sense check your development aspirations is the most important step, ensuring that pursuing obtaining planning permission for a development is worth both your time and money.


There are several scenarios which can play out when a site is initially identified at flood risk. The best and most straight forward scenario is where your chosen flood risk professional is able to provide valid evidence that your site is actually at lower risk than what is depicted within flood zone mapping. A scenario of this kind can be achieved by comparing site levels with corresponding local flood levels.


Where flood risk cannot be negated in such a straightforward manner, the LPA may request evidence of Sequential Testing. This process looks to assess whether there are any other development sites of similar nature within the local area which may be at less risk of flooding. Where there are limited or no options to locate a development elsewhere, the developer must then undertake an appropriately detailed Exception Test.


Exception Test


The Exception Test would outline any further considerations that would need to be incorporated within the design. This would include the minimisation of any risk to persons on site and elsewhere for the lifetime of the development. A cautionary note at this point should be made where the likelihood and potential depth of flooding is high. There are some scenarios where the risk posed would directly contradict local and national planning policies, making it infeasible and immoral to grant permission. A diligent flood risk professional would inform you of this at the earliest stage possible, in order for you to fully consider the financial risks that may be involved.


Where a development can legitimately pass the Exception Test, you may have to then prove to the LPA that any displaced flood water can still be located within your site. This is to avoid any detrimental flooding elsewhere.  The term often used to describe this is compensatory storage.


Fortunately, not all developments have to undertake such a process to obtain planning, but ultimately it must be noted that diligently managing this risk would lead to the avoidance further issues in future.


Future Proofing


Mortgage providers are now becoming far more diligent when lending on properties in flood risk areas, meaning they may ask for evidence of how a property can manage any residual risk that exists. Furthermore, property insurers also assess a site for the risk of flooding, meaning that insurance may be refused should they deem the risk too high for their requirements.


At each step of the process outlined above, an experience flood risk professional would be able to aid you in facing the challenges of flood risk, and help you maximise your development aspirations.





Should you require any assistance Developing a Flood Risk Site, please do not hesitate to contact us.



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