Preliminary Flood Risk Assessments For Planning Permission & Due Diligence
A Preliminary Flood Risk Assessment will include analysis of all potential sources of flooding at a site and their potential impact, taking into account a number of factors including, any proposed development and the use of the site. Often requested by the Local Planning Authority, a Preliminary Flood Risk Assessment will act as a in-depth scoping assessment to determine whether the risk of flooding at the site is acceptable or whether a more detailed assessment, including modelling and surveying site levels, is necessary.
Context (first stage in the process) – The first stage of a Preliminary Flood Risk Assessment includes a detailed description of the site, existing surface cover, proximity to nearby water bodies and the flood zone that the site lies within. Any proposed development will also be detailed, including the proposed footprint of any buildings, external landscaping and the proposed site levels. The most important part of this stage is determining the site's existing and proposed vulnerability classifications. These are central to the Preliminary Flood Risk Assessment as they will determine the scope of the assessment and help to identify the level of flood risk at the site.
Flood Sources – After the context and scope of the Preliminary Flood Risk Assessment has been determined, all the potential sources of flooding at the site are evaluated on a site-specific basis, using information from broader Strategic Flood Risk Assessments, if available, and any other relevant databases. These sources are addressed in more detail in the section below.
Conclusions (most important stage) – The final and most important stage of a Preliminary Flood Risk Assessment is to conclude the likely risk of flooding at the site from each of the previously considered flood sources. This will, in turn, determine whether further assessment is required, in the form of a Detailed Flood Risk Assessment, or if the flood risk is considered to be acceptable. It may also allow for flood mitigation measures, that would reduce the risk of flooding, to be recommended at this stage without the need for further assessment.
How we can help - We regularly carry out Preliminary Flood Risk Assessments for a range of projects, including development of new build homes and change of use on rural and urban sites.
I was planning a garden annex, with plans submitted to the local council. I was told I needed a flood risk assessment, I contacted a few companies that offered this service, but I was really happy that i chose Oakshire Environmental services. The service was first class, Joe and Louis, went above and beyond there remit, and helped deliver for a deadline that was looming. They helped me with answers to questions I had along the way, and I really felt like the assistance I received, I was in safe hands. Very professional, would not hesitate to use them again, for the wide range of services they offer.
- David
When is a Preliminary Flood Risk Assessment Needed?
Flooding can be caused by a number of factors including, but not limited to, the proximity of surface water bodies, the underlying hydrogeology at a site and the surface cover of the site and its surroundings. A Preliminary Flood Risk Assessment will evaluate all of these factors to determine the potential for flooding at a given site.
Fluvial (rivers & lakes) – Rivers and lakes are one the most important potential sources of flooding and exceptionally large areas can be affected during flood events. It is, therefore, important to carry out a Preliminary Flood Risk Assessment to determine the risk to individual sites based on the presence of any flood defences, the assumed flood risk zone that the site lies within and the estimated maximum depth of a flood event.
Pluvial (surface water) – Geology, surface cover and periods of heavy rainfall can lead to significant surface water flooding which can be exacerbated by poor drainage. These factors all need to be assessed in detail as part of a Preliminary Flood Risk Assessment in order to ascertain the potential for surface water flooding.
Groundwater – The underlying geology and hydrogeology at the site, along with the depth of the water table, are important factors in determining the risk to a site from groundwater flooding. Groundwater flooding occurs when the water table rises and reaches the surface, and this can have a lasting affect as it takes a long time for the water table to decline.
Canals & Sewers – It is rare for canals to flood as they are regularly monitored and can be managed in times of heavy rainfall. It is possible, however, for canals to flood as a result of river flooding in areas where canals meet rivers and in built up areas, such as inner-city regions, the flood risk can be very damaging. Similarly, when flooding occurs from other sources, usually from rivers, it can lead to flooding of sewers which can impact densely populated residential areas.
Effect on the wider area – As well as assessing the potential impact of flooding on the site, it is also important to determine the risk the development itself poses to surrounding sites. Development often leads to an increase in impermeable surfaces or the introduction of impermeable surfaces where none were previously present as buildings are built and areas of hardstanding are placed. This potential impact needs to be considered in a Preliminary Flood Risk Assessment and it will be necessary to show that the development will not increase the risk of flooding in the surround area.
Contact us →Meet Our Flood Risk Consultants
Louis Turner, Technical Director - Having graduated from the University of Nottingham with a degree in Environmental Science, Louis is recognised for his technical leadership and precision in environmental consultancy. Louis provides strategic oversight across all service areas, ensuring projects meet the highest standards of compliance, accuracy, and environmental responsibility. Louis leads the preparation of flood risk assessments, combining hydrological data, modelling, and site-specific analysis to evaluate potential hazards. His reports provide robust guidance for planning applications, helping clients mitigate flood risks and comply with Environment Agency and local authority standards.
Joe Turner, Operations Director - Providing practical expertise and a client-focused approach, Joe ensures that every project is delivered quickly, efficiently, and without unnecessary hassle. He has successfully managed a wide variety of project types across the consultancy, bringing a wealth of operational knowledge and a reputation for keeping projects on track. Joe's leadership guarantees a smooth process for clients, from initial enquiry through to final reporting. Joe manages the operational side of flood risk assessments, ensuring hydrological modelling and reporting are completed promptly and accurately. His oversight guarantees that clients receive clear, actionable guidance to satisfy planning conditions and mitigate flood hazards.
Richard Turner, Director - With over 30 years of experience in site development, he provides invaluable insight into pragmatic solutions that balance costs, practicalities, and client objectives. Richard has a detailed understanding of building regulations and a clear sense of what is and isn't possible on site, making him a trusted advisor for developments of all sizes. Richard's background in site development allows him to assess flood risk with a pragmatic eye, ensuring that proposed mitigation measures are realistic, cost sensitive, and suitable for the specific site conditions.
Request A Preliminary Flood Risk Assessment
Contact us for an informal discussion about your requirements or, if your requirements are more complex, a more formal consultation may be necessary. Following initial consultation we can provide an outline proposal detailing how we can help and the costs involved. If you're looking for more information about our services or our company then complete the below contact form and we will endeavour to respond to your enquiry in a timely manner, alternatively, give us a call on 0800 433 2906 and our experienced consultants can provide actionable advice and guidance.
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References
British Geological Society. BGS GeoIndex
Environment Agency. Flood map for planning
Environment Agency. Flood risk and coastal change
Environment Agency. Flood risk assessments: applying for planning permission