Flood Risk Assessments for Scotland

There are some council specific requirements that warrant the need for a Flood Risk Assessment as part of a planning application, Luckily, at Aegaea we have extensive experience across the entire country and can advise early during the planning process. 

SEPA have published online Flood Maps which are designed to help users understand the risk of flooding (from numerous sources) in areas throughout Scotland. If your development is located within or close to the Flood Risk Area (i.e. the Future Flood Mapping Extent) from any source, then a Flood Risk Assessment will be required as part of a planning application.

This should be made clear during the pre-application stage of the development.

SEPA’s flood maps show areas that are at risk of flooding from fluvial (river), pluvial (surface water) and coastal sources, for High Likelihood (each year this area has a 10% chance of flooding), Medium Likelihood (each year this area has a 0.5% chance of flooding) and Low Likelihood (0.1% chance of flooding).

The maps also contain predicted Future Flood maps for both fluvial and coastal sources (up to 2080), and from surface water / smaller watercourses (up to 2070) – otherwise known as the Flood Risk Area.

From a development planning perspective in Scotland, understanding the importance of the flood risk area is absolutely paramount. The intent of NPF4 is fundamentally avoidance – avoiding development in flood risk areas wherever possible. The policy framework is designed to steer development to safer locations.

There are of course exceptions to the above, where some forms of development are permitted within the Flood Risk Area – this includes Essential Infrastructure, Water Compatible Use and redevelopment of an existing site for an equal or less vulnerable use. Redevelopment of previously used sites in built-up areas is also permitted, provided that the Local Development Plan (LDP) has specifically identified a need to bring that site back into positive use, and that the proposal can demonstrate that long-term safety and resilience can be secured in line with SEPA advice.

Not necessarily. On top of demonstrating that your development is outside of the flood risk area (provided it does not meet any exception in accordance with NPF4 – we will also need to demonstrate that safe and dry access is provided to/from the development during a flood event.

Additionally, SEPA’s long term stance is that they define the Flood Risk Area as the 1 in 200 year flood extent (plus climate change, plus an appropriate blockage of any nearby structures) which may have been excluded from the online maps. Note that in some instances, this can mean a full 100% blockage of a structure’s opening. Site specific analysis will need to be undertaken as part of a detailed  Flood Risk Assessment.

The Flood Risk Management Act (Scotland) Act 2009 has set in place a statutory framework for delivering a sustainable and risk-based approach to managing flooding. This includes assessing both the likelihood and impacts of flooding, from all sources. SEPA and responsible authorities have a general duty, under section 1 of the Act, to exercise their flood risk related functions with a view to reducing overall flood risk and promote sustainable flood management and will be consulted for most developments deemed to be at risk of flooding.

However, SEPA have no site-specific guidance for the following development types (the Local Authority flooding team will still need input in regards to the application):

1. Permanently open-sided buildings used for storage or land cover such as agricultural buildings and polytunnels. Careful consideration should be given to mitigating the impact of significant coverage of land with polytunnels, particularly on sloping land – such development can increase surface water runoff and sediment movement, creating localised flood impacts. 
2. Sustainable drainage schemes (SuDS), including temporary for construction. SuDS can be accommodated in flood risk areas provided they do not affect the storage or conveyance capacity of the watercourse. SEPA has published guidance on potential pollution of the water environment. The management of surface water drainage and exceedance of surface water drainage systems (i.e., surface water flooding) are matters for the local authority to consider in conjunction with Scottish Water. 
3. Like-for-like (in dimension and/or gradient as applicable) replacement of watercourse crossings, culverts and bridges. A good practice guide for river crossings can be found on the SEPA website. 
4. Footpaths, access tracks, private roads, car parks and other landscaping proposals (including replacements and extensions). Cars can become mobilised by flood water and cause blockage or damage to structures if parked in an area of flood risk, particularly where bridges and culverts are located downstream of the car park. Signage can be used to warn of the flood risk and measures such as bollards can prevent cars from washing away and causing blockage. 
5. Hydro schemes (excluding where the development includes the transfer of flows between catchments). Powerhouses should be located as far back from the water corridor as is practicable. The construction of weirs to facilitate off-take mechanisms may increase the risk of flooding locally, particularly where there are nearby receptors. Further advice is provided in SEPA’s Controlled Activities Regulations (CAR) Flood Risk Standing Advice under ‘Discharge Alterations’.
6. Septic tanks and soakaways. Scottish Water guidance and SEPA regulatory information on septic tanks and private sewage treatment systems should be followed. 
7. Cemeteries. Flooding could be from surface water, small watercourses and/or groundwater, as well as larger fluvial and coastal sources. The long-term impacts of wave action and coastal erosion should also be considered for sites in exposed coastal locations. Further information on coastal erosion can be found in Scotland’s National Coastal Change Assessment. SEPA has published guidance on assessing the impacts of cemeteries on groundwater. Groundwater is often the most significant constraint when considering options for cemetery extension and assessing new sites. Other issues to consider include access constraints for staff and the public erosion risk, risk of flotation and risks to stability of gravestones.
8. Walls, fences, and other means of property enclosure/demarcation. Consideration should be given to the use of open-structure fences or materials that allow flood water to travel through. This type of development should not be constructed with the sole intention of flood protection as they are unlikely to withstand the hydro-static pressure created during a flood event and sudden failure can lead to rapid and therefore more dangerous inundation. 
9. The formation of new or alterations and extensions to existing garages, sheds, conservatories, greenhouses and other buildings and structures (including decking) that are incidental to the enjoyment of the main residential dwelling house (excludes the formation of any overnight accommodation or a new dwelling).
10. Small-scale street furniture (e.g., flagpoles, signage, benches, streetlights, electric car charging points etc.)
11. Small-scale* addition of non-residential buildings within a site that are ancillary to the existing use and are equal or less vulnerable in use. 
12. Allotments and plant nurseries. 
13. Mobile businesses and hot food vans.
14. Temporary construction accommodation (excluding the provision of overnight accommodation).
15. Reverse vending machines required to deliver Scotland’s Deposit Return Scheme

*Planning authorities should determine what constitutes small-scale and therefore whether consultation with SEPA is required or standing advice is applicable.  SEPA recommends planning authorities consider the following factors to determine significance: the size of the new building compared to the existing building; the size of the watercourse and predicted flood extent in the area i.e. large rivers with extensive floodplains are less likely to be impacted by a new building than a small watercourse with limited floodplain; proximity of receptors to the site; flood history for the area. 

At the very least, a Flood Risk Assessment must contain:

1. Clearly georeferenced plan at an appropriate scale, including geographical features and all watercourses/other water bodies
2. Site specific photographs showing areas of interest and potential hydraulic constraints
3. Topographical information showing (as a minimum) the existing site levels on site
4. Other topographical data including site cross sections in relation to the watercourse
5. Key structural information which may include conveyance capacity calculations
6. Other site-specific information including a historical flood study, and details of any flood alleviation measures in the vicinity
7. A clear assessment of flood risk from all sources including fluvial, pluvial, coastal, groundwater, sewer and artificial features.

If a more detailed FRA is required, this may include hydraulic modelling to determine the potential flood levels on site and if any further mitigation measures are required.