FLOOD PLAINS DEVELOPMENTS


prevent inappropriate development. This is to be achieved through the submission of an appropriate Flood Risk Assessment (FRA). An FRA may take several forms and is typically a highly bespoke assessment designed to address the particular concerns at the development site. Planning policy typically dictates that planning applications must be accompanied by an FRA in one of two situations; when situated inside Environment Agency defined Flood Zones; or when the proposed development exceeds 1 hectare in size. However FRAs run into tens of thousands of pounds and therefore it makes good sense to first commission a rapid and cost effective desktop flood risk screening report in order to understand whether an FRA is likely to be requested by the Local Planning Authority (LPA) and to inform dialogue with the LPA on what the requirements may be. This will provide an expert site assessment based on multiple data sets which considers the risk from all four major sources of flooding - river, coastal, surface water and groundwater.


In addition, many Local Authorities have developed Strategic Flood Risk


Assessments identifying areas at high risk, which are a good source of information and should be freely available from the Local Authorities’ websites.


Once a planning application has been made the LPA should more clearly outline its requirements for any FRA. This may be a simple exercise comparing the proposed floor levels against anticipated flood depths, be restricted to calculating potential surface water run off generated by the change to the built environment advising appropriate drainage schemes, or involve a more detailed assessment to fully satisfy the requirements of PPS:25. To secure planning consent in high risk areas, the FRA will typically be required to examine two tests outlined in PPS:25. These are the Sequential and Exception Tests. The Sequential Test involves examining alternative locations within the area to determine whether a more suitable area, with lower flood risk, has been put forward


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for development and would be more appropriate. However, if there are no other suitable locations then the Exception Test must be applied in order to make


recommendations on suitable flood protection measures and schemes that could be incorporated into the design of the development to minimise the risk of flooding and damage to people and property. Such measures could include flood resistance measures that prevent water entering a property (i.e. barriers, baffles and air brick covers) or flood resilience measures that minimise the disruption caused by flooding (i.e. tiled flooring and water resilient construction materials). Alternatively, on larger developments flood alleviation can be achieved through design features such as creating communal open spaces designed to flood, maintaining natural flow routes across the site or


Flooding causes


widespread devastation and destruction to both properties and contents


elevating vulnerable land uses such as housing.


The principles of PPS:25 also require that any proposed development does not increase the risk of flooding to neighbouring properties. A feature of increased urbanisation is larger volumes of surface water runoff during rainfall that must be adequately managed and drained. Consequently, LPAs are often concerned about surface water management and require an FRA to assess likely volume of surface water to be generated by the change of land use. This then informs the development of a suitable drainage system to reduce long term flooding impacts. Increasingly LPAs are seeking methods for the sustainable management of surface water. Traditional drains may become blocked or damaged and often connect to older systems unable to deal with the volume of water required. Through the


implementation of Sustainable Urban Drainage Systems (SUDS) such as green roofs, permeable surfaces, soak-aways, ponds and storage systems the rate of surface water runoff is reduced, allowing a more effective and managed discharge of surface water. As we have seen with the case of the flooding of the newly constructed Spencer Court flats in Newcastle in September (which are now being


demolished), development near watercourses and in areas at risk of flooding can lead to very substantial structural damage. However, through obtaining an appropriate flood risk report, informed design decisions be made to ensure the prolonged safety and value of a


development. The message is simple when it comes to flooding:


forewarned is forearmed. ■


For more information visit www.argyllenvironmental. com/flood


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