3.22 During the preparation of this Plan, the wider community highlighted strong concerns over flood risk, including concerns over rising sea levels, risk of flooding from the local rhynes, particularly around Lipgate Place, Bristol Road and Clevedon Road and the risk of surface water flooding in more recent development around the Marina. The North Somerset Strategic Flood Risk Assessment identifies Portishead as susceptible to groundwater flooding, with more than a quarter of the town considered at risk.

3.23 One of the major impacts of a changing climate is a further increased risk of flooding. The UK Met Office predicts that in a business-as-usual scenario, Britain could experience a decrease in summer rainfall by up to 47%, and up to 35% more rain in winter by 2070. This flood risk is exacerbated by the presence of the tidal Portbury Ditch within the Neighbourhood Area. The regular combination of high tides and high rainfall means that rainwater draining off the surrounding hills effectively has nowhere to go for the period of time around the high tide, particularly during spring tides.

3.24 A large proportion of the Neighbourhood Area, including the Marina and the area south to it lies within Flood Zone 3 and is within the wider catchment area of the Bristol Avon.

Fig 5: Flood Risk from Rivers, Sea and Surface Water:

3.25 Bristol Avon Rivers Trust (BART) is a local charity which delivers education, land and river management advice and practical river restoration work throughout the Bristol Avon catchment. One particular area of focus for the charity is Natural Flood Management (NFM), the ‘soft engineering’ of water on a landscape scale, in order to contribute towards “slowing the flow”. NFM projects are designed to complement existing flood projects that are being delivered by other organisations already working in the area. Natural Flood Management involves working with nature to try and ‘slow the flow’ of water through a landscape. There are a variety of techniques and land-based interventions that can be used, including; subsoiling, cross drains, earth bunds, leaky ponds, cover crops, hedge planting, tree planting and grass buffers.

3.26 In terms of new development, and the important task of ‘managing rainfall’ in Portishead, drainage should be designed to match natural routes, infiltration rates and discharge rates as far as possible. Therefore the aim must be for water to be discharged as high up the drainage hierarchy12 as possible: 1. into the ground (infiltration); 2. to a surface water body; 3. to a surface water sewer, highway drain, or another drainage system; 4. to a combined sewer.

3.27 The National Planning Policy Framework and Planning Practice Guidance together with the North Somerset Local Plan highlight the importance of development taking place in areas at least risk of flooding where possible, as well as the need to manage the flow of surface rainwater. North Somerset Council Development Advice Note ‘Development and Flood Risk Issues’ provides further guidance for those applying for planning permission in the Neighbourhood Area. Draft policy PEN3 adds local detail to the North Somerset Council policies.

Photo below shows flooding arounds Lipgate Place

Relevant Objective

O7 To deliver sustainable development which prioritises brownfield land, responds positively to the climate crisis, reduces our carbon footprint and energy demand, and mitigates the local impacts of climate change.

Local Policy Context

• CS3 Environmental impacts and flood risk management
• DM1 Flooding and drainage

POLICY PEN3 - FLOOD RISK AND NATURAL FLOOD MANAGEMENT

Natural flood management works to conserve and enhance the ecological flood storage value of the water environment, including watercourse corridors, such as the rhyne system and catchments will be supported.

Major development should include provision of Sustainable Drainage Systems (SuDs), where appropriate, as part of the Natural Flood Management approach and the wider Green and Blue Infrastructure network of Portishead, paying particular attention to the Green and Blue Infrastructure Assets and Priorities shown on Figure 4 and the Objectives and Recommendations included in the Portishead GBI Evidence Base Report.

Where development proposals are in areas with known surface water flooding issues, they should include appropriate mitigation and construction methods.

Development in the neighbourhood area should also demonstrate adherence to the National Design Guide (2019), which includes guidance on integrated water management that enhances the character of a place and makes it more resilient to impacts of climate change.