With climate change, increasing urban development and ageing drainage infrastructure, flood risk is a key consideration for anyone proposing to develop in Bristol.
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As a specialist Flood Risk Consultancy, with offices based in Bristol, GeoSon are well placed to support planning applications within the city and the wider South West region. We prepare Flood Risk Assessments and Surface Water Drainage Strategies for all development types, from small household extensions to major residential and commercial schemes.
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Our experience working in Bristol means we understand the local planning requirements, typical constraints and the expectations of Bristol City Council as the Lead Local Flood Authority.
Speak to a Chartered Flood Risk Consultant today for advice or a free quote
Call 01174 414993 or email info@geoson.co.uk
Flooding in Bristol
Flood risk in Bristol originates from a combination of sources including rivers, the sea, surface water runoff and sewer surcharge. The city sits at the confluence of the River Avon and River Frome, with the River Avon subject to tidal influence from the Severn Estuary.
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Given its unique location, Bristol has a long history of flooding and has experienced several notable flood events which continue to shape flood risk management and planning decisions within the city.
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One of the most significant events occurred in July 1968, when the River Avon exceeded capacity as more than five inches of rain fell in less than 24 hours. Roads were inundated, properties flooded and drainage systems were overwhelmed. Significant damage was caused as a result of this storm event, including the loss of life. Following the 1968 flood event, major improvements were made to the city's flood defences and drainage infrastructure.
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More recently, flooding in the summer of 2007 affected parts of Bristol, driven by prolonged heavy rainfall. Surface water flooding was particularly severe in low lying areas and locations with constrained drainage networks.
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Winter flooding in 2012 and 2013 saw high river levels on the River Avon and River Frome, with tidal influences exacerbating flood risk in some areas. Parts of the Floating Harbour and riverside areas experienced flooding, highlighting the ongoing risk from fluvial and tidal sources.
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In February 2020, Storms Ciara and Dennis brought heavy rainfall that led to surface water flooding and elevated river levels across Bristol and the wider region. These events reinforced concerns around climate change and increasing rainfall intensity.
Causes of Flooding in Bristol
Flooding in Bristol is often the result of several contributing issues occurring simultaneously.
Key causes include:
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Heavy and intense rainfall overwhelming surface water drainage systems
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High river levels in the Avon and Frome following prolonged rainfall
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Tide locking, where high tides prevent rivers and / or drainage systems from discharging effectively
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Urbanisation, which reduces natural infiltration and increases runoff
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Ageing drainage infrastructure struggling to cope with modern demands.
Surface water flooding is a particular concern across much of Bristol, especially in heavily developed areas where impermeable surfaces dominate.
Areas of Higher Flood Risk in Bristol
Certain parts of Bristol are recognised as being at higher risk of flooding based on geographic location, proximity to nearby watercourses and historical flood records.
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Flood risk areas in Bristol include:
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Locations along the River Avon including parts of Hotwells, Temple Meads and Avonmouth. These areas are particularly susceptible to fluvial and tidal flooding.
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The River Frome catchment affects areas such as Eastville, St Werburghs and parts of the city centre, where river levels can rise quickly during heavy rainfall.
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Low lying areas in South Bristol, including parts of Bedminster and Knowle. These areas have experienced repeated surface water flooding due to topography and drainage constraints.
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The Floating Harbour area is carefully managed but remains sensitive to extreme events, particularly when high tides coincide with high river flows.
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The River Trym affects areas in the north west of the city.
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The River Malago influences flood risk in South Bristol.
In addition to open watercourses, Bristol has several culverted streams and ordinary watercourses that can contribute to localised flooding during intense rainfall.
Bristol Flood Risk Management
Bristol City Council is delivering and supporting a number of specific flood risk management schemes aimed at reducing flood risk across the city, particularly in areas vulnerable to tidal, fluvial and surface water flooding.
One of the most significant initiatives is the Avonmouth and Severnside Enterprise Area (ASEA) Ecology Mitigation and Flood Defence Scheme, which will provide tidal flood protection for communities, key infrastructure and employment land in Avonmouth, Lawrence Weston and Severnside. The scheme (due to be completed in 2026/27) will provide approximately 17km of flood defences which will reduce flood risk to 2,500 homes and businesses.
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In central Bristol, ongoing improvements have been made to the Cumberland Basin area with the aim of reducing tidal flood risk along the Floating Harbour and lower River Avon, using a combination of improved gates, barriers and operational controls to manage high tide events more effectively.
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The council is also progressing with surface water management measures through its Surface Water Management Plan, which identifies Critical Drainage Areas and prioritises investment in highway drainage improvements, culvert upgrades and local flood alleviation works.
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Alongside engineered solutions, Bristol is increasingly incorporating natural flood management and green infrastructure, such as tree planting, open spaces, rain gardens and permeable surfaces, to slow surface water runoff and reduce pressure on the drainage network.​
Key Planning Policies and Documents in Bristol
Flood risk planning in Bristol is governed by a combination of national policy, local planning policy and technical guidance produced by Bristol City Council and the Environment Agency.
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The Level 1 and Level 2 Strategic Flood Risk Assessment (SFRA) documents inform planning decisions and underpin the requirement for site-specific Flood Risk Assessments to support new development throughout the city. The Level 1 SFRA and Level 2 SFRA should be used alongside the following documents to assess flood risk at a site:
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Bristol City Council Local Plan
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Bristol Surface Water Management Plan
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Central Area Flood Risk Assessment
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Bristol City Council Flood Investigation Reports
Dependent on the nature of the development, a Surface Water Drainage Strategy may also be required alongside a Flood Risk Assessment for Bristol City Council. The aim of a Surface Water Drainage Strategy is to demonstrate how post development surface water runoff will be managed so that flood risk is not increased elsewhere.
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Bristol City Council have published the West of England Sustainable Drainage Developer Guide which outlines how surface water drainage should be considered within the design process.
Contact Us for a Flood Risk Assessment in Bristol
If you are planning development in Bristol and need a Flood Risk Assessment or a Surface Water Drainage Strategy, we can help.
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Early consideration of flood risk and drainage can reduce planning delays, improve design outcomes and ensure compliance with Bristol City Council policy and national planning guidance.
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Given our experience of working within Bristol we are well placed to advise on the local policy requirements that need to be considered in order to enable your application to gain planning approval.
GeoSon already hold copies of the Environment Agency and Bristol City Council flood model datasets in-house. Therefore, we can quickly advise you on the relevant planning requirements you need to consider within your application, including:
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Finished Floor Levels (FFLs)
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Floodplain compensatory storage
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Flood evacuation routes
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Resistance / resilience measures
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Surface Water Drainage.
Addressing flood risk and drainage issues at an early stage can save time, reduce costs and significantly improve the chances of securing planning permission.
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Contact us today to discuss your project and find out how we can support your flood risk and drainage requirements in Bristol.
Areas that we cover include, but are not limited to: Ashley, Avonmouth and Lawrence Weston, Bedminster, Bishopston and Ashley Down, Bishopsworth, Brislington East, Central, Clifton, Clifton Down, Cotham, Easton, Eastville, Filwood, Frome Vale, Hartcliffe and Withywood, Henbury and Brentry, Hengrove and Whitchurch Park, Hillfields, Horfield, Hotwells and Harbourside, Knowle, Lawrence Hill, Lockleaze, Redland, Southmead, Southville, St George, Troopers Hill, Stockwood, Stoke Bishop, Westbury-on-Trym and Henleaze, and Windmill Hill.