Guidance for architects, and developers on flood risk, drainage and phase 1 contaminated land reports is summarised below with links to the key summary documents.
Bristol has a strong, industrial heritage which means that some land may have been contaminated by old industrial uses. This could cause harm to human health or the environment.
There are three phases of contaminated land investigation and management that may be undertaken dependent upon the condition of the site, these are:
The objective of the Phase 1 Desk Study is to obtain a good understanding of site history, setting, current and proposed use. Develop a ‘conceptual model’ based upon source-pathway-receptor to establish whether any significant pollutant linkages may exist, and so assess whether there are any risks to human health or the environment.
For the further phases required, please consult the above linked guidance.
A Site Walkover is required for Phase 1 desk studies for development sites in the area. This should:
Bristol City Council
There are two major rivers flowing through Bristol, the River Avon and the River Frome. Due to the proximity to the sea (Severn Estuary), the River Avon is influenced by the tide throughout Bristol.
The flow of water through Bristol is heavily influenced by the topography of the city area. The northern and southern extents of the city are located on high ground that both slope down towards the city centre. Therefore the rivers in the north and south follow this topography and flow down to the River Avon, which defines the lowest lying areas of the city. The most northerly extent of Bristol, in the vicinity of Avonmouth, is also low lying as it is located on a coastal plain of the Severn Estuary.
The flood risk in Bristol comes from a number of sources. Surface water, tidal flooding, flooding from rivers (fluvial flooding), groundwater, flooding from the underground surface water pipe network (sewers) and a combination of any of these sources all contribute towards the overall picture of flood risk. Climate change is expected to increase the frequency, severity and extent of flooding.
Surface water flood risk
Studies predict that approximately 22,300 residential properties are at risk of surface water flooding across Bristol and as such the city is recognised as one of the UK’s top 10 Flood Risk Areas that are susceptible to surface water flooding. This strongly suggests that flooding during very heavy rainfall is likely to be significant and presents the biggest risk to the city. The public surface water sewers only have capacity to accommodate a limited amount of rainfall. More intense storms beyond this are likely to overwhelm systems and lead to flooding.
Areas at high risk of surface water flooding include:
Tidal flood risk from the River Avon represents the most significant flood risk facing the city centre (the low lying parts of Bristol, located around the Floating Harbour) and predicts that approximately 1,000 properties (which include homes and businesses) are at risk from a high tide with a storm surge.
Fluvial flood risk
There are several rivers(which are also known as Main Rivers) in Bristol and these have historically been known to cause significant flooding to the communities that surround them. A number of smaller rivers, streams and ditches (which are also known as Ordinary Watercourses) also present a risk of flooding. Areas that are known to be at risk of such flooding are those at the base of the Dundry Hills in south Bristol and those around Henbury in the north of the city.
Site-specific Flood Risk Assessments (FRAs) will be required for most proposed developments and the level of detail will depend on the level of flood risk at the site. The onus is on the developer to provide this information in support of a planning application.
Bristol City Council
Surface water drainage is a material consideration when determining planning applications. Whether or not there is need to incorporate SuDS solutions into a planning application will vary and be dependent on the type and scale of development being proposed. Developers should consider the wider context of their emerging proposal and whether it would influence the drainage regime of the site and its surroundings.
If works to the land you are seeking to develop will affect the ability of the land to absorb rainwater and have a material effect on the drainage regime of the site and its immediate surroundings then it is likely that early consideration should be given to a SuDS solution. Bristol recommend early contact with the planning authority to establish whether a SuDS solution needs to be considered for the works proposed.
Developers are recommended to undertake preapplication consultation with the LPA for the purposes of identifying what supporting information would be appropriate to their emerging development proposals. This is expected to minimise delay in the planning approval process and ensure that the developer fully understands what is expected. Such discussions can occur before land purchase.
Outline planning applications
An outline planning application should give a level of consideration to SuDS and describe how they have been incorporated into proposals at the concept design stage to align with best practice for SuDS. The information and level of consideration for SuDS should be proportional to the scale and complexity of the proposed development and informed by pre-application discussions on the scheme. Consideration is needed on how the SuDS are intended to be maintained for the lifetime of the development.
As part of large-scale planning applications, a sustainable drainage strategy (surface water) should outline the principles for the proposed scheme, initial information regarding key drainage features in line with which detailed design should be carried out.
Full planning and reserved matters applications
For full planning and reserved matters applications, detailed design of proposed SuDS should be provided in support of the proposed development. Full site investigation should be undertaken in advance of full or reserved matters application, for major development, to inform the sustainable drainage strategy at an outline application stage.
At the detailed design stage, further site investigations should be conducted providing additional information on site specific ground conditions. The findings of investigations should be used in conjunction with the sustainable drainage strategy to develop the detailed design.
The responsibility for its ownership and future maintenance should be identified during the detailed design stage and presented as part of the sustainable drainage strategy in the planning application submission.
Bristol City Council
In the lower lying areas of Ashton in the south-west of the city and Avonmouth in the north, groundwater can get to within a few metres of the ground surface. Groundwater flooding has been reported at locations throughout the city but this has tended to be in basements, rather than groundwater rising above the ground surface. In addition, there are areas where springs can form, causing localised flooding. These areas are typically in Horfield, Redland and areas around Dundry Hills
The most notable single flood event was on November 21st and 22nd 2012. During these two days, between 20-30 houses flooded internally across the City, with many more experiencing flooding of gardens, garages and roads. Property flooding was experienced in areas such as Highridge, Henbury, Brentry and Bishopsworth and Hengrove. The nature of the weather in 2012 meant that the areas experiencing flooding tended to be located adjacent to green spaces that were saturated from the prolonged rainfall over the preceding summer and autumn. As a result, the ground could not absorb much water and it flowed overland.
On the 3rd January 2014, we experienced a large storm surge in combination with a high spring tide. This resulted in flooding in many areas along the Avon, notably at Sea Mills, Cumberland Road and Avon Crescent, Cattle Market Road and Crew’s Hole Road.
Thunderstorms in June 2016 resulted in surface water flooding of five properties around the Redland, Clifton and Cotham area.
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