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.
The developer and their environmental consultant, such as GeoSmart, will need to assess the potential risks from contamination on the basis of the proposed use and local circumstances. This should normally be done before the formal planning permission is given for the development. However, in some cases, permission can be granted subject to a condition, which will require developers to investigate whether there is any land contamination and, if necessary, devise a strategy to deal with it.
Where a developer is proposing to develop land that is suspected of being contaminated, it is advisable to contact the Contaminated Land Officer before submitting the planning application. It is useful to do this as the Council may have additional information that you are unaware of and may also be able to answer any particular questions that you have.
Procedure for dealing with land potentially affected by contamination:
Islington Council request a site walkover is undertaken as part of the desktop study.
The entirety of LBI is located in Flood Zone 1 (low risk) considered as land having a less than 1 in 1,000 chance of river flooding each year (0.1% AEP).
Overland flow and surface water flooding typically arise following periods of intense rainfall, often of short duration, that is unable to soak into the ground or enter drainage systems. This occurs most commonly in urban areas where water is unable to enter the ground due to the presence of impermeable surfaces. There are three Critical Drainage Areas (CDAs) which cover the majority the London Borough of Islington.
Areas of Islington to be susceptible to surface water flooding, include:
Within LBI the artificial flood risk sources include:
Within LBI, the areas which are likely to have the greatest potential for groundwater flooding to occur are generally in the south of the Borough, underlain by permeable superficial deposits These areas include; the eastern boundary with Hackney, from Leconfield Road to the junction of City Road and Tabernacle Street in the south. There are also areas along the western boundary with Camden, from Margery Street along Farringdon Road, to the southern edge of the Borough, and further north around Highbury and Islington station.
The NPPF states that a site specific FRA is required in the following circumstances:
As LBI is located entirely within Flood Zone 1, advice relating to Flood Zone 2 and 3 is not relevant here.
Islington is faced by a number of pressures which could influence flood risk in the future, both adversely and beneficially, these include:
Sites located in Local Flood Risk Zones (LFRZs) will be required to submit a Flood Risk Assessment (FRA) to assess the risk of flooding, particularly surface water flooding, taking climate change projections into account. Where the FRA indicates that an additional volume of run-off must be stored above and beyond the amount calculated based on the method above, this must be provided on site.
Development in Islington almost always takes place on previously developed land with an existing connection to the combined sewer. Most developments in the borough are also of very high densities with little outdoor space. In these situations, flow routes have been destroyed by previously developed urban features and natural drainage may be difficult to replicate. However, despite the challenges presented by this context, there are a number of opportunities to incorporate SUDS within new or refurbished developments in a way which meet design standards and provide a range of benefits for the development and the wider environment and local area.
Applications for major developments creating new floorspace and major Changes of Use that are likely to result in an intensification of water use are required to include details to demonstrate that SUDS have been incorporated and meet the following design standards:
i) Quantity: schemes must be designed to reduce flows to a ‘greenfield rate’ of run-off (8 litres/second/hectare for Islington), where feasible. The volume of run-off that must be stored on site should be calculated based on the nationally agreed return period value of a 1 in 100 years flood plus a 30%allowance for climate change for the worst storm duration. Where it is demonstrated that a greenfield run-off rate is not feasible, runoff rates should be minimised as far as possible. The maximum permitted runoff rate will be 50 litres/second/hectare.
ii) Quality: the design must follow the SUDS ‘management train’, maximise source control, provide the relevant number of ‘treatment stages’ and identify how the ‘first flush’ will be dealt with.
ii) Amenity and biodiversity: the design must maximise amenity and biodiversity benefits, while ensuring flow and volumes of run-off entering open space are predictable and water at the surface is clean and safe. Schemes should maximise areas of landscaping and/or other permeable surfaces to support this.
There are superficial deposits in the southern half of Islington comprising of River Terrace Deposits (Figure B, Appendix B). The named formations are Hackney Gravel Member (Sand and Gravel (S&G)), Taplow Gravel Formation (S&G), Alluvium (Clay, Silt, Sand and Gravel), Langley Silt Member (Silt), Boyn Hill Gravel Member (S&G) and Finsbury Gravel Member (S&G). The bedrock geology (Figure C, Appendix B) in the Borough is underlain primarily by Thames Group – clay, silt, sand and gravel.
Please see the SFRA document for more details.