Islington Council Planning Guidance

London Borough of Islington Council planning policy for sustainable drainage reports, flood risk assessments and contaminated land risk assessment are driven by environmental conditions and the local authority policy.

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.

• Contaminated Land: A Guide To Help Developers Meet Planning Requirements
• Islington Council Strategic Flood Risk Assessment
• Islington Council Local Flood Risk Management Strategy
• Promoting Sustainable Drainage Systems in Islington

Islington Council Contaminated Land

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:

• Step 1 – the desktop study. This should establish former uses of the site and adjacent buildings, include a site walkover survey, identify contaminants of concern, develop a site-specific conceptual model and compile conclusions and recommendations.
• Step 2 – detailed site investigation (when necessary). This should include the design of a sampling strategy and samples being taken (based on the conceptual model.) A quantitative risk assessment should be undertaken, comparing results of sampling with appropriate standard and should identify unacceptable risks. If necessary, it should identify appropriate remediation options available.
• Step 3 – remediation strategy (when necessary). Preferred remedial options should be selected and submitted for approval. Remedial works should be designed and implemented.
• Step 4 – validation report (where necessary). Following completion of works, developers should compile a validation report to demonstrate works have been carried out according to remediation strategy, and detail any changes that occurred.

Site Walkover Reconnaissance

Islington Council request a site walkover is undertaken as part of the desktop study.

Islington Council Sustainable Drainage Surface Water Flooding SuDs

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.

Islington Council Groundwater Flood Risk

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.