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Kensington and Chelsea Council Planning Guidance

The Royal Borough of Kensington and Chelsea 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.

Kensington and Chelsea 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

Kensington and Chelsea Council request a site walkover is undertaken as part of the desktop study.

Guidance for Contaminated Land

Kensington and Chelsea Council

VIEW KENSINGTON AND CHELSEA GUIDANCE FOR CONTAMINATED LAND

Kensington and Chelsea Flood Risk Assessment

The River Thames forms the southern boundary of the Borough and is the only exposed watercourse. There are two historic watercourses, the Westbourne River and Counters Creek, which are known as ‘lost rivers’. These have been culverted to become part of the local sewerage system. The main trunk sewer runs along the boundary with the London Borough of Hammersmith and Fulham. The closest water reservoirs are the Serpentine and the Round Pond in Kensington Gardens. The Serpentine was formed as a result of damming the Westbourne ‘lost river’ which runs through Hyde Park. The Grand Union Canal runs along the north boundary of the Borough.

The SFRA for Kensington and Chelsea identifies the most significant sources of flood risk within the Borough as:

  • A breach or overtopping of the Thames tidal defences;
  • Flooding from surface water; and
  • Sewer flooding due to lack of capacity.

There have been several episodes of flooding in the Borough. The main reason for flooding is the inability of the sewers to cope with the fast intake of surface water run-off, adding to the foul water in the sewers during intense storm events. The Borough is located at the lower end of the sewer system’s catchment which means surface and foul water from other boroughs such as Camden and Brent are already in the sewer system reducing its capacity. In 2007, over 500 properties reported flooding. This event was due to heavy rainfall which overloaded the sewer system leading to a combination of surface and sewer water flooding. In 2006, Notting Hill and Sloane Square stations were flooded also from heavy rainfall and surcharging sewers.

Basement sewer flooding associated with the Counters Creek sewer in the west of the Borough is a major local flooding concern.

The Council will require development to adapt to fluvial flooding and mitigate the effects of, and adapt to, surface water and sewer flooding. To deliver this the Council will:

  • resist vulnerable development, including self-contained basement dwellings, in Flood Risk Zone 3 as defined in the Strategic Flood Risk Assessment;
  • require a site-specific Flood Risk Assessment, including an ‘Exception Test’ for all development in Flood Risk Zone 2 and 3 as defined in the Strategic Flood Risk Assessment, for sites in areas with critical drainage problems and for all sites greater than 1 hectare;
  • where required undertake the ‘Sequential Test’ for planning applications within Flood Risk Zones 2 and 3, and for sites in areas with critical drainage problems;
  • require development at risk from flooding in Flood Risk Zones 2 and 3, in areas with critical drainage problems, or sites greater than 1ha to incorporate suitable flood defence or flood mitigation measures in accordance with the recommendations of the site specific Flood Risk Assessment;
  • require SuDs, or other measures, to reduce both the volume and the speed of water run-off to the drainage system ensuring that surface water run-off is managed as close to its source as possible in line with the hierarchy in the London Plan. In particular, major development must make a significant reduction in the current volume and speed of water run-off to the drainage system;
  • resist impermeable surfaces in front gardens;
  • require development adjacent to the Thames to be set back from the Thames flood defence to enable the sustainable and cost-effective upgrade of flood defences over the next 50 to 100 years.

Level 1 Strategic Flood Risk Assessment

Kensington and Chelsea Council

VIEW KENSINGTON AND CHELSEA STRATEGIC FLOOD RISK ASSESSMENT

Kensington and Chelsea Sustainable Drainage SuDs

Minor Developments

Their policy could be met through an increase in permeable surfaces, an attenuation of surface water run-off or a combination of both.

To ensure policy compliance the following information should be submitted:

  1. A detailed analysis of surface water run-off and attenuation volume required by policy CE2g (achieve a reduction of 50% of existing rates including climate change in the calculations and factoring in all flows into the sewer system including swimming pool discharges, groundwater or other flows). The storm events used in the calculations should include the 1 in 1-yr event.
  2. Information about the proposed SuDS types, their location, attenuation capacity, specification, structural integrity, construction, operation, access, and maintenance. More sustainable green SuDS should be favoured over attenuation tanks.
  3. Section/profile drawings of the SuDS if relevant (green roofs, blue roofs, sub-base attenuation, permeable paving, planters, species, etc.) and maintenance information.
  4. Drainage plans to show clearly how surface water run-off will be conveyed to the SuDS and any connections to the sewer system if necessary.

If this information is submitted at planning application stage this will reduce the need for pre-commencement conditions attached to the planning permission.

Major Developments

For major developments, SuDS should be considered from the outset at a very early stage of the process (masterplanning) to ensure they are fully integrated with the topography and conditions of the site. The Council have produced the following SuDS guide based on the design process and aimed at promoting best-practice. This guide should be followed when designing SuDS in the Royal Borough.

A SuDS strategy should be submitted including the information below. Developers should also fill in the SuDS proforma to ensure that all the relevant points have been addressed. The SuDS strategy should show how the development will comply with policy CE2g and achieve greenfield run-off for all events (factoring in other flows into the sewer such as swimming pool discharges, groundwater and other flows). The storm events used in the calculations should include the 1 in 1-yr event. The strategy should take into consideration the drainage hierarchy referred to in the London Plan and include the following information:

  • the proposed SuDS types, their location, landscape integration strategy, attenuation capacity, specification, structural integrity, construction, operation, and access. More sustainable green SuDS should be favoured over attenuation tanks.
  • Section/profile drawings of the SuDS if relevant (green roofs, blue roofs, sub-base attenuation, permeable paving, planters, species, etc.).
  • Drainage plans to show clearly how surface water run-off will be conveyed to the SuDS and any connections to the sewer system if necessary.
  • Details of surface water management during construction.
  • Details of exceedance flow routes.
  • Foul drainage
  • Adoption of SuDS (ownership), long-term maintenance regime (including maintenance schedule, costs) and communication to residents
  • Compliance with the non-statutory SuDS Standards

Surface Water Drainage Guidance

Kensington and Chelsea Council

VIEW KENSINGTON AND CHELSEA GUIDANCE ON SUDS

Kensington and Chelsea Council Groundwater Flood Risk

There is a risk that a rise in groundwater levels may lead to localised groundwater flooding. Groundwater flooding could be seasonal or happen as a result of periods of heavy rain.

The southern half of the Borough is highly susceptible to groundwater flooding, as illustrated in the maps included in the Council’s Local Flood Risk Management Strategy.

For further advice please contact us

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