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.
Nowadays Wandsworth is largely a residential borough with relatively few contaminating activities now in operation. Historically however there was a considerable amount of polluting industry. The increase in the residential use of land means that potentially there are more receptors that may be exposed to residual pollutants in the land where a pathway exists.
It is the responsibility of the developer to ensure that a site will be made suitable for its redeveloped use and that there are no unacceptable risks to health. When considering planning
applications/decisions the planning authority should assume a possibility of contamination in land with previous industrial use and take account the potential implication of contamination on a development site, including cases under ‘prior approval’ provisions.
Planning control is principally achieved by the inclusion of conditions in planning approvals requiring a site investigation and assessment and, when necessary, the submission and implementation of a site-specific scheme of remediation and/or mitigation to a standard suitable for the proposed use of the site and/or protective of the wider environment. Following works, a verification report that demonstrates that the developed site is suitable and safe for the developed use is required.
Risk assessment is a staged process involving a preliminary risk assessment informed by desk-based study; a site visit and walkover; a generic quantitative risk assessment; and various stages of more detailed quantitative risk assessment, continuing until a decision can be made whether or not the land is contaminated land under the Act.
Wandsworth require a site visit and walkover to be conducted as part of the risk assessment.
The London Borough of Wandsworth is at risk of flooding from both local sources of flooding and other sources, including the tidal River Thames, main rivers, sewers and artificial sources. It is predicted that this will increase in the future; influenced by climate change and increasing pressures on development and housing need.
Surface water flood risk
Wandsworth has a history of surface water flooding with significant surface water flooding occurring on the 20th July 2007 impacting several areas across the Borough. Intense periods of rainfall caused flash floods and the capacity of the existing drainage system to be exceeded in several locations across the Borough, causing overland flow and ponding in low lying areas that impacted residents, businesses and transport infrastructure across the Borough.
Within the London Borough of Wandsworth;
Balham, Summerstown, Wandsworth Town, Tooting Graveney, Putney and Southwest Battersea are highlighted to be particularly susceptible to surface water flooding.
Fluvial/tidal flood risk
Extensive areas in Wandsworth lie within Flood Zones 2 and 3 including: .Wandsworth Town, King George’s Park, Southfields, Earlsfield and Summerstown have areas in Flood Zone 2 and 3 of the River Wandle, Areas to the south of Tooting Graveney are in Flood Zone 2 of the River Graveney, and, A large area covering Battersea and Clapham Junction and smaller areas to the north of Wandsworth and Putney are in Flood Zone 3 of the River Thames, but these areas are protected by the TTD system.
The River Wandle enters Wandsworth from the south, near Summerstown, and flows northwards through the centre of the Borough, before discharging into the River Thames. The river splits in two in the vicinity of Wandle Recreation Ground and Armoury Way, and is culverted in sections, including beneath the Southside Shopping Centre. Wandsworth Town, King George’s Park, Southfields, Earlsfield and Summerstown have areas in Flood Zone 2 and 3 associated with the River Wandle,
Sewer flood risk
The wards of Balham, Thamesfield, and Latchmere are recorded as having experienced a greater number of sewer flooding incidents than the rest of the Borough.
A site-specific FRA is a report suitable for submission with a planning application which provides an assessment of flood risk to and from a proposed development, and demonstrates how the proposed development will be made safe, will not increase flood risk elsewhere and where possible will reduce flood risk overall in accordance with paragraph 100 of the NPPF and PPG.
The NPPF states that a site-specific FRA is required in the following circumstances:
The borough is very susceptible to surface water flooding as was shown by the heavy rainfall experienced in the summer of 2007. In order to reduce the risk of surface water flooding in the borough it is important to ensure that sites consider and implement the principles of Sustainable Drainage Systems (SuDS) over and above what would be covered by policy within the NPPF.
To reduce the risk of existing surface water flooding and to help reduce future problems it is important to ensure that development located within Critical Drainage Areas (CDAs), identified in the Council’s LFRMS, aim to achieve greenfield runoff rates or better. The satisfactory performance of SuDS depends not only on good design but also adequate maintenance, and the provision for adoption and maintenance must be made from the outset.
Applicants will be required to demonstrate a suitable approach to drainage through design layout, construction of development and maintenance of SuDS, in compliance with the National SuDS Standards, the London Plan Drainage Hierarchy, the Council’s Local Plan and the National Planning Policy Guidance notes.
Developments that propose to discharge surface water from the site to the public sewer network should contact Thames Water Utilities to undertake an impact study to confirm the sewer network has sufficient capacity to serve the new development. This should be carried out within the design process and confirmation submitted as part of an application.
Records of flooding which are reported to be from a groundwater source are presented in Appendix A Figure 5.3 (Wandsworth). It should be noted that there has not been a statutory obligation to record incidences of groundwater flooding in the past and therefore it is likely that the groundwater flooding incidents recorded are not exhaustive.