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Sustainable Drainage

The Flood & Water Management Act (FWMA) 2010 identifies organisations as ‘Risk management authorities’ and provides legislation for the management of risks associated with flooding. The Act places a number of roles and responsibilities on Local Councils who are a ‘Risk management authority’ by designating it a Lead Local Flood Authority (LLFA), in which the LLFAs are required to manage 'local' flood risk within their area. 'Local' flood risk refers to flooding or flood risk from surface water, groundwater or from ordinary watercourses.

With the enactment of the final part of the FWMA 2010 on the 15th April 2015 the Council Lead Local Flood Authority (LLFA) are designated as Statutory consultee for major developments which have surface water or other local flooding impacts. New policies and standards for drainage have been released with effect from 6th April 2015 within the National Planning Policy Framework and the applicant is advised to ensure any drainage design meets these standards to avoid delays and changes to any submitted drainage designs. Without the informationbelow, the LLFA will be unable to make any valid comments to the application.

The government have issued new policies and standards for sustainable drainage which make changes to the planning framework; the applicant is advised to design the drainage system in accordance with the new planning framework:

It is recommended before an application is submitted to the Planning Authority, to please get in contact with the planning department to discuss the application. During submission of the application, please makes sure that electronic copies of the documentation are available for viewing or future requests.

How the development proposal meets national and local planning policies (stating relevant policies), standards and guidance in relation to the sustainable drainage system, management of surface water flood risk, and climate change. Where applicable, the applicant may also wish to submit details of how the development proposal meets relevant design standards and regulations relating to sustainable drainage. Land Drainage Consent may also be required (is a watercourse going to be effected in the development, will it be altered or culverted) if this is the case Land Drainage Consent is required from the LLFA.

A management and maintenance plan for the lifetime of the development should be submitted to ensure that the sustainable drainage system (SuDS) will not pose a future flood risk as a result of poor maintenance. As a minimum this should include details of the arrangements for adoption by the appropriate party, arrangements concerning appropriate funding mechanisms for its on-going maintenance of all elements of the sustainable drainage system (including mechanical components, ongoing inspections, operation costs, regular maintenance, remedial works and irregular maintenance) to secure the operation of the surface water drainage scheme throughout its lifetime.

The minimum requirements in planning applications to enable the LLFA to provide informed response:

Desktop Study (incorporate maps showing):

  • Topography of the development site (contours at 1m intervals)
  • Existing surface water flow routes / drains / sewers and watercourses
  • Flood Risk from Rivers / Surface Water / Groundwater
  • Geological and Soil types

Flood Risk Assessment:

Indicative Site Drainage Strategy including:

  • Preliminary drainage proposals (SuDS Hierarchy)
  • Outfall Locations
  • Discharge Rates (NPPF guidelines) identified below
  • On-site storage requirements

Detailed site location and layout plans (legible, map key and scale, drawing details)

The minimum requirements in planning applications to enable the LLFA to provide informed response:

Detailed Desktop Study

  • Full Topographic Survey of the development site (base for plans submitted);
  • Existing surface water flow routes / drains / sewers and watercourses;
  • Flood Risk from Rivers / Surface Water / Groundwater;
  • Geological and Soil types in the Area/

Flood Risk Assessment

Drainage Strategy

  • Sustainable drainage proposals (SuDS Hierarchy);
  • Outfall Locations;
  • Discharge Rates (NPPF guidelines) identified below;
  • On-site storage requirements / Attenuation and Drainage Calculations;
  • Maintenance Plan / Lifetime Management;
  • Maintenance Strategy;
  • Ground Investigation Work (variable based on drainage proposal).

Calculations and Drawings (legible, map key and scale, drawing details)

  • Detailed design drawings including; details of inlets, outlets, and flow controls / long and cross section drawings of proposed drainage system(s), including design levels / details of appropriate water quality treatments;
  • Drainage system flow rates for the storm events 1 in 1 year; 1 in 2 year; 1 in 30 year and 1 in 100 year + Climate Change (both pdf and electronic files showing all output data)
  • Storm Simulation Results and Reports (e.g. Micro Drainage)
  • In regard to the flood risk assessment, the NPPF climate change figures have now been superseded with higher values as shown in the government report (19th February)
    https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances.

To aid in the response to the Planning Case Officer and Applicant the following points of the information submitted for both Outline and Full application must be given consideration:

  • Files submitted must be legible, and must be submitted in colour (maps, photographs etc)
  • Drainage Software output files must be submitted electronically to the LLFA
  • LLFA to be given notice of updates or new files submitted as part of the review