It is a priority for the council to reduce the impact of surface water on flooding in Salford. Developers are expected to design drainage infrastructure which takes the opportunities available on site to improve water quality, reduce discharge rates and where possible provide amenity opportunities.
Types of application that require this information:
- Any development proposals in High Flood Risk Zone (Zone 3)
- Any development proposals in Medium Flood Risk Zone (Zone 2)
- Any operational development of 1ha or above in Low Flood Risk Zone 1
- Residential development of 5 or more dwellings (except a change of use where no increase in permeable area is proposed)
- Development proposals on sites over 0.5 hectares in size located within ‘Critical Drainage Areas’
In addition to the above, Environment Agency Standing advice should be followed.
Details of what should be included
Outline applications
The following information should be presented in the form of a drainage strategy (please note this is not an exhaustive list and additional information may be requested):
- For all major applications the north west SuDS proforma must be completed and can be used to evidence the requirements of the ‘Sustainable drainage systems: non-statutory technical standards’
- Any constraints which affect the proposed development
- Topographical survey of the site, including levels and sections of any adjacent water courses for an appropriate distance upstream and downstream of the discharge point
- How the indicative drainage design meets the Flood Risk Assessment (FRA) requirements (if a FRA is required as per the NPPF)
- Existing utilities plan (if applicable)
- Impermeable areas estimate
- Infiltration testing, existing runoff rates and storage volume estimates
- Permissible or allowable peak flow rate
- Allowance for climate change factors
- SuDS components integration with any masterplan for the site/area and green infrastructure:
- source control and pre-treatment, storage locations, approximate sizing of SuDS
- details of phasing
- individual plot discharge and storage constraints
- who would be responsible for construction, maintenance and adoption of the regional and/ or linking components of the drainage system
- who would be responsible for controlling the overall surface water management of the site
- Flow control(s)
- Areas where SuDS will form recreational features and green infrastructure and integration with masterplan
- SuDS/Drainage Strategy Layouts and design calculations demonstrating the compliance with the ‘Sustainable drainage systems: non-statutory technical standards’
- Public health and safety consideration
- Identification of maintenance liabilities
- Ecology and water quality implications
- Where discharge of surface water is to a public sewer a viability assessment is required
- Include consultation with UU and EA where relevant
Due to the nature of outline planning applications and whether or not certain aspects of the proposed development are reserved, the amount of information which would be contained within the drainage strategy (set out above) should be considered to be a minimum.
If the drainage of the site is not reserved (and the layout and landscape design are also not reserved) then the drainage strategy should be more detailed as set out below.
Reserved matters and full applications
If a reserved matters application is being made, the submission on the detailed design and layout of the sustainable drainage system should update and enhance the drainage strategy, taking into account the advice from the council’s Flood Risk Management team, and be submitted as a detailed drainage strategy.
If a full planning application is being made then the submission should be a combination of the information required for an outline application drainage strategy and the following information, to produce a detailed drainage strategy:
- Final design calculations to demonstrate conformity with the design criteria for the site for peak flow, volume control and green field runoff, and/or brownfield runoff where appropriate. Based upon the non-statutory technical standards showing pre-development (greenfield or brownfield as relevant) and post-development runoff rates, critical storm duration and associated storage estimates to determine the scale (and associated land take) of conveyance and storage structures
- Existing and proposed site sections and site levels
- Long sections and cross sections for the proposed drainage system including design levels
- Plan of proposed SuDS with sub-catchment areas including impermeable areas and phasing
- Details of proposed connections to watercourses and sewers including consultation with approving bodies (ie United Utilities, Environment Agency etc)
- Operational characteristics of any mechanical features including maintenance and energy requirements
- Plan demonstrating flooded areas for the 1 in 100 year storm when the system is at capacity and demonstrating flow paths for design for exceedance
- Access arrangements for all proposed SuDS
- Construction details
- Completion of the SuDS Design Statement detailing the following:
- Flood risk outside the development
- Peak flow control
- Volume control
- Flood risk within the development
- Structural integrity
- Maintenance considerations
- Construction phase
SuDS Management Plan: operation and maintenance plan setting minimum standards over the lifetime, integration with green infrastructure, long term funding plan (annual charges and replacement of SuDS);
- Health and safety risk assessment including community engagement and risk management (specifically for water features such as swales, attenuation basins etc)
- Include consultation with United Utilities and Environment Agency where relevant
- For all Major Applications the North West SuDS proforma must be completed and can be used to evidence the requirements of the ‘Sustainable drainage systems: non-statutory technical standards’
- SuDS/Drainage Strategy Layouts and design calculations demonstrating the compliance with the ‘Sustainable drainage systems: non-statutory technical standards’
Useful links