Flood and Water Management / Drainage
Surface Water Drainage and SUDS
Milton Keynes Council is a Lead Local Flood Authority (LLFA) and as such is a statutory consultee to the planning process for surface water on all major developments. The consultation requirement and description of major development is detailed within the Town and Country Planning (Development Management Procedure Order). This applies to all new major planning applications. However it should be noted that Milton Keynes Council may also comment on non-major applications.
In assessing an application, the LLFA and Local Planning Authority will need to be satisfied that:
- Any proposals meet national and local policies;
- The proposed minimum standards of operation are appropriate;
- A minimum standard is set out to which the sustainable drainage systems must be maintained;
- Through the use of planning conditions or planning obligations there are clear arrangements in place for ongoing maintenance over the lifetime of the development, including clearly identifying who will be responsible for maintaining the sustainable drainage systems and that funding for maintenance is fair for householders and premises occupiers
Flood Risk and Surface Water Policy Requirements
Plan:MK (the Local Plan for Milton Keynes) was adopted on 20th March 2019. As outlined in the plan, the early masterplan for Milton Keynes sought to reduce flood risk via the development of an innovative approach to flood risk based on a strategic water management system and planned green infrastructure provision.
However as outlined in the Level 1 Strategic Flood Risk Assessment (2015), there are a number of areas across the Borough at risk of flooding from various sources and it is expected that, even with no further development, the impacts of climate change are likely to increase this risk. It is therefore necessary that a robust and sustainable approach is taken to reducing and mitigating the potential impacts that climate change may have upon the area.
Policies FR1 – FR3 of Plan:MK includes locally specific strategic flood risk management policies to maintain and continue the exemplar sustainable drainage model of Milton Keynes which prohibits development within the floodplain and seeks flood management and drainage infrastructure to be provided as strategically as possible and as part of a maintained, multi-functional blue-green infrastructure. The policies can be seen below:
Policy FR1 - Managing Flood Risk
- All new development must incorporate a surface water drainage system with acceptable flood control and demonstrate that water supply, foul sewerage and sewage treatment capacity is available or can be made available in time to serve the development. Suitable access is safeguarded for the maintenance of water supply and drainage infrastructure.
- Plan:MK will seek to steer all new development towards areas with the lowest probability of flooding. The sequential approach to development, as set out in national guidance, will therefore be applied across the Borough, taking into account all sources of flooding as contained within the Council’s Strategic Flood Risk Assessment (SFRA).
- Development within areas of flood risk from any source of flooding, will only be acceptable if it is clearly demonstrated that it is appropriate at that location, and that there are no suitable available alternative sites at a lower flood risk.
- Development proposed in an area at risk of flooding will be required:
- To be supported by a site specific Flood Risk Assessment (FRA) (subject to the triggers set out below);
- To take into account all forms of flooding including, but not limited to: fluvial, groundwater, surface water and reservoir flooding;
- To ensure that opportunities to reduce the causes and impacts of flooding to the site and the surrounding area are taken as far as possible, in order to improve the existing situation, taking into account climate change. At a minimum, proposals will need to demonstrate no increase in flood risk to the site or surrounding area;
- To clearly demonstrate that the benefits of the development to the community, outweigh the risk of flooding when applying the sequential test and exception test (where required);
- When applying the sequential test, to clearly demonstrate that the impacts of climate change are taken into account;
- To demonstrate the application of a sequential approach to the site design and layout to ensure highest vulnerability land uses are located within areas of the site at lowest risk of flooding;
- To build resilience into a site’s design;
- To ensure that a site's design and any flood mitigation measures implemented are designed with an allowance for climate change and the potential impact it may have over the lifetime of the proposed development(31);
- To provide a safe access and egress route for future users of the development; and
- To attenuate surface water run-off in line with Policy FR2.
- To consult the Fire and Rescue Service as to the feasibility of undertaking rescue and recovery operations during and in the aftermath of flooding events.
- A site specific FRA will be required for:
- All sites of 1ha or more in Flood Zone 1;
- All sites within Flood Zone 2 or 3;
- All sites highlighted as being at high risk from surface water flooding, or which are located within a Critical Drainage Catchment (CDC) (PDF, 1.5MB) as identified in the Milton Keynes Surface Water Management Plan. In this case the FRA will be required to demonstrate that the development will not increase the flood risk to the CDC and where possible will provide an improvement to the existing situation.
- The FRA should include an assessment of flood risk to and from the proposed development, and demonstrate how the development will be safe, will not increase flood risk elsewhere and where possible will reduce flood risk overall in accordance with the NPPF and PPG.
Policy FR2 - Sustainable Drainage Systems (Suds) And Integrated Flood Risk Management
- Plan:MK advocates the continuation of a strategic, integrated approach to managing flood risk which seeks the management of surface water to be planned at the largest appropriate scale for the new development and incorporated into the site at the earliest opportunity in the design process.
- New development is required to incorporate SuDS; in line with national policy and guidance and, which meet the requirements set out in national standards and the Council’s relevant local guidance. It is expected that:
- Flood risk management and SuDS will be provided at a strategic scale and in an integrated manner, wherever possible;
- Space will be specifically set aside for SuDS and fluvial flood risk reduction features and used to inform the overall layout of development sites;
- Above ground attenuation will be provided in preference to below ground attenuation;
- SuDS will be designed as multi-purpose green infrastructure and open space, to maximise additional environmental, biodiversity, social and amenity value, wherever possible. The use of land to provide flood storage capacity should not conflict with required amenity and recreation provision - floodplains and floodplain habitats should be safeguarded;
- SuDS will be designed with an allowance for climate change and the potential impact it may have over the lifetime of the proposed development;
- Proposals for development within Critical Drainage Catchments, as identified in the Milton Keynes Surface Water Management Plan, should investigate the potential for the scheme to reduce or mitigate existing risk in the surrounding area;
- All surface water drainage proposals for new development must include full details of the means of achieving future management, maintenance and adoption of the systems, prior to approval of any planning permission, to ensure that it will function effectively over the lifespan of the development. This will include details of funding and should be formulated through discussion with the relevant responsible bodies, including Milton Keynes Council, The Parks Trust, Anglian Water and the Internal Drainage Board;
- Development will ensure no adverse impact on the functions and setting of a watercourse and its associated corridor;
Development should avoid building over or culverting watercourses, encourage the removal of existing culverts and seek opportunities to create wetlands and wet grasslands and woodlands and restore natural river flows and floodplains.
Policy FR3 - Protecting And Enhancing Watercourses
- All new development must be set back at a distance of at least 8 metres from any main rivers, at least 9 metres from all other ordinary watercourses, or at an appropriate width as agreed by the Environment Agency, Lead Local Flood Authority or Internal Drainage Board, in order to provide an adequate undeveloped buffer zone. Development that restricts future de-culverting of waterways should be avoided.
B. The Council will resist proposals that would adversely affect the natural functioning of main rivers, ordinary watercourses and wet or dry balancing lakes, this includes through the culverting of open channels, unless for access purposes.
Milton Keynes Council has published specific guidance on the preparation of surface water drainage strategies (see below). This provides information on the level of detail we require depending on the type of planning application. The document should be used by all developers and their consultants who wish to submit an application in Milton Keynes. Surface Water Drainage Guidance for Developers July 2019 (PDF, 1.5MB)
Sustainable Drainage Systems (SuDS)
Sustainable Drainage Systems (SuDS) mimic natural drainage to manage surface water run-off from a development. SuDS allow for the collection, storage and treatment of surface water in order to reduce flood risk caused by development. SuDS generally replace traditional underground, piped drainage systems. The aim of SuDS is to keep water on the surface as much as possible. They can integrated into both rural and urban developments.
Benefits of SuDS
- Provides the potential to re-connect societies with water, providing benefits for amenity, health and well-being.
- SuDS can provide new natural habitats, connecting nature and wildlife with urban environments
- Keeping water on the surface allows any problems to be identified and managed quickly. Management of SuDS features can generally be cheaper, less time consuming and more straight-forwards than conventional drainage systems
The documents below provide important information relating to local flood risk across Milton Keynes and these should be reviewed as part of any Flood Risk Assessment / Drainage Strategy.
Last Updated: 12 July 2019