15 Flood risk and water management

15.1 National Planning Policy Framework (NPPF) sets out clear requirements that flood risk should be taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding and direct development away from areas at highest risk. It is also becoming increasingly important to consider flood risk from all sources. These include groundwater, land drainage, sewerage, and other artificial sources e.g. reservoirs and canals.

15.2 The policies in this section seek to direct development to areas at low risk of flooding and actively manage and reduce flood risk. The policies also seek to promote water efficiency measures and protect and enhance water quality. In Cheshire West and Chester there are many different types of flood risk present. Flood risk predominantly arises from fluvial (rivers and watercourses) and tidal (sea and estuarial) sources. The Strategic Flood Risk Assessments (SFRA) and the Environment Agency Flood Map for Planning show flooding from these sources.

15.3 Cheshire West and Chester is the designated Lead Local Flood Authority under the provisions of the Flood and Water Management Act and therefore must contribute to the achievement of sustainable development when carrying out flood risk management functions and has a duty to deal with enquiries and determine watercourse consents. The Council will be introducing a set of Land Drainage Byelaws for the borough which will control a range of activities in and around watercourses that may impact on flood risk. The purpose of these Byelaws is to strengthen the enforcement and consenting powers within the Land Drainage Act 1991 to provide effective flood risk action at the local level.

15.4 The Council will continue to work with the water utility companies serving the borough to ensure that there is adequate wastewater infrastructure and water supply capacity to serve proposed development.

DM 40 - Development and flood risk

Policy DM 40

In line with Local Plan (Part One) policy ENV 1, flood risk must be avoided or reduced by:

locating development within areas of lower flood risk through the application of a borough-wide sequential test and then, where required, applying the exception test in line with the National Planning Policy Framework; and
ensuring development proposals in flood risk areas are actively managed and reduce flood risk by applying the sequential approach at site level.

Where a site specific Flood Risk Assessment is required in line with the National Planning Policy Framework (NPPF)(National Planning Policy Framework - Footnote 20) a site-specific flood risk assessment is required for proposals of one hectare or greater in Flood Zone 1; all proposals for new development (including minor development and change of use) in Flood Zones 2 and 3, or in an area within Flood Zone 1 which has critical drainage problems (as notified to the local planning authority by the Environment Agency); and where proposed development or a change of use to a more vulnerable class may be subject to other sources of flooding., this will be expected to demonstrate whether a proposed development is likely to be affected by current or future flooding (including effects of climate change) from any source.

Development proposals for sites that are at risk will only be supported where the site-specific Flood Risk Assessment shows that:

the effects of climate change have been taken into account;
there is no loss in floodplain storage resulting from the development;
the development will not increase flood risk elsewhere;
there is no adverse effect on the operational functions of any existing flood defence infrastructure;
proposed resistance / resilience measures designed to deal with current and future risks are appropriate;
where applicable, appropriate Sustainable Drainage System (SuDS) techniques have been considered and are to be incorporated into the design of the site, in line with Local Plan (Part Two) policy DM 41; and
the development will be safe and pass the exceptions test, if applicable.

A Flood Risk Assessment will be required for development within a Critical Drainage Area (CDA) as notified by the Environment Agency. All development in a designated CDA will be required to incorporate measures to alleviate surface water flood risk through the layout and form of the development, including the appropriate application of SuDS to intercept and attenuate overland flow and drained water in line with Local Plan (Part Two) policy DM 41 and the Council's Draft SuDS Design and Technical Guidance.

Flood risk should be considered at an early stage in deciding the layout and design of a site to provide an opportunity to reduce flood risk within the development. Applicants will be required to provide schemes to reduce flood risk on individual sites through flood resilient design and on site flood risk management measures. It is essential that the scheme proposed does not create any additional flood risk outside the development in any part of the catchment, either upstream or downstream.

Existing structures and other features that help to reduce the risk of flooding or mitigate its impacts should be protected. Their loss, alteration or replacement will only be permitted where there would be no increase in flood risk.

Where appropriate, the Council may request that phasing of development should be carried out to avoid any cumulative impacts of flood risk.

Explanation

15.5 Local Plan (Part One) policy ENV 1 seeks to reduce flood risk and avoid inappropriate development in areas at risk of flooding by directing development away from areas at high risk. Development in Flood Zone 3b will not be permitted unless in exceptional circumstances such as for essential infrastructure or where development is water compatible.

15.6 Development proposals in areas at risk of flooding will only be supported where consideration has been given to the NPPF and Flood Risk and Climate Change Planning Practice Guidance and the Council's Strategic Flood Risk Assessment (SFRA) together with appropriate consultation with the Lead Local Flood Authority, the Environment Agency/Natural Resources Wales and the water companies, where applicable.

15.7 The objectives of a site-specific Flood Risk Assessment are to establish whether a proposed development is likely to be affected by current or future flooding (including effects of climate change) from any source. This should include referencing the SFRA to establish sources of flooding. Flood Risk Assessments will be used to improve the understanding of flood risk associated with a development proposal including whether the measures proposed to deal with any effects and risks are appropriate; providing the evidence for the local planning authority to apply the sequential test (if necessary) and to demonstrate that the development will be safe and pass the exception test, if applicable.

15.8 Climate change will increase flood risk over the lifetime of a development. In making an assessment of the impacts of climate change on flooding from the land and rivers as part of a Flood Risk Assessment, the sensitivity ranges shown in the SFRA should be considered which provide an appropriate precautionary response to the uncertainty about climate change impacts on rainfall intensities and river flow.

15.9 The Environment Agency revised the climate change allowances in February 2016, for use in Flood Risk Assessments. The Council's SFRA was updated accordingly. The allowances in the Council's SFRA and any subsequent revisions should be used when submitting details within a Flood Risk Assessment.

15.10 Considering the impacts of climate change within a Flood Risk Assessment will have implications for both the building type and design that is appropriate according to its vulnerability to flooding, finished floor levels and design standards for any SuDS or mitigation schemes proposed. Residential development may not be appropriate without suitable flood mitigation measures or flood resilient or resistant houses.

15.11 As the Lead Local Flood Authority (LLFA), the Council is responsible for developing, maintaining, applying and monitoring a Local Flood Risk Management Strategy (LFRMS). The strategy addresses flooding from surface runoff, groundwater and ordinary watercourses. Developers should consult the LFRMS and its supporting documents and be aware of the overall aims of managing and mitigating flood risk in Cheshire West and Chester and the wider implications of any new development on the surrounding area.

15.12 New development will be required to include or contribute to flood mitigation, compensation and/or protection measures where this is necessary to manage flood risk associated with or caused by the development.

15.13 The SFRA identifies a number of sites where a review of the site layout and/or design at the development planning stage is recommended in order for development to proceed. For these sites, a Level 2 SFRA or site-specific Flood Risk Assessment would be required to inform the site layout and design. Any site layout and design should take account of the eight metre easement buffer along watercourses where development is not permitted. This easement buffer is recommended by the Environment Agency to allow ease of access to watercourses for maintenance works. Any site redesign, where Flood Zone 3a is included within the site footprint, should allow water to flow naturally or be stored in times of flood through application of suitable SuDS.

15.14 Using a phased approach to development, should ensure that any sites at risk of causing flooding to other sites are developed first in order to ensure flood storage measures are in place before other sites are developed, thus ensuring a sustainable approach to site development. It may be possible that flood mitigation measures put in place at sites upstream could alleviate flooding at downstream or nearby sites.

15.15 The SFRA identifies indicative Areas of Critical Drainage (ACDs) across the borough for large sites and for areas where surface water flooding is considered significant. A formal CDA designation, following on from the indicative ACDs proposed in the SFRA can be formally designated and notified to the local authority by the Environment Agency.

DM 41 - Sustainable Drainage Systems (SuDS)

Policy DM 41

In line with Local Plan (Part One) policy ENV 1, proposals for major development will be required to incorporate Sustainable Drainage Systems (SuDS).

SuDS must be included in the early stages of the site design in order to incorporate appropriate SuDS within the development. SuDs schemes will be required to satisfy technical standards and design requirements having regard to the Council's Draft SuDS Design and Technical Guidance.

On greenfield sites, restrictions on surface water runoff from new development should be incorporated into the development at the planning stage and must mimic or improve upon greenfield rates. On brownfield sites, site runoff rates should be reduced to the greenfield rates wherever possible. Where this cannot be achieved a reduction of at least 30 per cent of the actual existing runoff must be provided, unless it can be demonstrated that this is unachievable or hydraulically impractical to do so.

Explanation

15.16 Local Plan (Part One) policy ENV 1 requires the drainage of new development to be designed to reduce surface water run-off rates and include the implementation of SuDS. Managing surface water discharges from new development is crucial in managing and reducing flood risk to new and existing development downstream. Carefully planned development can also play a role in reducing the amount of properties that are directly at risk from surface water flooding and provide opportunities to enhance biodiversity in line with Local Plan (Part Two) policy DM 44.

15.17 Development has the potential to cause an increase in the impermeable area, an associated increase in surface water runoff rates and volumes, and consequently a potential increase in downstream flood risk due to overloading of sewers, watercourses, culverts and other drainage infrastructure.

15.18 Changes to planning legislation give provisions for applications for major development to require sustainable drainage within the development proposals in accordance with the interim national standards published in April 2015.

15.19 The NPPF continues to reinforce how planning applications that fail to deliver SuDS above conventional drainage techniques could be rejected. Sustainable drainage should form part of integrated design secured by detailed planning conditions so that the SuDS to be constructed must be maintained to a minimum level of effectiveness. Maintenance options must clearly identify who will be responsible for SuDS maintenance. Funding for maintenance should be fair for householders and premises occupiers and set out a minimum standard to which the SuDS must be maintained.

15.20 The runoff destination should always be the first consideration when taking into account design criteria for SuDS including the following possible destinations in order of preference:

to ground;
to surface water body;
to surface water sewer;
to combined sewer.

15.21 Effects on water quality should also be investigated when considering the runoff destination in terms of the potential hazards arising from development and the sensitivity of the runoff destination. Developers should also establish that proposed outfalls are hydraulically capable of accepting the runoff from SuDS.

15.22 It is important to understand the location and capacity of existing drainage to determine what infrastructure could or should be reused in a SuDS scheme. When building on brownfield or pre-developed sites, existing on-site infrastructure should be documented and mapped.

15.23 Determining hydraulic impracticability may look at issues such as whether surface water flows are reduced to such a level over parts of the site as to be at risk of blockages, or where there would be a requirement to install pumps in order to pump water out of SuDS systems in a location where the downstream catchment is not at risk of flooding.

15.24 The CIRIA has produced a number of guidance documents relating to SuDS that should be consulted alongside the Council's Draft SuDS Design and Technical Guidance which provides guidance on:

the SuDS approval process
design considerations
the suitability of SuDS within Cheshire West and Chester
SuDS maintenance.

15.25 Above ground runoff attenuation for flood risk alleviation is always considered preferential to underground storage – in accordance with the latest SuDS treatment train approach (Ciria C753, 2015).

DM 42 - Flood water storage

Policy DM 42

In line with Local Plan (Part One) policies ENV 1 and ENV 3, development within or adjacent to* a flood water storage area, as defined on the policies map, which would have a negative impact on its function will not be supported.

As the Lead Local Flood Authority the Council, in partnership with the Environment Agency, may identify additional areas for flood water storage through the Local Flood Risk Management Strategy. If needed, these additional areas will be safeguarded as part of a review of the Local Plan.

*adjacent means within eight metres of the boundary of the flood water storage area as defined on the policies map or within eight metres of the landward toe of any associated flood defence structure.

Explanation

15.26 Under both the Water Resources Act (1991) and Flood and Water Management Act (2010) the Environment Agency and Lead Local Flood Authority (LLFA) has permissive powers to manage flood risk. This can involve constructing flood defences or holding flood waters in specific locations, to reduce the risk of flooding elsewhere. One such location is Finchett's Gutter, where there is flood risk due to fluvial/ tidal interaction at the confluence of Finchett’s Gutter and the sea. A scheme has been designed that allows Sealand Basin to flood, should the outlet of Finchett's Gutter become constrained at high tides. Maintaining the full, unimpeded capacity for the storage of floodwaters on any site is key, and it is for this reason that a location is designated.

DM 43 - Water quality, supply and treatment

Policy DM 43

In line with Local Plan (Part One) policies ENV 1, ENV 4 and SOC 5, development proposals will be supported where it can be demonstrated that the proposal will not cause unacceptable deterioration to water quality or have an unacceptable impact on water quantity (including drinking water supplies) or waste water infrastructure capacity by ensuring that:

sufficient water resources are available and the proposal does not have a detrimental impact on the flow or quantity of groundwater;
development does not affect the water quality of surface or groundwater;
development does not cause unacceptable harm to biodiversity;.
opportunities to improve water quality are used where possible;
water efficiency methods are optimised;
wastewater infrastructure already exists or can be provided in time to serve the development. Development should connect to the nearest point of adequate capacity.

The discharge of surface water to combined drainage systems will be regulated in accordance with requirements set by the relevant utility provider.

The Council will support the development or expansion of infrastructure associated with water supply, surface water drainage and wastewater treatment facilities where proposals are consistent with other relevant development plan policies such as the development strategy (including development in the Green Belt), flood risk, contamination, health and wellbeing and protection of the natural and built environment.

Explanation

15.27 Local Plan (Part One) policy ENV 1 seeks to ensure that development proposals comply with the Water Framework Directive in relation to water quality. Development proposals should demonstrate that there is adequate wastewater infrastructure and water supply capacity to serve the development or adequate provision can be made available.

15.28 Local Plan (Part One) policy SOC 5 also seeks to ensure that development which gives rise to significant adverse impacts on health and quality of life, including water quality and quantity water will not be allowed. Local Plan (Part One) policy ENV 4 seeks to safeguard and enhance biodiversity through the identification and protection of sites and/or features of international, national and local importance. The Council will need to be satisfied that the implementation of proposals will not have an unacceptable impact on these environmentally sensitive areas.

15.29 Local Plan (Part One) policy STRAT 11 supports the timely provision of additional facilities, services and infrastructure to meet identified needs, whether arising from new developments or existing community need, in locations that are appropriate and accessible. Shortages and gaps in capacity may affect the timing, delivery and design of development. Water supplies are limited and sewerage capacity varies locally. Adequate water supply, surface water and foul water drainage and sewage treatment capacity must be available to serve all new development. This is in addition to the supply and infrastructure capacity for existing development.

15.30 Improving water quality provides a better quality environment for and opportunities to enhance biodiversity; it will also help to maintain a good quality supply of drinking water and meet the requirements of the EU Water Framework Directive (2000/60/EC). This requires member states to prevent deterioration of all water bodies (groundwater and surface waters) and to improve them with the aim to meet ‘good status’ or ‘good ecological potential’ by 2027.

15.31 There are a number of Source Protection Zones (SPZ) in the borough, these are areas of groundwater storage or areas of extraction where the risk to groundwater quality may need to be considered. When assessing proposals for development, reference should be made to the Environment Agency’s Groundwater Source Protection Zones Map:
http://apps.environment-agency.gov.uk/wiyby/37833.aspx together with the Environment Agency’s Groundwater Protection guidance documents to ensure any impact of development on groundwater quality in the area is managed. These guidance documents can be found at:
https://www.gov.uk/government/collections/groundwater-protection

15.32 If a developer wishes to develop sites within a source protection zone they must demonstrate that there will be no risk to the source during construction or post-construction stages.

15.33 Developments in these zones will be subject to consultation with the Environment Agency, which will require evidence that the proposals will not put the source at risk. Developments within ‘Inner Protection Zones’ will be subject to the most rigorous scrutiny: certain types of development will be restricted, and significant mitigation measures are likely to be required. Outside of the inner zones development proposals will also be examined in detail but the restrictions and mitigation requirements will be less stringent.

15.34 The use of infiltration drainage as part of SuDS systems is also likely to be restricted by the presence of a source protection zone.

15.35 For some development sites, there will be a requirement for developers to contribute to the provision of off-site sewers to connect sites to the existing network and, dependant on the scale and density of the developments, for a hydraulic modelling assessment (HMA) of the network to be undertaken at the developers expense to establish adequate connection points and/or any network improvements are required. Network reinforcement works or specific improvements to a WwTW, where required in order to bring a development site forward and not included in the Asset Management Plan, will be secured by an appropriate planning condition or legal agreement.

15.36 Large scale schemes may have a major impact on infrastructure capacity, whereas smaller schemes can cumulatively have the same effect. All developers are therefore encouraged to liaise with the relevant water supply company as early as possible before submitting a planning application to establish:

the water supply infrastructure demand of the development both on and off site and whether this can be met;
the wastewater infrastructure demand of the development both on and off site and whether this can be met; and
the surface water drainage requirements and flood risk of the development both on and off site.

15.37 In some circumstances a study may be required to ascertain whether the proposed development would lead to an unacceptable overloading of existing infrastructure. Where there is an identified capacity problem, the Council may require the developer to fund appropriate improvements, which must be completed prior to occupation of the development.

Site under construction

15 Flood risk and water management