Cumnor Neighbourhood Plan

Policy RNE2: Flood Risk

  1. The Neighbourhood Plan identifies a zone of potential groundwater flooding, shown on Map 14 and on the Policies Map, as an additional evidential basis for applying national decision-making policy on the sequential test and for ensuring development is safe from flooding. Development proposals should be located and designed to take account of flood risk. Particular attention should be given to potential flood risk impacts in the following wards:
  • Farmoor (as shown on maps 14 and 15);
  • Cumnor Hill (as shown on map 15); and
  • Dean Court area (as shown on map 15)
  1. Inappropriate development in areas at risk of flooding will not be supported unless the exception tests in paragraph 159 of the NPPF are met. Where development is necessary in such areas, the development should be made safe for its lifetime without increasing flood risk elsewhere. For the purposes of applying national decision-making policy on ensuring development is safe from flooding development proposals located within the zone of potential groundwater flooding will be required to undertake a rigorous groundwater assessment to confirm groundwater conditions beneath the proposed development. Where proposals include excavation, the assessment should include:
  1. a minimum of 3 groundwater monitoring boreholes within the planning application boundary to confirm groundwater depths and establish groundwater flow directions;
  2. a minimum of 3 to 6 months of groundwater level monitoring, preferably monitoring annual seasonal groundwater fluctuations during the dry and wet season. Where project lead-in times allow, groundwater monitoring should be repeated over multiple years to confirm seasonal groundwater level fluctuations;
  3. groundwater monitoring information can be augmented or replaced by local Environmental Agency groundwater level monitoring information if found to exist; and
  4. an assessment of any post-construction groundwater flow truncation and subsequent groundwater rise effects should be evaluated and mitigation measures proposed if necessary, to prevent flooding or damage to adjacent properties.
  1. Development proposals should take account of impacts in terms of runoff generation and surface water drainage and should provide the required mitigation measures to ensure that there is no unacceptable increase in surface water discharge off site. For the purposes of applying national-decision making policy on sustainable drainage systems (SuDS), using infiltration-based SuDS in Cumnor Parish may be inappropriate in areas underlain by permeable strata located close to “contact springs” along the Oxford Clay boundary, shown on Map 14, as this could increase groundwater or surface water emergency downslope. Proposals will therefore be required to demonstrate that the following actions have been taken prior to choosing, designing and sizing SuDS or other drainage systems:
  1. estimating runoff generated within (and/or flowing into) the proposed development;
  2. excavating trial pits to gain information regarding soils and geological (superficial and bedrock)( layers underlying the site;
  3. assessing the ground infiltration capacity by undertaking ground permeability tests (using the excavated trial pits; and
  4. understanding the hydrogeological (groundwater) regime within and around the site area.
  1. Where it is appropriate to do so new developments should incorporate Sustainable Drainage Systems The Neighbourhood Plan identifies land used for water storage and/or flood risk management, as shown on the Policies Map, for the purposes of applying national-decision making policies on the principle of development within settlements, the control of development in the Green Belt and development which is not inappropriate development in the Green Belt.
  2. As appropriate to their scale, nature and location sustainable drainage should be suitably designed to ensure that discharge rates do not exceed greenfield rates with systems designed to add to the area’s biodiversity. Systems should be designed with full consideration for future maintenance.
Policies Map
  1. The policy recognises national decision-making policies on the sequential test (Provision F5) and for ensuring development is safe from flooding (Provision F7) in the NPPF and highlights that the Filchampstead area is unlikely to be suitable for new development. Other areas with significant flood risk are identified. identifies that there is updated evidence at a deeper level of detail than the Strategic Flood Risk Assessment (SFRA) published in the evidence base alongside this Plan titled Updated Flood Risk Assessment for Cumnor Parish April 2026 by GWP Consultants. The SFRA and Flood Map for Planning identifies fluvial, pluvial and reservoir flooding not necessary to duplicate at the Neighbourhood Plan level.
  2. National decision-making policy F5 The sequential test currently states:
    “1. The aim of the sequential test is to steer new development to areas with the lowest risk of flooding from any source. Where the test applies, development proposals should not be located in areas at risk of flooding where alternative sites, appropriate for the development, are reasonably available in areas with a lower risk of flooding. The area to which the test is applied should not be greater than the anticipated catchment of the development in terms of its likely occupiers or users. The sequential test should be used in areas known to be at risk now or in the future from any form of flooding, other than for:
    a. Sites allocated in the development plan which were subject to the sequential test during plan preparation;
    b. Sites where a site-specific flood risk assessment demonstrates clearly that:
    i. no built development within the site boundary, including access or escape routes, land raising or other potentially vulnerable elements, would be located on an area that would be at risk of flooding from any source, now and in the future (having regard to potential changes in flood risk); or
    ii. where the site would be at risk of surface water flooding only, the proposed layout, design, and mitigation measures would ensure that occupiers and users would remain safe from current and future surface water flood risk for the lifetime of the development without increasing flood risk elsewhere in accordance with policy F7.
    c. For the following types of development:
    i. householder development;
    ii. small non-residential extensions (with a footprint of less than 250m2); and
    iii. changes of use, other than changes of use to a caravan, camping or chalet site, or to a mobile home or park home site. The strategic flood risk assessment covering the area of the proposed development and the Flood Map for Planning should provide the evidential basis for applying the sequential test.”
  3. National decision-making policy F7 Ensuring development is safe from flooding currently states:
    “1. Development proposals should not present a risk from flooding to potential occupiers, users, or visitors, and should not increase flood risk elsewhere. Where development is proposed in a location known to be at risk from any form of flooding, now or in the future, it should be refused unless:
    a. Within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons which justify a different arrangement;
    b. The development will be safe throughout its lifetime taking account of the vulnerability of its users;
    c. Any residual risk can be safely managed, and safe access and escape routes are included where appropriate, as part of an agreed emergency plan;
    d. The development is appropriately flood resistant and resilient such that, in the event of a flood, it could be quickly brought back into use without significant refurbishment; and
    e. It can be demonstrated that flood risk will not be increased elsewhere.”
    (which reflects paras. 170 – 182 of the 2024 NPPF).
  4. The policy clarifies at a local level that there is the potential for groundwater flood risk and defines the area where this is relevant as the zone of potential groundwater flooding on the Policies Map, requires requiring groundwater flood risk to be assessed and to be reflected in the location and design of new development, including mitigation measures.
  5. The policy also provides further local level detail using the updated evidence which demonstrates that there is a need to scrutinise the types of SuDS being proposed in Cumnor Parish for the purpose of applying national decision-making policy F8 Sustainable drainage systems and watercourses which currently state: “1. Development proposals which could affect drainage on or around the development site should incorporate sustainable drainage systems to control flow rates and reduce volumes of runoff, in ways which are proportionate to the nature and scale of the proposal. The systems employed should provide multifunctional benefits wherever possible, facilitating improvements in water quality, biodiversity and amenity. 2. Sustainable Drainage Systems should: a. Be designed in accordance with the National Standards for Sustainable Drainage Systems67; b. Have maintenance arrangements in place to ensure an acceptable standard of operation for the anticipated lifetime of the development; and c. In the case of proposals for major development, take account of advice from the Lead Local Flood Authority. 3. Development proposals should not enclose existing watercourses where this is not already the case, unless there are compelling reasons to do so; and should where possible remove existing culverts and re-naturalise existing river channels, unless to do so would increase flood risk or result in other environmental harm. 67 National standards for sustainable drainage systems (SuDS) – GOV.UK.” (which reflects para. 182 of the 2024 NPPF).
  6. Finally, the policy identifies areas of land is particularly important for water storage and/or flood risk management on the Policies Map so that any future proposal/s can either avoid the whole or partial loss of undeveloped land in these areas or ensure that suitable compensatory provision is made which does not increase the risk of flooding either on or off-site as set out by the relevant national decision-making policies (Provision S4, GB6 and GB7). National decision-making policies S4 Principle of development within settlements, GB6 Control of development in the Green Belt, and GB7 Development which is not inappropriate in the Green Belt currently state: “S4: Principle of development within settlements 1. Development proposals within settlements should be approved unless the benefits of doing so would be substantially outweighed by any adverse effects, when assessed against the national decision-making policies in this Framework. 2. In applying policy S4, the circumstances in which the benefits of approving development are likely to be substantially outweighed by adverse effects include (but are not restricted to) situations where the development proposal would: a. Have an unacceptable impact in relation to: i. the allocation or safeguarding of land for particular uses in the development plan, unless there is no reasonable prospect of an application coming forward for the allocated use, or there is evidence that the safeguarding is no longer appropriate; or  ii. the application of the policies in this Framework for safeguarding existing open space, sport and recreation facilities (HC7), Local Green Space (HC8), designated wildlife habitats (N6) and for managing development within residential curtilages (L2); or  b. Involve the whole or partial loss of undeveloped land which is used for a cemetery or burial ground; or for water storage and/or flood risk management (unless suitable compensatory provision is made which does not increase the risk of flooding either on or off-site); or c. Fail to comply with one of the national decision-making policies which state that development proposals should be refused in specific circumstances.” (which reflects paras. 154 and 181 of the 2024 NPPF).“GB6: Control of development in the Green Belt 1. Development in the Green Belt is inappropriate unless it falls within one of the categories in policy GB7. 2. Inappropriate development is, by definition, harmful to the Green Belt and should not be approved except in very special circumstances. Such circumstances will not exist unless the potential harm to the Green Belt by reason of inappropriateness and any other harm resulting from the proposed development, is clearly outweighed by other considerations. In making this assessment, substantial weight should be given to the harm to the Green Belt which would be caused, including harm to its openness. 3. In the case of proposals for renewable and low carbon energy development, very special circumstances may include the wider environmental benefits associated with increased production of energy from renewable sources.” (which reflects para. 153 of the 2024 NPPF).“GB7: Development which is not inappropriate in the Green Belt 1. The following categories of development are not inappropriate in the Green Belt, and therefore should not be regarded as harmful to the Green Belt or required to demonstrate very special circumstances: a. Development which is for agriculture, horticulture and forestry;  b. The re-use, extension, alteration or replacement of an existing building, provided that: i. the existing building is of permanent and substantial construction; and ii. the extension or alteration will not result in a disproportionate increase in size over and above the size of the original building49; or iii. in the case of proposals for a replacement building, it is in the same use and not materially larger than the one it replaces. c. Limited infilling in villages; d. Limited affordable housing for local community needs under policies set out in this Framework or the development plan (for instance, on a rural exception site);  e. The redevelopment of previously developed land (including a material change of use to residential or mixed-use including residential), which would not cause substantial harm to the openness of the Green Belt; f. Certain other forms of development provided the impact on the openness of the Green Belt is minimised, and there would not be a significant conflict with the Green Belt purposes. These are:  i. mineral extraction; ii. engineering operations; iii. transport, electricity network and water infrastructure required in a Green Belt location; iv. development brought forward under a Community Right to Build Order or Neighbourhood Development Order;  v. material changes in the use of land (such as changes of use for outdoor sport or recreation, or for cemeteries and burial grounds); and vi. the provision of appropriate facilities (in connection with the existing use of land or a change of use), including buildings, for outdoor sport, outdoor recreation, cemeteries and burial grounds and allotments. g. Development where all of the following apply: i. the development would utilise grey belt land and would not fundamentally undermine the purposes (taken together) of the remaining Green Belt across the area of the plan; ii. there is an evidenced unmet need for the type of development proposed50;  iii. the development would be in a sustainable location, with particular reference to policy TR3 of this Framework51; and iv. In the case of major development involving the provision of housing, the development proposed complies with policy GB8;  h. Development for housing and mixed-use development which would:  i. be within reasonable walking distance of a railway station capable of providing a high level of connectivity to services and employment52;  be physically well-related to a railway station or a settlement within which the station is located;  iii. be of a scale which can be accommodated taking into account the existing or proposed availability of infrastructure;  iv. not prejudice any proposals for long-term comprehensive development in the same location;  v. in the case of major development, comply with policy GB8. 49The original building for this purpose is the building that existed on 1 July 1948 or, if constructed after 1 July 1948, as it was built originally. 50Which, in the case of applications involving the provision of housing, means the lack of a five year supply of deliverable housing sites, including the relevant buffer where applicable, or where the Housing Delivery Tests was below 75% of the housing requirement over the previous three years; and in the case of traveller sites means the lack of a five year supply of deliverable traveller sites. 51In the case of development proposals involving the provision of traveller sites, particular reference should be made to policy HO12. 52Well-connected rail stations and underground, tram and light rail stops are those in a top 60 Travel to Work Area located partially or fully within England by Gross Value Added (GVA) and which, in the normal weekday timetable, are served (or have a reasonable prospect of being served due to planned upgrades or through agreement with the rail operator) throughout the daytime by four trains or trams per hour overall, or two trains per hour in any one direction.” (which is also reflects paras. 154 and 155 of the 2024 NPPF although it is noted that the provision for development around train stations is new).
  7. Planning applications will need to be accompanied by sufficient materials to demonstrate how flood risk has been considered, including details of monitoring that has been carried out to inform the development scheme. Groundwater and surface water flood risk must be assessed. In areas where groundwater surface flooding risk exists (Map 15 and see para 105) or in other areas outside of the LIDAR coverage where groundwater flooding is considered at potentially high risk, the following actions are recommended and should be considered in the Design and Access Statement for major development or other accompanying technical report:
  1. A minimum of 3 groundwater monitoring boreholes within the planning application boundary to confirm groundwater depths and establish groundwater flow directions;
  2. A minimum of 3 to 6 months of groundwater level monitoring, preferably monitoring annual seasonal groundwater fluctuations during the dry and wet season. Where project lead-in times allow, groundwater monitoring should be repeated over multiple years to confirm seasonal groundwater level fluctuations;
  3. Groundwater monitoring information can be augmented or replaced by local Environmental Agency groundwater level monitoring information if found to exist;
  4. Groundwater monitoring information should be used to investigate whether or not maximum groundwater levels will come into contact with the proposed development. If so, dewatering requirements during the construction phase should be evaluated and an impact assessment undertaken on local houses, including identification of any necessary mitigation measures; and
  5. Furthermore, an assessment of any post-construction groundwater flow truncation and subsequent groundwater rise effects should be evaluated and mitigation measures proposed if necessary, to prevent flooding or damage to adjacent properties.
Previous Policy
Back to all policies
Next Policy