1 Introduction
1.1 The Minimum Development Control Standards for Flood Risk (MDCSFR) sets out the basic design principles, requirements, and mitigation measures in relation to Flood Risk and Surface Water drainage associated with planning applications within the Leeds City Council boundary.
1.2 This document should be read in conjunction with any additional requirements as required by other Stakeholders e.g. Environment Agency, Yorkshire Water and Ainsty Internal Drainage Board.
1.3 This document is a live document and will be reviewed and, where necessary, revised as required by National and Local policy changes and any other requirements.
1.4 This document is supported by adopted policies in the Leeds Local Plan and also by emerging policy in the Local Plan Update. Where the document is supported by emerging policy, applicants are encouraged to comply with the principle as best practice but this will not be a firm requirement until the policy has been formally adopted.
1.5 To aid users, the MDCSFR includes Informative Notes which provide additional advice relevant to the discussion at their location.
1.6 Where clarification or additional information is required, then users are recommended to contact Leeds C.C. FRM Development Control at
FRM@leeds.gov.uk.
1.7 The design of all Major development drainage systems shall be based on incorporating Sustainable Drainage Systems (SUDS) where possible, unless demonstrable as not viable, as required by current National Policies and guidelines.
1.8 This document should be read in conjunction with the
Leeds FRM Validation Requirements for Flood Risk & Surface Water Drainage. This document sets out the specific level of information required to be submitted for each type of planning application.
1.9 Where a non-compliant SUDS orientated site layout and subsequent surface water drainage design cannot comply with Paragraphs 167 and 169 of the NPPF, then a full justification statement shall be provided to demonstrate why it is not appropriate.
2 Classification of development
2.1 Major Development is defined as follows:
- a) 10 dwellings or more
- b) Non-residential development where the floor space to be created by the development is 1,000 square metres or more
- c) Gypsy – Traveller’s site with 10 or more pitches
- d) Any other development carried out on a site having an area of 1 hectare or more
2.2 Minor Development is defined as follows:
- a) 1-9 dwellings (less than 0.5 hectares (ha))
- b) Non-residential development where the floor space to be created by the development is less than 1,000 square metres (m2)
- c) Gypsy – Traveller’s site between 0 to 9 pitches
- d) Any other development carried out on a site having an area of less than 1 hectare
3.1 For these applications where the site layout is unlikely to be fixed, it will be necessary to provide details of a viable and deliverable surface water drainage strategy. Typically, the applicant will have determined the means and point of discharge, the post development discharge rate, and how any attenuation will be provided. SUDS should be used wherever possible and a description of the techniques to be utilised should be set out so that the future site layout can incorporate these into the final layout.
3.2 As required by Policy Water 6 and the NPPF, a site-specific Flood Risk Assessment (FRA) shall be provided for the following:
- a) All development in Flood Zones 2 and 3
- b) Sites of greater than 1 hectare in Flood Zone 1
- c) Land which has been identified by the Environment Agency as having critical drainage problems. Note - there are no defined Critical Drainage Areas within the Leeds Boundary
- d) Land identified in the Leeds Strategic Flood Risk Assessment as being at increased flood risk in future
- e) Land that may be subject to other sources of flooding (i.e. surface water flooding), where its development would introduce a more vulnerable use
3.3 For householder development and small non-residential extensions, falling within any of the above criteria which is less than 250m2, then a Flood Risk Statement complying with the GOV.UK standing advice can be submitted in lieu of a full Flood Risk Assessment.
3.4 The Flood Risk Assessment shall undertake a full evaluation of the flood risks and set out the proposed mitigation measures. In relation to main river, and where relevant, hydraulic modelling maybe required. In these instances, the modelling scope and any suggested mitigation measures must be agreed with the Environment Agency. For all schemes within Flood Zone 2 and, 3 early consultations with the Environment Agency is recommended.
Informative Note 1 – As the detailed site layout may not have been established at this stage, then unlikely to be possible to include a detailed drainage design. Therefore, for Outline Applications the drainage design is likely to be conditioned, with the full drainage design to be submitted at the Reserved Matters, Full, or Condition Discharge Application Stage.
Informative Note 2 – Where infiltration is the proposed drainage design solution either in part or in full for dealing with the surface water run off, then unless site specific permeability testing to BRE 365 has been undertaken to demonstrate that infiltration is viable, then an alternative compliant drainage strategy shall be set out. This must include details of the agreed post development discharge rate and the point of disposal off site.
Full planning applications
3.5 It is now not acceptable to leave the details of the drainage design, including details of the proposed SUDS measures, to a future planning condition. Therefore, it is now a necessary requirement to provide the full drainage design, supporting calculations and investigations to demonstrate that the proposed development will comply with the current Leeds CC Minimum Development Control Standards for Flood Risk.
3.6 For Major developments, a Flood Risk Assessment, Drainage and SUDS Assessment will be required to be submitted to support any future Outline or Full planning application.
3.7 For a full list of the exact details of documents to be submitted with an Outline, Full, Reserved Matters or Condition Discharge planning application, please refer to
Leeds C.C.FRM Validation Requirements.
Section 3 Policy/Guidance position.
Local Plan adopted Core Strategy policy EN5 and Natural Resources and Waste Local Plan Policy Water 6.
Local Plan Update emerging policy Water 6 and Water 6A
WYCA Sustainable Drainage Systems Guidance
4 Establishing post development run off rates and points of discharge
4.1 To determine a sustainable post development surface water discharge rate, it is essential to establish the site’s existing drainage mechanism and where (if any) the positive drainage connections serving the existing site are located.
Informative Note 3 – Where a drainage connection is to be made either to a watercourse or a privately owned sewer outside of the land owned by the applicant, it will be essential to obtain agreement with the landowner to lay an off-site sewer and also the riparian owner of any such receiving watercourse or sewer to accept the proposed discharge rate. Written confirmation as to the above two elements shall be submitted and included within the site-specific Drainage Assessment.
Greenfield sites
4.2 For greenfield sites, the pre-development greenfield run off rate must be calculated only from the post development impermeable and drained areas and NOT the whole site.
4.3 To support any existing site run-off assessment, a topographic survey shall be provided demonstrating the receiving catchments and discharge locations (i.e. watercourse or off-site sewer connection).
4.4 The assessment of pre-development greenfield run off shall be based on either the IH 124, ICP SUDS or FEH 2013 method.
4.5 For sites less than 1 ha, then a maximum allowable discharge rate of 3.5 l/s shall be applied for all storms up to the 1% AEP (1 in 100) + CC storm event. For larger sites, the above criteria can be adopted.
4.6 For all Major development, to minimise any increase in flood volumes off site, the peak flow rate shall be capped at Qbar to conform to the requirement for no increase of the 1% AEP (100 year) 6-hour event volume.
4.7 If there are existing downstream flood risk constrictions, concerns, or reported incidents, then FRM retains the right to request additional downstream improvements within the application boundary.
Brownfield sites
4.8 For brownfield sites a drainage survey will be required to demonstrate the site’s existing positively drained areas and the drainage mechanism (i.e. into the ground via infiltration, into an off-site sewer or to a watercourse).
4.9 Where no drainage survey or evidence via historical as-built information is available, then predevelopment greenfield discharge rates will need to be applied.
4.10 Similarly, where buildings have been demolished and the drainage system become redundant for a period of 12 months or more, again predevelopment greenfield discharge rates will apply.
Informative Note 4 – On buildings where the structure has been removed and the slab left in situ, then unless it can be demonstrated that the historic downpipe discharge points still collect the run-off from the slab area, pre-development greenfield run off rates will be applicable to the new development.
4.11 The existing discharge shall be the lesser of the capacity of the existing non surcharged pipe full capacity of the existing outfall or can be taken as 140 l/s/ha of connected roofs and paving, provided that in both cases the existing drainage is still functional and point of discharge confirmed by a drainage survey.
4.12 It should be noted that the post development discharge will be restricted to the self-cleansing capacity of each discharge point from the site and not on the theoretical overall discharge.
4.13 Where existing connections to either a watercourse or sewer have been proven, then for Minor development sites a minimum 30% reduction shall be applied and for Major developments a minimum 50% reduction shall be applied.
Informative Note 5 – The allowable discharge rate shall be set by the Lead Local Flood Authority (Leeds C.C.) as part of the planning process and not Yorkshire Water, who may advise on a higher discharge rate.
Section 4 Policy/Guidance position.
Local Plan adopted Core Strategy policy EN5 and Natural Resources and Waste Policies Water 6 and Water 7
Local Plan Update emerging policy Water 6
5 Climate change allowances
5.1 The Flood Risk Assessment shall assess the impacts of climate change and the
required mitigation as set out within the current Government guidance.
Fluvial
5.2 Fluvial flood mitigation measures are required for all developments which are at risk from fluvial flooding as informed by the site-specific flood risk assessment. Flood risk reduction mitigation measures will be based upon the Design Fluvial Flood Level + Freeboard.
5.3 Where sites are considered ‘defended’, the developer shall assess the residual risk of flooding in the event of overtopping/breach and include suitable mitigation measures. An emergency plan, or Flood Warning and Evacuation Plan, is likely to be fundamental in such circumstance to ensure users/occupants can be safe.
5.4 The Design Fluvial Flood Level is the 1% AEP modelled flood level + Climate Change allowance. The Climate Change allowance to be adopted is reference to Tables 1, 2 and 3.
| Flood Zone 2 | Flood Zone 3(a) | Flood Zone 3(b) |
|---|
| Essential Infrastructure | Use Higher Central Allowance
| Use Higher Central Allowance
| Use Higher Central Allowance
|
| Highly Vulnerable | Use Central Allowance | Development should not be permitted | Development should not be Permitted* |
| More Vulnerable | Use Central Allowance | Use Central Allowance | Development should not be Permitted* |
| Less Vulnerable | Use Central Allowance | Use Central Allowance | Development should not be Permitted* |
| Water Compatible | Use the Central Allowance | Use the Central Allowance | Use the Central Allowance |
Table 1 - Vulnerability / Flood Zone Matrix
*If (exceptionally) development is considered appropriate when not permitted within this matrix, then the Higher Central allowance should be used.
Informative Note 6 – It should be noted that the definition of the functional floodplain is Flood Zone 3(b) and the starting point for which is now regarded as the 3.3% AEP, or 1 in 30 year flood event.
| | Total potential change anticipated for the 2020’s (2015 to 2039) | Total potential change anticipated for the 2050’s (2040 to 2069) | Total potential change anticipated for the 2080’s (2070 to 2115) |
|---|
| Central (90 percentile) | 11% | 13% | 23% |
| Higher (70 percentile) | 15% | 18% | 31% |
| Upper (50 percentile) | 24% | 31% | 51% |
Table 2: River Aire & Calder - Peak River flow increases due to Climate Change (use 1981 to 2000 baseline)
| | Total potential change anticipated for the 2020’s (2015 to 2039) | Total potential change anticipated for the 2050’s (2040 to 2069) | Total potential change anticipated for the 2080’s (2070 to 2115) |
|---|
| Central (90 percentile) | 11% | 13% | 23% |
| Higher (70 percentile) | 14% | 18% | 31% |
| Upper (50 percentile) | 22% | 29% | 48% |
Table 3: Wharfe & Lower Ouse - Peak River flow increases due to Climate Change (use 1981 to 2000 baseline)
Surface water flooding
5.5 No specific allowances for climate change are available at present and therefore it is not possible to define fully the impacts of climate change.
5.6 However, until such time as more detailed national surface water flood mapping becomes available, then an initial assessment using proxies should be considered using the (1%AEP) outline to set the 3.33% +CC outline.
5.7 Consideration of the impacts of climate change shall only be required where there is a history of surface water flooding within or adjacent to the application site. Details of any historic recorded surface water flooding should in the first instance be obtained from Leeds CC FRM (FRM@leeds.gov.uk).
Surface water drainage design
5.8 In designing new surface water drainage systems the appropriate climate change allowance should be adopted as set out within Tables 4 and 5 below.
| Allowance | Total potential change anticipated for the 2050’s (2040 to 2069) | Total potential change anticipated for the 2070’s (2061 to 2125) |
|---|
| Central (90 percentile) | +25% | +30% |
| Upper (50 percentile) | +40% | +45% |
Table 4 Peak Rainfall Intensity Allowances – 1% annual exceedance rainfall event Aire & Calder Catchment
| Allowance | Total potential change anticipated for the 2050’s (2040 to 2069) | Total potential change anticipated for the 2070’s (2061 to 2125) |
|---|
| Central (90 percentile) | +25% | +30% |
| Upper (50 percentile) | +40% | +40% |
Table 5 Peak Rainfall Intensity Allowances - 1% annual exceedance rainfall event Wharf & Lower Ouse Catchment
5.9 For developments with a lifetime up to both 2060 and between 2060 and 2100, then the Central Allowance should be used.
Section 5 Policy/Guidance position.
National Planning Policy Guidance
Local Plan Update emerging policy Water 6 and Water 6A
Adopted Natural Resources and Waste Local Plan Policies Water 6 and Water 7
6 Setting finished floor levels
Fluvial flooding
6.1 Setting of Finished Flood Levels in relation to Fluvial flooding should be based on the Design Flood Level (including the relevant allowance for climate change) and should be no lower than 600mm for residential, 400mm for offices and commercial, 300mm for industrial and warehousing and 300mm for entrance to underground car parks.
Surface water and other forms of flooding
6.2 Where existing flood level data (either modelled or historical) is available then the Fluvial Flooding allowances and freeboard should be incorporated.
6.3 Where drainage systems have been modelled and an allowable element of site surface water flooding exists under the 1 in 100 + relevant CC storm event, then the minimum freeboard required shall be 150mm for all classifications of development.
6.4 For all developments identified at risk flooding from any source (including the relevant climate change scenario) the external levels shall fall away from all aspects of the relevant buildings.
Section 6 Policy/Guidance position.
Local Plan adopted Core Strategy policy EN5 and Natural Resources and Waste Local Plan Policies Water 6 and Water 7
Local Plan Update emerging policy Water 6
7 Drainage hierarchy
7.1 In accordance with current guidance the Drainage hierarchy shall be as follows:
- (i) into the ground (infiltration),
- (ii) to a surface water body,
- (iii) to a surface water sewer, highway drain, or another drainage system,
- (iv) to a combined sewer.
7.2 In addition to the above all water saving and recycling/re use techniques (e.g. rain water butts, grey water recycling, rain gardens and green roofs) should be actively considered to reduce and/or slow down the run off.
Informative Note 7 - Where site investigation studies or other relevant information indicate that the use of infiltration techniques may be viable, then to support a full planning application, permeability testing to BRE 365, shall be undertaken and the results adopted in designing the surface water drainage system.
It should also be noted that prior to accepting any surface water run off to a public sewer, Yorkshire Water will also require evidence that the use of infiltration techniques is not viable.
7.3 Where discharge is to an existing watercourse or other surface water body, then written approval will be required from the landowner of the land through which any off-site sewer is to be laid and also acceptance of the proposed discharge rate from the riparian owner of the receiving water body. This information shall be submitted as part of the planning application.
Section 7 Policy/Guidance position.
Document H of the Building Regulations
Local Plan Update emerging policy Water 7
WYCA Sustainable Drainage Systems Guidance
Natural Resources and Waste Local Plan adopted Policy Water 7
8 Sustainable drainage systems
The following sections sets out the basic surface water drainage design criteria associated with all developments.
The use of SUDS
8.1 For all Major Development SUDS must be incorporated into the surface water drainage design. However, a SUDS system is not only to restrict the discharge and provide on-site attenuation. It must provide a complete design which wherever possible includes the four pillars of SUDS. These are:
- a) Water Quantity – Controlling the Quantity of Run Off
- b) Water Quality – Managing the quality of run off to prevent pollution
- c) Amenity – Creating and sustaining better places for People
- d) Biodiversity – Creating and sustaining better places for Nature.
Major developments
8.2 To support all Major Developments a SUDS appraisal shall be submitted which deals with the following issues. The level of the SUDS Assessment will vary depending on the nature of the planning application. An outline application will involve a high-level assessment, whereas a full application will require a more details and thorough assessment.
8.3 It is important to consider the use of the various SUDS techniques within the original master planning and viability of the site and not trying to retro fit it into a pre-determined site layout.
8.4 Where it is not possible to provide a compliant SUDS based drainage design, then a full justification statement shall be provided to demonstrate why it is not appropriate.
Informative Note 9 - Examples to demonstrate the non-viability of SUDS could be infiltration testing results proving sub strata not suitable for the use of shallow or deep borehole soakaways, presence of contaminated ground, area located within a ground water source protection zone, topography of the land and geology would result in run off issuing on lower ground.
8.5 Where the land take required for viable SUDS features will result in the loss of units and potentially impact on the viability of a development, if this is to be suggested as the justification for not incorporating SUDS then full economic reasoning shall be provided. It will not be acceptable to simply state that the loss of a unit will impact on the viability of the development.
Minor developments
8.6 Where viable, minor developments should seek to incorporate SUDS considering the drainage hierarchy requirements set out within 7.1. and to comply with the water quality requirements set out within Section 10.
8.7 Typical examples of SUDS that can easily be incorporated into Minor Developments are as follows:
- a) The use of permeable paving or surfaces within driveways or access roads. Even where the ground conditions do not allow infiltration, permeable pavements can allow the run of to drain into the basal stone layer and then drain into the main site drainage systems.
- b) The use of rain gardens to receive run of from roofs and other hard surfaces.
- c) The use of rainwater butts and grey water recycling systems
- d) The use of soakaways and infiltration trenches.
Section 8 Policy/Guidance position.
CIRIA SUDS Manual C753
Local Plan Update emerging policy Water 2 and Water 7
WYCA Sustainable Drainage Systems Guidance
National Planning Policy Guidance
Natural Resource and Waste Local Plan adopted Policy Water 7
9 Drainage design criteria
General
9.1 For all new developments on greenfield sites where the drained area is less than 250m2, then no on-site attenuation will be required.
9.2 For brownfield sites, where existing drainage connections have been proved, then where the total drained area is less then 375m2, again no on-site attenuation is required.
9.3 For all other developments, suitable SUDS based on-site attenuation will be required.
9.4 The design of any drainage system shall ensure that there is no increase in flood risk for all storm events up to and including the 1 in 100 + relevant allowance for climate change storm event and where possible reduce the existing flood risk.
Design life and climate change allowances
9.5 Surface water drainage systems shall be designed based on the lifetime of the development and the relevant allowance for climate change as set out within Table 4.
9.6 All developments with a lifetime up to 2100 use the Central allowance. However, for longer life developments (such as residential which is also More Vulnerable) the Upper End allowance should be adopted.
Informative Note 10 - All residential developments including part residential/part commercial, shall be deemed to have a lifetime greater than 2100 and the Upper End allowance shall be adopted. In addition, all Highly Vulnerable developments shall also adopt the Upper End allowance.
Drainage design criteria
9.7 The design of all surface water drainage systems shall ensure that the following design criteria are complied with:
- a) For the 50% AEP storm event = pipe full / no surcharge (with exceptions).
- b) For the 3.33% AEP storm event = no surface flooding.
- c) For the 1% AEP event + Climate Change (CC) = no property flooding and any flooding retained within the extent of the application site.
- d) Where surface water flooding from events in excess of 3.33% AEP occurs, this can be accommodated within the site (e.g. in car parks, Public Open Space, etc.), provided that the associated risks are managed and that adequate freeboard to properties is provided.
Urban creep
9.8 This is allowance is intended to reflect the position where unregulated conversion of permeable surfaces to impermeable surfaces occurs over a period of time. It is best assessed on a ‘site by site’ basis but is limited to residential development. It is important that the appropriate allowance as set out within Table 6 below is included in the design of the drainage system over the lifetime of the proposed development.
| Residential dwelling density Dwellings per hectare | Change allowance % of impermeable area |
|---|
| ≤ 25 | 10 |
| 30 | 8 |
| 35 | 6 |
| 45 | 4 |
| ≥ 50 | 2 |
| Flats & apartments | 0 |
Table 6 - Urban Creep allowances to be applied to the impermeable area within the property curtilage*
*Non-Statutory Technical Standards for Sustainable Drainage – Appendix B
Flow control devices
9.9 Generally, these must not be less than 75 mm in diameter (C753), unless designed to prevent blocking. Where the flow control is to be adopted it should meet the latest adoption criteria.
Greenfield run off
9.10 For sites < 1 ha a maximum discharge rate of 3.5 l/s can be used for all storms up to the 1% AEP event +CC. Alternatively, IH 124, ICP SUDS and FEH methods in ICOP can be used.
Point of connection
9.11 To be stated by the developer. It must not create additional flooding due to increased flow rates or volumes. Where on third party land (excluding public highway), then written agreement from the landowner and the riparian owner of the discharge point shall be provided.
Rainfall
9.12 FEH 2013 analysis is required to be adopted in designing surface water drainage system including attenuation volumes. However, for small Minor developments (less than 5 units or 1000m2 of new drained area) then the use of FSR may be accepted.
Drainage calculation criteria - FSR criteria
9.13 The following design criteria shall be adopted in designing drainage systems
- a. Maximum Time of Concentration 5 mins
- b. MADD Factor 2
- c. M5-60 = 19mm
- d. Ration R = 0.35
- e. Winter Cv = 1.0
- f. Summer Cv =0.75
Separate drainage systems
9.14 All new drainage systems shall be based on separate foul and surface water drainage systems within the development site. Where the discharge is to an off-site combined sewer, then the separate sewers shall be combined within a manhole located as near as possible to the site boundary.
Discharge to River Aire and River Wharfe
9.15 Where gravity outfalls are to be made direct to the River Aire or River Wharfe, then the on-site drainage network shall be modelled to demonstrate that based on the agreed discharge rate, there is adequate on-site attenuation and storage for the 6-hour 100-year design storm when applied to the development site with consideration against the 1 in 20 defended river flood levels. The 6-hour period should be set to be 3 hours off the peak of the 1 in 100 + CC storm.
Exceedance routes
9.16 Exceedance flows and runoff in excess of design criteria should be considered, and calculations and plans shall be provided to show where above ground flooding might occur and where this would pool and flow.
Storage features and infiltration features should be able to half drain within 24 hours for all storms up to and including the 1 in 30-year storm.
9.17 When sizing attenuation storage it is necessary to demonstrate that all storage features have capacity for the 1 in 100-year storm event plus climate change allowance.
9.18 In addition to this, it must be demonstrated that 50% of the storage will be available within 24 hours following a 1 in 30-year storm event plus climate change.
9.19 If it is not possible to have a half drain time of less than 24 hours, the LLFA expects that the attenuation volume is capable of storing a 1 in 30-year storm event plus climate change and a subsequent 1 in 10-year event. This is also the case for all infiltration features. It should be noted that the feature should still have the capacity to attenuate water for the 1 in 100-year storm event plus climate change.
Section 9 Policy/Guidance position.
Local Plan Update emerging policies Water 6 and Water 8
National Planning Policy Guidance
CIRIA SUDS Manual C753
10 Water quality
10.1 A fundamental pillar of SUDS design is to ensure that the water quality of the receiving watercourse or sewer or ground is not impacted, and where possible improved.
10.2 For all major developments, it is a requirement to demonstrate that the three criteria as set out within Table 26.2 of The SUDS Manual (C753) i.e. Suspended Solids, Hydrocarbons and metals are adhered to.
10.3 To support each application, an assessment utilising the Simple Index Approach shall be submitted.
10.4 The assessment shall comply with the methodology as set out within Chapter 26 of The SUDS Manual.
10.5 Where several individual techniques are provided, details of the relative mitigation indices shall be provided and summarised within a separate table.
Informative Note 11 - Where Bypass Interceptors or other treatment systems are incorporated into the design, then supporting information from the Manufacturer shall be provided setting out the relative mitigation indices that each unit provide.
In respect to the use of silt traps and gulley’s, it should be noted that these generally only provide a small element of suspended solids treatment and a detailed assessment of the performance of each designed component in reducing the inflow and concentration of each pollutant type shall be provided as evidence of the adopted indices.
It will not be acceptable to assume that where the discharge is to a combined sewer system, that adequate dilution and reduction in pollution will be provided.
10.6 The Inspection & Maintenance regime shall ensure that the system is maintained and operational at all times to ensure that the relevant levels of water quality treatment are provided. This aspect should be considered in assessing the various levels of treatment proposed.
Section 10 Policy/Guidance position.
CIRIA SUDS Manual C753
Local Plan Update emerging policy Water 7
WYCA Sustainable Drainage Systems Guidance
National Planning Policy Guidance
Natural Resource and Waste Local Plan adopted Policy Water 2
11 Construction phase drainage and flood mitigation measures
11.1 As part of the site-specific Drainage Assessment, it is important to consider the flood mitigation measures that may be required during the Construction Phase to ensure that no adjacent properties are put at increased risk of flooding.
11.2 Therefore, within the site-specific Drainage Assessment, a section shall be provided which sets out the critical elements that may require mitigation during the Construction Phase.
11.3 It is accepted that the provision of the full temporary works and drainage method statement will not be available until a Contractor has been appointed. Therefore provision of such details will normally be conditioned and cross referenced to the specific Construction Phase key risks identified within the site-specific Drainage Assessment.
11.4 The provision of the temporary drainage measures will only be short term and operational until the main site development drainage measures, including attenuation, have been installed. Therefore, any drain age design will not be required to consider the impacts of Climate Change.
Informative Note 12 - Typical examples of where the Construction Phase temporary drainage measures will be required are on sloping sites underlain by an impermeable strata. In this situation, once the topsoil strip has occurred, sheet run off may drain off the site into adjacent properties, which will be unacceptable.
Section 11 Policy/Guidance position.
Local Plan adopted policy EN5
CIRIA Manual C532 Control of Water Pollution from Construction Sites
WYCA Sustainable Drainage Systems Guidance
Natural Resource and Waste Local Plan adopted Policy Water 2
12 Adoption and maintenance of non-adopted drainage
12.1 A key element of any drainage design is how it will be operated and maintained. Therefore, it will be necessary for the applicant to provide full details of how and by whom any non-adopted drainage systems will be operated and maintained. This will also include the temporary period between completion of the drainage works and final adoption by the relevant authority.
12.2 Where a Management Company is to be used to operate and maintain such drainage assets, then the applicant shall confirm how each leaseholder or owner occupier will be legally obliged to fund such measures for the lifetime of the development. It is expected that the requirement and scope of such services funded will be set out within the legal title of each contributing property.
12.3 As part of any Drainage Assessment, a full list of each drainage element shall be provided setting out the proposed inspection measures and when such inspections shall be undertaken.
12.4 An asset register shall also be provided to demonstrate that the required inspections (and any required maintenance) have been undertaken and that the drainage systems is left in an operational manner.
12.5 It is noted that all of the above information may not be available at the time of submitting the planning application and therefore the provision of an Inspection & Maintenance Manual will normally be left to a subsequent planning condition.
Section 12 Policy/Guidance position.
CIRIA SUDS Manual C753
Design & Construction Guidance, Sewerage Sector Guidance Document
Local Plan Update emerging policy Water 7
13 Residual risks
13.1 Following the assessment of all flood risks and identification of necessary mitigation, all appropriate residual risks (e.g. breach analysis, pumping station failure, culvert blockage, surface water conveyance system failure, safe access and egress etc) will require assessment and any necessary mitigation including within the design.
Section 13 Policy/Guidance position.
National Planning Policy Guidance
Local Plan Update emerging policy Water 5 and Water 6A
Natural Resource and Waste Local Plan adopted Policy Water 5
