Draft Flood Risk Supplementary Planning Document

2.5 Part 5 of FRA: Managing and mitigating flood risk

2.5.1 This Section will provide guidance on how to complete Part 5 of the FRA Pro-forma: Managing and mitigating flood risk.

What mitigation measures are required?

2.5.2 Where development takes place in an area at risk of flooding it must demonstrate, through the production of a site specific FRA that it is:

  • Safe for its lifetime;
  • Does not increase the risk of flooding elsewhere;
  • Where possible, reduces flood risk overall.

2.5.3 A range of mitigation measures can be integrated into a development in order to manage and mitigate flood risk and achieve the above. This addresses Part 2 of the Exception Test (See Section 2.4).

How should mitigation measures be designed?

2.5.4 All mitigation measures should be designed with an allowance for climate change over the lifetime of the development as follows:

  • 100 years for residential developments; and
  • 75 years for commercial/industrial development, or other time horizons specific to the non-residential use proposed

What are the options for mitigating flood risk?

2.5.5 Different measures will be appropriate/necessary in different circumstances depending on the nature of flood risk, vulnerability of the development, site conditions etc. For example the design of a safe route of escape or the height to which floor levels should be raised will be influenced by the predicted depth and velocity of flooding affecting a site. Table 13 provides a summary of each mitigation measure and the following sections provide further detail.

 

Table 13: Mitigation measures

Mitigation measure

Description

Development layout and sequential approach

Applying the sequential approach within development sites, directly more vulnerable development to areas of lower risk

Finished Floor Levels

Raising floor levels above flood levels

Flood Resistance

Aimed at preventing water ingress and minimising impact. Applicable to flood depths <0.3m. Include use of materials with low permeability, land raising, flood gates etc

Flood Resilience

Allows water entry but minimises damage to allow rapid re-occupancy. Applicable to flood depths >0.6m. Include use of materials with good drying/cleaning properties, raising electrical wiring, tanking basements etc

Safe access and egress

Enabling the safe evacuation of people, providing emergency services with access and enable flood defence authorities to carry out duties in times of flood

Floodplain compensation storage

Ensuring development does not impact upon the ability of the floodplain to store water in time of flood by providing level for level, volume for volume compensation.

Flood voids

Voids below buildings that allow water to flow and be stored. Can be used in combination with compensation storage or alone.

Flow routing

Allows the free flow of water and ensures floodwaters are not diverted or backwater effects

Riverside development

Retention of undeveloped buffer strips alongside main rivers and ordinary watercourses.

Sustainable Drainage Systems

Measures to reduce or manage surface water runoff to and from proposed development to achieve specific run-off rates. Two types: Attenuation and Infiltration. Attenuation applicable everywhere, Infiltration only applicable in some areas. Examples include, wetland ponds, permeable surfaces, green roofs etc

Flood Warning and Evacuation Plans

Plan to show what actions occupants of the site should take before, during and after a flood to ensure their safety, and to ensure safe access by emergency services etc

Development Layout and Sequential Approach

Locate the most vulnerable elements of a development in the areas at lowest flood risk

2.5.6 The principle of avoiding flood risk should be applied within development sites and buildings to locate the most vulnerable elements in the areas of lowest risk. For example, within a site residential uses should be restricted to areas at lowest risk of flooding whereas parking, open space and landscaped areas can be placed in areas at higher risk.

2.5.7 This principle can also be applied within buildings. For example, locating residential development on the first floor in a mixed-use scheme or locating sleeping accommodation on the first floor to ensure a 'safe place'.

FRAs should include plans showing how sensitive uses have been placed in areas of lower risk

Finished Floor Levels

For residential development finished floor levels should be set 300mm above the known or modelled 1 in 100 year flood level (Flood Zone 3) including an allowance for climate change or estimated flood depth for surface water flooding. Floor levels may not need to be raised for other types of development where buildings can be designed to be floodable eg Less Vulnerable.

2.5.8 Where development takes place in areas at risk of flooding ideally internal floor levels should be raised 300mm above the known or modelled 1 in 100 year (Flood Zone 3) flood level including an allowance for climate change or the estimated depth of surface water flooding (see page 15 for details on how to obtain estimated depths of flooding).

2.5.9 This may not be possible in all cases e.g. extensions or necessary where buildings can be designed to be floodable e.g. Less Vulnerable uses. In these cases, options for a reduction in floor levels subject to appropriate resistance/resilience measures should be set out within an FRA. The following table provides a guide to the requirements (Table 14).

FRAs must include plans showing finished floor levels in relation to Ordnance Datum taking account of indicative flood depths.

Table 14: Finished Floor Levels

Development type

Flood Zone 3

Flood Zone 2

Minor residential development

Floor levels within the proposed development will be set no lower than existing levels AND, flood resistance/resilience measure have been incorporated (see Section below)

OR,

Floor levels within the extension will be set 300mm above the known or modelled 1 in 100 (1%) year flood level including climate change.

Floor levels within the proposed development will be set no lower than existing levels AND, flood resistance/resilience measures have been incorporated (see Section below).

Other development -

Residential

Where appropriate, subject to there being no other planning constraints (e.g. restrictions on building heights), finished floor levels should be set a minimum of 300mm above the 1% annual probability flood level (1 in 100 year) including climate change. Sleeping accommodation should be restricted to the first floor or above to offer the required 'safe places'. Internal ground floors below this level could however be occupied by either Less Vulnerable commercial premises, garages or non-sleeping residential rooms (e.g. kitchen, study, lounge) (i.e. applying a sequential approach within a building).

Other development - Non-

residential

Finished floor levels may not need to be raised. For example, Less Vulnerable developments can be designed to be floodable instead of raising floor levels, and this may be beneficial to help minimise the impact of the development on the displacement of floodwater and the risk of flooding to the surrounding area. However, it is strongly recommended that internal access is provided to upper floors (first floor or a mezzanine level) to provide safe refuge in a flood event. Such refuges will have to be permanent and accessible to all occupants and users of the site and a Flood Warning and Evacuation Plan should be prepared to document the actions to take in the event of a flood (see Section below).

Basement dwellings

Basements, basement extensions, conversions of basements to a higher vulnerability classification or self-contained units are not permitted in Flood Zone 3b. Self-contained residential basements and bedrooms at basement level are not permitted in 3a. Internal access to a higher floor situated 300mm above the 1% annual probability flood level (1 in 100 year) including climate change must be provided for all other basements, basement extensions and conversions.

All basements, basement extensions and conversions must have internal access to a higher floor situated 300mm above the 1% annual probability flood level (1 in 100 year) including climate change.

Flood Resistance or Water Exclusion Strategy

Resistance measures should be employed where predicted flood depths are less than 0.3m and are likely to be for short duration.

2.5.10 Flood resistance measures aim to keep water out and give occupants time to relocate ground floor contents. There are a range of flood protection devices/methods including:

  • Using materials and construction with low permeability;
  • Landscaping e.g. creation of low earth bunds (subject to this not increasing flood risk elsewhere);
  • Raising thresholds and finished floor levels (See previous section) e.g. porches with higher thresholds than main entrance;
  • Flood gates with waterproof seals;
  • Sump and pump for floodwater to remove waste water faster than it enters;
  • Door guards and airbrick covers.

Flood Resilience or Water Entry Strategy

Resilience measures should be employed where flood depths are greater than 0.6m and where it is likely that structural damage will occur due to excessive water pressure.

2.5.11 Flood resilience measures are designed to allow water in but to limit damage and allow rapid re-occupancy. There are a range of options: 

  • Use materials with either good drying and cleaning properties, or, sacrificial materials that can easily be replaced;
  • Design for water to drain away;
  • Design access to all spaces to permit drying and cleaning;
  • Raise the level of electric wiring, appliances and utility metres (0.1m above flood level);
  • Ground supported floors with concrete slabs coated with impermeable membrane;
  • Tank basements, cellars and ground floors with water resistant membranes;
  • Plastic water resistant internal doors.

2.5.12 Resilience measures are appropriate for uses where temporary disruption is acceptable and suitable warning received.   It may be appropriate to use resistance measures alongside this with the aim of buying time for removal of valuables and safe evacuation.This approach is most suited where the rate of flood water rise is relatively slow i.e. several hours. 

2.5.13 For flood depths of between 0.3 and 0.6m a decision needs to be taken as to whether it is feasible or practical to adopt resistance measures. If structural integrity is a concern then it would be advisable to allow for partial water entry.

Refer to CLG, 2007, Improving the Floor Performance of New Buildings: Flood Resilient Construction [1]
FRAs must include details of the specific flood resilience and resistance measures to be employed including design drawings where appropriate.

Safety of Other Structures

2.5.14 Structures such as bus/bike shelters, benches and refuse bins should be flood resilient, firmly attached to the ground and designed to prevent debris becoming caught. Similarly, where depths greater than 300mm are expected, car parks should be designed to prevent vehicles from floating out of the car park.

1. Improving the Flood Performance of New Buildings: Flood Resilient Construction - https://www.gov.uk/government/publications/flood-resilient-construction-of-new-buildings [back]

Safe Access and Egress

2.5.15 Safe access and egress is required to enable the safe passage of people from the development and to provide emergency services and flood defence authorities with access to the development during times of flood.

A safe access/egress route should allow occupants to safely exit and enter the buildings via a 'dry' route above 1 in 100 year flood level to reach land outside the flooded area (e.g. Flood Zone 1) using public rights of way without the intervention of the emergency services or others. Where this is not possible, a route through limited depths of flooding may be acceptable taking account of depth and velocity (flood hazard). This is a particularly important consideration for sites located on a 'dry island' or where a change of use is proposed. Safe means of escape should also be provided for sites affected by surface water flooding taking account of predicted flood depths.

2.5.16 The Environment Agency uses a calculation of flood hazard to determine safety in relation to flood risk. Flood hazard is a function of flood depth and flow velocity (speed) with a suitable debris factor to take account of hazard posed by any material caught up in the floodwater (Table 15).

Table 15 - Hazard to People rating (HR=d x (v+0.5)+DF

Flood Hazard (HR)

Description

Less than 0.75

Very low hazard - Caution

0.75 - 1.25

Dangerous for some - includes children, the elderly and the infirm

1.25 - 2.0

Dangerous for most - includes the general public

More than 2.0

Dangerous for all - includes the emergency services

2.5.17 Safe access/egress must be as follows in order of preference taking account of the vulnerability of its users:

  • Safe dry route for people and vehicles
  • Safe dry route for people
  • If a dry route for people is not possible, a route for people where the flood hazard (in terms of depth and velocity of flooding) is low and should not cause risk to people
  • If a dry route for vehicles is not possible, a route for vehicles where the flood hazard (in terms of depth and velocity of flooding) is low to permit access for emergency vehicles.

2.5.18 The means of escape must not impede the flow of floodwater or increase the risk of flooding elsewhere.

Safe refuge

2.5.19 In exceptional circumstances, dry access/egress above the 1 in 100 year (Flood Zone 3) flood level including climate change may not be achievable. In these cases, the Council will need to ensure that the safety of site occupants can be safely managed. This will be informed by the type of development, the number of occupants, their vulnerability, and the flood hazard along the proposed egress route. For example, this may entail the designation of a safe place of refuge on an upper floor of the building from which occupants can be rescued by emergency services. Sole reliance on a safe place of refuge will only be considered as a last resort and provision will not guarantee that an application will be granted. 

FRAs must include a plan showing the proposed route of escape away from the site and/or details of safe refuge, including details of signage that will be on-site.

Floodplain Compensation Storage

Proposals in developed areas within the 1 in 20 flood outline (including minor) and within Flood Zone 3a (excluding minor) should not result in a net loss of flood storage capacity. Where possible, particularly on larger sites, opportunities should be sought to achieve an increase in floodplain storage.

2.5.20 Where a proposed development results in a change in building footprint, this should not impact on the ability of the floodplain to store water, and in areas of higher risk e.g. Flood Zone 3b, opportunities should be sought to provide betterment. Similarly, where ground levels are elevated to raise the development out of the floodplain, compensatory floodplain storage within areas that currently lie outside the floodplain must be provided to ensure that the total volume of the floodplain storage is not reduced. As shown in Figure 4 below, true (direct) floodplain compensation must be provided on a level for level, volume for volume basis on land which does not already flood and is within the site boundary. Where land is not within the site boundary, it must be in the immediate vicinity, in the applicant's ownership and linked to the site[2] . Floodplain compensation must be considered in the context of the 1% annual probability (1 in 100 year/Flood Zone 3) flood level including an allowance for climate change. When designing a scheme flood water must be able to flow in and out and must not pond.

2.5.21 It is possible to provide off-site compensation within the local area e.g. on a neighbouring or adjacent site, or indirect compensation, by lowering land already within the floodplain, however, this would not provide true compensation and evidence would need to be provided to demonstrate that the proposals would improve and not worsen the existing flooding situation or could be used in combination with other measures e.g. voids to limit the impact on floodplain storage.

2.5.22 It is recognised that full compensation may not always be possible, particularly for minor development schemes and sites wholly within Flood Zone 3. In these cases full justification must be provided and other measures incorporated to help mitigate any loss of floodplain storage e.g. flow routing, flood voids, removal of non-floodable structures.

Figure 4 - Example of direct Floodplain Compensation Storage (Environment Agency 2009)

Floodplain compensation storage

Removal of other structures

2.5.23 In considering flood storage capacity the Council will take account of the potential beneficial effects of the removal of other structures providing it can be demonstrated that these are non-floodable. It is important to note that structures such as sheds and garages with a floor level close to the ground, where flood water would not normally be prevented from entering would contribute little to additional flood storage capacity if removed.

Flood Voids

2.5.24 The use of under-floor voids with adequate openings beneath raised finished floor levels can be considered for development in Flood Zone 3. They are generally considered to provide indirect compensation for loss of floodplain storage.  

2.5.25 Voids may be suitable where it is not be possible to achieve all the direct compensation required or for minor development where it can be difficult to achieve full compensation. Ideally, void openings should be a minimum of 1m long and open from existing ground levels to at least the 1% annual probability (1 in 100 year/Flood Zone 3) plus climate change flood level. By setting finished floor levels at 300mm above the indicated flood level, there is usually enough space for the provision of voids below. There should be a minimum of 1m of open void length per 5m length of wall. Void openings should be provided along all external walls. If security is an issue, 10mm diameter vertical bars set at 100mm centres can be incorporated into the void openings. The use of under-floor voids will typically require a legal agreement or planning condition and maintenance plan to ensure they remain open for the lifetime of the development.  For minor development different design criteria may be acceptable.

2.5.26 Sole reliance on the use of under-floor voids to address the loss of floodplain storage capacity is generally not acceptable on undeveloped sites. 

Car Parks

2.5.27 Where car parks are specified as areas for the temporary storage of floodwater, flood depths should not exceed 300mm given that vehicles may be moved by water of greater depths. Where greater depths are expected, car parks should be designed to prevent the vehicles from floating out of the car park. Signs should be in place to notify drivers of the susceptibility of flooding and flood warning should be available to provide sufficient time for car owners to move their vehicles if necessary.

FRAs must provide calculations or results of modelling and include cross-sectional drawings where appropriate. Details of maintenance regime must be provided.
Appendix 3 of CIRIA 2004, CIRIA Report 624: Development and Flood Risk - Guidance for the Construction Industry[3]
2. In hydrological connectivity. [back]
3. CIRIA 624: Development and Flood Risk - http://products.ihs.com/Ohsis-SEO/467043.html [back]

Flow routing

2.5.28 Potential overland and sub-surface flow paths should be determined and appropriate solutions proposed to minimise the impact of the development, for example by configuring road and building layouts to preserve existing flow paths and improve flood routing, whilst ensuring that flows are not diverted towards existing properties. Opportunities should be sought to make space for floodwater:

  • Removing boundary walls or replacing with other boundary treatments such as hedges, fences (with gaps).
  • Considering alternatives to solid wooden gates, or ensuring that there is a gap beneath the gates to allow the passage of floodwater.
  • On uneven or sloping sites, consider lowering ground levels to extend the floodplain without creating ponds. The area of lowered ground must remain connected to the floodplain to allow water to flow back when levels recede.
  • Where proposals entail floodable garages or outbuildings, consider designing a proportion of the external walls to be committed to the free flow of floodwater.
  • Consider perimeter drainage to ensure that existing sub-surface flows are not disrupted. 
Evidence should be provided within FRAs to demonstrate that the proposed development will not impact on flood flows. This may require additional modelling.

Riverside development

All developments must retain an 8 metre undeveloped buffer strip alongside Main Rivers and a 5 metre wide buffer strip alongside Ordinary Watercourses.

2.5.29 An 8 metre wide undeveloped buffer strip alongside Main Rivers should be retained for maintenance purposes and to support the landscape and biodiversity of river corridors. Applicants, particularly for larger scale developments, will be expected to explore opportunities for riverside restoration.

2.5.30 A 5 metre wide undeveloped buffer strip should be retained alongside Ordinary Watercourses.

Plans should be included within FRAs to show how the development has been designed to incorporate riverside buffer strips.

2.5.31  Any proposed development adjoining the riverside should be designed to take account of other policies contained within the Elmbridge Local Plan and associated strategies as set out at the start of this SPD (Section 1.2). Applicants should consider how the proposed development enhances the landscape of the river including important views and vistas, contributes towards biodiversity, promotes heritage, supports public access wherever possible and recreational use of the waterway.

Flood Warning and Evacuation Plans

For all developments (excluding minor) proposed in Flood Zone 2 or 3, a Flood Warning and Evacuation Plan (FWEP) should be prepared to demonstrate what actions site users will take before, during and after a flood event to ensure their safety, and to demonstrate their development will not impact on the ability of the Council and the emergency services to safeguard the current population.

 

For sites in Flood Zone 1 where the area surrounding the site and/or any potential egress routes away from the site may be at risk of flooding from any source (‘dry island’) or where it is directly affected by any other source of flooding it may also be necessary to prepare a FWEP.

 

For all minor development in Flood Zones 2 and 3, the Environment Agency has a tool on their website to create a Personal Flood Plan. [4]The Plan comprises a checklist of things to do before, during and after a flood and a place to record important contact details.      

2.5.32 Evacuation is where flood alerts and warnings provided by the Environment Agency enable timely actions by residents or occupants to allow evacuation to take place unaided, i.e. without the deployment of trained personnel to help people from their homes, businesses and other premises. Rescue by the emergency services is likely to be required where flooding has occurred and prior evacuation has not been possible. FWEPs should include details of:

How flood warning is to be provided, such as:

  • Availability of existing flood warning systems;
  • Where available, rate of onset of flooding and available flood warning time; and
  • How flood warning is received.

What will be done to protect the development and contents, such as:

  • How easily damaged items (including parked cars) or valuable items will be relocated;
  • How services can be switched off (gas, electricity, water supplies);
  • The use of flood protection products (e.g. flood boards, airbrick covers etc);
  • The availability of staff/occupants/users to respond to a flood warning, including preparing for evacuation, deploying flood barriers across doors etc; and
  • The time taken to respond to a flood warning.

Ensuring safe occupancy and access to and from the development, such as:

  • Occupant awareness of the likely frequency and duration of flood events, and the potential need to evacuate;
  • Safe access route to and from the development or designated safe refuge;
  • If necessary, the ability to maintain key services during an event;
  • Vulnerability of occupants, and whether rescue by emergency services will be necessary and feasible; and
  • Expected time taken to re-establish normal use following a flood event (clean up times, time to re-establish service etc).
The FWEP or Personal Flood Plan - 'Make a Flood Plan' must be included as an Appendix to the FRA.

Flood Warning areas and Emergency Rest Centres

2.5.33 There are 13 flood warning areas in the Borough (Table 16). The Environment Agency issues flood warnings to residents and businesses that have registered for the service as to when flooding is expected.

Table 16: Flood Warning Areas

Watercourse

Flood Warning Area

River Wey

Walsham Meadow to Byfleet Town

Wisley and Byfleet

Weybridge

Thames

Hamm Court

Molesey

Sunbury

Walton

East and West Molesey

Thames Ditton

Thames Ditton Island

Lower Hailliford

Mole

Esher and East Molesey

Stoke D’Abernon, Cobham and South Hersham

2.5.34 Elmbridge has 7 emergency rest centres. It should be noted that although these have been identified as emergency rest centres, whether each of the centres are operational during a flood event is dependent upon the locations and extent of flooding across the Borough at that particular time. The Council will decide at the time of a flood event which centre will be used. See Appendix B, Figure B9 of the SFRA for details[5] .

These should be referred to within the FWEP or Personal Flood Plan
4. Environment Agency Tool ‘Make a Flood Plan’. https://www.gov.uk/government/publications/personal-flood-plan] [back]
5. 3 additional warning areas have been added since the publication of the SFRA [back]

Surface Water Management

All developments should not result in an increase in surface water runoff, and where possible, should demonstrate an improvement in terms of rates and volumes of surface water runoff. Sustainable Drainage Systems (SuDS) should be used to reduce and manage surface water run-off to and from proposed developments as near to source as possible.

2.5.35 Suitable surface water management measures should be incorporated into new development designs in order to reduce and manage surface water flood risk to, and from new development. This should be achieved by incorporating SuDS.

2.5.36 SuDS are typically softer engineering solutions inspired by natural drainage processes that manage water as close to its source as possible. A SuDS technique should seek to contribute to each of the three goals identified below:

  1. Reduce flood risk (to the site and neighbouring areas);
  2. Reduce pollution, and
  3. Provide landscape and wildlife benefits.

2.5.37 Generally the aim should be to discharge surface water run-off as high up the following hierarchy of drainage options as reasonably practicable and subject to suitability:

  1. Into the ground (infiltration)
  2. To a surface water body
  3. To a surface water sewer, highway drain, or another drainage system
  4. To a combined sewer

2.5.38 SuDS techniques can be used to reduce the rate and volume and improve the water quality of surface water discharges. The SuDS Manua[6]  identifies several processes that can be used to manage and control run-off. Each option can provide opportunities for storm water control, flood risk management, water conservation and groundwater recharge.

  • Infiltration: the soaking of water into the ground. This is the most desirable solution as it mimics the natural hydrological process. Where groundwater sources are vulnerable or there is risk of contamination, infiltration techniques are not suitable.
  • Detention/Attenuation: the slowing down of surface flows before their transfer downstream, usually achieved by creating a storage volume and a constrained outlet.
  • Conveyance: the transfer of surface runoff from one place to another, e.g. through open channels, pipes and trenches.
  • Water Harvesting: the direct capture and use of runoff on site, e.g. for domestic use (flushing toilets) or irrigation of urban landscapes. The ability of these systems to perform a flood risk management function will be dependent on their scale, and whether there will be a suitable amount of storage always available in the event of a flood.

2.5.39 The application of SuDS is not limited to a single technique per site. Often a successful SuDS solution will utilise a combination of techniques. In addition, SuDS can be employed on a strategic scale, for example with a number of sites contributing to large scale jointly funded and managed SuDS. It should be noted, each development site must offset its own increase in runoff and attenuation cannot be "traded" between developments. Table 17 below outlines typical SuDS techniques.

2.5.40 As part of any SuDS scheme, consideration should be given to the long-term maintenance of the SuDS to ensure that it remains functional for the lifetime of the development.

2.5.41 The Lead Local Flood Authorities of South East England have produced a useful document providing advice on what SuDS will be suitable in different locations and outlining the process for integrating SuDS into developments[7] .

 Table 17: SuDS Techniques (Y: primary process; * some opportunities, subject to design)

TechniqueDescriptionConveyanceDetentionInfiltrationHarvesting

Permeable Paving

Permeable paving/surfaces allow rainwater to infiltrate through the surface into an underlying storage layer, where water is stored before infiltration to the ground, reuse, or release to surface water.

Y

Y

*

 

Filter Drains

Linear drains/trenches filled with a permeable material, often with perforated pipe in the base of the trench. Surface water from the edge of paved areas flows into the trenches, is filtered and conveyed to other parts of the site.

Y

Y

   

Filter Strips

Grassed or planted areas designed to drain water and promote infiltration and cleansing

*

*

*

 

Swales

Shallow vegetated channels that conduct and/or retain water, and can permit infiltration when unlined.

Y

Y

*

 

Ponds

Depressions used for storing and treating water.

Y

*

Y

 

Wetlands

As ponds, but the runoff flows slowly but continuously through aquatic vegetation that attenuates and filters the flow. Shallower than ponds. Based on geology these measures can also incorporate some degree of infiltration.

*

Y

*

Y

Detention Basin

Dry depressions designed to store water for a specified retention time.

Y

     

Soakaways

Designed to allow water to quickly soak into the permeable layers of soil. Constructed like a dry well, an underground pit is dug filled with gravel or rubble. Water can be piped into a soakaway where it will be allowed to gradually seep into the ground.

Y

     

Infiltration Trenches

As filter drains, but allowing infiltration through trench base and sides.

*

Y

Y

 

Infiltration Basins

Depressions that store and dispose of water via infiltration.

Y

Y

   

Green Roofs

Planted soil layer constructed on the roof of a building to create a living surface. Water is stored in the soil layer and absorbed by vegetation.

Y

     

Rainwater Harvesting

Rainwater is collected from the roof of a building or from other paved surfaces and stored in an overground or underground tank for treatment and reuse locally e.g. irrigation, toilet flushing

*

*

*

Y

2.5.42 The use of infiltration techniques is highly dependent on the underlying ground conditions. An assessment of the suitability of using infiltration SuDS techniques across the Borough has been undertaken as part of the SFRA and should be referred to when determining the types of SuDS to be employed. Detention, conveyance and harvesting measures are not constrained by ground conditions. 

Infiltration SuDS suitability - Appendix B6 of SFRA

Water, People, Places: A guide for master planning sustainable drainage into development
[8] ; SuDS Manual, CIRIA C697[9]

Non Statutory Technical Standards and supporting guidance

2.5.43 A set of non-statutory Technical Standards have been published, to be used in conjunction with supporting guidance in the PPG and sector guidance, which set the requirements for the design, construction, maintenance and operation of SuDS[10] `.

Local Authority SuDS Officer Organisation Best Practice Guidance[11]
For major schemes a separate Surface Water Drainage Proforma will need to be completed and referred to within the accompany FRA. For all other schemes surface water management will need to be addressed within the FRA
7. Water People Places - https://new.eastsussex.gov.uk/environment/flooding/sustainabledrainagesystems/ [back]
9. CIRIA C697 SuDS Manual. http://www.ciria.org/Resources/Free_publications/the_suds_manual.aspx [back]
10. Non-statutory Technical Standards - https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory-technical-standards [back]
11. Local Authority SuDS Officer Best Practice Guidance - http://www.lasoo.org.uk/ [back]

Securing mitigation measures

2.5.44 The Council will use planning conditions and in some cases legal agreements in order to secure mitigation measures and ensure they are maintained and operational for their lifetime.

Removing permitted development rights

2.5.45 Where development could result in a loss of flood plain storage capacity or impede flow permitted development rights will be removed from all new developments within Flood Zone 3, in order to ensure the risk of flooding is not increased through unregulated development.