Draft Flood Risk Supplementary Planning Document

Appendix 2 - Flood Risk Assessment Proforma

Please note: Not all elements of this Proforma will need to be completed for all developments. The level and scope of the FRA will depend on the degree and type of flood risk, scale and nature of the development, its vulnerability classification and whether or not the Sequential and Exceptions Tests are required. Applicants should use this SPD to scope out the requirements and are strongly encouraged to use the pre-applications services available (Section 2.1).

What to Include in the FRA

Source(s) of Information

Summary

Reference to Section of FRA

1.Site Description   

Site address

-

-

   

Site description

-

-

   

Location plan

Including geographical features, street names, catchment areas, watercourses and other bodies of water

SFRA Appendix B

   

Site plan

Plan of site showing development proposals and any structures which may influence local hydraulics e.g. bridges, pipes/ducts crossing watercourses, culverts, screens, embankments, walls, outfalls and condition of channel

OS Mapping

Site Survey

   

 2. Proposed development

Current use

Identify the current use of the site.

-

   

Proposed use

Will the proposals increase the number of occupants / site users on the site such that it may affect the degree of flood risk to these people?

-

   

Vulnerability Classification

Determine the vulnerability classification of the development. Is the vulnerability classification appropriate within the Flood Zone?

SPD Appendix 1

SPD Table 7

   

 3. Assessing flood risk

The level of assessment will depend on the degree of flood risk and the scale, nature and location of the proposed development. Refer to Table 5-1 regarding the levels of assessment.   Not all of the prompts listed below will be relevant for every application.

Topography

Include general description of the topography local to the site. Where necessary, site survey may be required to confirm site levels (in relation to Ordnance datum).

Plans showing existing and proposed levels.

SPD Section 2.3

SFRA Appendix B, Figure B1

Site Survey

   

Landscape and Vegetation

Include a description of the landscape and existing vegetation on the site.

SPD Section 2.3

   

Geology

General description of geology local to the site.

SPD Section 2.3

SFRA Appendix B, Figure B2, B3

Ground Investigation Report

   

Watercourses

Identify Main Rivers and Ordinary Watercourses local to the site.

SPD Section 2.3

SFRA Appendix B, Figure B4

   

Flooding from Rivers

Provide a plan of the site and Flood Zones.

Identify any historic flooding that has affected the site, including dates and depths where possible.

How is the site likely to be affected by climate change?

Determine flood levels on the site for the 1% annual probability (1 in 100 chance each year) flood event including an allowance for climate change.

Determine flood hazard on the site (in terms of flood depth and velocity).

Undertake new hydraulic modelling to determine the flood level, depth, velocity, hazard, rate of onset of flooding on the site.

SPD Section 2.3

SFRA Appendix C

Environment Agency Products 1-7.

New hydraulic model.

   

Flooding from Land

Identify any historic flooding that has affected the site.

Review the local topography and conduce a site walkover to determine low points at risk of surface water flooding.

Review the Risk of Flooding from Surface Water mapping.

Where necessary, undertake modelling to assess surface water flood risk.

SPD Section 2.3

SFRA Appendix D.

Topographic survey.

Site walkover.

New modelling study.

   

Flooding from Groundwater

Desk based assessment based on high level BGS mapping in the SFRA.

Ground survey investigations.

Identify any historic flooding that has affected the site.

SPD Section 2.3

SFRA Appendix B, Figure B2, B3, B5.

Ground Investigation Report

Hydrology Report

   

Flooding from Sewers

Identify any historic flooding that has affected the site.

SPD Section 2.3

SFRA Appendix B Figures B7 and B8.

Where appropriate an asset location survey can be provided by Thames Water Utilities Ltd[1]

   

Reservoirs, canals and other artificial sources

Identify any historic flooding that has affected the site.

Review the Risk of Flooding from Reservoirs mapping.

SPD Section 2.3

Risk of Flooding from Reservoirs mapping (EA website).

   

Sequential Test

Determine whether the Sequential Test is required.  

Consult Elmbridge BC to determine if the site has been included in the Sequential Test.

If required, present the relevant information to Elmbridge BC to enable their determination of the Sequential Test for the site on an individual basis.

SPD Section 2.4

Land Availability Assessment[2]

   

Exception Test

Determine whether the Exception Test is necessary.

Where the Exception Test is necessary, present details of:

Part 1) how the proposed development contributes to the achievement of wider sustainability objectives as set out in the Elmbridge BC Sustainability Appraisal Scoping Report.

Part 2) how the proposed development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall. Details of how part 2 can be satisfied are addressed in the following part 5 ‘Managing and Mitigating Flood Risk’.

SPD Section 2.4

Refer to Elmbridge SA Scoping Report sustainability objectives.

SPD Section 2.5

   

5. Managing and Mitigating Flood Risk

Section 5 of the SFRA presents measures to manage and mitigate flood risk and when they should be implemented. Where appropriate, the following should be demonstrated within the FRA to address the following questions:

How will you ensure that the proposed development is safe for its lifetime?

How will you ensure that the proposed development and the measures to protect your site from flooding will not increase flood risk elsewhere?

Are there any opportunities offered by the development to reduce flood risk elsewhere?

What flood-related risks will remain after you have implemented the measures to protect the site from flooding (i.e. residual risk) and how and by whom will these be managed over the lifetime of the development (e.g. flood warning and evacuation procedures)?

Development Layout and Sequential Approach

Plan showing how sensitive land uses have been placed in areas within the site that are at least risk of flooding.

SPD Section 2.5

   

Finished Floor Levels

Plans showing finished floor levels in the proposed development in relation to Ordnance Datum taking account of indicated flood depths.

SPD Section 2.5

   

Flood Resistance

Details of flood resistance measures that have been incorporated into the design. Include design drawings where appropriate.

SPD Section 2.5

   

Flood Resilience

Details of flood resilience measures that have been incorporated into the design. Include design drawings where appropriate.

SPD Section 2.5

   

Safe Access / Egress

Provide a figure showing proposed safe route of escape away from the site and/or details of safe refuge. Include details of signage that will be included on site.

Where necessary this will involve mapping of flood hazard associated with river flooding. This may be available from Environment Agency modelling, or may need to be prepared as part of hydraulic modelling specific for the proposed development site.

SPD Section 2.5

   

Floodplain Compensation Storage

Provide calculations or results of a hydraulic modelling study to demonstrate that the proposed development will not increase flood risk to neighbouring or will result in an overall improvement.     This could be through the provision of compensatory flood storage or removal of non-floodable structures and should be subject to appropriate maintenance regimes for its lifetime. Include cross sectional drawings clearly showing existing and proposed site levels.

SPD Section 2.5

   

Flood Voids

Provide evidence of flood voids to be incorporated underneath finished floor levels

SPD Section 2.5

   

Flow Routing

Provide evidence that proposed development will not impact flood flows to the extent that the risk to surrounding areas is increased.   Where necessary this may require modelling.

SPD Section 2.5

   

Riverside Development Buffer Zone

Provide plans showing how a buffer zone of relevant width will be retained adjacent to any Main River or Ordinary Watercourse in accordance with requirements of the Environment Agency or Surrey County Council.

SPD Section 2.5

   

Surface Water Management

Completion of SuDS Proforma for all major development proposals in Flood Zones 1, 2 or 3.

Details of the following within FRA for all other developments located within Flood Zones 2 and 3:

Calculations (and plans) showing areas of the site that are permeable and impermeable pre and post-development.

Calculations of pre and post-development runoff rates and volumes including consideration of climate change over the lifetime of the development.

Details of the methods that will be used to manage surface water (e.g. permeable paving, swales, wetlands, rainwater harvesting).

Where appropriate, reference the supporting Outline or Detailed Drainage Strategy for the site.

Information on proposed management arrangements

SPD Section 2.5

Surrey County Council website[3]

Water, People, Places[4]

   

Flood Warning and Evacuation Plan

Where appropriate reference the Flood Warning and Evacuation Plan or Personal Flood Plan that has been prepared for the proposed development (or will be prepared by site owners).  

SPD Section 2.5

   

 

1. http://www.thameswater-propertysearches.co.uk/ [back]
2. http://www.elmbridge.gov.uk/ [back]
3. http://new.surreycc.gov.uk/people-and-community/emergency-planning-and-community-safety/flooding-advice/more-about-flooding/suds-planning-advice [back]
4. http://www.eastsussex.gov.uk/ [back]