Environmental Consultants - Flood Risk Assessment

 

Flood Risk Assessment


SWEL can undertake a flood risk assessment in any part of the UK, our standard report includes the sequential test, the exceptions test and a surface water management plan.

Flood Risk Assessment is now a big part of any new development, and you may well be asked to complete one in the planning stage of a project, you may be asked for a flood risk report during the planning phase. Where will SWEL undertake a Flood Risk Assessment?

The need for a FRA originates from the Pitt Review findings which has manifested its self in PPS 25 (Planning Policy Statements), and then from March 2012 the new Planning Policy Frame Work and its Technical Guidance.

Flood Risk Reports look at the sites characteristics and tries to gauge the risk of flooding.
Environmental Consultants - Flood Risk Assessment

Flood Risk Map for Taunton, Bridgwater, Bristol, Southwest UK

Flood Risk Assessment Reports:

Site Specific Flood Risk Assessment is used to establish flood risk for large sites such as housing developments, to where surface water management and flood data may have to be gather in a site specific context. However in most cases for small to medium sized projects a single phase flood risk report is all it takes to satisfy planning conditions.



Flood Risk FAQs

What is a Flood Risk Screening Study Report?   What is a Flood Risk Scoping Study Report?   What is a Flood Risk Detailed Study Report?
         
Flood Risk - What is the Sequential Test?   Flood Risk - What is the Exceptions Test?   What is a Safe / Temporary Refuge?
         
Finished Floor Levels in Relation to Flood Risk   Flood Risk - What is a Surface Water Management Plan?   Flood Design: Resilient vs Resistant
         
Flood Resistant Design in Building Homes and Offices   Flood Resilient Design in Building Homes and Offices   Flood Risk Photo Gallery

Explaining SFRAs

Level 1 - Screening Study   Level 2 - Scoping Study   Level 3 - Detailed Study

Demonstrating the flood risk (PPS25) Sequential Test for Planning Applications

SWEL have considerable experience in demonstrating the sequential test for small scale planning applications. Our method for the sequential test has met with 100% acceptance with a variety of local planning authorities.

Please feel free to telephone the office for an informal discussion regarding any of the services we provide.



Disclaimer - Information on this Site

What is a Flood Risk Screening Study Report?

A Flood Risk Assessment Screening Study is the least complicated of the three main flood risk report types. It is suitable for sites that are required to submit FRA Reports, but are sited in low risk areas.

A Flood Risk Assessment Screening Report contains the following information.

1
Screening
Study

(Requirements of)
• Strategic Flood Risk Assessment
• Environment Agency Flood Map
• Environment Agency Standing Advice
• PPS25 table D.1
• Surface Water Management Plan and Water Cycle Study
 

What is a Flood Risk Scoping Study Report?

 Flood Risk Assessment Screening Study is the least complicated of the three main flood risk report types. It is suitable for sites that are required to submit FRA Reports, but are sited in low risk areas.

A Flood Risk Assessment Screening Report contains the following information.


2

Scoping
Study
(Requirements of)
- Strategic Flood Risk Assessment
- Environment Agency Flood Map
- Environment Agency Standing Advice
- PPS25 table D.1
- Surface Water Management Plan and Water Cycle Study
- Regional or local policy statements or guidance (e.g. Regional Spatial Strategies,
  Local Development Documents)
- Regional Flood Risk Appraisals
- Catchment Flood Management Plans/Shoreline Management Plans/River Basin
  Management Plans
Flood Risk Assessment Scoping Study
- Surface Water Management Plans
- Consultation with the LPA/Environment Agency/sewerage undertakers and other
  flood risk consultees to gain information and to identify, in broad terms, what
  issues, related to flood risk, need to be considered including other sources of
  flooding
- Historic maps
- Local libraries and newspaper reports
- Interviews with local people and community groups
- Walkover survey to assess:
– Potential sources of flooding
– Likely routes for flood waters
– The site’s key features, including flood defenses, and their condition
- Site survey to determine:
– General ground levels across the site
– Levels of any formal or informal flood defenses relevant to the site
- Other documents listed in Appendix C of this Guide.

What is a Flood Risk Detailed Study Report?

A Flood Risk Assessment Detailed Study is the most complicated of the three main flood risk report types. It is suitable for large sites that are required to submit FRA Reports, which can be sited in low, medium or high risk areas.

A Flood Risk Assessment Screening Report contains the following information.


3

Detailed
study
(Requirements of)


- Strategic Flood Risk Assessment
- Environment Agency Flood Map
- Environment Agency Standing Advice
- PPS25 table D.1
- Surface Water Management Plan and Water Cycle Study
- Regional or local policy statements or guidance (e.g. Regional Spatial Strategies,
  Local Development Documents)
- Regional Flood Risk Appraisals
- Catchment Flood Management Plans/Shoreline Management Plans/River Basin
  Management Plans
- Surface Water Management Plans
- Consultation with the LPA/Environment Agency/sewerage undertakers and other
  flood risk consultees to gain information and to identify, in broad terms, what
  issues, related to flood risk, need to be considered including other sources of
  flooding
- Historic maps
- Local libraries and newspaper reports
- Interviews with local people and community groups
- Walkover survey to assess:
– Potential sources of flooding
– Likely routes for flood waters
– The site’s key features, including flood defences, and their condition
- Site survey to determine:
– General ground levels across the site
– Levels of any formal or informal flood Environmental Consultants defences relevant to the site
- Other documents listed in Appendix C of this Guide.
- Detailed topographical survey
- Detailed hydro graphic survey
- Site-specific hydrological and hydraulic modelling studies which should include
  the effects of the proposed development
- Monitoring to assist with model calibration/verification
- Continued consultation with the LPA, Environment Agency and other flood risk
  consultees.

What is a Safe / Temporary Refuge?

A temporary “safe refuge” - is any place or structure where individuals trapped by floodwater (those who did not receive or ignored flood warnings) can remain for a short period in relative safety whilst awaiting rescue thus lowering flood risk. Provision of refuges within buildings makes developments safer and lowers risk of flood related harm. PPS 25, para 4.66 states - safe refuges play a role in reducing the overall risk of flooding.

Safe refuges should be above the 0.1%AEP event tide level at the end of the development’s life. Effectively this means most buildings in the flood plain need to be greater than 1 story high. 

Please feel free to contact the office for an informal discussion regarding your requirements.

Finished Floor Levels in Relation to Flood Risk

Finished Floor Levels:

-To match existing (redevelopment).

-300mm above the general ground level of the site OR

-average ground level of the site in relation to 600mm above the 1 in 100 annual probability river Ordnance Datum flood (1%); or

-1 in 200 annual probability sea flood (0.5%) in any year (including an allowance for climate change).Basement rooms to have unimpeded access internally to an upper level.

Finished floor levels must take in to account level rises from climate change.

finished_floor_levels

Please feel free to contact the office for an informal discussion regarding your flood risk report requirements.

Flood Resistant Design in Building Homes and Offices

Material Water Penetration Drying Ability Retention of pre-flood dimensions
Bricks      
Engineering bricks (Classes A and B) Good Good Good
Facing bricks (pressed) Medium Medium Good
Facing bricks (handmade) Poor Poor Poor
Blocks      
Concrete (3.5N, 7N) Poor Medium Good
Aircrete Medium Poor Good
Timber board      
OSB2, 11mm thick Medium Poor Poor
OSB3, 18mm thick Medium Poor Poor
Gypsum plasterboard      
Gypsum Plasterboard, 9mm thick Poor Poor Poor
Mortars      
Below d. p.c. 1:3(cement:sand) Good Good Good
Above d. p.c. 1:6(cement:sand) Good Good Good

General advice for resilient design

Where concrete ground floor slabs are used, the block work substructure is often the weakest point in terms of water penetration from the ground into a dwelling. Whereas there is a general perception that water can ingress through the block work structure of the external face of a wall into the property, it is less apparent, but equally possible, that water will penetrate from the ground on the inside of the pro perty. Figures 6.2 and 6.3 illustrate these flow paths for two types of ground floor (ground bearing floor and suspended concrete floor), and different types of foundation (typical for construction in England).  Concrete blocks used in foundations should be sealed with an impermeable material or encased in concrete to prevent water movement from the ground to the wall construction.

Flood Risk Assessment - Flood Resistant or Flood Resilient Design?

Flood Resistant Flood Resilient
Flood Resistant – prevent the building from flooding. A “water exclusion strategy”. 

OK if you aren’t expecting more than 300mm flood depth.

 

For Example: Vent Covers

 

flood resistance

Rytons Flood Vent Covers

Flood Resilient – Doesn’t get too badly damage when it gets wet. A “water entry strategy”. 

Reduces risk of damage from water pressure on wall when flooding 600mm or more.

 

 

 

Where will SWEL undertake a Flood Risk Assessment?

We will carry out a Flood Risk Assessment in any part of the UK, we have offices in London, Bristol and Exeter.

Please feel free to contact the office for an informal discussion regarding your requirements.

Flood Risk Consultants Bristol

Flood Risk Consultants Exeter

Flood Risk Consultants London

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Flood Risk Consultants

Bristol - 01173 270 092

Exeter - 01398 331 258

London - 02076 920 670

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