FLOOD RISK

EMAIL:INFO@FLOODRISK-DRAINAGE.CO.UK

If your development falls into either of the categories it will require a FRA.

 

Flood Zone 1

 

• Larger than 1 Hectare in Size

• Change of use to a higher vulnerability classification

• Located within a CDA (Critical Drainage Area)

• Located within an area of pluvial (surface water) flooding

• Basement within an area of high groundwater

 

In general, the main focus of FRA’s within Flood Zone 1 will be to demonstrate that the site can suitably manage the increase in surface water runoff as a result of the development, which means developing a suitable drainage design to satisfy the statutory authorise.

 

Flood Zone 2

 

• Located within an area considered to be medium risk of fluvial (watercourse) flooding i.e. the 1 in 1000-year return period or 0.1% AEP.

 

Developments within Flood Zone 2 will require determination of flood depths across the site in relation to fluvial sources, this is generally achieved by undertaking a comparison of site levels against flood levels. As well as an appraisal of flooding from secondary sources such as surface water flow routes, groundwater, canals, reservoirs, infrastructure failure, blockage etc.

 

Once depths have been established, an evaluation of suitable flood mitigation measures which can be incorporated into the development can be undertaken, along with requirements to establish if safe access and egress can be achieved.

 

A drainage design will also have to be submitted as part of the FRA, to ensures that the site can suitably manage surface water flows as a result of the development.

 

New developments within Flood Zone 2 generally require a Sequential Test, to determine if there are any more preferable sites located of a lesser flood zone, within a defined geographical search area.

 

Flood Zone 3

 

• Located within an area considered to have a high risk of fluvial flooding i.e. the 1 in 100-year return period or 1% AEP.

 

Developments within Flood Zone 3 will have to undertake all of the same appraisal as developments within Flood Zone 2 with the addition of the following.

 

If the site is located within an area considered to be benefiting from flood defences (ABD), an evaluation of breach will be required. This will calculate a flood depth and velocity through the site in the event that the flood defence was to fail and the corresponding risk to people.

 

Any additional footprint of buildings or raising of levels within Flood Zone 3, will require Flood Storage Compensation provided on a level by level basis, within an area outside of Flood Zone 3. This is to prevent displacement of flood volumes as a result of the development, which can increase the flood risk to others downstream of the site.

 

Developments located within Flood Zone 3 will require a Sequential Test and the addition of the Exceptions Test, this will provide evidence that the proposal will provide sustainability benefits to the local and wider environment.

 

*Detailed Planning Applications will require a more in-depth appraisal compared to Outline Planning Applications.

 

Use the link below to see what Flood Zone your development is in.

Our NPPF Flood Risk Assessments are site specific and comply with requirements set by the Environment Agency, Lead Local Flood Authority and Planning Authorities. 

A Breakdown of what can be Included within our Flood Risk Assessments

 

Flood Risk

 

• Consultation with the Lead Local Flood Authority and Environment Agency (If applicable)

• Undertake a site visit – walkover and photographic survey. (If applicable)

• Research history of flooding both at and within the area surrounding the proposed development using flood data.

• Fluvial Flood Risk- i.e. major watercourses, minor ordinary watercourses

• Non-fluvial Sources of Flood Risk – undertake an evaluation of flood risk from the following sources:

o Groundwater

o Pluvial – sewers, ponding, surface water flood routes, overland flow

o Artificial – fishing lakes, canals, reservoirs

o Infrastructure failure – water mains, pumping stations, sluice gates; culverts, bridges

• Mitigation Measures

o Finished Floor Levels

o Resilience/Resistance (If Required)

o Flood Storage Compensation (If Required) 

o Access and Egress (If Required)

o Easements (If Required)

o Consents (If Required)

 

Surface Water/Foul Drainage

 

• Review Site Investigation reports and Percolation Test results

• Building Regulations Hierarchy:

o Infiltration – site investigation report; ground mapping and local borehole logs to examine feasibility for dissipation to ground

o Watercourse – identify location of nearest watercourse to site and evaluate feasibility for direct discharge

o Sewer – identify nearest public surface water and combined sewers to site; and any existing connections which can be re-utilised.

• Measure existing on-site area i.e. landscaped and hardstanding areas 

• Estimate existing surface water runoff/discharge rates

• Measure proposed catchment areas i.e. roof; hardstanding and landscaped areas

• Undertake preliminary calculation to determine a requirement for on-site attenuation

• Undertake detailed evaluation of SUDS appropriate for inclusion within the drainage strategy

• Hydraulic modelling proposed drainage system:

o 1 in 1 year or 2-year 

o 1 in 30-year 

o 1 in 100-year plus appropreate inclusion of climate change 

o Undertake modelling to test for local system failure.

• Foul arrangement and point of connection

• Provide necessary drawings as required for outline/full planning applications

• Provide Drainage Impact Assessment reporting