Flood Risk and Drainage for Planning

Not all planning applications need to provide the detailed flood risk and drainage information outlined on this page. Mid Sussex District Council’s Flood Risk and Drainage Team have created a criteria which should form a starting point for applicants as to whether this expanded level of information is needed.  

It is important to be aware, however, that the standard criteria is a starting point and other types of development may be asked to provide expanded flood risk and drainage information following consultation responses, or at the request of the planning officer.  

Planning Consultees 

Depending on the identified flood risk, the type of development and the size of the site, a variety of consultees may provide comment on a planning application.  

The Environment Agency – look at all applications for sites in Flood Zone 2 or 3, and all sites larger than 1 hectare along with any sites that are building adjacent to or over designated Main River. 

The Lead Local Flood Authority (LLFA) – in Mid Sussex this is West Sussex County Council and they provide comment on all major applications, applications for sites in Flood Zone 2 and 3, sites at a high risk of surface water flooding and sites larger than 1 hectare. They will also provide comment when asked to do so by the planners or MSDC’s flood risk and drainage team.  

Mid Sussex District Council – The Flood Risk and Drainage Team review major and minor applications and provide consultation responses in relation to flood risk and the proposed drainage arrangements

The basic flood risk and drainage information required is the same for all planning applications which meet our review criteria, regardless of scale, location or type of application. The level of detail within this information is what changes depending on the scale and type of application.  

This page provides guidelines to the information applicants should provide in relation to flood risk and drainage at the application stage and then at the discharge of conditions stage.

Below is a summary of the information we would expect to see at the application stage of a development. A downloadable checklist with full details is available here 

Application Details

• Application number 
• Site address 
• Site co-ordinates 
• Site area in hectares 
• Existing site usage 
• Proposed development 
• Block plan 
• Existing site plan 
• Proposed development plan

Flood Risk Details

• Flood zone the site is located within. 

This can be found via the online flood map for planning service provided by the Environment Agency (https://flood-map-for-planning.service.gov.uk/).  

• The surface water flood risk on the site.  

This can be found via the online long term flood risk service provided by the Environment Agency (https://flood-warning-information.service.gov.uk/long-term-flood-risk). 

• Flood Risk Assessment if appropriate (see below). 

When do I need a flood risk assessment?

The Environment Agency has provided guidance as to when a Flood Risk Assessment (FRA) needs to be submitted as part of planning. This includes developments with any part of the site:  

• within flood zones 2, 3 or 3b 
• within flood zone 1 with a site area of 1 hectare or more 
• within areas with critical drainage problems 
• within flood zone 1 where your LPA’s SFRA shows it will be at risk of flooding from rivers or the sea in future 
• that increases the vulnerability classification and is in flood zone 1 where your LPA’s SFRA shows it is at risk from other sources of flooding 

The requirements for a FRA are different depending on the type and severity of the flood risk on site. The Environment Agency and DEFRA have created three guides and advice on how to complete FRAs. The FRAs should be completed by an appropriately qualified person who should check which advice they should follow before starting work on the FRA (https://www.gov.uk/guidance/flood-risk-assessment-for-planning-applications). 

Many watercourses in the district have not been modelled by the Environment Agency so areas of flood risk from these watercourses are not included in flood zone 2 or 3. These flood areas are usually shown as areas of surface water flood risk.  

MSDC categorises areas of high and medium surface water flood risk as being the equivalent of Flood Zone 3 and areas of low surface water flood risk as being the equivalent of Flood Zones 2 in terms of flood risk.  

We would advise developers to take this into consideration when assessing a site in relation to flood risk and preparing an appropriate FRA.  

Site and development specific advice will be provided as part of the Flood Risk and Drainage Team’s consultation response at the application stage. However, the information below provides a summary of the basic information we would expect to see at the Discharge of Conditions stage of a development.   

A downloadable checklist with full details is available here. 

Application details

• Application number (including numbers for previous outline and reserved matter applications) 
• Site address 
• Site co-ordinates 
• Site area in hectares 
• Existing site usage 
• Finalised proposed development 
• Block plan 
• Existing site plan 
• Finalised proposed development plan 

Flood risk details

• The flood risk from all sources, including from rivers (fluvial), surface water, sewers and artificial sources both now and into the future; and any flood flow routes across the site arriving from other land.  
• Any measures included within the development to protect the development from flooding.  
• Any measures being taken to ensure that flood risk is not increased elsewhere including any intended or potential off site works. 

It may be that the Flood Risk Assessment provided at planning covers these points. In this event the FRA can be resubmitted with a covering note which confirms what flood protection or management measures will be used on site.  

Any application that could be described as containing any of the following should provide expanded details of the flood risk and drainage; 

• Any major development (as defined by planning). 
• Any new build development including demolition and rebuild which provides a new industrial, commercial or residential unit.  
• Large extensions which increase built footprint by approximately 50% or greater.  
• Construction of new or modifications to surface water features. This includes but is not limited to; the creation or changes to a pond within a watercourse, works to a watercourse, construction or alteration of a weir or the building of a new swimming pools etc. 
• Any subterranean development, including change of use. 
• Any development located in an area at risk of flooding from any source.  

The Flood Risk and Drainage Team may be consulted by Development Control and as a result request additional details from the applicant (for any type of development), however, the above forms the initial criteria used to determine whether the Flood Risk and Drainage Team provide a consultation response.