Dorset Council Level 1 Strategic Flood Risk Assessment

This page relates to the Level 1 Strategic Flood Risk Assessment (SFRA) for the Dorset Council area. The council is obliged to complete SFRA for its area to help guide work on local, minerals and waste, and neighbourhood plans, along with decision taking on planning applications.

Purpose of SFRA

SFRA provide an overview of the risks from all sources of flooding, assessments of the cumulative impacts that development might have on flood risks and forecasts of the effects of climate change on flood risks. The assessments presented in the SFRA are based on the best evidence that was available at the time they were prepared.

Background to the Level 1 SFRA for Dorset Council

The existing development plan documents in the Dorset Council area include local plans:

Christchurch and East Dorset Local Plan Part 1 – Core Strategy (2014)
North Dorset Local Plan (2016)
Purbeck Local Plan Part 1 (2012)
West Dorset, Weymouth & Portland Local Plan (2015)

And minerals and waste local plans, including:

Minerals Strategy 2014
Minerals Sites Plan 2019
Waste Plan 2019

And relevant neighbourhood plans (please refer to the council’s dedicated neighbourhood plan making pages for the full list).

The predecessor councils gathered their own evidence on flood risk to inform the plan making processes connected with these development plan documents. The spatial scope of the SFRA are tied to the development plan areas, and are based on the understanding of flood risks, planning policy and guidance at the time of the plans’ production.

Scope and content of the Level 1 SFRA for Dorset Council

Scope

Planning policy and guidance has changed over time, together with our understanding of flood risk. When Dorset Council was formed it committed to preparing a new local plan for the unitary authority area.

To inform this plan making process, along with plan making connected with other development plan documents, and decision taking on planning applications the council has prepared a new Level 1 SFRA for the Dorset Council area.

Content

The SFRA includes the latest information on the following sources of flood risk:

river and coastal flooding
surface water flooding
groundwater flooding
reservoir flooding

It also includes assessments which forecast future flood risks taking account of climate change. These assessments are limited to the design flood event (i.e. those events with a 1 in 100 year return period) in selected river catchments around several key settlements, and for surface water flooding.

Together with the data on flood risks the SFRA also presents information relating:

flood alert and warning areas
flood defences
records of historic flooding

Presentation of information in the Level 1 SFRA

The SFRA includes both a written report with appendices and maps showing flood risks. The report and appendices are presented as written documents which can be accessed below:

Alongside the technical reports, the maps showing the flood risks from different sources are presented on the council’s online Level 1 SFRA maps on Dorset Explorer. These maps show the flood risks from main rivers and coastal flooding (Flood Risk Zones) with allowances for climate change also applied to those flood events with a 1 in 100 return period in selected locations.

The SFRA also presents the following data on other sources of flood risk:

surface water flood risk mapping
surface water flood risk mapping for those flood events with a 1 in 100 year return period with an allowance for climate change applied (the climate change allowances have been applied to the modelled flood events across the council area)
groundwater risk of emergence data
reservoir flooding

Alongside this data the SFRA also presents contextual spatial information relating to flood risk that may be relevant when seeking to assess risk, or otherwise material to development proposals. This information includes details of historic flooding including:

Environment Agency data showing flood outlines and flood mapping;
council records of flood investigations (These have not been presented at property level scale as not all have been subject to verification. instead they show broad areas where investigations have been carried out and give an indication of the numbers of investigations within the given area. A darker colour indicates a greater number of investigations);

The information also includes flood alert and warning areas, and Environment Agency records on spatial flood defences

Further work and ongoing review

The SFRA is an important evidence document which must be taken into consideration when preparing local and neighbourhood plans and when taking decisions on planning applications.

In many instances the data on potential risks from other sources of flooding (surface water flood risks, groundwater risk of emergence and reservoir flooding) should be used by applicants as a prompt to undertake more detailed site-specific flood risk assessments to guide decision taking on their proposals. The council’s local validation requirements cross reference the data presented in the SFRA and outline the screening triggers for undertaking the more detailed site specific assessments.

The changing nature of flood risks and the publication of new evidence, means that the council will need to regularly review its approach to this issue in the longer term, taking account of the nature of forecast risks and the opportunities to effectively control, manage and mitigate these risks. Following preparation of the SFRA maps there have been some updates to Environment Agency Flood Risk Zones. Where there is now an inconsistency between an earlier SFRA map and the latest mapping showing Flood Risk Zones applicants should contact the council about the most appropriate way of resolving this issue. Where necessary we may ask applicant’s site specific Flood Risk Assessments to re-define Flood Risk Zones 3a and 3b using the Environment Agencies’ latest mapping. We are also considering whether updates to the existing evidence base are required.