Ordinary watercourse flood extents
Planning guidance to satisfy Lead Local Flood Authority (LLFA) requirements regarding ordinary watercourse, as well as their inclusion as part of a flood risk assessment.
Background
There are several watercourse designations which are highlighted on our Types of watercourses page.
The Environment Agency provide information on Main Rivers and as part of this they produce a map of Flood Zones. For further information see the designation of main rivers guidance - GOV.UK. We provide information on ordinary watercourses and have produced a map of ordinary watercourses flood extents (OWFE).
What are ordinary watercourse flood extents (OWFE) and what do they mean?
As part of our Surface Water Management Plan (2012), flood risk modelling studies were conducted on six ordinary watercourses within the city to determine flood risk:
- Ethel Brook (tributary of the Evington Brook)
- Gilroes Brook (tributary of River Soar)
- Hol Brook (tributary of the Saffron Brook)
- Portwey Brook (flows into the sewer network)
- Queen’s Road Brook (flows into the sewer network)
- Western Park Brook (tributary of the Braunstone Brook)
This modelling was updated and the ordinary watercourse flood extents were mapped, as part of the Strategic Flood Risk Assessment (2022).
OWFE (ordinary watercourse flood extents) are split into four categories and represent the areas of modelled flooding associated under set return periods, (with an estimated annual probability) as follows:
|
OWFE classification |
Return period |
Annual probability |
|
OWFE1 |
Less than 1 in 1000-year chance of flooding |
<0.1% |
|
OWFE2 |
Between 1 in 100-year and 1 in 1000-year chance of flooding |
1% - 0.1% |
|
OWFE3a |
Between the 1 in 20-year and 1 in 100-year chance of flooding |
5% - 1% |
|
OWFE3b |
Greater than 1 in 20-year chance of flooding |
>5% |
*Return period: is an estimated average time between events, which is statistically calculated. In this case, it refers to the estimated average time between flooding events of different magnitudes.
*Annual probability: is the likelihood of a flooding event occurring within any given year, expressed as a percentage.
Where are the OWFE published?
The OWFE can be viewed using our flood risk map.
Where a watercourse is not present on either of these maps, it will be considered an ordinary watercourse, but may not have been formally mapped due to its small or isolated nature.
*Please note: OWFE are not the same as Flood Zones - the flood map for planning presents the Flood Zones.
How are OWFE’s used in planning and what is expected as a developer or applicant?
OWFE’s have been integrated into our planning process and are considered planning constraints. The LLFA are consulted when:
- any development of one dwelling or greater (for residential and change of use)
- a proposed building has more than 200sq.m of new build footprint (for all other use classifications)
The OWFE are used by the LLFA to:
- Define modelled flood extents, depths and associated flood risk
- Inform and validate both flood risk assessments and flood risk statements
- Inform to the need to include flood protection (such as raised finished floor levels) and/or flood resilience measures (such as flood doors)
- Evaluate potential exceedance flow routes associated with a development
Ordinary watercourses are a potential source of flood risk to parts of the city, it is important that the flood risk associated with these watercourses is considered as part of an FRA (including the sequential and exception tests). We expect that the same level of adherence to Flood zones, will be applied to the OWFE, and similar information will be submitted as part of the FRA to support planning applications.
Alterations to watercourses and ordinary watercourse consenting
If you are planning to make any alteration to a watercourse, then you must receive consent from the relevant authority. If this is an alteration to an ordinary watercourse in Leicester, then an application for ordinary watercourse consent must be submitted to and approved by us: Apply for consent to alter a watercourse.
Queries and further information
The LLFA are happy to discuss any queries regarding ordinary watercourses and can be contacted by email: flooding@Leicester.gov.uk.
For further information on the Strategic Flood Risk Assessment (2022) and other flood risk studies carried out by us, visit our Flood risk studies section.
If you have a query relating to carrying out a development then please contact the Planning Service through the pre-application advice. If the query has implications for ordinary watercourses, their flood extents and management, then the Planning Case Officer will consult the LLFA.
- Not all ordinary watercourses have been modelled as part of the Strategic Flood Risk Assessment (2022). Further ordinary watercourses may be modelled as part of future modelling work. Although this is the most up-to-date information and data available, errors or omissions may be present. Leicester City Council gives no guarantee as to the accuracy of the information. The council provide this information "as is" without warranties of any kind.
- The OWFE have not been incorporated into the national Flood Zones. This is due to methodological differences (primarily the inclusion of flood defences) and because it is the LLFA (Lead Local Flood Authority) and not the EA (Environment Agency) who are responsible for them.
- The OWFE are published in Leicester City Council’s Strategic Flood Risk Assessment (2022) and have been integrated as a planning constraint so that flood risk to development can be identified and managed accordingly throughout the planning process. The LLFA issues advice as to how best to minimise and manage flood risk posed to development from ordinary watercourses. As a result, this advice is not compulsory, although applicants and developers choosing to ignore this advice, do so at their own risk. Leicester City Council cannot be held responsible for any impacts, loss or damage associated with flooding from an ordinary watercourse arising from failure to comply with this advice.