RP33: Large leaky woody dams

From:: Natural England
Published:: 10 March 2017
Last updated:: 18 September 2017, see all updates
Grant type:: Capital item
Land use:: Flood risk and Woodland
Tiers or standalone items:: Higher Tier
Funding (per unit per year):: More than £500

Find out about eligibility and requirements for the large leaky woody dams item.

How much will be paid

£764.42 for each dam

Where to use this item

Available for Higher Tier

Only:

in catchments targeted for flood risk measures
for dams in streams and river channels between 3m and 5m
where approved by the Environment Agency or Lead Local Flood Authority

How this item will benefit the environment

Leaky woody dams will slow the movement of water and help push flows onto the floodplain during floods. This will increase temporary storage of flood waters within water channels and out on to the floodplain, help delay the passage of flood water downstream, allow sediment to settle out, and reduce downstream flood risk.

Requirements

Agreement holders will need to:

follow the indicative drawings in the Higher Tier manual Annex 2c for maximum effectiveness
construct the dam from logs large enough to span the water channel and out on to the floodplain to provide a stable and long-lasting structure
secure the dam in line with the requirements of the Environment Agency or Lead Local Flood Authority
align dams at right angles to channel banks to reduce bank scour
build dams to allow low flows to pass unimpeded at all times
site dams on slow flowing reaches of the water course that have on average 2m of floodplain on either side
build dams to a height sufficient to encourage water to spread onto the floodplain upstream of the dam
build dams in series (minimum 3 dams) at a spacing between dams of about 5-7 times the width of the channel
make sure dams are not installed directly upstream of pinch points such as bridges or culverts that back up flows and are likely to swamp the dam
check and maintain dams to keep the structure effective
follow the requirements set out in any Feasibility Study or CSF Design Plan

Keeping records

Agreement holders will need to keep the following records and supply them on request:

any consents or permissions connected with the work
receipted invoices, or bank statements where a receipted invoice is unavailable
a copy of any feasibility study, or woodland management plan where applicable
please see the record keeping and inspection requirements as set out in the Higher Tier manual for more detail

Agreement holders will need to keep the following records and supply them with the claim:

photographs of the site during the different stages of the construction or build; or contracts, invoices or other documents confirming the technical specification for the completed works
photographs of the completed works in place and installed

Before applying, applicants must seek advice from the Environment Agency and where relevant the Lead Local Flood Authority to check if consent is required to carry out the planned work.

Applicants will have to send the following with their application:

a copy of any advice or consent received from the EA, and (where relevant) the Lead Local Flood Authority
photographs of the existing site
a copy of the Feasibility Study or CSF design plan (Water-Holding Feature Management Plan)

Advice and suggestions for how to carry out this item

The following section gives advice on carrying out this item successfully but does not form part of the requirements for this item.

Detailed design can vary and the siting of leaky woody dams in natural water courses will be dictated by local circumstances and availability of or easy access to import suitable materials to site. Higher Tier manual Annex 2c has details of indicative design of dams.

Check the dams for silt

The dam will need to be checked and may need de-silted regularly to prevent it collecting large amounts of silt.

Further information

The management of water on the land can be improved by using Rural Sustainable Drainage Systems (RSuDS). See the guide to RSuDS for more information.

Catchment Sensitive Farming (CSF) operates in parts of the country where there are water quality issues linked to farming. The scheme provides farmers with free advice and training. See guidance for further information on CSF support.

See the Higher Tier manual to find out more about the scheme and how to apply.

Document information

Published: 10 March 2017

Updated: 18 September 2017

+ full page history

14 September 2017 Capital item now includes woodland.
10 March 2017 First published.