Natural Flood Management Technical Guidance

Himalayan Balsam is an invasive plant that increases flood risk by outcompeting other vegetation and leaving slopes bare when it dies back in winter.

It should be cleared by pulling, strimming, or cutting. All plants must be completely removed from the site prior to setting seed. To receive the grant, sites must be seen to be clear of Himalayan Balsam at the end of June.

• Pulling: If the plants are to be removed by pulling, the root ball (shown in the photo below) usually comes out of the ground when the plant is pulled. Ensure the stems are then broken from the root-ball and both are composted in piles. If the plant is discarded on the ground without breaking, it may regrow.
• Strimming or cutting: If strimming or cutting, stems will need to be severed below the ‘basal node’ to prevent regrowth.

Picture of Basal Node - the 'join' is the thickest part of the stem:

Earth bunds are a bank of earth following the contour line, used to slow overland water. Ensure these are sited across a slope where there is no risk of landslips. Also, consider section 7 - Attenuation Basins.

• Remove the vegetation layer to be re-laid upon the new bund. Seed bare soils with native grass/wildflower mix.
• Channel to be up to 0.8m in depth, form the bund downhill of the channel using the removed material.
• Side slopes grade to be no more than 1 in 3.

Fascines are tightly packed bundles of branches, felled trees, or coppiced wood. They are laid across a slope to slow down overland water flows and reduce erosion.

The material used is freshly cut to last as long as possible. Any species of wood is suitable, but some species such as Hazel and Willow are easier to work with.

• Fascines are typically designed so they can be carried by hand over rough terrain. Fascines should be 180cm (6 feet) long and 30cm (1 foot) in diameter.
• Tie with 3-ply sisal string in three places to prevent snagging during transit. They will still hold together if one string is damaged while in storage. Sisal makes a strong cord, but one which will eventually biodegrade.
• The fascines are laid out along the contours of eroded or bare slopes. They are held in place with wooden stakes. Use three stakes per fascine, two below near either end or one near the middle, forced through the fascine. The stakes need to be strong enough to last longer than the fascine and are typically around 60cm long and between 20mm and 40mm thick.
• Installation should start at the bottom of the slope, working uphill. The distance between rows is judged by the severity of the erosion and the angle of the slope. The steeper the slope, the nearer the rows are to each other. The more rows there are, the better the result!

Example Fascine:

Image credit: Forus Tree

Leaky barriers or dams are used to slow down water within a stream, small river, or channel during times of high rainfall. They can offer several benefits in terms of reducing downstream flood risk and improvements to water quality.

Spacing: Leaky dams should be spaced seven times the width of the channel. So, if the channel is 1m wide, the dams should be placed every 7 metres.

Specified method:

1. Two logs at the base with another two logs directly on top of them.
2. A final log is placed on the top, positioned in the dip between the two logs below it.
3. The base of the lower logs is positioned at the mid-point between the channel bed and bank top to permit the unhindered passage of low to medium levels and fish.
4. The lower logs are dug 50cm into the bank on either side of the channel or braced against a bankside tree or stump. The top log is positioned on top of the bank and extends out onto either side of the floodplain to enhance floodwater storage.
5. The top log is secured into place using cross stakes driven into the ground and wired together.
6. All logs are wired together to ensure stability.

Image Credit: Applicant's guide for Higher Tier agreements starting on 1 January 2024 - GOV.UK

The installation of leaky dams using stone and other materials may be acceptable. Please discuss this with the CMBC NFM team before undertaking the work.

Live willow revetments are used to slow water that flows through shallow depressions and gullies in times of high rainfall. Living willow is woven around thick upright willow posts. Implement these during winter or early spring. Ensure they are dug into the bank on either side of the channel to reduce collapse.

Spacing: Like leaky dams, these should be spaced seven times the width of the channel. So, if the channel is 1m wide, then they should be placed every 7 metres.

Ditches are to be used to direct overland water into an attenuation basin; your engineer should design the depth of the ditch to accommodate the volume of water required to suit your land. Minimise straight sections of the ditch to reduce fast flows and introduce bends where suitable. Use large stones to reduce erosion where required. Seeding may be required to vegetate the banking of the ditch to reduce erosion.

Attenuation basins temporarily capture rainwater flowing either overland, or from a stream or river in times of high rainfall. By holding this rainwater, the basins slow its journey to our villages and towns below, helping to reduce flooding.

Example Attenuation Basin below Gadding's Dam:

Attenuation basin construction:

Failure to adhere to the below guidance will result in the grant being withheld.

To ensure attenuation basins offer flood protection and do not pose a risk to downstream properties, there is strict guidance on the construction process, and this should be overseen by a suitably qualified engineer with adequate public liability insurance. An ordinary watercourse consent is required for attenuation basins; further details are available in the Application Guidance document.

Choosing a site:

• Consider unmarked and marked underground services/culverts. If you are unsure, it is recommended that trial pits are dug prior to applying for a grant.
• Retain existing routes of the water flowing over your land as much as possible; redirecting water is likely to cause problems.
• The gradient of the slope in which the attenuation basin is placed, and the proximity of property downstream are relevant to the risk. They will be considered by the CMBC flood team when accessing the Ordinary Watercourse Consent application.

Brief for the overseeing engineer:

• Attenuation basins should be excavated below existing ground levels.
• They should only hold 1m depth of water.
• They should have an outlet pipe at the bottom of the bund; the diameter of this must allow for attenuation.
• The basin must drain down within 5 – 20 hours.
• Embankment and cut slopes should be 1 in 3 or shallower.
• The height of the bund should not exceed 1.3 metres.
• The construction of the attenuation basin bund must be photographed, and the photos are to be made available to the council upon request.
• An overspill should be cut into the bund to reduce the height to 1.0 metres. This will allow the basin to accommodate only a water depth of 1.0 metres before overflowing. The route the water will take through the overflow should be protected with stone to reduce erosion.
• Any earthworks shall be constructed from suitable clay soils.
• Placed material shall be compacted in 150mm layers by four passes of the excavator tracks.
• Stone should be used on the inlet and below the outlet pipe to reduce erosion.
• Seed bare soils with a species-rich perennial meadow seed mix designed for swales and basins.

The grant recipient is responsible for Construction (Design and Management) Regulations 2015 and Land Drainage regulations.

Trees should be native species and locally sourced where possible.

Trees should be planted between November and March between 1.5m and 2m apart. It is important that they are planted as soon as they are delivered to the site.

Tree with spiral and cane: when planting tree ‘whips’ (single-stem young trees), you must protect them with a tree spiral and cane.

Tree with 1.2m shelter and stake: it is recommended that this method is used when using more mature trees or where greater protection is needed against animals and the wind.

Hedgerows will only be funded if they are planted across a slope to intercept the overland flow of water.

Hedge plants must be native species and should be locally sourced where possible.

Planting method: six plants per metre arranged in two rows, with three whips in each row, offset from each other in a zig-zag pattern. The distance between the rows: 300mm.

Plants should be protected by hedging protection ‘spirals’, which are biodegradable where possible.

Fencing and gates will only be funded when used to protect other activities included in your application.

Wooden posts with galvanized mesh tightly strung between the posts. Use this category in locations where a tractor can aid installation.

Fencing and gates will only be funded when used to protect other activities included in your application.

Wooden posts with galvanized mesh tightly strung between the posts. Use this category in locations where a tractor cannot be used to aid installation.

Fencing and gates will only be funded when used to protect other activities included in your application.

Use wooden posts with 1.8m galvanized mesh tightly strung between the posts

Fencing and gates will only be funded when used to protect other activities included in your application.

The gate can be wooden or metal but must be the same height as the fencing and be fitted with adequate hinges and a method of closure.

Considered woodland thinning can enhance the health of a woodland, increase biodiversity, and offer natural flood management benefits. Removal and coppicing of selected trees allow more light to the woodland floor, encouraging vegetation to grow, which will interrupt the flow of water overland.

A felling license is likely to be necessary to undertake this work: Tree felling licence: when you need to apply - GOV.UK

If you include woodland thinning in your application, please consider adding fascines using the cut material and planting new trees.

For the employment of a professional tree surgeon to undertake woodland management on more mature trees.

A felling license is likely to be necessary to undertake this work.

Tree felling licence: when you need to apply - GOV.UK

If you include woodland management in your application, please consider adding fascines using the cut material and tree planting.

Use this category when proposing a project outside the scope of the other categories of the grant, where access is difficult, or the work is complex. If you are seeking funding under this heading, contact the Calderdale Natural Flood Management Team before proceeding with the application: [email protected]

All ‘Special Projects’ will require detailed plans to be drawn up by a professional, and the grant offered will be based on a contractor quote supplied by the applicant upon application. Projects with a cost of over £2,500 will require quotes from two different contractors.

Use this category for support from an engineer and/or project manager. Project management costs should not exceed 10% of the total cost of capital works.

An interpretation board shall be made of hard-wearing materials with an expected lifespan of at least ten years.

The interpretation board must be printed clearly, and feature text provided by the Council regarding Calderdale’s NFM work, and the source of the grant funding (Environment Agency).

The Calderdale NFM team can assist with the design of your interpretation board for free. The supply and installation of the board is managed by the applicant (or their project manager).