Devon field boundaries: restoration standards for agri-environment schemes (TIN039)

Earth bank restoration

The aim is to restore degraded earth banks to their original profile. The profile can be established by reference to other hedge banks on the holding, and traditional practices in the area. All old fencing must be removed before work starts and under no circumstances should it be buried under the new earth.

The original soil, which has slipped from the bank over time, should be used to build the bank up to the required height. There are often clues to the original height of the bank, such as old laid stems or exposed tree roots, but where no evidence remains a rough guide to height is 1.2 - 1.5m (4 - 5ft). Do not build the bank to an excessive height, as this will compromise stability.

Figure 1 Good example of restored earth bank with hedge laying

When it is necessary to add a considerable amount of soil to re-establish the original profile of an eroded bank, the soil should be built up in well consolidated layers, to ensure that the structure is stable. Where little soil is readily available a narrow margin of the field close to the bank may be stripped, setting aside the turves for use later. If these bare margins are to be sown at a later date you should discuss this with your local adviser, so that a suitable seed mixture can be chosen.

Where small sections of the bank have been stone faced, but it is not practical to restore the facing along the entire length, you are required to repair these using the fallen stone found on site. Stone work around gateways should also be restored. Where no such stone work exists it is good practice to stone around the gateway to prevent erosion and damage from livestock or machinery (for details see section on stone walling).

To ensure stability the finished face of the bank should slope inwards to create a ''batter,'' such that the base of the bank is wider than the top (see figure 2). Turves should be laid onto the crown and sides of the bank, this will help bind the structure together and prevent soil slippage in wet weather. On completion the ''top line'' of the bank should be level, and where appropriate a hedge established or restored on top.

NB. Turf will not be needed on top of the bank when a new hedge is to be planted, as a mulch will be used around the new plants.

Figure 2 Earth Bank showing ideal degree of batter

There will be some shrinkage as the earth settles and the soil dries out. With this in mind, if you are planning to plant a new hedge on top of the bank, you should wait at least twelve months so that the earth has time to settle.

New banks

When planning to build a new bank you should always liaise with your local adviser, who can advise you on any possible landscape impact, the form of the bank and the appropriate planting options bearing in mind local environmental conditions. Similarly, if you are planning to incorporate a ditch into your new hedge bank, your local adviser can advise on the likely impact on surrounding agreement land.

New banks should be sited on the line of an old boundary wherever possible. This can be ascertained from old Ordnance Survey maps or by checking aerial photographs. Ensure that the soil used to create the new bank stays firmly in place by building it up in layers, using turf and compacting it well into shape. Subsoil-type material (preferably with clay content and some stone) should be used for the lower layers, and topsoil (with no stones) for the upper layers. You should allow plenty of time for each layer to settle before adding the next layer.

It is essential that the soil is moist and well consolidated, especially when building on a slope or when working with light soils. In difficult conditions stone facing up to approximately half of the height will help to stabilise the structure. Where this is not necessary the bank should be turfed on the sides and crown. Please refer to figure 3 for the suggested dimensions.

It is not acceptable to simply scrape loose earth and debris into a pile to create your bank. This will not create a stable structure and the earth will soon slip away in wet weather. This standard of work would not qualify for an agri-environment scheme capital grant.

For advice on planting a hedge on top of your new bank, please refer to the hedge planting section.

Figure 3 Cross section showing construction of new earth bank

Dropped banks

Where you have a dropped bank, with only a small bank (if any) on the higher side of the slope, do not build this up too high as the earth will only slip back downhill. The main face of the bank will be on the lower side and the degree of batter (slope) should be greater than a normal bank (approximately 15-25 degrees on higher side and 65- 75 degrees on lower side) to ensure stability. The degree of batter will however vary according to site and conditions (figure 4).

Casting up

Casting up is the term used for the process of digging out material slumped from the bank (or burrowed out by animals) and replacing it on the crown of the bank. The finished surface should be level. Casting up allows a level fence line close to the foot of the bank.

Figure 4 Dropped bank showing degree of batter

When casting up a hedge bank with a ditch, the material cleared from the ditch will be placed on the crown of the bank. Ditches of high environmental value, often indicated by standing water and a range of aquatic plants, should be cleared out in stages to lessen the impact on the wildlife habitat. For example, clear out either one side of the ditch along its full length, or both sides along half its length up to a maximum of 50m. Clearance must not cut deeper into the ditch than the original base level.

Figure 5 Maintenance of stone faced bank by casting up and erecting a fence

When putting material on top of the bank ensure that newly coppiced stools or laid material are not buried in deep earth.

For further guidance on restoring ditches please contact your local adviser.

Protective fencing

Unless otherwise agreed in writing with your local adviser, on completion of restoration work you will need to safeguard the new bank from livestock damage by erecting protective fencing close to the base of the bank.

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