APPENDIX XVIII AGRI-ENVIRONMENT SCHEMES: BREACHES OF SCHEME RULES
PROCEDURES FOR DEALING WITH BREACH CASES
An extract from 'Conserving Bogs: The Management Handbook S. Brooks & R. Stoneman (Stationery Office), kindly supplied by SNH (copyright holders).
Introduction
Pre-formed recycled plastic piling takes its design from metal piling used in the construction industry. So far, its use to block drains on peat bogs has been limited to just a few sites and, therefore, the technique is experimental.
Results so far have been favourable, and it appears that the material has considerable advantages over standard peat dams and plank dams. The material is light (making transport easier), durable (at least a 150-year life expectancy) and easy to work with (dams can be constructed very quickly).
Practical considerations
There are two types of plastic piling in the UK. The main differences concern the joining mechanisms and the final configurations (Figure 5.25). Choosing between the two systems depends upon individual requirements and personal preference.
Installation procedure (to 5m wide)
The piling sections should be driven into the ditch, starting at the centre, and working progressively outwards. They can either be driven in with the hydraulic arm of an excavator or manually installed with a heavy rubber maul. Sections can be cut or ordered to any length (max. 8m).
- Step 1. Insert the central pile first. The central piles will usually be the longest and, if installing by hand, the most difficult. Piling with lengths greater than 3m cannot be easily or safely installed by hand.
Figure 5.25 Joint mechanism for two types of plastic piling. Both materials provide a reasonably watertight seal if the dam is constructed correctly
Place a solid plank across the ditch and use this to work from. This makes installation easier and safer (by reducing the distances one has to stretch). To keep the piles in a straight line, run a taut line across the ditch and use as a guide. |
- Step 2. The join acts as a guide for the next section. It should be possible to push the section the first 30 cm into the unconsolidated peat. It is important to keep the piling as vertical as possible at the start.
To increase the effectiveness of the seal, flex each section against the next whilst hammering in. This should produce a watertight seal when the water backs up behind the dam. It is important to flex the sections in the direction of flow (Figure 5.26). |
- Step 3. Work progressively towards the banks (Figure 5.27). Sections may be trimmed with a panel saw.
The dam may initially leak through the joins. These soon seal as peat particles plug the gaps. To aid this process, a few handfuls of unconsolidated peat can be tossed into the upstream side of the dam. |
Figure 5.26 Flexing the dam, during installation, in the direction of flow increases the strength of the seal.
Figure 5.27 Plastic piling dams are best constructed in the following sequence, starting from the centre and working onwards towards the sides of the ditch.
- Step 4. When the correct height of the dam is reached, that is, level with the surface of the bog, knock down the central pile about 3 cm to form a spillway (Figure 5.28). Note that the design of the dam requires a fairly high water pressure to help seal the joins by 'bowing', so a top stringer should not be added.
A second configuration of the plastic piling sections is possible by inverting every other pile. This will form a 'box' section, as opposed to the standard 'deep-V' (Figure 5.29). The box section is technically a stronger design but forms a weaker seal (due to opposing forces) and is also more expensive (more sections are required per metre).
Figure 5.28 A completed plastic piling dam, Langlands Moss, Scotland. (Stuart Brooks)
To impound large volumes of water, it may be necessary to construct the dam in a 'box' sectioned format (Figure 5.29). However, from the experiences gained with smaller dams in box section, it appears that opposing forces on the seals open the joins and the dam leaks. In this instance, a 'hydro-seal' or an expanding polymer can be inserted into the gap (contact suppliers for advice). With the hydro-seal added, horizontal strength can be gained through the addition of backing stringers. These can be made from hardwood or recycled plastic ( see 6.11) and bolted onto the back of the dam across its top edge (Figure 5.30).
Figure 5.29 Plastic piling dams can be constructed in two configurations, the deep 'V' minimises cost and is usually adequate for most situations but where the ditch is very large the dam may be best constructed in box configuration.
Figure 5.30 A long plastic piling dam, constructed in box configuration, can be strengthened using stringers and made watertight by inserting sealant or hydro-seal into
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