Fences
Sand-trapping fences are discussed in the previous chapter. Many of these fences are suitable also for access control.
Around car parks, buildings and along path edges where you want to avoid sand build-up, post and wire fencing is the cheapest and most suitable. Strong straining posts must be constructed. For short lengths, post and rail or chestnut paling may be preferable, as these do not need straining posts.
For details of wire and methods of fastening, see here. Full details are given in Fencing – Handling, straining, fixing and joining wire. Note that high tensile wire has advantages in use, provided adequate straining posts can be constructed. For short lengths of post and wire fencing, say up to 50m in length, mild steel wire may be sufficient, although radisseurs or other adjustable devices will be needed to keep the wires taut.
The following types of strainers have been developed by Cornwall County Council for straining high tensile wire fencing in sand dunes:
- The A frame shown below is strong enough to support three lines of 3.15mm high tensile wire. These strainers are very effective, but are cumbersome in materials and time consuming to erect.
The A frame can be adapted as shown for straining at corners, or for turning posts, at which the wire is not fastened off, but is run on to the next straining post.
- This is an adaptation of the New Zealand style ‘box strainer’ (see Fencing – Fence mechanics), where the strain of the fence is taken by the brace and the angled wire. This adaptation has been designed specifically to take up to five high tensile wires in soft sand. The strainer can be pre-fabricated in a workshop and then assembled on site.
To assemble, first dig three holes at the required spacing using a shuv-holer. Nail on the timber ‘feet’, and set the posts in the holes, but do not backfill until the brace has been fitted. Finally, staple on the angled wire, making sure it is taut.
The fence wires can either be stapled to the post, or attached with spiral fence connectors.
At corners, the following design of turning post should be used. The fence wires are not terminated at the post, but are run on to the next straining post. Like the strainer, this should be prefabricated in a workshop.
To erect, dig out a trench at least 1.15m long and 1.025m depth. Nail the timber baulks to the posts, and lift the structure into the trench, taking care not to dislodge the sand as you do so. Fit the brace and then backfill the trench. Finally staple on the angled wire.
Where high tensile fences cross undulating ground, special attention must be paid to holding down the intermediate posts at the base of dips and hollows. This should be done by nailing cross pieces about 1m long at the base of the post, and then cover by piling large rocks on top.
Some further designs which have been used on sand dunes are shown below. The first design is used by the National Trust at Formby, Merseyside. The high tensile 3.15mm wires are terminated at the ‘A’ frame straining posts with spiral fence connectors. Where there is particularly heavy public pressure on the fences, the top wire is replaced by a tanalised rail of round timber. Barbed staples are used to hold the wires where the fence follows an inside curve.
Two other designs are shown, the three wire fence being suitable for average use, and the six wire fence for sites where a greater deterrent is needed. Sometimes it is better to choose a design which allows people to climb through if necessary, particularly for fences around recreational areas, where balls, kites and so on need to be retrieved. This saves on the damage which would otherwise be done to more secure fences.
Where you need to combine access control and sand build-up, 1.2m (4′) chestnut paling fixed to posts is usually adequate. See here for methods of stapling to posts. An alternative method of erecting chestnut paling is to fasten it to strained wires. This is more expensive and time consuming, because of the need to erect straining posts, and should not be necessary where sand is likely to rapidly build up. It probably is worth doing for access control chestnut paling around car parks and along pathways, where a permanent fence is needed. The paling should be attached to the 3.15mm mild steel wires with gordian rings or netting rings (available from major fencing suppliers), spaced about every 450mm (18″). Twists of baling wire can also be used.
A method used at Morffa Dyffryn NNR, Gwynedd, where chestnut paling is used for access control alongside a boardwalk, is to erect the paling with a gap of about 200mm (8″) beneath. This prevents sand building up against the fence and over the boardwalk, but allows it to blow underneath to be trapped by brushwood fences beyond. The paling is attached to a strained wire fence, in order to prevent it sagging. Some of the posts need supporting with struts, as the extra height makes the fence more vulnerable to wind damage.
‘Psychological’ fences are often as effective as other types and are cheap and easy to place. They are worth trying where you have to enclose a number of small areas such as dune stabilisation sites or experimental plots. All you need for such fencing are posts about 900mm (3′) high, with a single strand of plain wire hand-tensioned and stapled at the top, and small explanatory signs if the purpose of the fence is not obvious.
Pathways may be fenced on one or both sides to keep people from straying. Often it is best to fence just one side at a time, since this antagonises people less and vandalism is less likely. A single fence with explanatory signposting conveys the erosion-control message adequately to most people. The fence should be shifted from one side to the other every few years, or when it needs replacing, to equalise weai on the two sides. A boardwalk handrail makes an effective fence, because people tend not to realise that this safety device is also being used to restrict their access.
Plantings and cuttings
Fencing is obtrusive at best and often acts as a focus of vandalism. In some places live vegetation or deadwood cuttings can be used cheaply to replace access control fences. Sea buckthorn (Hippophae rhamnoides) is the obvious choice on sites where it already flourishes. Rather than plant more of this invasive species, it may be best to cut out pathways through dense sea buckthorn thickets and so effectively channel people. Where this is not possible, ‘kidding’ (cut stems) can be pushed into the sand to form dead hedges about 1m (3′) high and 300mm (1′) thick. This has been done extensively at Gullane, East Lothian, and on a smaller scale at Gibraltar point, Lincolnshire. Dead buckthorn is even tougher and scratchier than the living plant and such hedges should remain effective for about five years, although they may need bulking out where occasional breaks occur. Check such hedges the year after ‘planting’ and cut out any stems which have survived to take root.
Where sea buckthorn is not already present it is best to use other species. Burnet or Scotch rose (Rosa spinosissima) has been used at Longniddry, East Lothian. This shrub grows to about lm (3′) and may be propagated by cuttings in the same way as elder. At Ynyslas Dunes, Dyfed, efforts have been made to transplant this shrub but without success. Gorse (Ulex europaeus) has been planted along path sides in the Gower peninsula (Trew, 1973, p47). At Camber, East Sussex, several species have been used for walkway planting including blackthorn (Prunus spinosa), hawthorn (Crataegus monogyna) and the Duke of Argyll’s tea-plant (Lycium halimifolium), an introduced species which flourishes mainly on the south and east coasts (Pizzey, 1975, p281).
Car barriers
These may be needed to control the limits of car parking within dunes and on beaches. Barriers can also be used to delineate parking lines and bays within car parks.
Spur posts
These are posts set in the ground, and spaced just sufficiently to prevent cars passing between
them. The posts should be 1.2-1.5m (4-5′) long, and set in the ground with about 450mm (l.5′) projecting. They should be spaced no more than 1.5m (5′) apart. Normally tanalised timber about 125mm (5″) diameter should be used.
On sandy sites, it is important to nail a 300mm (1′) cross piece to the bottom of the post to make it harder to pull up. Make sure the big end of the post is downward. If you have to install posts where the water table is high, use three people, two each with shuv-holers to scoop out the sand, and the third to quickly drop the post in before the hole collapses. Posts in these conditions on backshores need fairly frequent maintenance, as they tend to be forced upwards by the water table and loosened by wave action.
Spur posts are effective and economical in terms of materials, but they are laborious to install. Because they can cause real damage to cars, they are sometimes attacked in retaliation. It may help to paint the tops white to make them more obvious. At Braunton Burrows, Devon, ex-MoD corkscrew-shape metal pickets have been found equally effective and easier to install. They look fierce but cause little damage if accidentally run into, so they are seldom pulled up in return. They are sometimes joined by a string ‘fence’ to mark out newly seeded areas next to car parks. Old concrete fence posts have also been used at this site, as wooden posts tend to get vandalised and burnt.
Log barriers
Large tree trunks, about 3m (10′) long and at least 250mm (10″) diameter, or old telegraph poles, make effective barriers if dug part way into the ground or set on posts. Where the logs are big enough, it is easiest to dig them in, but they are likely to be rolled aside unless bolted to posts or anchored to buried concrete blocks by chains. Smaller timbers of about 150mm (6″) are best set across short supporting posts as shown below. Softwoods should be pressure treated.
This method of fixing reduces the problems of rotting and weakness associated with notch-type joints. Although this sort of raised-log barrier is fairly easily vandalised, it has the advantage of being usable as a seat and play-rail for children. Sets of posts can be placed with 1m (3′) gaps between them to mark out car parking bays – a continuous barrier is needed only if you want to keep motorcycles from getting through.
Barriers can either be set along a straight line, or staggered as shown, to indicate individual parking spaces.
Turf banks
Car parks and trackways can 6e defined by peripheral banks and ditches. The ditches provide spoil for the banks and, if positioned on the side of the banks towards the cars, increase the effective height of the barrier.
When you dig the ditch, first cut out turfs at least 50mm (2″) thick and lay them aside. After building the bank nearly to the required height (600mm, 2′ minimum, to accommodate settling), place the turfs along the inner (ditched) face as shown and tamp them well down. If possible, water the new bank to promote the survival of the turfs and the spread of vegetation.
Turf banks are much less obtrusive than other sorts of barriers but they are relatively easily broken through. They are most useful where the out-of-bounds area is only moderate attractive for parking or holds only a few cars. The ditches do tend to collect litter and may speed erosion if dug near a cliff edge or in soft sandy soil.
