3.0 Introduction to Surface Techniques
An upland path has to withstand the pressures of walkers and the elements. If these are great, erosion will inevitably occur, and a hard wearing path surface becomes necessary in order to reduce the environmental impact and provide a durable and pleasant route.
A well surfaced path should be attractive to use, so that walkers will not take alternative routes, causing further erosion scars, but not be so smooth and regular that it detracts from the experience of walking in an upland landscape. Path edge work and landscaping will help to reduce the impact of a hard surface in the surrounding landscape (see vegetation restoration).
The traditional surface techniques used on upland paths in Scotland are:
- aggregate, with on-site material
- stone pitching
Their use, and variations, will depend on an assessment of the characteristics of the path, its use, and the site through which it passes.
ASSESSING THE SITE
The need for surfacing will be determined by the extent of the erosion problems, as identified during a path survey. Typical erosion problems include:
- loss of surface vegetation and soil - from pressure of use and water flow
- path braiding to either side with further erosion of vegetation - from walkers avoiding rough or wet areas
- further eroded paths, and short-cuts across corners or straight down slopes - from walkers avoiding the path completely
- deep eroded gullies - from walkers continuing to use a path after water damage to a mobile surface
The key factors that determine which technique to use, and the path alignment, are the topography of the land, and path gradient; and the nature of path use (see also Sections Environmental impact & Path assessment).
The surface technique is largely influenced by gradient, and associated ground conditions.
- Stone pitching is generally used on slopes exceeding 15°, but can also be used on lower gradients if necessary. This is normally where an aggregate path will not provide a stable and durable surface due to the mobility of aggregate on the slope.
- Aggregate paths are generally used on gradients below 8°. Higher gradients should be avoided as the aggregate will be more susceptible to migration down the path, from the pressure of feet and water flow, as well as gravity. This will depend on the quality of the surface binding material, which depends on the geology. For instance granite derived aggregate does not bind well and will be mobile on gradients greater than 5°.
- On steeper slopes aggregate may be used with anchor bars incorporated in the construction, particularly if the binding material is good.
- Over wet and peaty areas the aggregate path may need to be floated on a geotextile base.
The path alignment is influenced by the land that the path crosses, as well as the eventual destination. In most cases, the general line will already be established, and only slight alterations can be made.
- Gradual curving lines, making use of natural features will enhance the aesthetic and natural appearance. Incorporating variations in width will avoid a formal appearance. This may be determined by physical factors or restrictions.
- Obstructions such as large boulders and bedrock may affect the alignment, and width. They can be used to define the path line, where the path turns, or as markers to aim for on long stretches of open ground.
- Steep gradients should be avoided, as the path will tend to erode quickly, particularly with high levels of use. Where they are inevitable an angled, or zigzag, line should be chosen to reduce the gradient.
- Particularly wet and peaty areas of ground should be avoided by keeping the path above the water table. An alternative alignment on drier, or easily drained ground should be chosen wherever possible.
It may not always be necessary, or appropriate, to change the line of an established route. However, there are cases where slight re-alignments will be the difference between the surface technique succeeding or failing. The alignment should always fit in with the character of the surrounding landscape.
To help determine the alignment, and achieve the balance between an aesthetically pleasing path, its ease of use, and durability, consideration must be given to the characteristics of the path use. For instance is the path:
- regularly used in winter or wet conditions - more serious path damage occurs from pressure of use in wet conditions
- used more often in descent or ascent - downhill use causes quicker erosion, and more short cutting
- a traditional route or a newly created desire line - changing the alignment may make the path unattractive to use
- at the end of a long route - tired walkers are more prone to cut corners or walk off a rough path surface
An alignment designed to reduce the gradient on steep slopes should keep zigzags as short as possible, to discourage descending walkers from taking short-cuts straight down the slope. The choice between an aggregate and pitched surface on a slope may also be dictated by the characteristics and number of people using the path.
The popularity of paths in an area will also help to determine an appropriate width. This will generally be between 900mm for single track and 1200mm for walking two abreast. The path may need to be as wide as 2000mm to cope with heavy use and high numbers, or on corners or open slopes.
Availability of materials
The materials for aggregate and pitched paths are normally sourced from the surrounding area. The large quantities required for pitching and long sections of aggregate path may therefore influence the choice of technique, width, and alignment. If the source is limited, it may be necessary to realign the path to be closer to an available source, or to import material.
Wherever previous work, to a good standard, has proved successful in achieving the objective of the pathwork, a similar style should be used to maintain continuity. In locations where traditional stalkers’ paths are present the same style of construction is usually most appropriate.
The following gives some typical examples of problems experienced on upland paths, and the potential solutions:
Eroded surface vegetation with path starting to widen and deepen
Aggregate path, at a suitable width to cope with expected use
Path widening through a a deep, wet peat bog
Aggregate path floated on geotextiles
Gullying and braiding a steeper path gradient
Aggregate path on anchor bars
Deep eroded path on steep path gradient
MAIN PROBLEMS TO AVOID
Upland path surfaces should be carefully chosen and used in appropriate situations. These should be identified during the path assessment. The most common problems that arise are:
- Wrong Position - walkers do not stick to the path line and take short-cuts.
- Wrong Style - the path is visually obtrusive, not fitting in with the surrounding landscape.
- Poor Construction - cannot cope with the pressure of use and water; walkers choose to walk off the path.
The following technical sheets give guidance on some of the surfacing techniques used on upland paths. Each sheet has a section on materials as well as the technical detail required for construction.