2.4 Amber surveys
Amber path surveys measure the condition of paths and path systems using a series of more than 30 measurements. The measurements collected cover slope, width and other real figures, along with indices of path condition and assessment of factors such as drainage and dynamism.
Amber data are either numerical, degrees gradient or metres of trampled vegetation, or coded, two letters representing the type of vegetation or surface. All these data can be entered into a database, and this enables measurements from a large number of paths to be collected and compared. The system is particularly good at generating data for meaningful comparisons between individual paths and paths in geographical areas. Area-based Amber path surveys have now been undertaken in Loch Lomond and The Trossachs, Lochaber and North Argyll, Glencoe, Upper Deeside and Wester Ross, Mar Lodge in the Cairngorms and Rum. These data have the potential to inform strategic programmes of path management and can be used to support funding applications and project monitoring.
Amber path surveys provide:
- an assessment of the current path condition;
- an assessment of future management needs of the paths surveys;
- an indicative estimate of the cost of repair works;
- baseline for monitoring long-term path condition and change.
Types of Amber data
The Amber survey provides four types of data:
- Descriptive data: a set of codes to describe path location, path type and vegetation.
- Physical measurements: path length, width, gradient, gully depth, number of braids.
- Assessment of path condition: indices describing the roughness, drainage, erosion, condition dynamism and work urgency.
- Prescription: codes and comments describing the type of path management required, comments about work required and comments about site conditions.
This information should provide clear and unambiguous instructions about where the survey commenced and where it ended. Subsequent to survey completion other individuals should be able to locate the path and be confident about the start and end points. Provide a grid reference at the start of the path and a note of the feature at which you start the survey and repeat for the end point.
Each path comprises sections that are more or less homogeneous in nature. The path is divided into sections in the field and a new section commences when an obvious change in path character occurs, for example a significant change in width or gradient. Path sections are numbered consecutively from the start point and path length is measured using a measuring wheel. Depending on the lengths of the path sections, an 8 figure GPS grid reference is essential at the start of each section. This will probably be impractical if the sections are consistently less than 250 m. If this is the case, decide the frequency of grid references before the field survey. It should be possible for future users of the survey information to locate the start and end points of sections, either in the field or on a map.
Identifying path sections in the field is not an easy task and requires the surveyor to use judgement and experience. The Amber survey method is designed to be fairly rapid, and if required more detailed information can be collected later using the Red survey method. Do not get bogged down in too much detail; there will be variations within path sections due to the informal development of paths and variations in terrain. Using the Amber method it is important to consider the parameters that are significant for path management in the area where the survey is being conducted: the presence or absence of poorly drained peat is always significant; long gradient is significant in terms of erosion processes and management; path sections over 15º will be difficult to sustain unless they are pitched or realigned (depending on drainage and surface material), etc.
The reason for a section change should be noted on the survey sheets.
The average ground cover and indigenous species for surrounding vegetation should be noted. Surrounding vegetation can have a large impact on path development: certain species may be extremely tolerant to trampling or may confine the path width. However, surveyors should not spend a long time running through the National Vegetation Classification (NVC) methodology; the important point is to illustrate how the surrounding vegetation may be affecting path development.
Although many upland paths have evolved largely as a result of recreational use, some paths have been constructed, mainly in the Victorian era, and are still in use today. The following categories can be used to describe path type.
- Stalker-type path: These paths are constructed as, or in the style of, stalkers’ paths. Typical features are relatively low gradients, metalled surfaces, drainage by top-side ditch and stone culverts or open cross-drains.
- Recently built path: These are often stalker-style paths. This category includes older stalkers’ paths that have been repaired in the last 10 years.
- Forest or estate road: It is unusual to include roads in path surveys but they may be an integral part of a longer route.
- Evolved slope: These are paths that have evolved more or less directly up or down a slope.
- Ridge route: These are unmanaged paths that more or less follow ridge lines.
- Evolved line: These are paths that have evolved but are not ridge routes and do not directly ascend slopes. They are typically found as routes through glens or paths traversing slopes.
- Other: These are path sections that do not fit into any of the above categories, such as All Terrain Vehicle tracks and historical roads now restricted to pedestrian use.
It is more usual to find a composite of materials on a path surface, especially if the path has not been constructed. However, stalkers’ paths that might originally have had a fairly uniform aggregate surface have evolved over time, especially if they have been regularly maintained; their surface may thus also comprise a mixture of materials.
Especially on many evolved paths, within one section the surface can be made up of a combination of exposed peat, aggregate, block stone and exposed soil in varying quantities. Usually, it is unnecessary to record that all were present. It is necessary only to record the materials that have had the most impact on individual sections. For example, if a section is 100 m long and has a surface of exposed peat combined with block stone, but also includes 4 x 3 m sections of aggregate path, the section should be noted as having a surface of exposed peat and block stone. The isolated aggregate sections will have little or no significance for the management of the path surface in that section. However, the presence of some aggregate indicates that it may be possible to obtain surfacing material from on-site borrow pits if repairs take place. This information should be included in the ‘site comments’ section.
Number of paths and braids
Record the number of both the paths present and the braids that it will have to be managed. It is uncommon to manage more than one path if two paths arrive at the same destination point. However, this may occur if the paths have distinctly different properties and attributes. For example, one route may be preferable for ascent and the other better for descent; one may provide good ridge walking but be quite exposed, whereas an alternative may provide more security but less spectacular views. In such cases, where both lines are also strong desire lines, it is likely that both will have to be managed.
Braid lines, on the other hand ,occur in close proximity to the main line and usually develop as walkers try to find more comfortable lines. For example, the braids might have less rough surfaces, easier gradients or dryer footing. Braids are path lines separated from the main path by a strip of vegetation or untrampled ground; they are not simply the trampled path margins. Again, some judgement is required to record information which illustrates the nature of the path. Braids are often only 10 or 20 m long, and it is clearly impractical to have a section change every time a braid occurred or disappeared. The record should however provide a flavour of the site – for example if braiding occurs over a large proportion of the site and the section is likely to remain braided.
Both the bare width and the trampled width should be recorded. These should be expressed as ranges – the minimum and maximum – of the bare width in a section and the minimum and maximum trampled widths, as well as a typical bare width and typical trampled width.
If the path is braided the total amount of bare ground across the braided section should be given; thus, if the path comprises three lines each 1 m wide, then the bare width would be 3 m.
It is a little more difficult to measure trampled width accurately. The edge of the trampled path margins are not usually clearly defined, but damage to vegetation and changes in species composition are good indicators of trampling.
The eroded path depth is defined as the depth at which the path surface is below the surrounding ground. If the path surface is gullied measure the maximum depth in the section.
Long gradient is measured along the path and is the gradient of the path expressed in degrees. It is not necessarily the angle of the slope that the path is climbing or descending, for the path may meander or zigzag up steep slopes in order to reduce path long gradient. If path formation is intermittent or indistinct over steep ground, make a note in the site comments section, because a constructed path is unlikely to follow such a steep line.
If long gradient is to trigger a ‘section’ change it should be because it increases or decreases across a threshold that is significant in terms of erosion or path management processes.
Cross-fall is defined as the steepest angle, in any direction, on the slope over which the path runs, i.e. the route and angle that a stone would naturally roll away, or the fall line for the skier.
Managing paths with low cross-gradient can be quite problematic. If low cross-fall is accompanied by low long gradient, it is difficult for water to run away from the path and drainage may be difficult.
When low cross-slope is accompanied by steep long gradient, i.e. the slope is steep and open, a number of problems may occur. Erosion may be a problem on steep paths, and this often leads to roughening of the path surface. Paths in this condition often widen as walkers avoid rough surfaces and the low cross-slope provides little incentive to remain on the path line. Steeper cross-falls, on the other hand, act as an incentive to remain on a ‘benched’ path line that is more comfortable to walk on.
Paths that are ‘benched’ into slopes often tend to hold snow and ice longer than surrounding slopes, and this can cause braiding on the path margin (as walkers avoid it) and path erosion due to the volume of water released during thaw conditions. Evidence of problems with snow ‘lie’ should be noted in the site comments section.
Cross-slope is significant in path management depending on other factors, especially path roughness.
Assessment of path condition
Five indices are used to assess a range of less quantifiable factors within each path section. The five factors are path roughness, drainage, erosion, dynamism and condition. A scale of 1–5 is used to score each section for each of the five indices. Work urgency is assessed using the same scoring system.
Throughout the survey a score of 1 represents the worst condition, most active or higher priority sections, and a score of 5 the least damaged, least active and lowest priority sections.
For each of the five indices used, photographs should be appended to show examples of sections scoring 1 (most damaged/highest priority), 3 (average damage/medium priority) and 5 (lowest priority/least damage).
This is an assessment of the condition of the path surface: 1 = very rough and you may need to use hands to scramble along the path; 5 = smooth and you should be able to look at a view while walking on the path.
Research has demonstrated that path roughness has a strong influence on path width. If the path surface is rougher than the surrounding ground, walkers are likely to stray from the path line and cause trample-related damage either on the path margins or on other more comfortable lines.
Take care when recording this information, especially if the path being surveyed is extremely rough along its whole length. Bear in mind the scoring system above and do not start scoring path sections on a relative basis. For example, if section 1 is extremely rough and requires the use of hands to scramble along the path and section 2 is not quite so rough although it still requires the use of hands then both sections should score 5.
This index measures a combination of water flow (including seepage), seepage and standing water. Therefore, a path section scoring 1 for drainage would show evidence of high-flow, deep standing water and/or saturated surface material. A score of 5 would indicate that the path was dry with no standing puddles and that there was no flow of water along the path.
It is obviously easier to get a better idea of drainage conditions during or immediately after heavy rainfall, although this is not always practicable and sometimes assumptions will have to be made about drainage. However, there are a number of indicators that provide clues to drainage conditions when a path is surveyed in dry conditions, some of which are fairly obvious.
Examine the surrounding ground. The presence of peat usually indicates that it is poorly drained, whereas sandy soils and bouldery ground are better drained. Shallow soil depth and bedrock close to the surface encourage very rapid runoff of water after rain. Vegetation types usually coincide with different drainage conditions to a large extent and can be used as indicators of drainage.
Observe the condition of the path; if it is gullied it is was probably subject to high water flows. Look for material that has been washed from the path surface on to surrounding vegetation. Check the composition of the surface material: an absence of fine materials may indicate that they have been washed out by surface water. An accumulation of silt, on the other hand, can indicate the presence of standing water during wet conditions. A wide path and braid lines could also have resulted from poor drainage. Make a note of blocked or damaged culverts or cross drains on constructed paths, since damage to these structures will cause drainage problems.
Topography and path alignment should also be examined. The length of slope above a path will provide an indication of the volume of water that will have to cross the path. Channels and rills that are intersected by a path can cause both localised and more widespread drainage problems.
Finally, be aware of the weather characteristics of the area; Wester Ross, for example, has higher rainfall than the Cairngorms and this will affect drainage systems.
Erosion is strongly influenced by path drainage and path gradient. However, levels of use, surface material, topography, altitude and vegetation also affect rates of erosion. This index assesses the current rate at which material appears to be dislodged on the path line: 1 = current highly active and large movement of material; and 5 = stable, no change. Erosion is an ongoing process, and a one-off visit to a site will provide an estimate of the rate at which erosion is occurring. However, that estimate should be based on the surveyor’s experience and a variety of indicators.
Rates of erosion depend on combinations of factors; some steep sites may be reasonably stable if they are well drained and the path surface material is well bound, whereas poorly drained paths on steep gradients with poorly bound surfaces will experience high rates of erosion.
Combinations of steep gradient, loose surface material, high levels of use, sparse vegetation, bedrock close to the surface, high rainfall and/or rapid thawing and path alignment indicate high rates of erosion.
Evidence of high rates of erosion includes gully formation or path surface well below surrounding ground and path surface material washed onto surrounding ground or vegetation. The path on Mount Keen displays signs of rapid erosion and, although it is not seriously gullied along most of its length, the whole path is at least 250 mm below the surrounding ground level. The path is also wide, the surface is poorly bound, gradients are between 10o and 20o and large areas of vegetation adjacent to the path have been inundated by material washed from the path surface.
Dynamism has been used to describe the rate at which a path is developing (usually deteriorating). Assessment of this process will be based on judgements about rates of erosion and how quickly path width is increasing, or the path is braiding. A score of 1 = highly active future change, whereas 5 indicates that the path is not likely to change.
This is quite a difficult process to assess as a path may be highly damaged but reasonably stable and therefore not dynamic. Conversely, a path may not be in very poor condition at present but might have just passed a threshold that will lead to rapid breakdown; for example, surface vegetation might have recently been removed through trampling pressure exposing the mobile surface material underneath.
This is an assessment of overall current path condition including bare width and trample width, drainage and surface condition: 1 = gross damage over a wide area and 5 = little damage.
When recording this information relate the assessments to reference photographs and do not score path sections on a relative basis, especially if the path being surveyed is in poor condition along its whole length.
Path management, information and comments
This is the urgency with which work is required to prevent damage or further damage occurring to the path in its present condition: 1 = extremely urgent, gross damage immenent (or already occurring) if no action is taken; and 5 = path reasonably stable, improvements are of low priority. A high score should be allocated if a path is currently in reasonable condition but likely to degenerate rapidly if no pre-emptive work is undertaken.
In terms of time scales:
- 1 = high priority: work should be undertaken within the next 1–3 years;
- 3 = medium priority: work should be undertaken in the next 3–5 years;
- 5 = low priority: work may be required in the next 5–10 years, often depending on the results of monitoring information.
Work urgency is not necessarily a priority rating. Other factors will influence priority, such as availability of funding, desirability of undertaking work in remote areas, importance of a path in terms of network connections and popularity.
This is a rapid survey method and is not designed to provide specification details; the information gathered here describes the general type of work required. From this information, costs can be calculated at a later stage of the project. To simplify matters, prescriptions can be categorised into a list of treatments required, such as ‘rebuild existing path, construct new path, stone pitching, intensive pre-emptive work, minor pre-emptive work’, etc. The list of treatments can be adapted to specific management styles and the needs of different geographical areas.
Some care should be taken with this assessment; remember that paths are dynamic. Do not under-specify if a path is particularly dynamic as further degradation is likely to occur before funding is secured and repair work starts. On the other hand, do not over-specify; repairs should reflect the context of the path in terms of setting and use.
Record the length of time taken to walk to the start of each section from the nearest vehicle access point. Time spent walking to and from a work site has significant cost implications. If a site is an hour’s walk from the nearest access point then 2 hours, or a quarter of an 8-hour working day, would be spent simply walking to and from the site.
Include any information not collected elsewhere on the pro forma which is important in terms of path formation or management. Also note any useful reference points.
Include notes about the availability of suitable materials, access for machinery, alternative alignments, etc. Comments about the site conditions should include any localised conditions that have not been clarified elsewhere. For example, an erosion problem caused by a burn overflowing or a path section with a peat surface and short aggregate section might not have been previously noted.
Photographs are useful for providing a visual record of path condition and setting. Include typical sections and some that are in good condition, not just the worst sections. Note the cumulative distance and direction in which they were taken.
How to collect the data
Amber surveys can only be carried out with an in-depth site visit backed up by entry of data in the office. Data are collected in the field and recorded on survey sheets set out for all the measurements required. The data are then transferred directly to a database in SMiFI. Data can be recorded directly into a palmtop computer at the site. This can save time, but there is some concern about the reliability of palmtops in cold and wet weather. Dictaphones can also be used.
Distances are measured using a measuring wheel such as a Trumeter. This provides relatively accurate measurements over most terrain. Shorter lengths are measured using a tape. A hand-held global positioning system (GPS) is used to generate accurate eight figure GPS grid reference information. Gradients are measured with a lightweight clinometer. A camera – which should be waterproof – is essential, preferably a digital camera.
- Be objective: do not emphasise the most damaged parts of a section. Data should reflect the characteristics of whole path lengths.
- Be consistent: some data collection relies on the judgement of the surveyor. Apply decisions consistently throughout the survey, and if more than one surveyor is involved spend some time together in the field to standardise the approach.
- Be adaptable: if the data sets do not provide information that you require, modify the criteria or type of data that you collect.
- Be aware of the function of the survey: do not describe paths in minute detail. This is a broad-brush look at path condition and management requirements and will not provide costs with a dependable accuracy of more than ± 20%.
- Timing: area-based surveys can be very time-consuming. Allow enough time to undertake the field survey outside the winter months, especially if higherground paths are included.
- Employ suitably experienced staff: Amber surveys rely to some extent on the judgement and experience of the surveyor. Pertinent and relevant data are likely to be collected if the surveyor has extensive experience of path development processes and path repair techniques.
- Health and safety: produce a risk assessment for the field survey stage and monitor the effectiveness, especially reporting-in procedures.
- Access: ensure that the survey method complies with any restrictions relating to access. These will probably relate to access restrictions to Sites of Special Scientific Interest or Sites of Historical Interest.
Target notes for completing an Amber path survey
|VARIABLE||NUMBER||MEASURE||WHAT TO RECORD|
Reason for change
|Section number |
IA Increase angle
DA Decrease angle
IW Increase width
DW Decrease width
SB Start braids
EB End braids
SD Start of drainage problem
ED End of drainage problem
CV Change of vegetation
O Other (specify)
|Grid reference/features||2||Eight-digit reference/two words||Grid reference at start of section using GPS to give eight-digit reference, with notes on any obvious features at the start of sections. Include also finish reference and features for last section in run|
|Length/distance||2||m/m||Section length measured in metres and cumulative distance from start of path, both measured using wheel|
|Type of path/surface||2||Two-letter code/two-letter code||RD Forest/estate road SP Stalker’s type path RB Recent built (<10 years) EL Evolved line (one or more lines) RR Ridge route ES Evolved slope route O Other (specify)||VG Vegetated EP Exposed peat ES Exposed soil SM Fine silt/mineral AG Aggregate BS Block stone BR Bedrock O Other|
|Surrounding vegetation/cover||2||Two-letter code/cover||NVC or Phase 1 (upland selected list) Semi-natural woodland AP Plantation woodland BI Acid grassland B5 Marshy grassland C1 Bracken D1 Dwarf shrub heath D3 Lichen/bryophyte heath D5 Heath/acid grass mosaic E1 Bog E2 Flush and spring O other (specify)||Average % groundcover for surrounding vegetation to nearest 10%|
|No. paths/no. braids||2||#/#||Number of path lines in use which are to be managed, followed by total/maximum number of other path lines apparent which are to be blocked off|
|Bare width range||2||m/m||Minimum width of bare unvegetated ground in section, followed by maximum width of bare ground in section|
|Trample width range||2||m/m||Minimum width of ground showing evidence of trampling, followed by maximum width of showing trampling and change of vegetation|
|Gully depth range||2||m/m||Minimum depth of gullying below normal ground height to deepest point in path width, followed by maximum depth of gullying anywhere on section|
|Long gradient/cross-fall||2||%||Average gradient along path section measured from start looking up path line using clinometer, followed by average cross-fall measured up drain or fall line using clinometer|
|Roughness||1||1–5||Where 1 = hands needed to scramble up path, while 5 = ability to look at view while walking on path|
|Drainage||1||1–5||Where 1 = permanently saturated with water, or very high flows of water, and 5 = very well drained ground, or very low flows of water|
|Erosion||1||1–5||Where 1 = evidence of large amounts of movement of material on path line and 5 = no movement of material from path line. A retrospective assessment of damage|
|Dynamism||1||1–5||How rapidly the path can be expected to deteriorate, where 1 = path very likely to deteriorate rapidly, and 5 = a very stable path. The future rate at which material is likely to move|
|Condition||1||1–5||Where 1 = very severe damage and 5 = little evidence of damage. An overall estimate|
|Work priority||1||1–5||A combination of path condition and dynamism. Include high priority for pre-emptive work to prevent severe path damage. Where 1 = very high priority and work is recommended within the next year, and 5 = very low priority and work is unlikely to be needed for 10 years How soon does work need to happen?|
|Cost per metre Extra costs||2||£ per metre extra per metre||Average cost per metre based on priorities 1–5 from Red surveys. Information to be added – only indicate if path has obvious extra cost (e.g. helicopter costs)|
|Walk-in time||1||0.25 ± hours||Approximate one-way walk-in time to nearest access point in hour intervals|
|Comment||2||(a) site: 10–20 words (b) work: 10–20 words||Comment: (a) on path condition, site, available materials and features; (b) on types of work, style of construction and any adaptation of usual construction|
|Photographs||1–34||Grid Ref/direction||Approximately 4–8 photos per path in report. Take 10–20 on site. Include setting of site, general path line, good section, bad section, typical section, major work sections, other features.|