Assessing the magnitude of soil compaction

Soil compaction measures

Natural factors influencing soil compaction

Most land-based recreational activities carried out in the vicinity of marine features, whether carried out on foot, horseback or vehicle, exert forces on the surface of that feature which can result in compaction. The magnitude of the pressure and the characteristics of the feature will determine the nature of any impact.

Impacts can include:

• erosion of soils and upper levels of less durable marine features

• changes in the level and diversity of vegetation within a site or feature

• changes in feature density, porosity and penetrability

Changes to a feature associated with soil compaction do not necessarily imply a significant adverse impact. There is an important difference between change and impact and this can only be determined at the specific site-level.

It is possible to make an assessment of the magnitude of soil compaction caused by different activities by reviewing the different static ground pressures exerted by activities. This involves dividing the weight exerted by an activity on the ground by the area in contact with the ground. 

Liddle (1997)

The greatest static pressure is exerted by horse and rider, mainly because of the small ground area over which the weight is spread, followed by motorised vehicles. This has implications for those features which are particularly sensitive to compaction, such as sand dunes, where activities such as horses riding are likely to occur.

In those areas where wildfowling takes place, there may be observable trampling effects on vegetation, although because the activities tend to take place in tidal areas, compaction impacts are likely to be minimal. Wildfowling is likely to cause less overall trampling-related impacts than an activity such as dog walking for example, as levels of participation in wildfowling are at a much lower level.

Natural Factors Influencing Soil Compaction

Marine features are supported by underlying layers of rock and soil which determine their overall resilience to ground pressure. The different natural characteristics are just as important in determining the impact of recreational activities, as are the relative ground pressures exerted by those activities. Uneven, stony or rocky ground, as found on rocky shores, results in a person’s weight being distributed over a much smaller area. In such an area, the static pressure of a person can be greater than that of a vehicle, with associated implications for sensitive rocky shore vegetation.

For example, in areas where underwater reefs extend to the shore, people who go ‘rock pooling’ or gathering rock pool species at low tide can exert a significant static ground pressure, with consequential implications for density and diversity of species.

Conversely, soft ground such as mudflats, sandflats and saltmarsh enables the load of a person to be spread over a greater area and therefore results in lower ground pressure. However, communities found in such habitats can be very vulnerable to even low pressure activities, particularly if they live in the upper layers of the mud or sand flat. Heavy vehicles accessing these areas therefore have the potential to cause significant damage to such communities.

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