VEGETATION ASSESSMENT
General
As part of the study, a vegetation assessment
was undertaken to identify whether the existing vegetation was contributing to
or negating against failure of the slope and whether there was opportunity for
landscape related works to contribute towards a potential solution. The
following section summarises the results of this assessment.
Roger Clark MCLI, a Technical Director of
Ironside Farrar with over 20 years practical experience, visited the site on
21st March. Weather conditions were dry following heavy rain earlier in the
day.
It is noted the existing topographic survey
records the position of areas of slippage but does not record the position and
girth of all trees in the study area. This will be required if the project
progresses to a further stage together with a tree survey to record species and
condition.
Site Assessment
The site is steep with a path down to the
river and sits over an exposed rock face gorged out by the River Esk. Tree
cover is not particularly dense and comprises mix of mature specimens over 1.5m
girth with some new growth. There are a few intermediate sized trees.
Most trees are deciduous, and although a few
conifers and evergreen species are present in the area, new growth appears to
be mainly birch. Understorey vegetation is well developed, notably ivy. Many
trees are in poor condition and much deadwood was noted, but this is not seen
as a contributor to the slope stability issue.
The paths are enclosed by fences. These are
in the main concrete post and wire, although some vertical bar fences are also
present. It was noted that the mature tree at the upper dogleg bend appears to
have arrested further slippage from above by the way the vertical bar fence and
path have both slewed into the side of the tree. See photograph overleaf. The
immediate area to the downslope side of the tree showed no sign of slippage,
suggesting the tree was stable when the slip occurred.
Conclusions
Felling the trees will not assist in
overcoming slope stability problems at this locus as the soil is not stable.
Trees are not the problem and are possibly assisting in maintaining ground
stability, particularly on slopes less than 50% (1:2).
There is nothing to suggest that the trees
are a problem on the steeper slopes (80%) above the dogleg path where there is
at present no slippage visible.
It is considered that removing trees may
increase the potential for slippage to occur as an unvegetated slope offers far
more opportunity for surface water runoff to develop momentum which may lead to
scour of the surface and different type of stability problems.
Trees will always fall off the cliff face
into the river as the overlying clayey sands and gravels erode and slide toward
the cliff. This is a naturally occurring feature of gorges overlaid by softer
material.
It is recognised that trees in good health
may have better root systems than those in poor condition and dead wooding and
canopy thinning of mature trees may assist in promoting healthy vigorous roots
and stimulate regeneration. Coppicing of smaller suitable trees such as birch
may also assist in stimulating root development.
Bioengineering techniques should also be
considered such as brush layering at the base of slip areas using live willow
whips possibly in conjunction with live willow stakes and fascines made from
woodland thinnings. There has been a resurgence in the use of this traditional
and low cost method of stabilising ground in recent years. Drawing 8162_701
identifies a typical arrangement for this type of technique.
The
photograph below shows a rudimentary facine made by utilising the concrete post
and wire fence and woodland thinnings already exists at the base of the steep
slope above the dogleg path. ***
Recommendations
- No felling of trees to occur.
- Dead wooding and crown thinning of mature
trees is recommended.
- Coppicing of smaller trees less than 500mm
girth is recommended
- Bioengineering opportunities to be further
examined for implementation in next plant dormant season (autumn).

*** - this is the wood pile created on water
tower wood…….ahead of our time! photograph could not be copied over though.
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