|To repair the Leat, extensive work was required.
Firstly, Rhododendron covered the entire project area. Although the
Trust had already done some clearance, a significant amount still had to be cleared.
Rhododendron is an alien species and renders areas sterile and physically
impenetrable. Its clearance is, in itself, a major task. This was done by
Trust staff, those on Career Contact and volunteers. The same workforce also carried
out all the manual labour required to complete the Leat Project. This included all
the extensive gabion basket work, concreting, stone walling, the installation of the
sluice and steel pipes.
The Victorian Leat was damaged in two places. The worst area
of damage had resulted in flood water washing out a deep ravine. Thus the line
of the Leat now had to descend a sheer drop of 13 metres. In order to ensure that
flood water could be carried safely through this steep gradient it was decided to pipe the
Leat for this short distance. The Ravine was first filled in using two 20 tonne
swing shovels. It then had to be compacted to prevent settlement. A trench was
dug into the compacted soil so that a 42 metre length of steel pipe could be laid.
The pipe was buried and collection and discharge areas constructed. These were of
gabion basket construction, local stone was used for stone walling. This method of
containing the Leat over trouble spots was used in another two sections. One of 6
metres, the other 18 metres. Again collection and discharge areas together with
stone walling were constructed.
Surveys were carried out by the Forestry Commission Civil Engineers
Department from the Somerset and South Devon Forest District and by the contractor Peter
Williams. They revealed an average gradient for the mile long Leat of 1:60. This
gradient was ideal, as the resulting water flow was neither too fast to cause erosion, nor
too slow so that silting would occur.
Two ponds were also created as part of this substantial project.
At the most northerly upstream part of the reserve, where the valley was narrowest,
a large pond, Monument Pond was constructed. Its purpose was to ensure that all
water entering the reserve at this point was collected. Monument Pond has two
outlets. These outlets are controlled by a sluice. This ensures that at low
water flows, all water goes down stream to the existing wetland habitats. At times
of flood, excess water enters a newly constructed section of Leat. From here it
cascades into a new pond, Dragonfly Pond. From Dragonfly Pond the only exit is to
the original Victorian Leat. This had been cleaned out and small weirs constructed