|Parapara Hydroelectric Scheme Homepage Environmental Effects Assessment.. page 19 contents|
Environmental Impacts / Mitigation
As this operation will involve machinery, a similar approach will be taken to that in the work behind the
Richmond Flat Dam will be adopted both before equipment is brought to the site and whilst it is working.
Containment procedures for any accidental spillage of hydraulic oil will be practised and dispersion agents and
absorption materials will be kept on site.
8) Pipeline construction
Detailed investigation of possible pipeline routes is required to establish the preferred cost effective option. From a hydraulic efficiency position, a 1.2 m diameter concrete pipe falling at a grade of 1;200 from the tunnel portal is preferred however the civil engineering of negotiating two side creeks and possible areas of instability on the side slopes lower in the catchment may preclude the following of this route.
Alternatively the pipe route can follow that established by the PHSC towards the saddle into Appos Creek and then sidle towards the generator site at a lower level than the 180m contour above. In this case pipes of higher head rating will be required and the access road to the power house will be incorporated with the pipeline bench to avoid any duplication of land and vegetation disturbance. This route investigation will be carried out on foot with the possible digging of a number of 500 mm wide test pits to ascertain slope stability parameters.
Where pipes are required to be laid away from access roading, a bench of 3.5 metres in width is proposed into which the pipe will be bedded and placed in a trench adjacent to the upslope batter of the bench so that the pipe is covered with a minimum of 500 mm of backfill material. This bench will provide access for maintenance purposes if required. Low growing vegetation of a hardy nature from the local species will be encouraged to colonise the backfill. Essentially this will be gorse from the seed available in the topsoil however this will fit the local natural environment and provide for rapid stabilising of the disturbed surface. Possible mowing of this vegetation may be required after a period of five years to ensure access for unexpected repairs is not impeded.
Environmental Impacts / Mitigation
Attention to minimising down slope migration of disturbed soils will be required and best practice techniques for this adopted. The visual impact of this work will be apparent from the road following the ridge to Red Hill. This impact will be similar to that of the original pipeline except that in this case the clearing of re-generating 25 year old vegetation will mark the route. Establishing covering vegetation will mitigate this effect to a degree.
9) Penstock construction
The position of the penstock will depend on the route of the pipeline to above the generator site. If the higher level route is practicable then the penstock will be positioned on the ridge leading up from the point where the Parapara River discharges from the gorge at GR 816.5508.0
Alternatively the penstock will be required at the point where the pipeline system falls away from the 1:200 grade from the tunnel portal. This will comprise a concrete chamber including a stand pipe of sufficient height to match the static head feeding the penstocks leading to the generator house. The dimension of the head of this structure will be in the order of 4m x 4m x 6m high built of precast and poured in place concrete with inlet and outlet pipes to the turbine(s).
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