"April 1975"

25 appendices

Includes 17 bibliographical references.

Describes and assesses the environmental impacts of proposals for development of the upper Clutha valley upstream from Roxburugh. Deals with the overall development proposals and their principal environmental affects as far as these can be envisaged from dam locations, the levels and operating ranges and impoundments, the overall programme and means of construction, irrigation possibilities and similar considerations. Details of individual schemes will be discussed in subsequent reports. The Clutha and Kawerau rivers would be affected along their whole lengths in the project area as a result of damming and lake formation. Flow regiemes would be altered, and problems of bank stability and siltation would require strict attention in design of the projects. The proposals do not include storage in the new lakes for flood control purposes. This would be provided only at the expense of extra inundation. Bank stability characteristics under conditions of inundation, level fluctuation and wave action would have a large influence on the degree to which banks would slump and reach a stable form. The upper Clutha fishery will be affected. It is possible that an acceptable stable state of siltation in the lakes might eventuate with the rivers silt burden passed through the stations. If this did not happen, means have been envisaged for passing the silt downstream via suitable services. Consideration must be given to maintaining existing levels of water quality. Inundation of land is the most important primary impact under consideration. The affected land is partly in the gorges but mostly in the upper Clutha valley where the lakes are more extensive. About 1500 acres would be inundated; including 1500 acres of low grade land and gold tailings. Visual impacts of the project would be considerable. In particular, there has been much comment on changes to the appearance of Cromwell. Farming including pastoral and cropping, and horticulture comprise the main industry of the region and would suffer various effects, temporary and permanent, spread over a period of years. Substantial returns are expected from irrigation of suitable soils under the proposal. Transport would be affected in various ways, giving rise to roading replacement programmes which would have scope for improvement and some rationalization of the state highway system. No adverse impact is expected on the tourist operations in the area. There will be a substantial social impact with farming jobs lost initially, construction jobs gained, and an increase in agricultural work eventually. 51 persons will be displaced from existing homes; the settlement of Cromwell will undergo major changes. (auth/PGE)

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