LAKE COLERIDGE AREA

Press, Volume LXXXIII, Issue 25207, 11 June 1947, Page 9

LAKE COLERIDGE AREA

CATCHMENT PROBLEMS REVIEWED WATER RETENTIVITY HAS DECREASED The problems of the Lake Coleridge catchment area are the subject of a repprt to the North Canterbury Catchment Board of an investigation by Mr W. P. Packard, assistant lecturer in geography at Canterbury University College, which appears in the current issue of the “New Zealand Geographer.” Mr Packard says that flye-sixths of the vegetation cover is in a critical condition, four-fifths of the catchment suffers from apparent soil erosion, surface run-off has increased and water retentivity has decreased. About 60 miles west of Christchurch the Lake Coleridge hydro-electric power station generates a fifth of the South Island power supply, being the second largest unit. Waitaki, the largest single unit, generates half the South Island total. Weakness of Waitaki Mr Packard says that the Waitaki scheme is dependent, however, on a snow-fed river having a natural decrease in water supply, and consequently in power production, at the season of greatest demand. Lake Coleridge station, with its effective natural reservoir, the lake, suffers no such decline in winter water supply, and at periods of breakdown or abnormal demand must be prepared to generate the power deficit. In order to carry out this unusual function of both constant and emergency production. Lake Coleridge must be assured at all times of an adequate flow of water from the Harper river which, with its tributary, the Avoca, has been diverted into the lake since 1924. Wide fluctuations in water supply and apparently increasing .flood levels have led the hydro-electrical authorities at Lake Coleridge to suspect that the water supply to the lake might be endangered by depletion of surface cover, and the investigation was undertaken by Mr Packard as a result largely of their anxiety and that of the North Canterbury Catchment Board.

Restoring Stability From the viewpoint of conservation of vegetation, water and soil, the Lake Coleridge catchment is a problem area, says the report. Disturbance of the fine state of balance of the primitive vegetation by the early and subsequent fires, by the introduction and grazing of vermin and by the continued over-grazing of merino sheep, has reduced the plant cover by no less than 30 per cent. If stability is to be restored and vegetation, soil and water conserved the sub-alpine areas should be retired from grazing and. along with the mountain beech forest, rid of deer and other vermin, it is stated. A system of rotational grazing and long-term spelling, in conjunction with the complete cessation of all burning, is necessary on the tussock grasslands.