Lake Heron wildlife evaluation wanted

Press, 6 July 1983, Page 33

Lake Heron wildlife evaluation wanted

Intensive investigation was needed before any big developments at Lake Heron could be evaluated, a special meeting of the North Canterbury Catchment Board’s resource committee was told on Monday. The meeting had been called to consider draft reports on the options for developing Lake Heron and Lake Coleridge. The reports will become part of the draft management plan for the Rakaia River and the central plains groundwater, the first half of which will be published on July 18. Mr R. W. Cathcart, the resource planning manager, said that the meeting had been called to give board members the chance to contribute to the drafts. The report said that conflicting demands on the possible use of Lake Stream and its catchment, particularly Lake Heron and the Cameron Fan wetland complex, had led to considerable controversy. The area had outstanding wildlife values, with a highly rated fishery and considerable scenic appeal. On the other hand, Lake Heron could be used for water storage to supplement river flows for irrigation on the Canterbury Plains. The lake and a 20rn margin round it had a reserve classification under the Reserves Act, 1977, but this meant little if Cameron Fan or the upper reaches of Lake Stream, which were an integral part of the Lake Heron system, were not protected.

These areas could be protected by gazetting the area as a scenic reserve, including it in a Water Conservation notice, or including it in covenants under the Queen Elizabeth II National Trust or the Lands Act, 1948. The Wildlife Service had rated the Lake Heron system as having outstanding environmental value because of its importance as a habitat for rare birds and also because it was the only untouched ecosystem of its type in New Zealand. Fifty-four bird species had been recorded in the Lake Heron system, and 38 of them used the Cameron Fan wetland. It was a valuable habitat for several protected native birds such as the southern crested grebe.

Lake Heron was also among the best angling lakes in Canterbury. It contained brown trout, quinnat salmon, and some rainbow trout. Local streams provided spawning grounds for brown trout and were important rearing habitats for

young trout. Because Lake Heron was shallow, with 60 per cent of its total less than 5m deep and 40 per cent less than 2m deep, its storage potential was quite limited unless major development work was undertaken, the report said. The board had received two water right applications to develop parts of the Lake Stream catchment, particularly the Lake Heron system. One, by Mount Arrowsmith station was to discharge water from the drainage of 200 ha of wetland. The other, by the Highbank-Barrhill Irrigation Association, was to use water from Lake Heron to irrigate land south of the Rakaia River.

Another development option was to re-route some water from the Cameron River into the south branch of the Ashburton River.

The proposed developments were at a very early stage and no detailed investigations had been carried out, the report said. However, it appeared that the changes in the level of water in the lake caused by the schemes would be severe because the lake was shallow. Fluctuations in the level of the lake would cause changes in the water-table within the Cameron Fan wetland. This was likely to affect wildlife habitats.

In particular, the changes would damage the summer breeding habitat of the southern crested grebe, which had an estimated population of between 240 and 250 in 1981.

If a weir was built on Lake Stream or water from Lake Heron was diverted into the Ashburton River, there could be a reduction in the fish population, which would reduce the value of the lake for recreation. The report said that there were many environmental concerns associated with the potential developments of the Lake Heron system, but some of the discussion had to be hypothetical because there was so little information about some aspects of the area. There were five management options for the area: @ Management as a refuge and reserve area, with an attempt to rehabilitate wetlands that had already been drained.

® Maintenance of the area as it was now, with some wetland drainage but no further development. © Management for increased agricultural production in the Lake Heron area, with full wetland drainage. ® Diversion of the Cameron River and a 2m fluctuation in lake levels to allow for increased agricultural production on the plains. ® A combination of the last two options. The report concluded that because of the lack of knowledge about the area, the “status quo” option was the preferred one. Extensive investigations would have to be carried out before any major developments could be evaluated. Mr R. W. Grant said that the draft report should include a “middle-of-the-road” option which would allow for some water storage in

the lake, but which wouk not allow the lake to fluctu ate beyond its natural rangf of o.Bm.

The report on Lake Coleridge said that there would not be enough water for full irrigation on the plains from the Rakaia River unless the Coleridge power station were used to supplement river flows between January and March. Lake Coleridge was not a particularly important wildlife habitat, but it had considerable scenic value and was listed as the fourth most popular fishery in the North Canterbury Acclimatisation Society district in 1976.

Fishery interests were concerned that sediment from the Wilberforce Diversion could adversely affect the lake’s recreational use. There was no clear evidence if this was the case and the effect of sediment discharge should be monitored before the diversion’s water right expired in 1985. The meeting was told that the lake could be used for storage, but the effects on weed growth and water temperature were not known. The main detrimental effect of changing the water level of the lake would be on the fish life. An “enormous” amount of work would have to be done to find out what the effects were of proposed developments on the lake.

The report said that it was vital to have co-opera-tion with the New Zealand Electricity Division to reach a satisfactory compromise between the competing uses of Rakaia water.