Publications: Research reports and publications

Review of biological data relating to the Waimea River catchment

1 January, 2005
Cawthron Report 996. Prepared for Waimea Water Augmentation Committee.

EXECUTIVE SUMMARY

Water in the Waimea River Catchment has come under increasing demand for out of stream uses, particularly irrigation, to the extent that in the lower catchment water currently is over allocated. Augmentation of flow in the river during periods of low flow, from a water storage reservoir, currently is being considered as a way to alleviate this problem. This report reviews existing biological data from the catchment, to make a preliminary assessment of what instream values, including the stream biota and habitat values, could be affected, and to identify gaps in existing knowledge that may need to be addressed in order to allow informed decision making.

Biological and water quality data from a range of sources indicate that the rivers of the Waimea Catchment generally are characterised by good water quality, although there are some concerns with nutrient enrichment and faecal contamination in the Wai-iti River. There also seem to be issues with elevated water temperatures, especially during prolonged periods of low flow in summer.

The Wairoa River's macroinvertebrate community does not appear to contain any rare or endangered species, however, the Wairoa River's fish community is considered to be of regional importance due to its diversity and includes dwarf galaxias and longfin eel, which are both classified as chronically threatened by DoC. Algal and macroinvertebrate communities are strongly influenced by flow conditions. Unsightly accumulations of algae are common in the Waimea River and in the lower reaches of the Roding, Wairoa and Wai-iti rivers. These algal growths presumably are responsible for the change from a mayfly dominated community to a worm dominated community that has been documented in the Waimea River and lower reaches of the Wairoa River during periods of low flow.

In general, there is a relatively large amount of information on the Waimea River, Roding River, and on the lower reaches of the Wairoa and Wai-iti rivers. Other areas of the catchment have been studied as part of the Tasman District Council's SoE monitoring programme, but little is known about the water quality, macroinvertebrates, or algae present in the Left and Right branches of the Wairoa River, the upper Lee River, or the tributaries of the Wai-iti River. Records of fish distribution within the catchment are reasonably well spread. Recent surveys in the middle and upper reaches of the Wairoa and Lee rivers have provided useful information on the fish communities present in these parts of the catchment. The most obvious knowledge gap is the paucity of information about the distribution of blue duck. There are anecdotal reports of blue duck in the Left Branch of the Wairoa River and in the lower reaches of the Lee River. It is not known if blue duck are found in the upper reaches of the Lee River or in the Right Branch of the Wairoa River, although these areas would be expected to provide good habitat. If the proposed dam site is chosen in these areas, further information on blue duck distribution and abundance would be required.

There is a range of potential water storage options being considered as part of the Waimea Water Augmentation Project. Based on existing information, storage systems on the Western tributaries of the Wai-iti River would have the least potential ecological impacts. The ecological effects of storage systems on the Lee River, and Right and Left branches of the Wairoa River are likely to be similar, although the perceived high value of the trout fishery in the branches of the Wairoa River probably means more potential impacts there. The confirmed presence of blue duck in the Left branch of the Wairoa River means that an assessment of the impacts of a storage system on blue duck would definitely be required in that part of the catchment. A storage system in the mid reaches of the Wairoa River would be expected to have the greatest ecological impacts of any storage option due to the large proportion of flow potentially retained there and the substantial change to the hydrological regime downstream.