Important to protect little battler stream
The potential for adverse impacts on Kaikorai Stream in Dunedin from the Dunedin City Council's Mount Grand water project needs to be studied, writes Simon McMillan. It is also important that the community continues to recognise and confront issues that impact on water quality.
Today, people are inextricably linked to the valley and its stream. This has been the case since this area was first settled. A historical analysis of human settlement in Kaikorai Valley before and around the 1840s informs us that the stream water was of the purest kind. However, a downgrading of the water quality occurred from 1840 to about 1990, particularly with the development of industry along the valley floor.
In 1908, for example, Kaikorai Valley was the most heavily industrialised area in New Zealand. At the time, Kaikorai Stream was described as "but an open sewer carrying sewage, factory refuse, and filth of all descriptions". "Vote for Smellie and get the smell out of Green Island" was a slogan for a local body election in the 1930s. Since 1990, community groups, businesses, organisations and local government have taken renewed and positive steps to improve water quality in the stream: water quality monitoring, riparian planting and restoration, and sealing of the leachate from the city landfill are examples of what has been done.
But what then are the factors that continue to affect the stream? The water quality and aquatic environment of Kaikorai Stream are influenced by many factors, some common to other streams, like surface runoff, some not. Like many urban streams, Kaikorai Stream has been influenced by pollution events involving industrial wastewater, sewage and contaminated stormwater discharge. Analysis in the early 1990s for example, showed that urban stormwater is a significant source of metals, sediment and faecal coliforms; all of these regularly exceeded criteria for protection of aquatic organisms.
Add to this the physical removal or modification of habitat through addition of fill, concrete channelling and altered land use, and we can see that human activity is still adversely impacting on water quality. The amount of human impact on the water quality can be measured in different ways. Macroinvertebrates are small animals that live in the water and in and around the stream bed.
They can be used as indicators of water quality because some can only live in the purest of water while others can tolerate much lower quality. Importantly, macroinvertebrates give us information on the usual day-to-day quality of the environment in which they live. The macroinvertebrates found in the Brighton, Green Island and Burnside areas show the water quality to be degraded. However, as we go up the stream, at Kaikorai Valley College more sensitive examples can be found, indicating a better water quality.
At Glenross and in Fraser's Gully sensitive and more diverse types of macroinvertebrates occur, indicating water quality is better still. Such a trend is on the one hand encouraging (at least some reaches of the stream are in good shape), but on the other troubling - our activities appear to be adversely affecting the middle to lower catchment area. While this is the current state of affairs, the quality of the aquatic environment in and around the stream will soon change due to a special feature of water supply in the catchment. The flow of Kaikorai Stream is enhanced by a contribution from Deep Stream in the Taieri catchment.
Water that is not able to be used by the Mount Grand treatment plant for Dunedin's supply has overflowed into a tributary of the stream in the upper part of Fraser's Gully since the mid 1970s. This is ordinarily a source of cool, clear water of high quality that would otherwise not be available in the Kaikorai Stream catchment. Under fine weather flow conditions, in the order of two thirds of the flow of the Kaikorai Stream at Kaikorai Valley College comes from this source.
Significant alteration of the amount, or removal, of this extra water would clearly impact on the flow rate of the stream and its ability to cope with pollution events from other points down its stream course. Just such an alteration is going to occur as the city council continues to implement its Mount Grand upgrade in accord with our expectations of a higher quality and secure amount of water. Whatever eventuates in Kaikorai Stream, it is important all interested parties act together in a co-ordinated supportive way.
It is also important that the community continues to recognise and confront the issues that impact on water quality. As we become increasingly aware of the need to live sustainably, urban streams give us a tool, an indicator, to measure how successful we will be. Kaikorai Stream, so close and near to where we live, so tied to our activities, will be just such an indicator. (Kaikorai Valley and Kaikorai Stream are the subjects of the upcoming exhibition, "Water Like Wine" at the Settlers Museum."
Dr Simon McMillan is a teacher at Kaikorai Valley College. He is undertaking research on the Kaikorai Stream while on a science, mathematics and technology teaching fellowship this year.
Wednesday 23 June 2004
This information obtained from and with the permission of the Otago Daily Times.