Water quality in some Christchurch waterways is gradually improving, the latest data shows.
The Christchurch City Council has just published its annual Christchurch Surface Water Quality Report, an analysis of water quality data collected in 2017.
The Council’s Waterways Ecologist, Dr Belinda Margetts, who has led the research, says in most waterways the water quality is unchanged from previous years.
“Encouragingly, two waterways – Ōtākaro/Avon River and Pūharakekenui/Styx River – are showing improvements on previous years,” Dr Margetts says.
Christchurch has many waterways because it has been built on a swamp.
“As a city we are highly vested in our waterways and a lot of what we do as a Council can affect the quality of the water.”
Water quality is measured monthly at 42 sites across five catchments. During 2017, more than 13,000 tests were conducted, with 7335 being assessed against guideline levels to determine the water quality.
The testing measures contaminants and other water qualities – metals (copper, lead and zinc); pH levels; conductivity; total suspended solids; turbidity (how murky the water is); dissolved oxygen; temperature; biochemical oxygen demand; ammonia; nutrients (nitrogen and phosphorus) and Escherichia coli (an indicator of bacteria and viruses).
For the first time, waterways were scored using a Water Quality Index developed by Dr Margetts and her team, drawing on guidelines used overseas.
The sites were scored from 0 to 100, with 100 being perfect water quality and 0 the worst possible. In 2017, no Christchurch waterway scored in the very good range and none were very poor.
“At best, Ōtukaikino and Pūharakekenui/Styx typically scored in the good category and at worst, Ōpāwaho/Heathcote typically scored in the poor,” she says.
The best sites were at The Groynes Inlet and the Waimairi Stream (both 89), and the worst were Haytons Stream (44) and Curletts Road Stream (46).
The median Water Quality Index scores for each waterway catchment were: Ōtukaikino River 84; Pūharakekenui/Styx River 77; Ōtākaro/Avon River 75; Huritini/Halswell River 70; Ōpāwaho/Heathcote River 58.
“Most Christchurch waterways have fair or poor water quality, indicating they are historically and currently subjected to contamination, from stormwater, waterfowl and other factors,” Dr Margetts says.
It is difficult for urban waterways to achieve a very good score because of the effects of human activity.
“That doesn’t mean we shouldn’t strive to have the best possible,” she says. “If we could bring all our waterways up at least into the good category that would be great. I think that’s an achievable goal to work towards.”
Water quality is just one aspect of waterway ecology. The Council works with other agencies to address other issues, such as habitat loss.