State of the River

The Ōpāwaho Heathcote River has an overall water quality of “POOR” according to 2022 CCC monitoring; it has  ‘urban river syndrome*’.

The river has the worst water quality of all the Christchurch rivers according to CCC, but it is not all gloom! The Cashmere Stream and Steamwharf Stream which are important tributaries have water quality ratings of GOOD.

Monitoring along the river length

Contaminant levels change along the length of the river due to environmental factors.  Check out these results three results from the top, middle and end….and click any of these for more details and to see the results from the 15 monitoring sites available from LAWA.

What is causing this?

Sediment

Sediment is soil particles washed into the river largely, but not exclusively, from the Port Hills.  Sediment smothers the habitat of macroinvertebrates and fish, reduces visibility and introduces excess nutrients into the waterway. Sediment is a particular problem in this catchment because the hill soil is “loess” – very fine grained, easily eroded and hard to control. Saltwater is a flocculant for it meaning that saltwater causes the loess to come out of suspension and deposit in the estuary. This makes sediment a problem for both the river and the estuary.

Where does the sediment come from that turns the river brown when it rains?
From land use in the Cashmere Valley that exposes the soil; construction, forestry and activity like the Adventure Park.

Zinc

Dissolved zinc is largely the result of water runoff from unpainted/old exposed zinc roofs and gutters or from road runoff as a result of tyre wear.  It is toxic to instream biota.

Copper

Dissolved copper enters the waterway from two sources: a) copper worn off car/truck brake pads which would easily be avoided if the available copper-free brake pads were used. b) water runoff from copper roofs and gutterings also contributes to the problem. Dissolved copper is toxic to instream biota.

E. coli

Bacteria prevents use of the water for recreation and can cause serious ill-health.  The source includes avaian (birds) but also dog source e coli is a significant issue with any rain event and wastewater overflows contribute sewage following significant rain events.  Longer riverbank grasses and planting reduces e coli.

Nutrients

nitrate, nitrite, ammonia, organic nitrogen, phosphate, total phosphorus

The nitrates are from farming. The nitrates are highest in the source springs, and actually decrease as you go down the river. Farming controls in the unconfined aquifer is the solution. Excessive nitrates increases sediment problems as it encourages higher weed growth which it turn slows water and causes sediment to precipitate.

2022 Water Quality Index Results

WQI scores were used to categorise the CCC sites as being ‘very poor’ (0 – 39.9), ‘poor’ (40 – 69.99), ‘fair’ (70 – 79.9), ‘good’ (80 – 89.9) or ‘very good (90 – 100).

Below are 2022 Water Quality Index (WQI) scores, categories, and direction of significant temporal trends (2016–2022) at each of the Christchurch City Council surface water quality monitoring sites on the river

Catchment Site WQI Score WQI Category WQI Temporal Trends
Ōpāwaho-Heathcote Curlett at Motorway 40.7 Poor
Ōpāwaho-Heathcote Curlett U/S of Heathcote 51.7 Poor
Ōpāwaho-Heathcote Cashmere at Worsleys Rd 56.5 Poor
Ōpāwaho-Heathcote Heathcote at Ferrymead Bridge 57.1 Poor
Ōpāwaho-Heathcote Haytons Stream 63.4 Poor
Ōpāwaho-Heathcote Heathcote at MacKenzie Ave 64.9 Poor
Ōpāwaho-Heathcote Heathcote at Rose St 65.2 Poor
Ōpāwaho-Heathcote Heathcote at Ferniehurst St 67.0 Poor
Ōpāwaho-Heathcote Heathcote at Catherine St 69.7 Poor
Ōpāwaho-Heathcote Heathcote at Opawa Rd 70.8 Fair
Ōpāwaho-Heathcote Heathcote at Bowenvale Ave 72.1 Fair
Ōpāwaho-Heathcote Cashmere at Sutherlands Rd 79.5 Fair
Ōpāwaho-Heathcote Steamwharf Stream 80.7 Good
Ōpāwaho-Heathcote Heathcote at Warren Cres 81.9 Good

Source: CCC – Christchurch City Surface Water Quality Annual Report 2022, pages-26-27

Note: This Water Quality Index (WQI) was developed in 2013 for the CCC monthly monitoring sites, based on a Canadian WQI. The parameters used in the CCC WQI were copper, zinc, pH, TSS, DO, temperature, BOD5, total ammonia, nitrate, DRP and E. coli.

Map of monitored sites

Monitormap
Click to enlarge

The problem with sediment

Stream Ecosystem Low Sediment 1 Web
Stream Ecosystem High Sediment 2 Web

Water Quality Monitoring Results

Take a look at the actual water quality testing results for this river

Status3
Click here to find out the current water quality status of Ōpāwaho Heathcote River
Waterqual22

What are ECAN & CCC doing about it?

The City Council and ECAN are doing quite a few things to try to improve the health of the river.

Read about them here

What can I do to help?

You can help increase the pace of improvement.

Click here to see what you can do

* Urban River Syndrome

This term describes the ecological degradation of streams draining urban land caused mostly by stormwater runoff but also sewer overflows, wastewater treatment plant effluents, and legacy pollutants.

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