Authored by Justine Coup, Caleb Clarke and Brian Sharman. Prepared for Water NZ 2012 Stormwater Conference.
Urban stormwater and combined sewer overflows discharging into the Meola Creek (Auckland, New Zealand) have potential risks for public health and aquatic ecology. Monitoring was carried out by Auckland Council at selected stream, marine and discharge sites over summer and autumn 2010/2011 to characterise stream and coastal water quality.
Continuous monitors were installed and synoptic dry weather and wet weather events were sampled for heavy metals, nutrients, suspended sediment, indicator bacteria and norovirus. Stream ecological valuations (SEV) were also carried out at four sites and biofilm assessments at two sites to assess stream ecological health.
Wet weather monitoring provided evidence of the first flush phenomenon from combined sewer overflows and stormwater inputs. Norovirus was detected during both wet and dry weather monitoring. Dissolved oxygen in the upper catchment falls to levels below that of life-sustaining capacity (0 ppm) overnight during summer periods of low flow.
SEV values ranged from 0.574 to 0.645, revealing a trend of increasing ecological value moving from upper to lower catchment. Macroinvertebrate Community Index (MCI) values and biofilm sampling showed a similar trend, highlighting the influence of water quality on aquatic ecology.