Water Quality of the Hauraki Rivers and Southern Firth of Thames, 2000-09

Report: TR 2011/06
Author: B Vant

Abstract

The Firth of Thames is the largest semi-enclosed coastal waterbody in the Waikato region. There are four moderately-large rivers that flow into the southern part of the Firth: the Kauaeranga, Piako, Waitoa and Waihou Rivers.  The Waitoa joins the Piako River about 40 km upstream of its mouth. A fifth river, the Ohinemuri, is a major tributary of the Waihou River. In this report these rivers are collectively called the “Hauraki rivers”.

The Waikato Regional Council operates a routine river water quality monitoring programme that includes a number of sites on the Hauraki rivers. It also issues the resource consents that permit the discharge of treated wastewaters to these rivers; consent holders are required to monitor the flow and water quality of these discharges and to provide the information to the council.

This report collates, analyses and interprets the available information to address the following matters:

• What is the current water quality of the Hauraki rivers?
• Has this changed in the past 20 years, and if so how?
• What mass flows of N and P do the Hauraki rivers currently carry into the Southern Firth of Thames?
• What are the main sources of these mass flows of N and P — how important are consented discharges of wastewaters?
• What is the current water quality of the Southern Firth of Thames, in particular what are the concentrations of N and P, and what level of algal biomass do these nutrients support?