Storm water inflow to Oranga Lake, University of Waikato Hamilton Campus

Abstract

Oranga Lake is one of three constructed lakes located on the University of Waikato Hamilton campus. It has had persistent problems of high turbidity, prolific seasonal macrophyte growths and phytoplankton blooms. Recent restoration measures of pest fish removal, sediment removal and alum dosing resulted in some improvements in water clarity. But these improvements appear to have been largely temporary and water clarity is low, reducing the aesthetic value of the lake which is located in a prominent area of the campus. This study was commissioned by Facilities Management Division of the University of Waikato to determine the extent to which inputs from the main storm water inflow to Oranga Lake contribute to poor water clarity in the lake. Discharge, suspended sediment and nutrients were sampled from the main inflow on 12 occasions. These samples related to four storm events over a three-month period from November 2013 to January 2014. Sampling was conducted with the objective of capturing periods of high, medium and low flows during three separate storm events. This was achieved on two occasions during November; however, the low-intensity, short-duration storm events that occurred in January resulted in limited runoff and were not considered representative of a major summer storm event.