Drinking Water Quality - Forecasting Salinity Intrusion in Whakatane River

The Whakatane River can experience sufficiently low flows in summer months that allow saline intrusion to reach, and pass, the town water supply intake. Such intrusion events have led to water quality issues with the town water supply. It has been necessary for the Whakatane District Council to manage such intrusion events to minimise the impact on drinking water quality. Having advanced warning of the timing and duration of such events is useful to council.

A modified version of a MIKE 11 river model was been developed (known as MIKE 11 XZ) where the model operates in a two dimensional mode in the vertical (X-Z) plane allowing vertically stratified flow to be simulated. This model has been applied to an existing MIKE 11 model of the Whakatane River and predictions made using both observed and predicted tidal levels and both observed and design low river flows. Forecasts made by the model were found to have strong agreement with actual salinity intrusion events.

This paper will present the work carried out for the Whakatane River salinity intrusion forecasting and demonstrate that it is possible to exploit existing investments in river models to make predictions of important water quality events.