Controlling the indirect effects of flow diversions on water quality in an Australian reservoir

Abstract

The water quality effects of a planned diversion to a water treatment plant of the main inflow to Prospect Reservoir in Australia are predicted with a coupled hydrodynamic-ecological model (DYRESM Water Quality). The model combines a one-dimensional, process-based hydrodynamic model (DYRESM) with numerical descriptions of phytoplankton production, nutrient cycling, and oxygen dynamics. The hydrodynamic component is free from calibration, which improves water quality predictions for extreme hydrodynamic forcing events and allows for identification of the specific processes that influence water quality. The model simulations show that diversion of the main inflow would affect the oxygen dynamics through removal of the major source of dissolved oxygen from the hypolimnion. The simulations also show increased phytoplankton concentrations resulting from anoxic release of phosphorus from the sediments. The increased phytoplankton concentrations were observed only following turnover, however, when phosphorus released from the sediments was redistributed through the water column. The results illustrate the ability of an interactive hydrodynamic-ecological model to capture the subtle interactions between the hydrodynamics and biochemical processes that influence water quality.