CONTROLLING THE INDIRECT EFFECTS OF FLOW DIVERSIONS ON WATER-QUALITY IN AN AUSTRALIAN RESERVOIR

The water quality effects of a planned diversion to a water treatment plant of the main inflow to Prospect Reservoir in Australia are predic ted with a coupled hydrodynamic-ecological model (DYRESM Water Quality ). The model combines a one-dimensional, process-based hydrodynamic mo del (DYRESM) with numerical descriptions of phytoplankton production, nutrient cycling, and oxygen dynamics. The hydrodynamic component is f ree from calibration, which improves water quality predictions for ext reme 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 dynami cs through removal of the major source of dissolved oxygen from the hy polimnion. The simulations also show increased phytoplankton concentra tions resulting from anoxic release of phosphorus from the sediments. The increased phytoplankton concentrations resulting from anoxic relea se of phosphorus from the sediments. The increased phytoplankton conce ntrations were observed only following turnover, however, when phospho rus released form the sediments was redistributed through the water co lumn. The results illustrate the ability of an interactive hydrodynami c-ecological model to capture the subtle interactions between the hydr odynamics and biochemical processes that influence water quality.