Control of algal blooms in reservoirs with a curtain: a numerical analysis

Two vertical curtains, having depths to cover the epilimnion thickness, wer e installed across the Terauchi Dam Reservoir in the western island of Japa n to curtail the nutrient supply from nutrient-rich inflows to the downstre am epilimnion of the reservoir. The withdrawal level was also regulated to keep the downstream epilimnion away from the nutrient supply. This method m arkedly reduced algal blooming in the reservoir downstream of the curtains during spring and summer. The physical and biological processes in the rese rvoir ecosystem were analysed using the 2-D reservoir model DYRESM and chem ical and biological submodels, to predict the water quality and algal speci es composition in the reservoir. The horizontal variability was maintained in the model by dividing the horizontal layer into parcels. Temperature, ch lorophyll-a, soluble phosphorus, nitrate, ammonium, dissolved oxygen, bioch emical oxygen demand, internal nitrogen, internal phosphorus were considere d as state variables in the model. The simulated results revealed the mecha nism of how algal blooming is reduced, during early spring high algal conce ntrations consume large amounts of nutrients, which reduces the nutrient su pply to the downstream zone of the reservoir, whereas during late spring an d summer, nutrient dispersion from the upstream epilimnion to the downstrea m epilimnion is curtailed by the curtains, markedly reducing algal blooming in the downstream zone. (C) 2001 Elsevier Science B.V. All rights reserved .