Evaluation of the impact of water dilution within the hypereutrophic Lake Barato, Japan

Abstract Field data and three-dimensional numerical simulations were used to evaluate the impact of water dilution on eutrophication. To dilute eutrophic water in Lake Barato, Japan, an Inlet Project was carried out during the summer of 2005 via a 1 m3/sec inlet. River water was discharged from the margin of the upper basin of the lake to dilute the water. We undertook a numerical simulation of total nitrogen (TN) and total phosphorus (TP) distribution considering five inlet cases by using Princeton Ocean Model (POM). Total N and TP concentrations of inlet water were TN: 1.3 mg/l and TP: 0.08 mg/l. Model results suggest the most effective and feasible way to achieve dilution is via a 5 m3/sec inlet (78% related to the total volume in the lake) and opening the Shinko Gate, connecting the lake with Ishikari Bay. Following this scheme, TN and TP concentrations would be reduced by 28% following 30 days of discharge according to the simulation results.