Modeling of Water Quality in Tidal River Network in Osaka, Japan

摘要

An urban tidal river network is one of the most difficult targets to simulate the flow and water quality in various kinds of water areas because the model must simulate both the vertical feature of the intrusion of sea water and the horizontal feature of water quality that is affected by human activities. In this paper, we determine the applicability of a three-dimensional flow and water quality model when reproducing the process of water with high concentrations of nitrogen, phosphorus and other constituents flowing through an urban tidal river network. We applied a three-dimensional model to Neya River, its tributaries and its downstream rivers in Osaka. The model can simulate well the vertical stratification of temperature and salinity near three river mouths, the mixing process of two different sources of water originating from Yodo River, and Neya River and its tributaries, the longitudinal profiles of chemical oxygen demand (COD), dissolved oxygen (DO), total nitrogen and phosphorus. Calculated water levels in the upstream area of Neya River system, however, are not coincident with the observations. A 3D water quality model, which is a potent tool in ocean and lakes, proved to be a versatile enough tool to simulate complicated and tidal urban river networks.