Author(s): S. Onishi; Y. Kitamura
Linked Author(s):
Keywords: River; Lagoon; Tidal change; Stratification; Water quality; BOD; Saline wedge; Harbor
Abstract: Effects of building a new harbor on the surrounding water environment, choosing Uchikawa River and Hojyozu Lagoon located near by the seacoast of Toyama Bay in Japan. The river is of 2km length and 2.5m water depth, and the water surface area of the closed lagoon is about 1.5 square kilometers. The water level at the lagoon changes 1.5hr behind the sea. And difference between the maximum tidal level and the minimum at the sea is approximately 0.33m, while the difference at the lagoon is 0.23m, in effect, the former is 70 % of the latter. Directions of the river flow change periodically in response to the tidal change at the sea. Analyses indicate that the river currents are apt to become stratified flow, and the current toward the lagoon has more energy to stir the sediments larger than the current toward the sea. Consequently the water quality of the lagoon will deteriorate more and more if any countermeasure against it were taken. Building of a new channel between the lagoon and neighboring sea is one of countermeasures against the getting worse tendency of water environment in a local district. In the studied case a new harbor has been constructed by digging the lagoon area. As result, the environment of lagoon area could be preserved. But the river leading the lagoon water to the sea has been deprived the natural hydraulic mechanism to keep the water favorable. BOD in Uchikawa River became are 8.4 lmg to 12.0 lmg, which are remarkably larger than the neighboring rivers are.
Year: 2003