Study on the Development of the Tidal Dam in Oder to Prevent the Oxygen-Deficiency in an Enclosed Bay

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In order to prevent the stagnation and to reduce the less oxygen bottom water in stratified seasons in a partly enclosed bay, a new technique, called the tide-dam, is suggested. The simple structure is designed to improve the water quality environment by generating the vertical circulation of the stratified sea water.The present study consists of the theoretical and experimental investigations on the hydraulic parameters of the tide-dam and the field experiments on the water quality improvement in an actual sea. In the former part, the principle of this idea, its basic structural design, the fundamental hydraulic parameters, the entrainment intensity of jet flows from ejecting pipes, and the way to determine the geometrical dimensions of this facility are investigated by hydraulic and numerical experiments. In the later part, the field experiments were carried out using the small scale prototype constructed in Uranouchi Bay. The above hydraulic model and the effectiveness of the dam op … More eration on the bottom water quality environment were verified. And the problems which may occur in the practical use are examined. The important results obtained in these studies are as follows :1) the hydraulic parameters of pipelines connecting the dam reservoir with a bay and the entrainment rate due to jet flows into the sea bottom are accurately estimated by the present model ;2) the tidal range of Uranouchi Bay is usually larger than that of the adjacent open sea, therefore, the tide-dam which utilizes only the tidal potential energy is a quite effective measure for water quality improvement ;3) the dissolved oxygen concentration of the stratified bottom sea water increases by the dam operation, and the decomposition process of the organic bottom mud is accelerated ;4) the dam reservoir can be used as the fish nursery because many kinds of fishes and shellfishes can live in the dam reservoir during the field experiment.To turn this technique to practical use, the quantitative analysis of the improved environment of bottom sea water, the measure against adhesive organisms on the connecting pipes and the economic effect should be investigated as the next step. Less