FIELD SURVEY AND ANALYSIS OF THE WATER AND SEDIMENT QUALITY IN A HIGHLY ENCLOSED SEA

Abstract

 Reducing the inflow load, improving the sediment quality by dredging and sand capping, and promoting water exchange by artificial flow control are necessary measures for regenerating the water environment in highly enclosed urban coastal areas such as harbors. In this study, field surveys and analyses were conducted in the old port of Sakai to clarify the water and sediment quality characteristics and the water quality fluctuation because of an external disturbance.

 In the summer, hypersaturation and hypoxia were caused in the surface layer and the bottom layer, respectively, by density stratification in the port. Even though high concentrations of organic nitrogen and phosphorus were detected in the surface layer because of the impact of combined sewer overflow during rainfall, a high concentration of inorganic nutrients was observed in the bottom layer under the influence of nutrient elution from the polluted sea mud. During Typhoon No. 21, the water mass of the amount corresponding to the port volume flowed inside from outside the port. The water quality in the port was not completely mixed despite the strong wind and the storm surge. Further, the water environment in this port was observed to be strongly dependent on the bottom sediment. Accordingly, the improvement of the sediment quality is considered to be the most effective methodology for improving the water quality.