EFFECT OF THE GENTLY SLOPING RUBBLE MOUND SEAWALL TOWARD AN ECOSYSTEM
田端竹 千穂 関西国際空港? 技術部長
Takechiho TABATA GENERAL MANAGER , ENGINEERING DEPARTMENTKANSAI INTERNATIONAL AIRPORT CO, LTD
野田頭 照美 関西国際空港? 技術二課長
Terumi NODAGASHlRA MANAGER, 2ND ENGINEERING DIVISION KANSAI INTERNATIONAL AIRPORT CO , LTD
KEYWORDS : offshore airport , rubble mound type seawall, ecosystem, creation of environment.
ABSTRACT: The Kansai International Airport is located in the eastern part of Osaka Bay, 5 kilometers off shore of southern area "Senshu" in Osaka Prefecture. The Area is 511 hectare, and the water depth is approximately 18 meter. This offshore airport was constructed by the reclamation using 4 types of seawalls 11 kilometer in length. Rubble mound type seawalls account for about 80 percent of the total length. In order to make an artificial reef, some seaweed was planted on the rubble mound seawalls since December, 1988. Since then observation of the seaweed and fish have been held on the site. The results, show that more than 50 species of seaweed and 110 species of fish were seen and these species have become gradually diversified. The influence of environmental conditions to the ecosystem were analysed such as waves, sea currents , sun light, water quality and sea bottom materials. The results were as follows, 1. Wet weight of periphyton induced correlatively with the number of waves at the southern seawalls where the waves are strongest. 2. Water mass moved 50 kilometers during 3 days. The current velocity at the lower level in the sea tends to be slower than that of the upper Level. 3. Wet weight of seaweed was correlated with the sun light strength. At the northern seawalls, both the sun light strength and wet weight of seaweed was less than other seawalls. 4. The wet weight of seaweed is supposed to be influenced by the water temperature. 5. Judging from the diversity of species, the seawalls of the airport island were similar to that of the inner coastline of Osaka Bay just after construction of the island. The vertical seawalls of the island have become more similar to the inner coastline, whereas the rubble mound seawalls have become gradually similar to the eastern coastline of Awaji Island.
