Influence of Sea Level Rise and Coastal Development on Tidal Current Change in Hakata Bay

博多湾の潮流変化に影響を及ぼした沿岸開発と海面上昇

Influence of Sea Level Rise and Coastal Development on Tidal Current Change in Hakata Bay

Creators HIRUMA Toyoharu

本研究は,高度経済高長期に海面の埋立てや海底浚渫により,自然海浜や干潟を失った沿岸海域について,潮汐に与えた影響を分析した。加えて,人類の活動によって排出された温室効果ガスによる地球温暖化という全地球的な気候変動に伴った海面上昇が,湾内の流動変化や物質交換機能の低下をもたらすものという考えから潮流変化の推定をおこなったものである。研究対象海域は,北部九州に位置する博多湾を選定し,湾内の開発が与える潮汐現象の変化と海面上昇による潮流速度の低下を予測したものである。沿岸開発によって,湾奥の潮差は約3cm縮小し,潮流速度は,6～7cm/sec低下すると予測した。さらに,平均海面の上昇約40cmによる流速の低下は,3～4cm/secとなり,合わせて9～11cm/secの低下となった。したがって,今世紀末の湾奥の潮流速度は,沿岸開発や海面上昇の影響を受けていなかった1900年初頭の流速15～20cm/secが7～8cm/secにまで減速し,約50%以下に低下するという予測結果を得た。 : The human activities have effected adversely on the environment of the enclosed coastal seas. Increased population and accompanied economic growth have brought more pollution loads to the sea, and consequently the water quality of the enclosed coastal seas has been degraded. Reclamation of sea has often been carried out to meet the increasing economic activities, and has decreased the seaweed beds, tidal flats, and natural beaches. Enclosed coastal seas have always been endangered by human activities. The following results were obtained by the analysis on Hakata Bay. In recent 30 years, the tidal range was lowered by about 3 cm and the current speed became 6 to 7 cm/sec slower. Environment deterioration and frequent occurrence of red tide were driven by reclamation. In addition to the above, one of the most serious impacts by global warming is the rise of mean sea level. The rise of mean sea level in Hakata Bay by global warming is forecasted as about 40cm in coming 100 years. As the result, tidal current speed will become 2 to 4 cm/sec slower and this decrease, in turn, will deteriorate the water quality and carry about frequent occurrence of red tide. At the end of this century, the tidal current speed of eastern sea area in Hakata Bay will be slowed down to 50% or less by coast development and the sea level rise.

[ISSN]1348-8414