海洋深層水の放水による海水交換促進工法の羅臼漁港への適用性(Applicability to Rausu fishing port of the seawater exchange hastening method by using deep-sea water discharge)
- 標題
- 海洋深層水の放水による海水交換促進工法の羅臼漁港への適用性(Applicability to Rausu fishing port of the seawater exchange hastening method by using deep-sea water discharge)
- 作者
- 瀬戸 雅文(Masabumi SETO)
- 文件屬性
- 日本研究
- 知識分類
- 基礎研究
- 出版年
- 2008
- 刊名
- 海洋深層水研究
- 卷
- 9
- 期
- 2
- 頁
- P 59-68
- 點閱數
- 2469
摘要
漁港泊地内の海底面に沿って海洋深層水を噴流状態で放出すると, 周辺の海水を大規模に連行しながら流れの幅を扇状に増大させる. 連行による流量の増加とともに噴流内の流速は減少し, 流れは次第に密度流的な同心円状の拡がりに変化しながら, 下層密度流として港口の下層部より流出し, 流出量に相当する外海水が表層より漁港内へ流入し海水交換が促進される. 本研究は, 2006年より海洋深層水の本格取水が開始された羅臼漁港をモデルケースとして, 港内で最も閉鎖性が高く水質低下が認められる, 西側澗内より海洋深層水を放出した場合の海水交換促進効果を数値解析および水理模型実験より検討した. その結果, 海洋深層水の放水による当該海域の海水交換速度は, 大潮時における海水交換速度と比較して2～12倍の促進効果が, 密度フルード数で評価される放出条件に依存して発現することがわかった
A technology of hastening the seawater exchange using deep seawater (DSW, known as clean and cold seawater) was tested in a case study on Rausu Fishing Port using a hydraulic model and a numerical simulation. The technology was proposed by the authors as follows in 2006. When cold seawater is continuously emitted in the state of a buoyant jet along the bottom of an anchorage in a port, the jet increases its width in the shape of a fan immediately by entraining the surroundingseawater. Although the jet flow velocity decreases with the increase in the entrainment velocity, the buoyant jet expands in the shape of a concentric circle. When the buoyant jet flows out through the lower layer of the port, outside freshseawater flows into the port through the upper layer in order to compensate the flux. At Rausu Fishing Port, Hokkaido, water quality was reported to be worsenedparticularly at the west anchorage in autumn, but 4, 560 ton/day of DSW has been pumped from a depth of 350m for industrial use since 2006. In the present study, a hydraulic model (1.5×8×1m, with topography in the port and its vicinity of 1/250 in scale) was used with a wave producer assuming the use of emission pipes with inner diameter 25 or 50 cm. The numerical simulations were conducted using a 3-dimension fluid analysis model in the case of emission of 5, 000 t/day of DSW (5°C, 33.3 psu) as a buoyant jet at an initial velocity of 1.18 m/s into the west anchorage (12°C, 33.5 psu representing the autumnal condition) toward its center. The amount of seawater exchange was calculated to be 2 to 12 times largerthan that obtained at the spring tide. The validity of the technology was discussed.
A technology of hastening the seawater exchange using deep seawater (DSW, known as clean and cold seawater) was tested in a case study on Rausu Fishing Port using a hydraulic model and a numerical simulation. The technology was proposed by the authors as follows in 2006. When cold seawater is continuously emitted in the state of a buoyant jet along the bottom of an anchorage in a port, the jet increases its width in the shape of a fan immediately by entraining the surroundingseawater. Although the jet flow velocity decreases with the increase in the entrainment velocity, the buoyant jet expands in the shape of a concentric circle. When the buoyant jet flows out through the lower layer of the port, outside freshseawater flows into the port through the upper layer in order to compensate the flux. At Rausu Fishing Port, Hokkaido, water quality was reported to be worsenedparticularly at the west anchorage in autumn, but 4, 560 ton/day of DSW has been pumped from a depth of 350m for industrial use since 2006. In the present study, a hydraulic model (1.5×8×1m, with topography in the port and its vicinity of 1/250 in scale) was used with a wave producer assuming the use of emission pipes with inner diameter 25 or 50 cm. The numerical simulations were conducted using a 3-dimension fluid analysis model in the case of emission of 5, 000 t/day of DSW (5°C, 33.3 psu) as a buoyant jet at an initial velocity of 1.18 m/s into the west anchorage (12°C, 33.5 psu representing the autumnal condition) toward its center. The amount of seawater exchange was calculated to be 2 to 12 times largerthan that obtained at the spring tide. The validity of the technology was discussed.