事例研究 CASE STUDY

長良川河口堰湛水域における一時的な水温成層の形成

村上 哲生¹⁾・ 服部典子²⁾

1)名古屋女子大学家政学部生活環境学科
2) 名古屋女子大学大学院生活学研究科生活環境学専攻

Tetuo MURAKAMI¹⁾ and Noriko HATTORI²⁾: Formation of temporary thermal stratification in impoundment of the Nagara Rivermouth Barrage Ecol. Civil. Eng. 4(2), 179-184, 2001.

1) Depertment of Life Environmental Science, Faculty of Domestic Science, Nagoya Women's University, 3-40, Shioji-cho, Mizuho-ku, Nagoya 457-0003, Japan
2) Division of Life Environmental Science, Grsduate School of Domestic Science, Nagoya Women's University, 3-40, Shioji-cho, Mizuho-ku, Nagoya 457-0003, Japan

Abstract:Continuous hourly measurements of the vertical distribution of water temperature and dissolved oxygen concentration in the impoundment of the Nagara Rivermouth Barrage showed that temporary thermal stratification developed under fine weather conditions with light wind and that it obstructed vertical mixing of the water, which in turn, might lead to an oxygen deficit in the bottom water. The temporary thermal stratification was maintained for a few days. Diurnal minimum oxygen concentration in the bottom water was recorded at twilight, and vertical mixing caused by cooling of the surface water at midnight recovered the oxygen deficit. However, complete mixing including the bottom water did not occur every day. Judging from the rapid oxygen consumption rate by the water column and sediment, the temporary thermal stratification could cause frequent oxygen deficit in the impoundment in summer.

Key words: dam impoundment, Nagara Rivermouth Barrage, oxygen deficit, temporary thermal stratification, water temperature

摘要

長良川河口堰湛水域において，水温と溶存酸素の鉛直分布を一時間毎に連続観測し，快晴で弱風の気象条件の下で，一時的な水温成層が発達することを明らかにした．成層は水柱の鉛直混合を阻害し，さらに，底層の酸素不足を引き起こす可能性があることが示された．底層酸素濃度は，宵の内に最も低い値が記録され，深夜には表層水の冷却による鉛直混合のために底層の酸素不足は解消された．しかし, 底まで達する全水層の完全な混合は毎日起こるわけではなく，一時的な水温成層は, 数日間維持されることもあった．水柱や堆積物による急速な酸素消費速度から判断すれば，一時的な水温成層は，夏季の湛水域底層でしばしば観測される酸素不足の原因となる可能性がある．

2001年4月16日受付，2001年9月21日受理
1) e-mail: murakami@nagoya-wu.ac.jp