Sediment cross-shore movement and vertical mixing in and out of the surf zone(Fostering Joint International Research)

2019 Fiscal Year Final Research Report

• Project/Area Number: 15KK0202
• Research Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research)
• Allocation Type: Multi-year Fund
• Research Field: Hydraulic engineering
• Research Institution: Yokohama National University
• Principal Investigator: Suzuki Takayuki 横浜国立大学, 大学院都市イノベーション研究院, 准教授 (90397084)
• Project Period (FY): 2016 – 2019
• Keywords: 底質移動 / 鉛直混合 / 沿岸流 / 戻り流れ / 漂砂

Outline of Final Research Achievements

The sediment cross-shore and vertical movements in the area of the swash zone to the offshore end of the surf zone were investigated using the fluorescent sand in the field experiments and the laboratory experiments. From the observed data of the field experiments, we found that the fluorescent sand that installed in the swash zone and surf zone were drifted toward the trough area. Therefore, it can be considered that the sand movements are separated onshore side and offshore side of the bar, and if the bar does not exist, sand at the offshore side of the bar could move toward the nearshore. However, the fluorescent sand installed at the offshore was not moved to the nearshore. Moreover, we found that the sediment properties have a direct influence on the change of the bed profile. For the mixing depth analysis, based on the laboratory experiments, the spatial distribution of mixing depth was measured and found the correlation between mixing depth and sediment diameter.

Free Research Field

海岸工学

Academic Significance and Societal Importance of the Research Achievements

本研究の主題は，社会的要請の強い砂浜海浜の保存施策の短期的・長期的動態機構を科学的，客観的に示すことであり，現地観測結果ならびに室内実験結果に基づいた，前浜からバー沖側端までの底質移動の動態解明と鉛直混合メカニズムの解明と検証を実施した．これまでの研究では，遡上域，砕波帯，バー形成領域と区分されそれぞれの領域に着目し研究がなされてきたが，ここではこの3領域を一帯としてとらえ，それぞれの相互作用や鉛直再配分効果などに着目した動態解明を実施することに本研究の特色があり，この成果は今後，広く海浜マネジメント技術の革新に資するものであると考える．