報告書番号

U02014

タイトル（和文）

混合粒径砂を用いた大型岸沖海浜変形実験 -－粒径別漂砂の特性解明とモデル化－-

タイトル（英文）

Grain size screening process and size graded sediment transport by large scale cross-shore beach deformation experiments using mixed-sized sand and numerical modeling

概要 （図表や脚注は「報告書全文」に掲載しております）

当所の大型造波水路を用いて, 粗砂と細砂の２粒径混合砂を対象に現地スケールの岸沖海浜変形実験を東京電力と共同で実施した．入射波は規則波で，堆積型地形，侵食型地形，その中間型地形を生じさせる4ケースの波浪を作用させた．波高，流速，浮遊砂フラックスの岸沖・鉛直分布を計測した．海底地形の計測に加え海底砂面のコア試料を粒度分析し粗砂と細砂の混合率の空間分布を求めた．地形変化と混合粒径砂の分級過程，砕波帯内外の漂砂の粒径別特性と波浪外力との関係を明らかにした．実験で得られた混合粒径砂特有の幾つかの現象をモデル化し，従来の海浜変形予測モデルの改良を試みた．一部実験との比較により，アーマリング効果や粒径別漂砂量，浮遊砂濃度，バームの粗粒化等を再現できる可能性を示した．

概要 （英文）

As a joint experiment observation of CRIEPI with Tokyo Electric Power Company, proto-scale experiments using the CRIEPI large wave flume were performed on cross-shore beach deformation of mixed-sized sand compounding fine and coarse sands. Incident waves were regular and 4 cases, which cause beach deformations of accretionary, erosional and their intermediate types.Wave height, current, suspended sediment flux were measured in horizontal and vertical direction of the wave flume. By measuring sea bed change and sand grain size analysis of sampled cores, the spatial distribution of sand mixing ratio was evaluated in detail. Beach deformation, grain size screening process, and relationship between size graded sediment transport in and outer the surf zone and incident wave condition were elucidated experimentally. By modeling several sediment phenomena peculiar to mixed-sized sand, improvement of a beach deformation numerical model applied to uniform-sized sand was tried for mixed-sized sandy beach deformation prediction. Comparing the computation result with some experimental data, it was found that the improved model would have the potential of reproduction of armoring effect, graded sediment transport rate, suspended concentration, and accretion of coarse sand on the berm surface near shore line etc.

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