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Bottom‐slope‐induced net sheet‐flow sediment transport rate under sinusoidal oscillatory flows
Author(s) -
Yuan Jing,
Li Zhiwei,
Madsen O. S.
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011996
Subject(s) - sediment transport , geology , bed load , sediment , bedform , flow (mathematics) , geotechnical engineering , shear stress , submarine pipeline , surf zone , mechanics , soil science , geomorphology , hydrology (agriculture) , physics , oceanography
It is generally believed that the slope of beaches can lead to a net downslope (usually offshore) sediment transport rate under shoaling waves, but very few high‐quality measurements have been reported for a quantitative understanding of this phenomenon. In this study, full‐scale (1:1) experiments of bottom‐slope‐induced net sheet‐flow sediment transport rate under sinusoidal oscillatory flows are conducted using a tilting oscillatory water tunnel. The tests cover a variety of flow‐sediment conditions on bottom slopes up to2.6 ° . A laser‐based bottom profiler system is developed for measuring net transport rate based on the principle of mass conservation. Experimental results suggest that for a given flow‐sediment condition the net transport rate is in the downslope direction and increases linearly with bottom slope. A conceptual model is presented based on the idea that gravity helps bottom shear stress drive bedload transport and consequently enhances (reduces) bedload transport and suspension when the flow is in the downslope (up‐slope) direction. The model predicts both the measured net sediment transport rates and the experimental linear relationship between net transport rates and bottom slope with an accuracy generally better than a factor of 2. Some measured net transport rates in this study are comparable to those due to flow skewness obtained in similar sheet‐flow studies, despite that our maximum slope could be milder than the actual bottom slope in surf zones, where sheet‐flow conditions usually occur. This shows that the slope effect may be as important as wave nonlinearity in producing net cross‐shore sheet‐flow sediment transport.