A Field Investigation of the Spatial and Temporal Structure of Longshore Currents.
PURDUE UNIV LAFAYETTE IND GREAT LAKES COASTAL RESEARCH LAB
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This field investigation was conducted to obtain simultaneous and continuous measurements of the horizontal, vertical and temporal variability of the longshore current flow field. The present study has resulted in a two-dimensional mapping, across the surf zone and with depth, of the longshore current field. The vertical structure of the mean longshore current flow field is nearly uniform with depth, with a narrow bottom boundary layer and sharp velocity gradients at the water-sediment interface. This investigation has also shown that the total longshore current velocity vector, at any point across the surf zone, is composed of three distinct velocity components. These components are 1 a steady longshore current velocity component 2 a long-period fluctuating velocity component which tends to be out-of-phase with the incident wave field and 3 a short-period fluctuating longshore current velocity component which tends to be in-phase with the incident wave field. The results of this study have further indicated that neither the deterministic radiation stress approach to the prediction of longshore currents, nor a probabilistic formulation, provide adequate prediction of the magnitude or distribution of the longshore current velocity across the surf zone. In addition, the existence of a low velocity zone in the longshore current flow field has been isolated over the submarine bar. It appears that existing analytical formulations for longshore current flow prediction must be re-evaluated in light of the findings of this study. Author
- Physical and Dynamic Oceanography
- Fluid Mechanics