An experimental study is carried out to investigate the transformation of oscillatory bound ary layer from ordinary to depth-limited one by using an oscillating tunnel with trian- gular roughness pasted on the top and bottom surfaces. The velocity is measured by one-component LDV. It is proved that only longer period of osci1lation is not sufficient to induce depth-limited properties. Instead, the ratio of boundary layer thickness to the distance from the bottom to the free surface must be used in order to distinguish a depth- limited oscillatory boundary layer from an ordinary one. The experimental data for mean velocity, phase difference, fluctuating velocity, friction coefficient and boundary layer thick- ness are presented in order to elaborate the structure of depth-limited oscillatory bound- ary layers on a rough bottom. On the basis of the present experiments, a modification has been made in an existing criterion to distinguish between ordinary and depth-limited wave boundary layers. A typical field situation is discussed to show the usefuiness of the proposed criterion.
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