The logarithmic layer in a tidal channel
Abstract
Twentyminute averaged velocity profiles taken with a bottommounted ADCP in a 30m deep tidal channel have been fitted to a logarithmic form with 1 % accuracy. The height of the loglayer varies tidally and reaches 20 m above the bottom during peak flows of 1 m s ^{1}. The height is well predicted by 0.04 u _{*}/ω, where u _{*} is the friction velocity and ω is the angular frequency of the dominant tidal constituent. The mean nondimensional shear,(∂U/∂z)(u _{*}/κz), is within 1 % of unity at the 95% level of confidence inside the loglayer. The friction velocity varies tidally and reaches O(0.05) m s ^{1} during peak current flow. The bottom drag coefficient referring to the depthmean flow is 4 × 10 ^{3}. The observed loglayer is not connected to the skin friction, but possibly to the form drag. Deviations of the measured velocity from the logarithmic profiles above the loglayer can be explained by the zerostress boundary condition at surface and by the entrainment of shallow water at middepth. The deviations are inconsistent with the effects of acceleration/deceleration and stratification.
 Publication:

Continental Shelf Research
 Pub Date:
 December 1997
 DOI:
 10.1016/S02784343(97)000496
 Bibcode:
 1997CSR....17.1785L