Lefebvre, Alice; Ernstsen, Verner Brandbyge; Winter, Christian (2013): Estimatin of roughness lengths with a ship-mounted ADCP from Knudedyb, Denmark in October 2009. PANGAEA, https://doi.org/10.1594/PANGAEA.812064, Supplement to: Lefebvre, A et al. (2013): Estimation of roughness lengths and flow separation over compound bedforms in a natural-tidal inlet. Continental Shelf Research, 61-62, 98-111, https://doi.org/10.1016/j.csr.2013.04.030
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The hydraulic effect of asymmetric compound bedforms on tidal currents was assessed from field measurements of flow velocity in the Knudedyb tidal inlet, Denmark. Large asymmetric bedforms with smaller superimposed ones are a common feature of sandy shallow water environments and are known to act as hydraulic roughness elements in dependence with flow direction. The presence of a flow separation zone on the bedform lee was estimated through analysis of the measured velocity directions and the calculation of the flow separation line. The Law of the Wall was used to calculate roughness lengths and shear velocities from log-linear segments sought on transect-averaged and single-location velocity profiles. During the ebb tide a permanent flow separation zone was established over the steep (10-20°) lee sides of the ebb-oriented primary bedforms, which generated a consequent drag on the flow. During the flood, no flow separation was induced by the gentle (2°) lee side of the primary bedforms except over the steepest (10°) part of the lee side where a small separation zone was sometimes observed. As a result, hydraulic roughness was only due to the superimposed bedforms. The parameterized flow separation line was found to underestimate the length of the flow separation zone of the primary bedforms. A better estimation of the presence and shape of the flow separation zone over complex bedforms in a tidal environment still needs to be determined; in particular the relationship between flow separation zone and bedform geometry (asymmetry, relative height or slope of the lee side) is unclear. This would improve the prediction of complex bedform roughness in tidal flows.
Latitude: 55.313675 * Longitude: 8.505769
Date/Time Start: 2009-10-15T23:09:00 * Date/Time End: 2009-10-20T19:25:00
Datasets listed in this publication series
- Lefebvre, A; Ernstsen, VB; Winter, C (2013): Summary of average roughness length calculated from the moored and ship-based ADCP velocity profiles on 17 Oct and 20 Oct around the time of maximum velocity. https://doi.org/10.1594/PANGAEA.812063
- Lefebvre, A; Ernstsen, VB; Winter, C (2013): Summary of water depth, velocity magnitude and direction, shear velocity and roughness length calculated from the moored ADCP velocity profiles averaged for an hour around the time of maximum velocity. https://doi.org/10.1594/PANGAEA.811998