• Governing Equations
  • Model Sensitivity & Site Location
  • Model Calibration
  • Results of Long-term Studies

    Ripple Geometry and Bottom Roughness

    1) The equilibrium range is characterized by long-crested vortex ripples.
    2) In this range, ripple height (eta) and length (lambda) are proportional to Ab, the maximum excursion amplitude.
    3) To predict these ripple properties, we modified Wikramanayake and Madsen's (1991) parametric model by combining historical data sets they used and data collected by WHOI scientists at LEO-15. The results are shown below.


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    Bottom Roughness



    The two panels above illustrate the importance of the relative direction between the wave and current in calculating bottom roughness. The left panel shows a wave dominated scenario, where the mean flow is advected back and forth along lines running nearly perpendicular to the ripple crests (wave direction). The right panel illustrates current dominated conditions, where the mean current primarily flows along a ripple crest or trough with little relative lateral motion. Even though the direction between the wave and current is large for both cases, the effect of the ripples under wave dominated condtions will be important for the current.



    Shown above are shear stress (u*c) and hydraulic roughness (z0c) estimates using two roughness models under wave dominated conditions. One is a function of the angle between the wave and current, and the other the angle between the combined stress and the wave stress. When the wave and current are at near right angles (83o for year day 247 and 88o for year day 248), the kb formulation written as a function of the angle between the combined stress and the wave stress is superior. For all other cases the angle between the wave and current is less than 64o and both models produce similar results.

    Questions???

    styles@arctic.rutgers.edu