Kathleen Graham

Three experiments were performed using a newly developed ripple cart facility, in which the sand bed moves relative to the water, to study the growth and development of 2D and 3D bedforms under oscillatory flow conditions. Conditions of the experiment were designed to stimulate wave conditions in a nearshore marine environment, with an oscillation period = 10 s, excursion amplitudes of 50, 60 , and 80 cm, and median grain size = 250 μm. Digital photographs of the bed elevation profile were collected at 15 or 30 minute intervals depending on the rate of change of the bedforms. The ripple profiles were analyzed to quantify the temporal development of ripples. Ripple wavelengths were plotted against time and compared to a logistic growth model. Principal findings of this study are: (1) that the equilibrium ripple wavelengths are comparable to those expected for vortex-type orbital ripples; and (2) that temporal evolution of ripple wavelengths is well-represented by the logistic growth model.

Keywords: Logistic growth, ripple growth, ripple profiles, oscillatory flow, equilibrium bedforms, oscillating bed, sediment dynamics
Pages: 54
Supervisor: Alex Hay