AN ABSTRACT OF THE THESIS OF Thomas Charles Lippmann for the degree of Doctor of Philosophy in Oceanography presented on September 9. 1992 Title: Edge Wave Response to a Modulating Incident Wave Field Abstract Approved:

Modulations in wave height of oceanic sea and swell cause momentum transfer to the water column at group (infragravity) time and space scales, on the order of 1O21O3 s and 1O21O3 m. In the surf zone, this momentum flux arises principally through dissipation of incident wave energy by breaking. In this thesis, the generation of low frequency waves by the spatial and temporal modulations of breaking incident waves is addressed first, followed by field estimates of the time and space scales of wave breaking distributions. Lastly, nearshore sand bar behavior, linked theoretically to infragravity waves, is investigated over a five year period. A theoretical forcing mechanism for driving resonant, longshore progressive edge waves is derived from the momentum equations. Forcing within the surf zone is examined through group scale modulations in incident wave dissipation by depth-limited brealdng. The nonlinear forcing, provided by the unbalanced temporal variations in radiation stress gradients, is shown to be comparable to previous offshore forcing theory. Initial surf zone growth rates are predicted and found to be rapid, with edge wave amplitudes growing to the size of the incident waves on the order of 10-2