Robert E. Jensen
US Army Corps of Engineers, Coastal Research and Development Program,
Evolution of Wave Spectra in Shallow Water Work Unit
The evolution of an ocean wave spectrum transforms significantly once it enters shallow water. These transformations are based on specific mechanisms: spatially-dependent changes, or shoaling and refraction processes; and time-dependent source/sink term specification such as the atmospheric input (Sin), nonlinear wave-wave interaction (Snl), high-frequency dissipation (Sds), bottom effects (Swb e.g. frictional losses), and depth-induced spectral breaking. These mechanisms simultaneously act on a spectrum when it enters shallow water, the relative magnitude of each mechanism and its resulting change in the spectrum as well as the time required for the change are not well understood.
Sufficient high resolution, 1- and 2-D wave spectra are required to adequately investigate the problem. This research will have a data base with sufficient measurements to:
b. learn from the measurements the physical processes controlling that evolution;
c. test hypotheses using 3rd generation wave model technology assessing all terms in the energy balance equation (spatial and temporal gradients); and
d. then apply what has been found from the data and simulations to present numerical wave models.
Our first goal is to have an excellent data set to study the processes. The CoOp program will be a starting point of the investigation. During CoOp, estimates of the bottom boundary layer will be made in water depth of 8m supplying information to evaluate the Sw-b sink term. A trade-off between the short time span (3 months) is the amount of data in the spatial domain to investigate single events. The 3 NDBC directional buoys requested for this study will remain for 6-12 months, thus increasing the data base.
Collaboration is planned with CoOp (Herbers, Guza, Elgar), FRF/CERC (Long), and RSMAS/U. Miami (Graber)
For a list of addresses of the investigators involved in Duck 94 click here.