HR: 0800h
AN: OS11A-0487    [Abstracts]
TI: Wave Friction Factors from Energy Flux Comparisons Outside of the Surf Zone
AU: * Eshleman, J L
EM: jeshleman@usgs.gov
AF: U.S. Geological Survey, Coastal and Marine Geology MS 999 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Dean, R G
EM: dean@coastal.ufl.edu
AF: University of Florida, Civil and Coastal Engineering Department 575 Weil Hall, Gainesville, FL 32611-6590 United States
AU: Hathaway, K K
EM: Kent.K.Hathaway@erdc.usace.army.mil
AF: Coastal and Hydraulics Laboratory Field Research Facility, 1261 Duck Road, Kitty Hawk, NC 27949 United States
AB: Pressure and current measurements were recorded at 5.5 m, 8 m, and 13 m water depths in the outer surf zone and inner continental shelf region off the coast of Duck, NC. The instrumentation was deployed in October, 1997 and remained operational through December, 1998. This data set was analyzed to investigate wave dissipation and evolution by comparing estimates from linear wave theory with field measurements. The analysis was restricted to six significant storm events that occurred during four months to ensure that significant energy was present for meaningful measurements. The range of significant wave heights included is 1.75 m $<$ H$_{s}$ $<$ 3.5 m. Energy flux calculations combining shoaling and refraction theory that did not account for energy dissipation, showed smaller measured than predicted energy flux values at the two inshore locations. Some of these values were smaller by more than one third of the total energy flux, emphasizing the importance of bottom friction in wave energy loss. A representative friction factor for each 34-minute record was determined by accounting for frictional energy loss in the energy flux calculations, using velocity time series measured 20 cm above the sea floor. Estimated friction factors varied throughout storm events, but most fell within a range of 0.002 to 0.03. This range of values was compared to other wave friction factor estimates both inside the surf zone and outside. A representative value of 0.021 was identified through the use of energy flux and energy loss values averaged over all storm events. This study emphasizes the importance of including bottom friction when considering wave energy dissipation.
DE: 4546 Nearshore processes
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting