HR: 1300h
AN: OS52C-01    [PDF]
TI: Nearshore Sediment Transport Along the Mixed Grain-size Beaches of Kachemak Bay, Alaska
AU: * Adams, P N
EM: padams@es.ucsc.edu
AF: Earth Sciences Dept., University of California at Santa Cruz, Room A232, Earth & Marine Sci. Bldg., UCSC, Santa Cruz, CA 95064 United States
AU: Ruggiero, P
EM: pruggiero@usgs.gov
AF: US Geological Survey, Coastal and Marine Geology, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Gelfenbaum, G
EM: gelfenbaum@usgs.gov
AF: US Geological Survey, Coastal and Marine Geology, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Schoch, C
EM: carl\_schoch@fishgame.state.ak.us
AF: Kachemak Bay Research Reserve, 2181 Kachemak Dr., Homer, AK 99603 United States
AU: Oltman-Shay, J
EM: joan@nwra.com
AF: Northwest Research Associates, 14508 NE 20th St., Bellevue, WA 98007 United States
AB: The spatial variability and dynamics of heterogeneous sediment systems are largely unknown, yet these dynamics are crucial to erosion, habitat quality, water quality, and therefore to the management of coastal development, preservation, and restoration. The north shore of Kachemak Bay, Alaska on the western side of the Kenai Peninsula provides a unique natural laboratory to study the effects of varying oceanographic conditions on sediment transport, as the 8+ meter tidal range exposes a wide (~300m) swath of heterogeneous sediment twice daily. Our objective is to test the hypothesis that the amount of exposed rocky habitat on the north shore of Kachemak Bay is a function of periodic and episodic sand wave migration and that the variability of sand wave migration rates is a function of storm magnitude, frequency, and direction (as opposed to tidal currents). Using an Argus Beach Monitoring System (installed in February 2003), we are collecting a continuous time series of digital photographs over an ~1km (8 overlapping cameras) reach of coastline that documents relatively rapid movement (44cm/day) of sand waves of medium to coarse-grained sand, over a cobble/boulder-strewn substrate. Comparison of data from a nearby meteorological station and a wave/tide gage deployed in shallow water shows that periods of strong sustained winds ($>$ 6m/s) from the southwest generate significant wave heights of nearly 1m. However, winds of similar magnitude from the southeast result in smaller waves ($<$ 0.5m), presumably because of shielding by the Kenai highlands and the short fetch across the narrow axis of Kachemak Bay. Microseisms recorded with a portable broadband seismometer coupled to a newly constructed sea wall, serve as a proxy for wave energy reaching the inner nearshore and coastal bluffs. The temporal pattern of wave energy delivery to the bluffs reflects the semidiurnal tidal signal as well as short intervals of large waves, associated with southwesterly winds. Analysis on this rich data set will include a comparison of sediment movement and wave energy delivery with discrete meteorological events (storms, anomalously large waves) and extreme tidal conditions, as well as an investigation into the source of littoral sediment in the region.
DE: 1824 Geomorphology (1625)
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
DE: 4560 Surface waves and tides (1255)
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting