Processes of Shoreface Profile Adjustment


Investigator

Peter A. Howd, Kent Hathaway

Funding Source

US Army Corps of Engineers, Coastal Research and Development Program

Objective

The long-term beach profile measurement program at the FRF, now in its second decade, has repeatedly shown that the dominant profile changes in depths exceeding ~4m occur at time scales ranging from months (primarily depositional events) to many years (erosional trends). It is obvious that these time scales are much longer than those associated with the passage of individual storms, and of the intensive experiments for which the FRF is noted.

The primary objective is to quantify the relative roles of wind-driven currents and wave-driven currents and orbital velocities in cross-shore profile evolution on the shoreface (the outer surf-zone to inner shelf transitional region). A long data set is expected to be necessary due to the qualitatively defined relationships between sequences of storms, existing morphology, and resulting profile response. A wide range of environmental and morphological conditions will be necessary to begin to understand the nature of the non-linear relationships involved.

Secondary objectives are to supplement the DUCK94 cross-shore array, and to provide large scale continuity between the DUCK94 and CoOP measurements and SandyDuck (Fall, 1997). This work will constructively overlap the efforts of Thornton, Guza, Herbers, Elgar, Haines, Smith, Drake, and the CoOP investigators.

Approach

We proposed to establish three instrumented locations in 5m, 8m, and 13m depths for the period spanning the DUCK94 and SandyDuck experiments. The locations will support multiple (3) electromagnetic current meters, a pressure sensor, and an acoustic altimeter. Efforts will be made to accommodate short-term deployments of additional instrumentation belonging to interested PIs.


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Results

The 5m and 13m bipods were deployed in October, 1994 and sucessfully recorded near bottom flows and bottom elevation fluctuations through the experiment period. Collection continued and the effects of Hurricane Gordon in November 1994 were measured as well. Flows during this hurricane exceeded 2 m/s in the longshore direction and 0.5 m/s offshore at the 5 m site. In June, 1995 the 8m bipod was deployed. Future plans call for current meter upgrades during the summer of 1996 and a great deal of ongoing data analysis and management.

For a list of addresses of the investigators involved in Duck 94 click here.