Waves and currents interacting with bottom sediments produce changes in the beach and
nearshore bathymetry. These changes can occur very rapidly in response to storms, or slowly as
a result of persistent but less forceful seasonal variations in waves and current.
Since 1981 the FRF has been conducting detailed surveys of the nearshore bathymetry. These data now cover fifteen years and include hundreds of surveys. This data set is unmatched worldwide in terms of accuracy, and temporal coverage. They provide quantitative measures of the dynamic nature of the nearshore zone, including during storms when changes are most rapid. In addition, the natural long-term cycle of beach erosion and rebuilding, which may take many years, is well documented. These data are being used to refine theories of nearshore morphologic change and to develop and test numerical simulations of nearshore response to changing conditions.
Nearshore bathymetry at the FRF is characterized by regular shore-parallel contours, a moderate slope, and a barred surf zone (usually an outer storm bar in water depths of about 4.5 m and an inner bar in water depths between 1.0 and 2.0 m.) This pattern is interrupted in the immediate vicinity of the pier where a trough runs under much of the pier's length, ending in a scour hole at the pier's seaward end where depths are up to 3.0 m greater than the adjacent bottom. Profile configuration is typically single-barred with the most active zone extending from the base of the dune to about the 6-m (20-ft) water depth. Maximum vertical change occurs just seaward of the shoreline.
The surveys are conducted over a series of 26 shore perpendicular "profile lines" which extend from the dune to approximately 950 m offshore. These lines which are surveyed monthly during the "Bathymetry Survey" are shown in the figure above. In addition, 4 of the 26 lines (58,62,188, 190) are surveyed biweekly as part of a "4-line Survey."
The surveys are conducted with the Coastal Research Amphibious Buggy (CRAB), a 10.7 m tall amphibious tripod, and a Trimble 4000SE GPS survey system (starting in June 1996).
This section is divided into several sub-sections as explained below.
Suggested reading for anyone planning to use FRF survey data. Easily printable.
Two PC programs used to process survey data at the FRF are ISRP, a general purpose program for entry, processing, and analysis of survey data, and VOLUME which computes volumetric, elevation, and shoreline changes. The two programs are available for downloading.