into the GIS. The wet/dry shoreline, duneline and groins are drawn from the aerial
photography for each year and the change in position of the shore and dune line will be
compared over time to assess the movement of the shoreline and dune line in each cell, as
well as the width of the intertidal beach. The datum-based shoreline will also be drawn
based on the mean high water (MHW) local elevation from the local NOAA tide gage
using elevations from the beach profiles. These two lines for shoreline identification will
be compared over the monitoring period to assess shoreline stability.
Conclusions
The project was constructed between August and October 2002 with placement of
72 Beachsaver Reef units in cell 5 and 22 Double-T sill units in cell 6. A monitoring
program will evaluate the performance of these two structures. The primary purpose is to
evaluate how these structures retain sand within their respective groin compartments.
Based on this evaluation, a projection will be made to determine how each structure will
affect the maintenance and life cycle cost of a beach nourishment project scheduled for
construction in 2004.
Three types of performance measures are proposed to evaluate the projects
effectiveness: functional performance (sand retention), economic performance (reduction
of renourishment quantities/lengthening of renourishment cycles), and structural
performance (structure stability). Relative performance of the Beachsaver Reef vs. the
submerged Double-T sill will also be assessed. Parameters used to measure performance
will be determined from monitoring data. For each category, measurement parameters
were defined, and performance criteria suggested.
Performance Criteria
Functional Performance (Sand Retention): focuses on the degree to which the
offshore structures retain sand and reduce sand loss from groin cells. Sand loss may
occur due to cross-shore processes (post-construction equilibration, seasonal beach
profile change, and storm-induced beach erosion) and due to longshore processes (natural
gradients in longshore sand transport, and interruption of sand transport by structures).
Functional performance measures will be evaluated from beach profile surveys starting
from initial construction and continuing throughout the monitoring program.
Measurements in beach volume and dry beach width will be used to evaluate
performance. Differences will be compared between structured and non-structured cells
and between the Beachsaver Reef and Double-T configuration. If 30% more sand
volume is retained within the structured cells relative to the control (and relative to the
other type of structure) it will be successful. Success will also be achieved if the dry
beach width is 30% wider in the structured cells relative to the control cell (and relative
to the dry beach width in the cell with the other type of structure).
Economic Performance (Reduction of Renourishment Quantities/Lengthening of
Renourishment Cycle): focuses on project cost savings realized for the Federal beachfill
project as a result of reduced renourishment quantities and/or a longer renourishment
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