temporal variations in the distribution of sediments are found at this site, with coarser
sand on the beach and finer sands in the nearshore. Sand also gets slightly coarser from
the ocean side to the bay side cells. A seasonal component is also present where coarser
sands are present in the winter and finer sands are found in the summer months. A
distinctive yellow color and coarse pea size gravel size distribution was also introduced
when the upland fill material was placed in cells 3 and 4 in the summer of 2000. Some of
this material is still found on the backshore of the two cells. Heavy minerals and mica
flakes are also more concentrated in the high water line area in cells 5, 6 and 7.
Additional sediment samples will be collected 1 year after construction to
determine if any change in grain size distribution occurs following placement of the
structures. Samples will be collected at the dune base, berm crest/highwater line, mid-
tide, swash/low-tide line and at the 0.91 m and 1.83 m location inshore of the
structures and seaward of the structures at 2.74 m and 3.66 m NAVD88 along selected
profile lines covering all of the cells. Sediment monitoring will provide a measure of
how these structures retain sand in the perched beach concept and if the grain size
distribution will change from the pre-construction time frame. Both cross-shore and
between-cell grain distributions will be monitored for change.
Waves and Currents
Since both waves and tidal currents are suspected to transport sediment in this
area, wave transmission across these two types of breakwaters will be measured. Initial
planning calls for a short period of deployment of four wave gages (one set each on the
landward and ocean side of the Double-T sill and Beachsaver Reef units) to measure
(ADCP) is also planned to identify circulation patterns within the cells with structures
and in the control cell 4 and just outside the groin compartments to determine changes in
scour and/or depositional patterns related to the units. Visual observations of the pre-
installation indicate a seaward rip current common along the sides of the groins. Visual
observations of ice chunks flowing around the Cape on a flood tide in March 2003 after
installation of the structures indicated that ice was trapped in cell 5 behind the
Beachsaver Reef and the circulation in both cells 5 and 6 were more circular in the
center of the groin compartments. Both the Beachsaver Reef and Double-T sill
elevations were lower in the center of their respective lines and may be influencing
circulation in their groin compartments. The rock tying in the structures to the ends of
the groins may be inhibiting formation of the near-groin rip currents observed before
installation.
Aerial Photography
Detailed aerial photography that shows the wet/dry line on the beach
photographed at low tide can be helpful in assessing the change in shoreline position,
beach width and duneline position, as well as intertidal sediment deposition patterns.
Photos are available for the past several years and will be flown on an annual basis for
this project. The newer photo sets are digital and rectified and are easily incorporated
13
Previous Page
