Individual beach profile volume change data both up-and down-net annual long-shore drift at the installation site show profile volume gains (net beach accretion) either at or in excess of analytical resolution at both 500 feet and 1000 feet offshore.
When the local beach sand cover is thin or not present (common when the long-shore drift is southward on the south flank of the experimental structure) rapid scour of this substrate probably occurs.
Low net/gross long-shore drift occurs at the experimental structure installation sites.
Coastal change response to the experimental Undercurrent Stabilizer System[TM] shore protection structure can be evaluated in three components: (1) protection provided to the back-shore area immediately behind the experimental structure: a revetment effect; (2) alternating accretion/erosion observed immediately adjacent to the experimental structure within approximately 150 feet offshore during reversals of long-shore drift: a conventional groin effect; and (3) down-drift and offshore accretion beyond the offshore extent of the experimental structure (between 150 feet and 500 feet offshore): an unconventional groin effect.
This coastal response is consistent with a shore-perpendicular obstruction to long-shore drift and seasonally reversing long-shore transport patterns; a conventional groin effect.
Contrary to most conventional (and mostly anecdotal) observations of coastal response to small-scale shore-perpendicular structures, net accretion occurs periodically down drift of the annual average long-shore drift direction at all sites rather than simply up-drift and within the extent of the structures.
The up-drift, conventional groin effect accretionary fillet (formed during fluctuating long-shore drift periods) apparently creates a disequilibrium "feeder beach" to offshore bars as a result of subsequent periods of reversed long-shore transport, steep, high-energy waves, and offshore-directed currents.