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 City of Solana Beach
Section 2
Shoreline and Coastal Bluff Management Strategies Draft MEIR
Project Description
Offshore Breakwaters
Offshore breakwaters are established measures for artificial sand retention. They
reduce wave heights and alter the wave direction in their lee (shelter from the wind and
waves), allowing sand to build up in their wave shadow zone. Breakwaters reduce wave
energy by direct blocking of wave energy and eliminate surfing areas. The best benefit-
to-cost offshore breakwater structure would be designed to include the following
(SANDAG 2001b):
Length of 1,000 feet
Distance offshore of 1,000 feet to maximize cost/benefits and minimize risk of
tombolo formation3
Maximum width (i.e., distance offshore) of salient4 of 500 feet
Total length of retained beach (alongshore dimension) of 3,000 feet
Total retained beach area of 750,000 square feet (about 17 acres)
Structure crest elevation of +6 feet MLLW (about 3 feet above mean sea level).
Artificial Sand Retention Reefs
Artificial reefs are three-dimensional features that reduce wave heights in the lee. Reefs
reduce transmitted wave energy through breaking and dissipation and can enhance
surfing opportunities. To effect wave dissipation, reefs are wide in the cross-section
direction. Large and irregularly shaped reefs refract waves thereby altering their
approach direction toward the shoreline. A shore-connected reef is recommended over
an offshore or barrier type reef for the following reasons (SANDAG 2001b):
Shore connected reefs reduce wave diffraction around the reef which can reduce
salient size.
Shore connected reefs force any water ponding to occur over the reef reducing the
possibility of scouring currents in the lee.
The volume of a reef constructed close to shore is less because of the shallower
water, resulting in Iower construction cost.
Natural examples of shore-connected reefs in Southern California exist which can
assist in development of design guidance.
A typical design, which would meet the above criteria, would include:
Total reef plan area of 5 acres
Retained beach salient area of 2 acres
Reef alongshore length of 900 feet
3
The build up of beach sand all the way out to the breakwater as a result of too large of a wave shadow
zone.
4
A buildup of sand behind a sand retention structure such as an offshore breakwater.
Project No. 323530000
Page 2-25
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