ERDC/CHL CHETN-II-44
September 2001
remove material from the surf zone and transport it offshore. Komar (1998) reviews the
literature of embayments created by rip currents on the open coast. Development of rip current
embayments along the Oregon coast is a primary factor in the erosional loss of property on
foredunes on sand spits and in cutting away of sea cliffs backing beaches.
Rip currents tend to form and persist next to piers, groins, and jetties. Dolan et al. (1987)
estimated that about 75,000 m3/year of sediment was lost from the Oceanside, CA, littoral cell by
seaward deflection of the longshore current at harbor structures and by rip currents along the
open beach. Much of this material seems to have been deposited far offshore.
CONCLUDING DISCUSSION: Considerable information is available to predict, prevent,
mitigate, and account for EHSs. Some causes of EHSs cover large space and time scales
(Table 2) and cannot be remedied by typical means. Other types of EHSs are temporary and can
either be mitigated or allowed to run their course. Table 3 gives example remedial measures that
can be taken and are consistent with the cause (Table 1) and transport processes and scales
(Table 2) of the type of EHS.
Table 3
EHS Type and Possible Preventative and Remediative Measures1
Type
Prevention and Remediation
1. Dredge selectivity
Take coarsest sand at borrow site; be consistent; cap with coarser
sand
2. Residual structure-induced slope
Account for differential volume requirements at the initial placement
to allow the slope to reach equilib.
3. Wave transformation over borrow pit
Dredge shallow and as far offshore and in longest linear segments
parallel to shore as possible
4. Gaps in bars
Recognize temporary nature; be prepared for addition of extra fill if
not acceptable; fill dunes and/or berm
5. Mechanically placed fill
Ensure that fill volume and density are consistent with hydraulically
placed fill or material on adjacent beaches
6. Profile lowering in front of seawalls or
Have trigger for renourishment before shoreline reaches seawall; be
cliffs
prepared for additional fill
2
7. Headlands and encroachments
For discontinuities and headlands, either do not fill in area or hold
the fill with structures. For unfavorable shoreline orientation, hold the
fill with structures
8. Residual fill bathymetry
Reduce irregularities in fill planform
9. Permanent offshore loss
Fill with coarser sand; attempt to redirect rip current, as through
submerged dikes or perched beaches
10. Nonuniform offshore translation of
Compensate with overfill and/or accept the temporary accelerated
beach fill
loss behavior
11 Wave transformation over nonuniform
Compensate with overfill and/or accept the loss
offshore bathymetry
(Continued)
1
Several preventative and remediation measures taken from Dean, Liotta, and Simon (1999) and from Bodge,
Gravens, and Srinivas (1999)
2
"Hold fill" preserves a design rate of loss while also feeding downdrift beaches
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