ERDC/CHL CHETN-II-44
September 2001
be compatible by type of EHS and in chronology of presentation with previous work. Also,
names of some of the types given in the original references were modified slightly.
Table 1
EHS Type and Cause
Type
Cause of Erosion
1. Dredge selectivity
Variable sediment size or fall speed alongshore
2. Residual structure-induced slope
Legacy beach slope of pre-existing structure (typically, groin)
3. Wave transformation over borrow
Wave transformation (divergence, reflection) and associated longshore current (see
pits
type 11 for natural counterpart)
4. Gaps in bars
Wave focussing; possible rip current creation (see type 18)
5. Mechanically placed fill
Less fill placed as compared to adjacent sections hydraulically filled
6. Profile lowering in front of
seawalls or cliffs
Sediment deprived; adjustment to equilibrium profile
1
7. Headlands and encroachments
Encroachment of development in the nearshore; uneven coastal relief; change in
orientation of the coast
8. Residual fill bathymetry
Local wave focussing
9. Permanent offshore loss
Sediment lost offshore without possibility to return, as through reefs or to submarine
canyons
10. Nonuniform offshore translation
Local wave focussing; areas offshore of high and low waves
of beach
11 Nonuniform offshore bathymetry
Nearshore borrow sites; hard-bottom outcrops
12. Borrow pit located within active
Sediment transported offshore
profile
13. Updrift barrier
Blockage of longshore transport
14 Relict inlet offset
Headland effect (type 7) and bathymetry change (type 11) associated with a past
(relict) inlet
15. Translatory longshore sand
Periodic discharges of sediment from rivers or bays; periodic breakup of ebb shoals
waves
16. Standing and random longshore
Seasonal changes in wave climate over irregular offshore/nearshore topography
sand waves
17. Isolation of beach from
Uneven input and output; reduction or elimination of sediment supply
longshore transport inputs
18. Rip currents on open beach or
Sediment transported offshore
near groins, jetties
1
Includes local abrupt changes that are artificially created, headlands, and unfavorable shoreline orientation with respect to
dominant wave direction.
Because types 1-12 have been documented in three University of Florida reports (Bridges 1995;
Dean, Liotta, and Simn 1999; Weber 2000), emphasis is given to types 13-18. Table 2
summarizes EHSs by dominant direction of transport, duration, and lateral extent. Some of the
types could be grouped together through similar general causes. For example, nonuniformity in
bathymetric contours or in wave focussing might be combined. However, because specifics can
greatly differ, for example, as naturally occurring instead of artificially induced, it is beneficial to
treat them separately at the present stage of understanding.
3
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