ERDC/CHL CHETN-II-44
September 2001
Table 2
EHS Type, Dominant Transport Direction, and Associated Time and Space Scales
Dominant Transport
1
Type
Direction
Duration
Lateral Extent
1. Dredge selectivity
Cross-shore
Short-medium
Local
2. Residual structure-induced slope
Cross-shore
Short-medium
Local
3. Wave transformation
Alongshore
Medium
Local
4. Gaps in bars
Alongshore
Short-medium
Local
5. Mechanically placed fill
Cross-shore
Short
Local
6. Profile lowering in front of seawalls or cliffs
Cross-shore
Persistent
Local
7. Headlands and encroachments
Alongshore
Persistent
Local project wide
8. Residual fill bathymetry
Alongshore
Short
Local project wide
9. Permanent offshore loss
Cross-shore
Persistent
Local
10. Nonuniform offshore translation of beach
Alongshore
Short
Local
11 Wave transformation over nonuniform
offshore bathymetry
Alongshore
Persistent
Local project wide
12. Borrow pit located within active profile
Cross-shore
Medium-persistent
Local
13. Updrift barrier
Alongshore
Persistent
Local project wide
14 Relict inlet offsets
Alongshore
Medium
Local
15. Translatory longshore sand waves
Alongshore
Short-medium
Local, but moving
16. Standing and random longshore sand
waves
Alongshore
Short-medium
Local
17. Isolation of beach from longshore
transport inputs
Alongshore; Cross-shore
Persistent
Local
18. Rip currents on open beach; near groins
and jetties
Cross-shore
Short
Local
1
Short = order of year; Medium = order of several years; Persistent = life of typical project, property ownership, or longer
(geologic time scale)
Dredge Selectivity: EHSs are expected if a material with different sediment sizes is placed
alongshore (with the finer material experiencing greater relative erosion). Significantly different
grain sizes might be present in one offshore borrow site or among multiple borrow sites.
Different locations on the beach may receive significantly different sediment sizes because of
random withdrawal of sediment during pumping, a cost-reduction incentive to reduce pumping
distance, efficiency in pumping finer sediments longer distances, or because of other reasons.
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