EM 1110-2-1100 (Part V)
31 Jul 2003
Functional Properties Attributed to Groins and their Critical Evaluation (from Kraus, Hanson, and Blomgren
1. Wave angle and wave height are leading parameters
Accepted. For fixed groin length, these parameters determine
bypassing and the net and gross longshore transport rates.
2. Groin length is a leading parameter for single groins. (Length Accepted, with groin length defined relative to surfzone width.
controls depth at tip of groin.)
3. Groin length to spacing ratio is a leading parameter for groin
Accepted. See previous item.
4. Groins should be permeable.
Accepted. Permeable groins allow water and sand to move
alongshore, and reduce rip current formation and cell circulation.
5. Groins function best on beaches with a pre-dominant
Accepted. Groins act as rectifiers of transport. As the ratio of
longshore transport direction.
gross to net transport increases, the retention functioning
6. The updrift shoreline at a groin seldom reaches the seaward
Accepted. Because of sand bypassing, groin permeability,
end of the groin.
and reversals in transport, the updrift shoreline cannot reach the
end of a groin by longshore transport processes alone. On-
(This observation was not found in the literature review and
shore transport is required for the shoreline to reach a groin tip,
appears to be original to the present paper.)
for a groin to be buried, or for a groin compartment to fill
7. Groin fields should be filled (and/or feeder beaches
Accepted. Filling promotes bypassing and mitigates downdrift
emplaced on the downdrift side).
8. Groin fields should be tapered if located adjacent to an
Accepted. Tapering decreases the impoundment and acts as a
transition from regions of erosion to regions of stability.
9. Groin fields should be built from the downdrift to updrift
Accepted, but with the caution that the construction schedule
should be coordinated with expected changes in seasonal drift
Accepted. Filling a groin field does not guarantee 100% sand
10. Groins cause impoundment to the farthest point of the
updrift beach and erosion to the farthest point of the downdrift
bypassing. Sand will be impounded along the entire updrift
reach, causing erosion downdrift of the groin(s).
11. Groins erode the offshore profile.
Questionable and doubtful. No clear physical mechanism has
12. Groins erode the beach by rip current jetting of sand far
Questionable. Short groins cannot jet material far offshore, and
permeable groins reduce the rip current effect. However, long
impermeable jetties might produce large rips and jet material
beyond the average surfzone width.
Tentatively accepted. Oblique orientation may reduce rip
13. For beaches with a large predominant wave direction,
groins should be oriented perpendicular to the breaking wave
Shore Protection Projects