EM 1110-2-1100 (Part V)
31 Jul 2003
engineering practice is to combine beach nourishment with groin construction to permit sand to immediately
begin to bypass the groin field. At the end of the sediment cell, terminal groins may be used to anchor the
beach and limit the movement of sand into a navigational channel or onto an ebb-tidal shoal at tidal inlets.
(b) Figure V-3-24 shows a photo, profile and cross section of a rubble-mound groin at Westhampton
Beach, New York. Sheet-pile construction with timber (Figure V-3-25) timber-steel (Figure V-3-26)
prestressed-concrete (Figure V-3-27) or cellular-steel (filled) sheets (Figure V-3-28) have also been
constructed in the United States.
(c) Kraus, Hanson, and Blomgren 1994 cite the following situations when the groin field alternative for
shore protection and sand management should be considered.
At divergent, nodal points for littoral drift.
In the diffraction, shadow some of a harbor breakwater, or jetty.
On the downdrift side of a harbor breakwater or jetty.
At the updrift side of an inlet entrance where intruding sand is to be managed
To reduce the loss of beach fill, but provide material to downdrift beaches in a controlled manner.
Along the banks at inlets, where tidal currents alongshore are strong.
Along an entire littoral cell (spit, barrier island, submarine canyon) where sand is lost without return
in an engineering time frame.
(d) Groins may not function well and should not be considered under the following conditions (Kraus,
Hanson, and Blomgren 1994):
Where a large tidal range permits too much bypassing at low tide and overpassing at high tide.
Where cross-shore sediment transport is dominant
When constructed too long or impermeable, causing sand to be jetted seaward
When strong rip currents are created to cause potentially dangerous swimming conditions
(e) Coastal zone management policy in many countries and the United States presently discourages the
use of groins for shore protection. Many examples of poorly designed and improperly sited groins caused
by lack of understanding of their functional design, or failure to implement the correct construction sequence,
or failure to fill up the groin compartments with sand during construction, or improper cross-sectional shape
are responsible for these restrictions. However, when properly designed, constructed and combined with
beach nourishment, groins can function effectively under certain conditions, particularly for increasing the
fill life (longevity) of renourished beaches.
(f) Groins are now being reevaluated as sand-retention structures (Kraus, Hanson, and Blomgren 1994;
Kraus and Bocamazo 2000) by now asking the question "how much sand can be allowed to pass," while still
maintaining a minimum width of beach at the groin for some level of shore protection.
Shore Protection Projects
V-3-61
Previous Page
