Fact Sheet
US Army Corps of Engineers
U.S. Army Engineer Research and Development Center
January 2003
Public Affairs Office
3909 Halls Ferry Road
Vicksburg, MS 39180-6199
(601) 634-2504
http://www.wes.army.mil
Monitoring of Pocket Wave Absorbers in Parallel, Vertical-Wall Jettied
Entrance Channels
Purpose: To determine the effectiveness of pocket wave absorbers in reducing wave heights in entrance channels
where they are utilized in conjunction with parallel steel sheet-pile jetty configurations.
Background: Parallel jetties at dozens of harbor entrances in the Great Lakes were constructed of rock-filled tim-
ber crib structures, many in operation for
over 100 years. Many of the structures
have been rehabilitated by encasing them in
steel sheet pile. The wave climate between
the jetties appears to increase significantly,
due to the reflective surfaces, causing navi-
gational difficulties and damage to moored
vessels. To mitigate for the more energetic
wave climate, the U.S. Army Engineer Dis-
trict, Detroit, has removed small sections of
steel sheet piling at selected harbor en-
trances and replaced them with pocket
wave absorbers. A pocket wave absorber is
created when a section of sheet pile wall is
removed, or recessed from the remainder of
the jetty, and stone is placed in the area to
provide a rough, porous sloping surface to
increase dissipation of wave energy. The typical length of a pocket is 200 to 300 ft. The wave absorbers have been
installed as a single pocket, and in pairs, on opposite sides of the channel.
Facts: As part of the Monitoring Completed Navigation Projects program of the Headquarters, U.S. Corps of Engi-
neers, pocket wave absorbers at Pentwater Harbor, Michigan, are being monitored to determine their effectiveness in
reducing wave heights in the entrance channel. At Pentwater Harbor entrance, a pair of pockets has been installed
on opposite sides of the channel. Prototype wave gauges will be installed along the channel side of the jetties both
lakeward and shoreward of the absorbers. In addition, incident wave conditions will be measured lakeward of the
entrance. Wave periods and heights in the channel will be correlated with incident wave and wind directions. Data
obtained will be used to validate physical model experiments. A physical model of Pentwater Harbor entrance will
be constructed and unidirectional spectral waves reproduced to study pocket wave absorber design parameters.
Upon validation with prototype data, the model will be used to study a wide range of incident wave conditions
(wave heights, periods, and directions). Design parameters such as pocket location, pocket length, structure slope,
and stone size will be studied to develop design guidance relative to pocket wave absorber parameters. Currently,
little to no design guidance is available for predicting the effectiveness and optimizing the design of the many feasi-
ble variations of pocket wave absorbers.
Points of Contact: For additional information, please contact Mr. Robert Bottin at 601-634-3827
( ) or Mr. Dennis Markle at 601-634-3680 )"> ).