In: Proceedings Coastal Sediments '03. 2003. CD-ROM Published by World Scientific Publishing Corp.
and East Meets West Productions, Corpus Christi, Texas, USA. ISBN 981-238-422-7.
SHORELINE RESPONSE TO BREAKWATERS WITH
TIME-DEPENDENT WAVE TRANSMISSION
Ty V. Wamsley1, Nicholas C. Kraus1, and Hans Hanson2
Abstract: Wave transmission is a leading parameter determining the response of the shoreline to a
detached breakwater, reef, or spur attached to a jetty. To improve the predictive capability of the
shoreline response numerical model GENESIS, published empirical formulas for the wave
transmission coefficient were incorporated to calculate time-dependent wave transmission and
shoreline response. Simulations for different structural configurations, wave climates, and water
levels demonstrate the functional utility of time-dependent wave transmission on shoreline response
predictions. Results indicate that variable wave transmission is of significance for modeling the
response of the beach to submerged and emergent near-surface structures. Predictions of the model
are examined in application to a functional design of a submerged spur being studied as a possible
sediment-control measure for the north jetty at Grays Harbor, WA. Results show that for design
applications, beach response under time-varying forcing cannot be anticipated with a constant
transmission coefficient. The improved capability is expected to have wide applicability.
Detached breakwaters and breakwaters attached to jetties are constructed parallel to shore to
serve as a shore protection measure. The planform response of the shoreline to the placement of a
breakwater must be considered in the design process. The response can take the form of a tombolo
that extends from shore to attach to the structure, a salient or cusp in the shoreline that extends
partially to the structure, or a null response. Herbich (1999) reviews available empirical and
numerical predictive capabilities for the functional design of detached breakwaters.
Hanson and Kraus (1989, 1990) identified 14 parameters controlling beach response to detached
breakwaters. They performed extensive numerical simulations over a wide parameter range,
validated by reference to performance of structures in the field, to produce the following predictive
expression for beaches with 0.2 mm median grain size:
≤ N (1 - Kt ) 0
where X = length of breakwater, L = wavelength at the breakwater located in depth D, Kt = wave
transmission coefficient, H0 = deepwater wave height, and N = empirically determined coefficient
distinguishing response of the beach to the structure. Their work demonstrated that wave
transmission is a leading parameter determining shoreline response. It is not reliable to apply an
1) U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, 3909 Halls Ferry
Road, Vicksburg, MS 39180, USA. Ty.V.Wamsley@erdc.usace.army.mil;
2) Department of Water Resources Engineering, Lund University, Box 118, S-221 00, Lund, Sweden.