T-HEAD GROIN ADVANCEMENTS IN ONE-LINE MODELING
Hans Hanson and Nicholas C. Kraus
The GENESIS model has proven its capabilities in numerous
projects worldwide for simulating shoreline change and longshore sediment
transport on wave-dominated beaches. Even though the model has been made
generally applicable to "almost arbitrary" configurations of shoreline shapes and
structural measures, some important features are not yet represented. This paper
describes a new major capability recently implemented in the model,
representation of tombolos at detached breakwaters and T-head groins.
Illustrative examples indicate promising results for this major enhancement to the
Chronic erosion and an undesirable distorted hook-shaped shoreline are
typically found on beaches located down-drift of inlet jetties where a dominant
direction of longshore sediment transport exists. Dredged material or beach fill
placed in such areas is rapidly transported away, with a substantial portion
possibly moving into the navigation channel. If an ebb-shoal attachment bar
forms, the beach between the jetty and the attachment bar may become isolated
from natural sediment paths, increasing the erosional trend at the beach and
further distorting the shoreline.
Several remediation measures have been proposed and implemented for
reducing erosion and increasing the longevity of material placed in such hot spots.
These include lengthening the down-drift jetty, placement of an external spur
breakwater on the down-drift jetty, groin fields, detached breakwaters, T-head
groins, and combinations. A quantitative tool is lacking for developing,
designing, and comparing the functioning of such proposed solutions.
In its original version, the GENESIS shoreline-response model (Hanson
1989; Hanson and Kraus 1989; Gravens et al. 1991) allows calculation of
shoreline response for a wide variety of coastal features and engineering
activities, under the assumption that wave-generated currents dominate the
longshore sediment (typically sand or sand-sized particles) transport. These
features and activities include protective measures such as groins, jetties, seawall,
beach fills, bypassing operations, and linear or point sources and sinks of
1) Department of Water Resources Engineering, Lund University, Box 118,
Lund, Sweden S-221 00. Email: Hans.Hanson@tvrl.lth.se.
2) U.S. Army Engineer Research and Development Center, Coastal and
Hydraulics Laboratory, 3909 Halls Ferry Rd., Vicksburg, MS