T-head Groin Advancements in One-line Modeling (genesis/t)

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 model. INTRODUCTION 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: [email protected]. 2) U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, 3909 Halls Ferry Rd., Vicksburg, MS 39180. [email protected] Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 2002 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE T-Head Groin Advancements in One-Line Modeling (Genesis/T) 5a. CONTRACT NUMBER