Master of Science (MS)
Oceanography and Coastal Sciences
Short-term, wave induced erosion along bay beaches in the northern Gulf of Mexico has been linked to the postfrontal phase of cold front passages. Not until recently has consideration been given to the importance of wave erosion on marshes fringing large bays during the entire cold front event. Two WAVCIS (Wave-Current-Surge-Information System) stations were established on the north and south flank of a small marsh island in Terrebonne Bay, Louisiana, to measure and elucidate the hydrodynamic response to these events. Data from WAVCIS stations, which includes wind speed and direction, air temperature, significant wave height and water level, were collected between June 1999 and January 2002. These data were coupled to measured shoreline change data obtained from a series of north/south repetitious profiles along the length of the island. Four high-resolution topographic surveys were conducted between April and June 1999 and a fifth in December 1999. These surveys were complimented by annual surveys conducted in spring from 2000 on with an additional survey in October 2003. Data obtained from this effort allows the conclusion that low-energy fringing marshes undergo substantial geomorphological change from locally generated high-frequency waves developed by strong winds (12.99-14.14 m/s maximum wind speed) associated with cold fronts. On marsh islands, 80% to 90% percent of erosion occurs during the winter causing the island to thin in space 2.5 m/yr. Erosional patterns observed on the marsh edge include 1) neck and cleft formation, 2) neck cut off and 3) undercutting and marsh toppling. When compared to tropical storms, erosion associated with a season of cold fronts is equal to erosion from one tropical storm. This work underscores the significance of locally generated waves in marsh loss of coastal Louisiana over short time scales (years).
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Watzke, Dana Ann, "Short-term evolution of a marsh island system and the importance of cold front forcing, Terrebonne Bay, Louisiana" (2004). LSU Master's Theses. 3139.