Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

Irving A. Mendelssohn

Abstract

Surface feature maps were derived from color-infrared aerial photographs for Louisiana's Timbalier Island and Eastern Isles Dernieres. These provided a basis for the implementation of a barrier island Geographic Information System (GIS), a quantitative spatial framework through which specific proximal and temporal interactions could be examined. This system was utilized to observe relationships between changes in island shorelines and surface areas relative to location and extent of island cover categories. It was further employed to test the applicability of the rollover and deltaic barrier cycle models of island dynamics within the context of the Louisiana coastal environment. Both islands exhibited significant changes, including net losses in island width and surface area. However, results indicated that areas containing marsh or swale experienced significantly lower rates of shoreline erosion than other areas. Combining shoreline change data from this study with that from previous studies indicated a consistent long-term trend of shoreline retreat. Based on these combined observations, Timbalier Island can be expected to persist through the year 2140, and the Eastern Isles Dernieres through 2040. The rollover model (Godfrey and Godfrey, 1974) describes a shoreward migration of barrier islands in response to increasing sea levels. The deltaic barrier cycle (Penland and Boyd, 1981) describes a sequence of stages associated with the formation, abandonment, and eventual subsidence of major river deltas. Neither Timbalier Island nor the Eastern Isles Dernieres showed significant accretion on their bay sides, precluding any net landward migration, responses fundamentally inconsistent with the rollover model. Timbalier Island underwent a steady westward lateral migration, consistent with the flanking barrier stage of the deltaic barrier cycle. However, the Eastern Isles Dernieres, which represents the transgressive barrier arc stage, exhibited a westward, rather than eastward lateral migration and no net landward migration, responses inconsistent with the deltaic barrier cycle model.

Pages

269

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