Temporal and Spatial Variations in Shoreline Changes and their Implications, Examples from the Texas Gulf Coast

Abstract

ABSTRACT Shoreline changes from sandy oceanic coasts worldwide show temporal and spatial variations that are similar to, and exemplified by, composite data from the Texas coast for four time periods extending from 1850 to 1975. The quantitative data, which exhibit remarkably similar distributions for the first two and latter two periods, show that both total length of eroding coast and rates of erosion have substantially increased since 1955-60. As a result, some shoreline segments that prograded following sea-level stillstand are presently eroding. Spatial variations in shoreline changes occur on regional and local scales. Regional tendencies toward accretion or erosion closely correspond with physiographic provinces, which in Texas are defined by transgressive and regressive beaches and barriers. Within each province, rates of accretion and erosion display periodicities that are irregular to quasi-sinusoidal in form and are attributed to shoreline rhythms resulting from differential rates of sediment transport. Natural processes, such as decreases in sediment supply and continued relative sea-level rise are largely responsible for long-term shoreline retreat. Short-term (historical) shoreline changes reflect the long-term trends. but they also reflect secular sea-level variations and human activities. The latter, in the form of coastal engineering modifications, are clearly responsible for the highest short-term rates of accretion and erosion. On the Texas coast nearly half of the total beach sand supplied by updrift erosion, presently a major sediment source, has been trapped by jetties at harbor entrances. This impoundment of sand at impermeable barriers together with reduced sediment influx from damming of rivers suggest that anthropogenic augmentation of natural shoreline erosion will likely increase from local to regional effects.