Beach Sedimentology of Mustang and Padre Islands: A Time-Series Approach

Abstract

Systematic profiling and sampling of 11 beach sites along more than 90 miles of Mustang and Padre Islands shows seasonal as well as geographic trends. On the basis of sediment characteristics and beach morphology, three geographic areas can be delineated; the northern, convergence, and southern provinces. Mean grain size and sorting values in both the northern and southern provinces show little seasonal variation; in the convergence province they display great temporal variation. Skewness shows a wide temporal variation throughout the entire study area. Foreshore sediments in the convergence province are generally coarser, less sorted, and less skewed than those of the other two provinces. Beach morphology also varies throughout the area. The northern and southern provinces have rather flat profiles without a pronounced berm and with a gently sloping foreshore. The convergence province contains beaches with a steep foreshore, well developed berm, and a landward sloping backshore. Although there is a general tendency for each beach to retain its own general morphology, there are seasonal modifications and geographic variations. Changes in beach morphology, as shown by monthly surveys, indicate that the 11 sites tend to respond as a single group or that the changes may be associated with a single province. There is a general tendency for beach morphology to conform to seasonal trends. Long after the termination of the systematic study, each of the sites was resurveyed and the profiles obtained were not significantly different than those surveyed in the same month two years previously.