SURF-BEACH DYNAMICS IN TIME AND SPACE - AUSTRALIAN CASE-STUDY, AND ELEMENTS OF A PREDICTIVE MODEL

Inshore morphology and circulation on a medium- to high-energy surf beach - Durras, N.S.W., Australia - is analysed from a semi-continuous run of data maps covering a 2.25-km length of beach monitored at 50-m intervals. Twenty surveys were made over about five weeks, the only significant gap being an interval of twelve days between the thirteenth and fourteenth records. Nearshore waves and winds varied considerably during the observation period; inshore morphology was highly changeable and longshore and rip circulation rarely was well fitted to morphology. From statistical analysis of morphologic and circulation patterns we identify a set of seven inshore states, related not only to immediate wave climate but also to antecedent morphology and wave changes. We address the problem of adjustment to energy changes, for the two-dimensional inshore-nearshore profile, using a model in which wave-work on the bed is uniformly distributed. Model profiles fit closely to our bathymetric data, and appear to predict reasonably the surf-zone width variations resulting from energy changes. © 1979.