A beach equilibrium model is developed that treats the outer (shorerise) portion of the profile independently from that of the inner (bar‐berm) portion. The two portions are matched at the breakpoint‐bar. The partitioning of the profile in this way is consistent with the different forcing modes on either side of the breakpoint. This formulation utilizes beach profile data not previously available. It is shown that both portions of the profile are well fitted by curves of the form h = Axm, where h is positive downward and x is the positive offshore coordinate. Surprisingly, the value of m ≈ 0.4 is nearly the same for shorerise and bar‐berm and does not change significantly with seasonal beach changes (summer/winter). The principal difference between seasonal profiles is that in winter (higher waves) the breakpoint‐bar is deeper and farther offshore while the berm crest is displaced landward. Thus the changes in seasonal equilibria are manifested by simple, self‐similar displacements of the bar‐berm and shorerise curves as a consequence of changes in surf zone width and O(1) variations in the factor A.

No abstract

ARSTRACT: Over the past 50 yr, direct observations of the inlet status (open or closed) of San Dieguito Lagoon, a typical southern California lagoon located in Del Mar, California, have shown that river flooding is the major natural determinant of inlet conditions on time scales longer than a few years. River flooding is strongly dependent on rainfall in the San Diegnito River watershed and on the influences of two water storage reservoirs in the area. Rainfall fluctuates on yearly and longer time scales and undergoes cycles of wet and dry periods. Over short thne periods, ranging from a few months to several years, inlet status is prhnarily determined by the available tidal prism and littoral sand transport. Recognition of these factors is crucial in order to correctly evaluate the probability that a small lagoon will remain open naturally. A probability approach is essential because the variables controlling inlet conditions are random in nature. The results of our study show that the inlet will remain open naturally 34% of the time. The tendency to remain open is vastly smaller during years of dry weather (12%) versus times of above-average rainfall (66%).

No abstract