M. Hany S. Elwany

Shorerise and bar‐berm profiles on ocean beaches

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.

Opening and closure of a marginal southern California lagoon inlet

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 Dieguito 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 time periods, ranging from a few months to several years, inlet status is primarily 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%).

WAVE CLIMATE CYCLES AND COASTAL ENGINEERING PRACTICE

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Modification of coastal currents by power plant intake and thermal discharge systems

Abstract Powerplant cooling systems that entrain large volumes of seawater in multiple discharge jets can produce changes in the local field of flow. A case history of observed flow modification is provided by dye studies and records of currents around the diffusers of the San Onofre Nuclear Generating Station (SONGS), which entrain a volume of flow on the order of 1000 m3 s−1. Field observations of dilutions and velocities in the discharge plume agree well with the results of hydraulic modelling of the diffuser system. Synoptic observations and long-term statistical distributions of current speeds and directions show systematic patterns of altered flow around the diffusers that are more complex than the flow in the model because of interactions with flow modification by local beds of giant kelp.

Dye studies of dilution and flow near a multiport diffuser

This paper describes a method to measure the instantaneous near-field dilution of a continuous discharge, which requires only a short period injection of dye into the intake. The method assumes steady discharge and quasi-steady conditions of current and water stratification and does not depend on any theoretical assumptions for diffusivity. The paper describes the application of this method to the heated discharge from a multiport diffuser with other dye studies to examine the complicated dynamics of this discharge impinging on ambient water. The results of this study would be useful in calibrating and testing existing numerical models and for designing future multiport diffusers.