Todd L. Walton

CAPACITY OF INLET OUTER EARS TO STORE SAND

A significant portion of the damage by hurricanes is the storm surges. The National Weather Service has developed a dynamical-numerical model to forecast hurricane storm surges. The model is used operationally for prediction, warning, and planning purposes. The model requires fixed oceanographic and real time meteorological input data. The oceanographic data were prepared for the Gulf and East coasts of the U.S. and are stored as an essential part of the program. Meteorological data for any tropical storm are supplied by the forecasters or planners using the model. The model was applied to hurricane Camille 1969. Comparison between the observed and computed surges for Camille was satisfactory for prediction purposes.The main consideration in harbor master planning is to maximize the amount of time that the harbor can be used. The potential level of harbor utilization can be evaluated by analyzing vessel performance during harbor operations in terms of the range of imposed environmental conditions. The harbor utilization level is expressed statistically as the probable amount of time that the harbor can be used as planned.The design and construction of a major ocean outfall and diffuser system for disposal of wastewater effluents is a complex process involving an interplay of requirements originating from various disciplines. These include, among others, considerations of physical oceanography, mixing and dispersion, treatment processes, regulatory requirements, marine geology, economics and construction. The recently completed Sand Island Outfall and the newly designed Barbers Point Outfall are both on the southern coast of the island of Oahu, Hawaii, and are designed for treated sewage effluents from the densely populated portion of the City and County of Honolulu. In this paper, some design considerations of these outfalls will be examined. The emphasis in this paper is on the hydrodynamics, although other design aspects are also discussed briefly.The height of dikes and other coastal structures can only be calculated after determination of the wave run-up. Several formulas for the calculation of wave run-up are developed after model tests as a rule. But the influences of scale effects and natural wind conditions are practically unknown. To clear these questions further investigations and especially field measurements should be carried out. By measuring the markerline of floating trash on the slope of the seadikes the maximum wave run-up could be found out after four storm surges in 1967 and 1973In two graphs it will be shown that on the tidal flats the run-up depends on the waterdepth. The run-up was higher than it could be expected after model tests of 1954. With a newly developed special echo sounder the run-up could be measured in January 1976. The waves and the run-up could be registrated synchronously during two severe storm surges. As shown in Fig. 9 it was found a logarithmic distribution of the wave height, wave period and the higher part of the wave run-up. The found wave run-up is considerably higher than estimated before. The measured 98 % run-up is found about twice the computed value. That is an interesting and important result of the first synchronous recording of wave run-up on sea dikes.In March 1972 the authors firm in association with two Portuguese firms of consulting engineers, Consulmar and Lusotecna, were appointed by the Portuguese Government agency Gabinete da Area de Sines to prepare designs for the construction of a new harbour at Sines on the west coast of Portugal. The location is shown in Figure 1. The main breakwater, which is the subject of this paper, is probably the largest breakwater yet built, being 2 km long and in depths of water of up to 50 m. It is exposed to the North Atlantic and has been designed for a significant wave height of 11 m. Dolos units invented by Merrifield (ref. 1) form the main armour. The project programme required that studies be first made of a wide range of alternative layouts for the harbour. After the client had decided on the layout to be adopted, documents were to be prepared to enable tenders for construction to be invited in January 1973. This allowed little time for the design to be developed and only one series of flume tests, using regular waves, was completed during this period. Further tests in the regular flume were completed during the tender period and a thorough programme of testing with irregular waves was commenced later in the year, continuing until August 1974 when the root of the breakwater was complete and the construction of the main cross-section was about to start. The model tests, which were carried out at the Laboratorio Nacional de Engenharia Civil in Lisbon, were reported by Morals in a paper presented to the 14th International Coastal Engineering Conference in 1974. (ref. 2)Estuaries may be sequentially classified into highly stratified, moderately mixed and vertically homogeneous. An important difference between moderately stratified or vertically homogeneous estuaries, and highly stratified estuaries (salt wedges) is that, in the former, tidal currents are sufficient to cause turbulent mixing of fresh water and sea water over the full depth of the estuary. In the latter, a distinct interface or interfacial layer exists which separates the two nearly homogeneous layers. The vertical advectlon of salt in this two-layer flow is the dominant process in maintaining the salt balance. This paper presents an analytical model describing this process. Experiments have been conducted in the laboratory to compare with the developed theory.

Beach Erosion: Causes and Stabilization

Natural and human-related causes of beach erosion are discussed and illustrated by examples. Sea level rise, trapping of sand by natural inlets and migration of natural inlets are the most pervasive natural causes. Construction of navigation works, followed by reduction in sediment delivery to the coast and subsidence induced by ground fluid extraction are the most prevalent human-related causes. Application of the Bruun Rule to sea level rise is discussed including its limitations and extensions to include beach nourishment and barrier islands. Prediction of shoreline changes caused by natural phenomena on decadal scales can only be accurately calculated with historical data. However, predictions of shoreline and volume changes due to human-induced effects such as construction of a littoral barrier or a beach nourishment project can reasonably be calculated with analytical and numerical models. Societal responses to beach erosion are expensive and limited to: retreat, stabilization with structures, nourishment and combinations of the last two. Each beach is unique thus placing a need to understand the cause of the erosion, develop a prognosis for “without response” conditions and prescribe the best approach for the future. Fortunately, long-term shoreline changes are available in some areas as are the effectiveness of some stabilization projects to guide this process. It is concluded that it will be possible to maintain some highly developed areas for one or two centuries with available technology and resources. Some areas will undoubtedly require abandonment within this period.

Addressing an Optimal Schedule for Inlet Bypassing

Abstract St. Augustine Inlet is located on the NE coast of Florida, connecting the Atlantic Ocean to the Tolomato and Matanzas rivers. The inlet is unique because it was relocated in the 1940s, resulting in considerable perturbations to the adjacent coastal system, especially the downdrift (southern) shoreline. The relatively low, permeable, and short north jetty has allowed sediment to move around, through, and over the jetty, resulting in deposits on the interior lagoon/bay and on the ebb shoal system. Since 2001, dredging has occurred on the ebb shoal and bypassed to the downdrift side of the inlet on St. Augustine Beach. At present, dredging and bypassing have occurred on an irregular schedule, although questions remain about what a reasonable schedule would be to prevent excessive problems on both the updrift and downdrift beaches. This article presents an evaluation of a potential approach for use in addressing the dredging and bypassing schedules to assess how various intervals of dredging/bypassing can affect an idealized downdrift beach having the same net sand transport as that near the St. Augustine Inlet.

Analytic Solution Shoreline at Jetty Under Varying Wave Climate

Future shoreline changes on a sandy beach with a structure such as a jetty or groin can be predicted when wave climate is known. An existing solution for the linearized partial differential equation for shoreline change is presented for the situation where wave climate is not changing and when the angle of the shoreline is small with respect to the waves breaking at the shoreline. The novel solution provided in this paper allows the previous constant wave condition solution to be utilized to be extended to the case where wave climate (i.e. wave direction and wave height) is time varying. Example usage of the method presented shows that shorelines are of different final planform shape for time varying wave conditions even though the sediment transport is the same from time step to time step. Reversals of wave climate time series are shown to provide very different final shoreline shapes even though time series consist of the same wave conditions although in different ordered time.

Computer algorithm to calculate longshore energy flux and wave direction from a two pressure sensor array / by Todd L. Walton, Jr. and Robert G. Dean.

Abstract : A documented (FORTRAN IV) computer program is discussed as originally written for the CERC Longshore Sand Transport Research Program to analyze wave data collected at Channel Islands Harbor, California. The program performs the basic analysis of two wave gage pressure records necessary to compute wave direction and wave energy at a given frequency and computes the longshore energy flux used in sand transport for the entire energy spectrum of the wave record. This program uses linear wave theory for the wave transformation process and includes the assumption of straight and parallel bottom contours necessary for application of Snells law of refraction. The necessary steps in an analysis of wave data and sample outputs for some wave records from the Channel Islands wave gage pressure sensor pair are given. The program presently accepts data in the standard CERC magnetic-tape format where record lengths consist of 4,100 values. (Author)