· · · Repository Hydraulic Engineering Reports

The Conference on Coastal Engineering at Long Beach was conceived originally as a local meeting of engineers and scientists interested in shoreline problems and was sponsored by the University of California. It early became evident that there was widespread interest in the subject and that the program should be planned on a more ambitious scale. The aim was to aid engineers by summarizing the present state of the art and science related to the design and planning of coastal works rather than to present a series of original scientific contributions. Starting from a rather comprehensive outline, invitations were issued to recognized authorities to report on specific phases of the subject, and the authors cooperated splendidly both in their treatment of the subjects assigned and in their avoidance of overlapping other subjects. Although much remains to be done in the way of developing reliable design methods, the series of papers presented at the conference and published in this volume do represent a rather thorough summary of coastal engineering as now practiced. Engineers engaged in the design of coastal works have had available to them a large number of papers dealing with various phases of the science related to their problems, but proper dealing with design were limited in number and scope. Only a few books on coastal engineering have been published. The quality and scope of the papers and the need for a comprehensive and modern treatment of the subject convinced the sponsors of the conference that publication in a single volume was desirable rather than piecemeal in the scientific and technical journals. The newly-formed Council on Wave Research secured funds to underwrite the publication costs from its parent organization, the Engineering Foundation. A word about the term "Coastal Engineering" is perhaps in order here. It is not a new or separate branch of engineering and there is no implication intended that a new breed of engineer, and a new society, is in the making. Coastal Engineering is primarily a branch of Civil Engineering which leans heavily on the sciences of oceanography, meteorology, fluid mechanics, electronics, structural mechanics, and others. However, it is also true that the design of coastal works does involve many criteria which are foreign to other phases of civil engineering and the novices in this field should proceed with caution. Along the coastlines of the world, numerous engineering works in various stages of disintegration testify to the futility and wastefulness of disregarding the tremendous destructive forces of the sea. Far worse than the destruction of insubstantial coastal works has been the damage to adjacent shorelines caused by structures planned in ignorance of, and occasionally in disregard of, the shoreline processes operative in the area. The Council on Wave Research takes this opportunity to thank the authors of the papers and the many others who assisted in organization of the conference and in the preparation of this volume for publication.

Shock pressures of high intensity and short duration may occur during breaking of waves on coastal structures, slamming of ships, landing of seaplanes, and water entry of naval projectiles with flat nose. The phenomenon of shock pressures resulting from the impact between a solid and a liquid can better be described as a water hammer phenomenon wherein the elasticity of the solid and the compressibility of the liquid are the governing factors. The water hammer theory predicts the extreme values of shock pressures since it neglects the effect of air that might be entrapped between the solid an the liquid at the moment of impact. Analytical formulations of shock pressures as a water hammer phenomenon and as the compression of a thin layer of air entrapped between the solid and the liquid at the moment of impact are presented in this report. Tests were conducted by dropping a steel, aluminum or plastic plate whose edge was hinged at the water surface into a 3- by 3- by 6-ft steel tank that was partially filled with water. The shock pressures were measured at two locations by means of strain gage and piezoelectric type pressure cells mounted in the plate with special adapters. The ratio between the recorded and theoretical pressures when treated statistically was found to fit the Poisson distribution well. Correlation between the recorded pressures and the shape of the surface of contact between the solid and the liquid at the moment of impact indicated that although shock pressures have a great intensity, they have a short duration and occur only at some spots on the surface of the solid. Therefore (a) they should not be applied as static pressure for checking the stability of the coastal structure as a whole, (b) they may be absorbed by flexible structures, (c) they may cause cracks in rigid structures such as steel caissons filled with rock, and (d) they may affect the stability of structures that have natural frequencies within the range of duration of shock pressures. Equations and diagrams for the prediction of the magnitude and duration of shock pressures resulting from the impact between a solid and a liquid are presented herein.

The objective of this paper is to bring some international perspectives on the policy, design, construction, and monitoring aspects of Hydraulic and Coastal Structures in general, and whenever possible, to present some comparison (or reasons for differences) between the experiences of various countries and/or geographical regions. This chapter reviews the trends of our hydraulic/coastal engineering profession and presents an overview of miscellaneous aspects, which should be a part of the entire design process for civil engineering structures. This overview ranges from initial problem identification boundary condition definition and functional analysis, to design concept generation, selection, detailing an costing and includes an examination of the construction and maintenance considerations and quality assurance/quality control aspects. It also indicates the principles and methods, which support the design procedure making reference as appropriate to other parts of the chapter. It must be recognized that the design process is a complex iterative process and my be described in more than one way. Some speculation on the possible future needs and/or trends in hydraulic and coastal structures in the larger international perspective is also presented briefly.

Coastal rock structures are widely used in coastal engineering for a variety of purposes, including controlling the morphological development of beaches and providing protection against coastal erosion or flooding by wave overtopping. Strict adherence to existing design guidance has resulted in many of these structures being built using multiple layers of different rock sizes, high quality imported rock and carefully prepared foundations. Some innovative structures have, however, used locally available rock with simpler cross-sections placed on unprepared foundations, apparently without significant reduction to the overall performance of the scheme. This report gives guidance from a short research project which examined practical experience on rock structures from around the UK, with particularly emphasis on those that depart from conventional design rules. The report demonstrates that there are opportunities for lower cost rock structures for beach control and coast protection. Established design guidance provides a good degree of confidence in predictions of performance of coastal structures, but it is widely perceived that simple design rules can be overly prescriptive, particularly for nearshore structures in shallow water depths. The opportunities for lower cost structures principally relate to improved assessment of armour size for depth-limited waves, reduction in armour size for closer armour packing, and the need for complex underlayer / filters. The report emphasises the need to understand the performance of individual structures in the context of the overall scheme and ultimately national objectives, which provides an incentive to re-explore the balance between cost and structure performance. It also encourages the consideration of cost issues during the design of rock structures. Although the use of lower cost structures may also provide safety and environmental advantages, the structures described are envisaged to be of greatest benefit in locations where conventional structures would not be economically justified.

Design manual for coastal structures. Note that this manual is replaced by the Coastal Engineering Manual. However, this document contains quite some useful information for present day coastal engineers