As the name implies, a breakwater is a barrier constructed to break up and disperse heavy seas, to shield the interior waters of a harbor from winds and waves, and to provide shelter and protection for ships, shipping facilities, and other harbor improvements. Breakwaters are structures used to improve a naturally protected (sheltered) harbor or to create a sheltered harbor at locations required for shipping, refuge, recreation, etc. Breakwaters may be roughly divided into two main groups, the

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... ertical-wall type and the rubble-mound type. A possible third group, the composite type, consists of the wall-type placed upon a rubble-mound foundation. Since the experience of the San Francisco District, Corps of Engineers, has been limited to the construction of rubble-mound breakwaters and jetties in as much as practically all breakwaters on the Pacific Coast are of rubble-mound construction, the second half of this paper has been limited to the consideration of this type of structure. The first half of the paper discusses general subjects (choice of location and type of breakwater, etc.) relevant to both types. Until recently, the design and construction of breakwaters was largely an empirical "art" based mainly on the designer's observations of the performance of previously constructed breakwaters. Great latitude was given personal discretion and judgment, since those factors which might influence or standardize design were little understood.