Anchorage. Floating tire breakwaters must be securely anchored to prevent displacement.
Mooring loads can be determined from Figure 62. Danforth and other embedment anchors, as well as
screw anchors and large concrete blocks, have been used with mixed results. They are probably best
suited for seasonal use in a mild wave climate, but they tend to creep over long periods in soft bottoms
and are not always desirable for permanent installations. In those cases, driven piles are generally the
best means of stable anchorage over long periods. Giles and Eckert (1979) provide guidance on
anchorage systems.
Other Materials. Other floating materials can be used in place of scrap rubber tires. Bundles of
logs can be chained together or other barriers can be fabricated from treated timber. Modules of
lightweight concrete filled with flotation foam have also been successful. The proportioning and design
factors presented for rubber tire breakwaters would also apply to these.
Fixed Breakwaters and Sills
An important feature of a fixed breakwater is its height, which determines how much wave
energy passes over the structure. In building a fixed breakwater, some settlement should be anticipated
in the structure's design height, the actual amount being a function of the soil type, the weight of the
structure, and type of foundation.
Longard Tubes
Wave Height Range: Below five feet.
The advantages and disadvantages of Longard tube bulkheads generally apply to breakwaters. An
added disadvantage is that the protective epoxy coating cannot be applied to wet tubes so that damages
are more likely. Therefore, they should not be used where the tube may be exposed to vandalism or
water-borne debris. Figure 63 contains before and after views of a Longard tube slashed by vandals,
eventually causing it to entirely deflate.
The tube should be installed over a layer of synthetic filtercloth with factory-sewn, 10-inch
Longard tubes on each edge to reduce the potential for failure due to toe or heel scour. Where a 69-inch
tube cannot provide sufficient height, an alternate breakwater system should be used.
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