Environmental Factors
Many different materials can be used for shore protection structures, including rock, concrete,
timber, metal, and plastics. The choice often depends on the relative permanence of the desired
protection. Durable materials usually cost considerably more than shorter-lived materials used for
temporary protection. Materials are important because the coastal environment is a harsh testing ground
for all man-made structures. Aside from wave forces, which themselves are formidable, a host of
chemical, biological, and other natural factors can degrade structural materials.
Corrosion is a primary problem with metals and concrete in brackish (saline) water. Plain carbon
steel used for sheet piling in bulkheads or as bolts for fasteners has a life of probably less than five years
under some conditions. Corrosion-resistant steel marketed under various trade names is better for such
applications, while aluminum sheet piling can also be used in many areas instead of steel.
Stainless or galvanized steel and wrought iron can be used for bolts and other fasteners.
Different kinds of metals, however, should not be mixed in structures -where they directly contact each
other, because galvanic action accelerates corrosion of one of the metals. For instance, aluminum and
carbon steel will quickly deteriorate when in contact with stainless steel.
Concrete can also be degraded by chemical reaction with salt water. Concrete used in structures
should be high quality, and aggregates should be durable and not reactive with cement. Dense (cement
rich) mixes should be used, typically about 7 bags of type II or V portland cement per cubic yard of
concrete. These are suitable for use in salt water because they are moderately and highly resistant,
respectively, to sulfate attack. Types I (general purpose portland cement) or II are acceptable in fresh
and brackish water. Water content should be kept to the minimum possible for workability and air
entrainment is necessary to minimize damage from freeze and thaw cycles. Portland cement already
containing air-entraining agents is available.
Timber structures submerged in brackish and salt water are subject to damage from marine borers.
Timber used for bulkhead or other construction in such areas should be heavily treated with 20 pounds of
creosote or 2.5 pounds of preservative salts per cubic foot of timber. Where borer activity is severe, 20
pounds of creosote and 1.5 pounds of preservative salts in a dual-treatment process is recommended.
The ultraviolet component of sunlight rapidly degrades untreated synthetic fibers, such as those
used for filter cloth or sandbags, totally deteriorating them in less than one season if heavily exposed.
Therefore, any fabric used for shore protection devices should be stabilized against ultraviolet light. The
addition of, for instance, carbon black to the synthetic compound gives it a black or dark color in contrast
to the white or light gray color of unstabilized cloth. Even filter cloth covered by a structure should be
stabilized since small cracks or openings in the structure could admit enough light to destroy the fabric.
Abrasion damage occurs in all structures where waves move coarse sediments such as sand and
gravel back and forth across their faces. Coarse gravels and cobbles can also cause impact damages
when hurled by large waves. In either case, little can be done to prevent damages beyond the use of
durable rock and concrete as armoring in such critical areas as along the bottom of structures like sheet
pile groins. It is along the sand line that such structures typically experience the greatest abrasion.
Cold region waterbodies develop ice covers whose extent depends on the size, geographic
location, and exposure of the waterbody. Large bodies such as the Great Lakes usually develop partial
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