Corrosion and Freezing. Corrosion is a primary problem with metals in brackish and saline water.
This is particularly true in the splash zone, where the materials are subjected to continuous wet-dry
cycles. Plain carbon steel, for instance, probably has a life of less than five years under some conditions.
Corrosion resistant steel marketed under various trade names is useful for some applications. Aluminum
sheet piling can also be used in many areas in place of steel. Stainless, galvanized, or other corrosion-
protected steel, or wrought iron can be used for bolts and other fasteners. However, care should be taken
not to mix dissimilar metals in structures where they directly contact each other. The resulting galvanic
action will quickly corrode the more active metal of the pair (e.g., aluminum is more active than stainless
steel).
Concrete can be degraded by chemical reaction with salt water and by freeze-thaw cycles.
Guidance on producing suitable high quality concrete is presented in Mather (1957). Aggregates should
be durable and not reactive with cement. Dense (cement rich) mixes should be used, typically about 7
bags of portland cement per cubic yard. Types II or V should be used in salt water, while Types I or II
are acceptable in fresh and brackish water. Potable water should generally be used, but brackish or salt
water may sometimes be acceptable for mass concrete. Fresh water, however, should always be used for
reinforced concrete. Maximum water content should be no more than 5 1/2 gallons per bag of cement,
including the moisture content of the aggregates. Finally, air entrainment (typically 4 to 7% of the
concrete volume) is necessary to minimize damages from freeze-thaw cycles.
Marine Borer Activity. Timber structures submerged in brackish and sa-1 water are sub ' ject to
damage from marine borers. Any wood or timber used for bulkhead or other construction in areas of
moderate borer activity should be treated with 20 pounds of creosote or 2.5 lbs. of preservative salts per
cubic foot of timber. Where borer activity is severe, 20 pounds of creosote and 1.5 pounds per cubic foot
of preservative salts in a dual-treatment process is recommended for all lumber. Timber piles should be
dual-treated with 20 pounds of creosote and 1.0 pound of preservative salts per cubic foot in such areas
[American Wood Preservers' Association (1977)].
Ultraviolet Light. The ultraviolet component of sunlight rapidly degrades untreated synthetic
fibers such as those used for filter cloth or sand bags, totally deteriorating them in less than one season if
heavily exposed. Any fabric used for shore protection devices should be stabilized against ultraviolet
light. This typically involves adding carbon black to the synthetic compound, which gives the finished
product 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 cloth.
Abrasion. 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. Little can be done to prevent abrasion damages beyond the use of
durable rock and concrete as armoring in critical areas such as along the sand line of sheet pile groins. It
is here that such structures typically experience the greatest amount of abrasion.
Ice Forces. Ice forces are primarily a problem on cold region waterbodies such as the Great
Lakes. Ice covers will typically vary with the size and location of the waterbody, and local climatic
conditions. Large bodies, such as the Great Lakes, usually develop partial ice covers, while smaller
embayments within them may be totally covered.
The ice covets are never totally stationary and movement creates several categories of ice forces
on structures. For instance, dynamic forces result from wind and current-driven ice sheets or floes.
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