Normally a pier, or dock, extends straight out from the shoreline. So why are the piers in Seattle angled? How would you build them?
Piers are constructed by first driving numerous pilings into the bottom of the bay to support the pier deck. The longer the pilings are, the less stable the structure will be, because longer pilings bend more easily and buckle more than shorter ones when under load. Experience has shown that the maximum piling length from the bottom of the bay to the pier should be about 50 feet.
Another factor dictating the length of pilings is the material they are made of. Early Seattle had plenty of tall trees to use for pilings. Since they were driven into the harbor bottom for a depth of up to 30 feet, some of the pilings needed to be about 80 feet long. But to find trees of a more-or-less constant diameter over a length greater than 80 feet is a tall order now, even in the tree-rich Northwest. Concrete and steel pilings can be made longer than this, but then stability problems become a concern.
So, you can't really build in water deeper than 50 feet. And there's our problem.
Elliott Bay is a natural deep-water bay and the seafloor drops off quickly from the water's edge. At Bell Street Pier, 400 feet straight out from the seawall the water is about 70 feet deep. If you
built a 400-foot pier at this point, the water at the end of the pier would be 20 feet deeper than your 50-foot limit.
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To solve the problem, you have to swing an arc with a 400-foot radius until its over the minus-50-foot contour line on a map of the bottom. If you build your pier at this angle, it can be 400 feet long without exceeding a 50-foot depth.
Piers built in pre-1889 Seattle were constructed in whatever fashion the builder wanted; consequently, there was no apparent order. In 1889, the Great Fire leveled 25 blocks of Seattle—and every pier from King Street on the south to Union Street on the north. But when reconstruction began, it was as haphazard as before.
The decision to angle piers in an east-west orientation came with a replat of underwater property adopted by the State in 1897. Besides making it possible to build long piers inside a 50-foot depth, angling provides added benefits—slips between the piers are more protected from the prevailing south and southwest storm winds; ships entering from Elliott Bay have a more direct shot at the slips; and angled piers were easier to serve by rail, since the curve from Railroad Avenue was not as sharp as a right-angle turn.