28 July 2005
maintenance. The geotechnical characteristics of a given site, and economic
analysis of alternate structural types will often dictate structural requirements.
For instance, in areas with poor near surface soils but with good end bearing for
piles, an open pile supported structure with a shallow bulkhead (or no bulkhead)
will be most economical. Conversely, in areas with good near surface soils and
poor pile bearing, a solid bulkhead may be more economical.
The structural type is seriously influenced by aquatic and plant life existing along
the shore of the planned facility. In environmentally sensitive areas such as river
estuaries, the solid-type wharf, which would disturb or destroy a considerable
length of shoreline, should not be considered. Select the open structural type,
which would have the least impact on the shoreline.
When the facility extends beyond an established bulkhead line (the limit beyond
which continuous solid-type construction is not permitted) use open type
Tidal or Stream Prisms.
Where it is required to minimize restrictions of a tidal or stream prism (the total
amount of water flowing into a harbor or stream and out again during a tidal
cycle) use open type construction.
Along shores where littoral currents transporting sand, gravel, and silt are
present, use open type construction to mitigate shoreline erosion and accretion.
In general, open type structures are vulnerable and should be carefully
investigated at sites where heavy accumulations of sheet or drift ice occur. Also,
when ice thaws, large blocks of ice may slide down the piling, impacting adjacent
batter or plumb piles. Thus, the solid type may be preferable at such sites.