different quadrant. When the winds and waves change direction, the transport direction also changes
(transport reversal).
The gross longshore transport rate is the quantity of sand (usually in cubic yards per year) that
moves past a fixed point in either direction. The net longshore transport rate is the quantity that moves in
the predominant direction minus the quantity that moves the other way. The net transport rate is
specified by both quantity and direction (e.g., 10,000 cubic yards per year to the east).
Transport rates are important when considering accretion devices such as breakwaters and groins
because it is necessary to judge the effects of device construction on the littoral system, particularly with
respect to potential downdrift damages. A precise estimate will not usually be possible, but it may be
feasible to examine similar structures or harbor works that have been constructed in the past for evidence
of accretion over known periods of time. If nothing else, this should reveal the predominant transport
direction and a crude measure of the possible transport rate. This should be an acceptable level of
precision for small scale, low cost devices.
Slope Stability
Slope stability analysis is covered in standard geotechnical engineering textbooks [e.g., Lambe and
Whitman (1969) and Winterkorn and Fang (1975)]. Major stability problems are most likely at high
bluff shorelines where the heights are 20 feet or more. Except where toe protection is needed, slope
stability problems on high bluffs tend to be beyond the range of low cost solutions.
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