Coastal Construction Manual - National Ready Mixed Concrete ...

IDENTIFYING HAZARDS 3
one of erosion (72 percent of the stations examined experienced long-term erosion), with shoreline change
rates averaging -3.0 feet per year (i.e., 3.0 feet per year of erosion). However, variability along the shoreline is
considerable, with a few locations experiencing more than 20 feet per year of erosion, and over one-fourth of
the stations experiencing accretion. A study of the Pacific County, WA, coastline found erosion rates as high
as 150 feet per year, and accretion rates as high as 18 feet per year (Kaminsky et al. 1999).
Erosion rates can also vary over time at a single location. For example, Figure 3-38 illustrates the shoreline
history over a period of 160 years for the region approximately 1.5 miles south of Indian River Inlet, DE.
Although the long-term, average annual shoreline change rate is approximately -2 feet per year, short-term
shoreline change rates vary from -27 feet per year (erosion resulting from severe storms) to +6 feet per year
(accretion associated with post-storm recovery of the shoreline). This conclusion—that erosion rates can vary
widely over time—has also been demonstrated by other studies (e.g., Douglas, et al., 1998).
Designers should also be aware that some shorelines experience
large seasonal fluctuations in beach width and elevation. These
changes are a result of seasonal variations in wave conditions and
water levels, and should not be taken as indicators of long-term
shoreline changes. For this reason, shoreline change calculations
at beaches subject to large seasonal fluctuations should be based
on shoreline measurements taken at approximately the same
time of year.
NOTE
Apparent erosion or accretion
resulting from seasonal
fluctuations of the shoreline is
not an indication of true shoreline
change.
Figure 3‐38.
Shoreline changes through time at a location approximately 1.5 miles south of Indian River Inlet, DE
DATA SOURCES: NOAA AND THE STATE OF DELAWARE
COASTAL CONSTRUCTION MANUAL
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