includes ail profiles surveyed. The two February 1972 storms at Jones
Beach include ail profiles away from the influence of inlets, reducing
the number of profiles from 15 in the December 1970 storm to 10 in the
February 1972 storms. The November 1953 storm gives relatively high
storm damage which may partly resuit from the long time interval between
pre-storm survey and the storm. (See Columns 1 and 3.) These results
are also affected by the fact that they omit some profiles ”believed to
be influenced by the presence of a seawall or a bulkhead.” (Caldwell,
1959, p. 4.)
Although the data in Table 4-5 are not completely comparable, the
results do suggest that the average volume of sand eroded above mean sea
level from beaches about 5 or more miles long has a certain range of values. A moderate storm may remove 4 to 10 cubic yards per foot of beach
front above MSL; an extreme storm (or a moderate storm that persists for
a long time) may remove 10 to 20 cubic yards per foot; rare storms that
are most destructive in beach érosion due to a combination of intensity,
duration, and orientation may remove 20 to 50 cubic yards per foot. These
values are average for beaches 5 to 10 miles or more long, and they are
compatible with other, less complété, data for notable storms. (Caldwell,
1959; Shuyskiy, 1970; and Harrison and Wagner, 1964.) For comparative
purposes, a berm 100 feet wide at an élévation of 10 feet MSL contains 37
cubic yards per foot of beach front, a quantity that would be adéquate
except for extreme storms.
In terms of horizontal changes rather than the volume changes in
Table 4-5, a moderate storm can erode a typical beach 75 to 100 feet or
more, and leave it exposed to greater érosion if a second storm follows
before the beach has recovered. This possibility should be considered
in design and placement of beach fills and other protective measures.
Extreme values of érosion may be more useful than mean values for
design. Column 17 of Table 4-5 suggests that the ratio of the most eroded above-MSL-profile to the average profile for east coast beaches ranges
from about 1.5 to 6. If the average érosion per profile is based only on
those profiles showing net érosion, then this ratio is probably between
1.5 and 3.
r
Although the dominant resuit of storms on the above MSL part of
eac es is érosion, most post-storm surveys show that the storm produces
local accretion as well. Of the 90 profiles from Cape Cod, Massachusetts,
to Cape May New Jersey, surveyed immediately after the December 1970
storm, 16 showed net accretion above mean sea level.
(Compare Columns 4,
11, and 12 m Table 4-5.) Similar results are indicated for a number of
more severe storms. (Caldwell, 1959.)
Stonn surveys also show that the shoreline on many beaches may
prograde seaward even though the profile as a whole loses volume, or
.
T^a* This possibility suggests caution in interpreting aerial
photos of storm damage. (Everts, 1973.)
4-74
Beach include ail profiles away from the influence of inlets, reducing
the number of profiles from 15 in the December 1970 storm to 10 in the
February 1972 storms. The November 1953 storm gives relatively high
storm damage which may partly resuit from the long time interval between
pre-storm survey and the storm. (See Columns 1 and 3.) These results
are also affected by the fact that they omit some profiles ”believed to
be influenced by the presence of a seawall or a bulkhead.” (Caldwell,
1959, p. 4.)
Although the data in Table 4-5 are not completely comparable, the
results do suggest that the average volume of sand eroded above mean sea
level from beaches about 5 or more miles long has a certain range of values. A moderate storm may remove 4 to 10 cubic yards per foot of beach
front above MSL; an extreme storm (or a moderate storm that persists for
a long time) may remove 10 to 20 cubic yards per foot; rare storms that
are most destructive in beach érosion due to a combination of intensity,
duration, and orientation may remove 20 to 50 cubic yards per foot. These
values are average for beaches 5 to 10 miles or more long, and they are
compatible with other, less complété, data for notable storms. (Caldwell,
1959; Shuyskiy, 1970; and Harrison and Wagner, 1964.) For comparative
purposes, a berm 100 feet wide at an élévation of 10 feet MSL contains 37
cubic yards per foot of beach front, a quantity that would be adéquate
except for extreme storms.
In terms of horizontal changes rather than the volume changes in
Table 4-5, a moderate storm can erode a typical beach 75 to 100 feet or
more, and leave it exposed to greater érosion if a second storm follows
before the beach has recovered. This possibility should be considered
in design and placement of beach fills and other protective measures.
Extreme values of érosion may be more useful than mean values for
design. Column 17 of Table 4-5 suggests that the ratio of the most eroded above-MSL-profile to the average profile for east coast beaches ranges
from about 1.5 to 6. If the average érosion per profile is based only on
those profiles showing net érosion, then this ratio is probably between
1.5 and 3.
r
Although the dominant resuit of storms on the above MSL part of
eac es is érosion, most post-storm surveys show that the storm produces
local accretion as well. Of the 90 profiles from Cape Cod, Massachusetts,
to Cape May New Jersey, surveyed immediately after the December 1970
storm, 16 showed net accretion above mean sea level.
(Compare Columns 4,
11, and 12 m Table 4-5.) Similar results are indicated for a number of
more severe storms. (Caldwell, 1959.)
Stonn surveys also show that the shoreline on many beaches may
prograde seaward even though the profile as a whole loses volume, or
.
T^a* This possibility suggests caution in interpreting aerial
photos of storm damage. (Everts, 1973.)
4-74