Such différences are often visible on aerial photos. Photos may
show two or more distinct wave trains in the nearshore area, with the
wave train most apparent offshore decreasing in importance as the surf
zone is approached. (e.g., Harris, 1972.) The différence appears
be
caused by the effects of refraction and shoaling on waves of different
periods. Longer period waves, which may be only slightly visible offshore, may become the most prominent waves at breaking, because shoaling
increases their height relative to the shorter period waves. Thus, the
wave period measured from the dominant wave offshore may be less than the
wave period measured from the dominant wave entering the surf zone when
two wave trains of unequal period reach the shore at the same time.
4.323 Winds and Storms. The relation of a shoreline locality to the
seasonal distribution of winds and to storm tracks is a major factor
in determining the wave energy available for littoral transport. For
example, strong winter winds in the northeastem United States usually
are from the northwest, but because they blow from land to sea, they do
not produce large waves at the shore. These northwest winds often immediately follow a northeaster - a low pressure System with strong northeast winds that generate high waves offshore.
A storm near the coastline will influence wave climate with storm
surge and high seas; a storm offshore will influence wave climate only
by swell. The relation between the meteorological severity of a storm
and the resulting beach change is complicated. (See Section 4.35.)
Storms are not uniformly distributed in time or space: storms vary
seasonally and from year to year; storms originate more frequently in
some areas than in others; and storms follow characteristic tracks deter
mined by prevailing global circulation and weather patterns.
An investigation of 170 damaging storms affecting the east coast of
the U.S. from 1921-1962 (Mather, et al., 1964), classified the storms m o
eight types based on origin, structure, and path of movement. Of these
eight types, although 33 percent were hurricanes, two types, comprising
only 19 percent of the total, characterized by weather fronts east an
south of the U.S. coasts produced more damage per storm because of long
fetches. (Damage is defined by Mather, et al., as at ®s
j
damage,” and includes "wave damage, Coastal flooding, an
i
tion," but specificially excludes wind damage.)
of coast will expérience storm
location in relation to storm
The probability that a given section
waves dépends on its océan exposure, its
tracks, and the shelf bathymetry.
4-33 nearshore wave climate
4,331
Value Data on U.S. Littoral Wave
period data for some localities of the U.S. are e
iOcalities still
available (e.g., Thompson and Harris, 1972) but most localises still
lack such data. However, wave direction is diffic
conséquently direction data are rarely available.
4-29
show two or more distinct wave trains in the nearshore area, with the
wave train most apparent offshore decreasing in importance as the surf
zone is approached. (e.g., Harris, 1972.) The différence appears
be
caused by the effects of refraction and shoaling on waves of different
periods. Longer period waves, which may be only slightly visible offshore, may become the most prominent waves at breaking, because shoaling
increases their height relative to the shorter period waves. Thus, the
wave period measured from the dominant wave offshore may be less than the
wave period measured from the dominant wave entering the surf zone when
two wave trains of unequal period reach the shore at the same time.
4.323 Winds and Storms. The relation of a shoreline locality to the
seasonal distribution of winds and to storm tracks is a major factor
in determining the wave energy available for littoral transport. For
example, strong winter winds in the northeastem United States usually
are from the northwest, but because they blow from land to sea, they do
not produce large waves at the shore. These northwest winds often immediately follow a northeaster - a low pressure System with strong northeast winds that generate high waves offshore.
A storm near the coastline will influence wave climate with storm
surge and high seas; a storm offshore will influence wave climate only
by swell. The relation between the meteorological severity of a storm
and the resulting beach change is complicated. (See Section 4.35.)
Storms are not uniformly distributed in time or space: storms vary
seasonally and from year to year; storms originate more frequently in
some areas than in others; and storms follow characteristic tracks deter
mined by prevailing global circulation and weather patterns.
An investigation of 170 damaging storms affecting the east coast of
the U.S. from 1921-1962 (Mather, et al., 1964), classified the storms m o
eight types based on origin, structure, and path of movement. Of these
eight types, although 33 percent were hurricanes, two types, comprising
only 19 percent of the total, characterized by weather fronts east an
south of the U.S. coasts produced more damage per storm because of long
fetches. (Damage is defined by Mather, et al., as at ®s
j
damage,” and includes "wave damage, Coastal flooding, an
i
tion," but specificially excludes wind damage.)
of coast will expérience storm
location in relation to storm
The probability that a given section
waves dépends on its océan exposure, its
tracks, and the shelf bathymetry.
4-33 nearshore wave climate
4,331
Value Data on U.S. Littoral Wave
period data for some localities of the U.S. are e
iOcalities still
available (e.g., Thompson and Harris, 1972) but most localises still
lack such data. However, wave direction is diffic
conséquently direction data are rarely available.
4-29