a. Shelf Profiles. The shelf profile is typically a smooth, concaveup curve showing depth to increase seaward at a rate that decreases with
distance from shore. (bottom profile in Figure 4-18.) The smoothness of
the profile may be interrupted by other superposed geomorphic features,
such as linear shoals. (Duane, et al., 1972.) Data for shelf profiles
are usually obtained from charts of the National Océan Survey (formerly,
U.S. Coast and Geodetic Survey).
The measurable influence of the shelf profile on littoral processes
is largely its effect on waves. To an unknown degree, the shelf may also
serve as a source or sink for beach 'sand. Géologie studies show that
much of the outer edge of a typical shelf profile is underlain by relatively coarse sédiment, indicating a winnowing of fine sizes. (Dietz,
1963; Milliman, 1972; and Duane, et al., 1972.) Landward from this residual sédiment, sédiment often becomes finer before grading into the relatively coarser beach sands.
b. Nearshore Profiles. The nearshore profile extends seaward from
the beach to depths of about 30 feet. Prominent features of most nearshore profiles are longshore bars; see middle profile of Figure 4-18 and
Section 4.525. In combination with beach profiles, répétitive nearshore
profiles are used in Coastal engineering to estimate érosion and accretion along the shore, particularly the behavior of beach fill, groins,
and other Coastal engineering structures. Data from nearshore profiles
must be used cautiously. (see Section 4.514.) Under favorable conditions nearshore profiles hâve been used in measuring longshore transport
rates. (Caldwell, 1956.)
c. Beach Profiles. Beach profiles extend from the foredunes, cliffs,
or main 1 and out to mean low water. Terminology applicable to features of
the beach profile is in Appendix A (especially Figures A-l and A-2). The
backshore extends seaward to the foreshore, and consists of one or more
berms at élévations above the reach of ail but storm waves. Berm surfaces are nearly fiat and often slope landward at a slight downward angle.
(See Figure 4-1.) Berms are often bounded on the seaward side by a break
in slope known as the berm crest.
The foreshore is that part of the beach extending from the highest
élévation reached by waves at normal high tide seaward to the ordinary
low water line. The foreshore is usually the steepest part of the beach
profile. The boundary between the backshore and the foreshore may be
the crest of the most seaward berm, if a berm is well developed. The
seaward edge of the foreshore is often marked by an abrupt step at low
tide level.
z
r
r
Seaward from the foreshore, there is usually a low-tide terrace which
horizontal surface at about mean low tide level.
(Shepard,
rinniA^ j3'6?* 1971.)
low-tide terrace is commonly covered with san
svsLm
w her mtn°r bed f0rms* and may c<>ntain a large bar-and-trough
shore?commun 1S Llandward~migrating sandbar (generally parallel to the
e) common in the nearshore following storms. Seaward from the low-tide
4-56
distance from shore. (bottom profile in Figure 4-18.) The smoothness of
the profile may be interrupted by other superposed geomorphic features,
such as linear shoals. (Duane, et al., 1972.) Data for shelf profiles
are usually obtained from charts of the National Océan Survey (formerly,
U.S. Coast and Geodetic Survey).
The measurable influence of the shelf profile on littoral processes
is largely its effect on waves. To an unknown degree, the shelf may also
serve as a source or sink for beach 'sand. Géologie studies show that
much of the outer edge of a typical shelf profile is underlain by relatively coarse sédiment, indicating a winnowing of fine sizes. (Dietz,
1963; Milliman, 1972; and Duane, et al., 1972.) Landward from this residual sédiment, sédiment often becomes finer before grading into the relatively coarser beach sands.
b. Nearshore Profiles. The nearshore profile extends seaward from
the beach to depths of about 30 feet. Prominent features of most nearshore profiles are longshore bars; see middle profile of Figure 4-18 and
Section 4.525. In combination with beach profiles, répétitive nearshore
profiles are used in Coastal engineering to estimate érosion and accretion along the shore, particularly the behavior of beach fill, groins,
and other Coastal engineering structures. Data from nearshore profiles
must be used cautiously. (see Section 4.514.) Under favorable conditions nearshore profiles hâve been used in measuring longshore transport
rates. (Caldwell, 1956.)
c. Beach Profiles. Beach profiles extend from the foredunes, cliffs,
or main 1 and out to mean low water. Terminology applicable to features of
the beach profile is in Appendix A (especially Figures A-l and A-2). The
backshore extends seaward to the foreshore, and consists of one or more
berms at élévations above the reach of ail but storm waves. Berm surfaces are nearly fiat and often slope landward at a slight downward angle.
(See Figure 4-1.) Berms are often bounded on the seaward side by a break
in slope known as the berm crest.
The foreshore is that part of the beach extending from the highest
élévation reached by waves at normal high tide seaward to the ordinary
low water line. The foreshore is usually the steepest part of the beach
profile. The boundary between the backshore and the foreshore may be
the crest of the most seaward berm, if a berm is well developed. The
seaward edge of the foreshore is often marked by an abrupt step at low
tide level.
z
r
r
Seaward from the foreshore, there is usually a low-tide terrace which
horizontal surface at about mean low tide level.
(Shepard,
rinniA^ j3'6?* 1971.)
low-tide terrace is commonly covered with san
svsLm
w her mtn°r bed f0rms* and may c<>ntain a large bar-and-trough
shore?commun 1S Llandward~migrating sandbar (generally parallel to the
e) common in the nearshore following storms. Seaward from the low-tide
4-56