For coastal engineering, the accuracy of shelf profiles is usually
less critical than the accuracy of beach and nearshore profiles. Generally, observed depth changes between successive surveys of the shelf do
not exceed the error inhérent in the measurement. However, soundings
separated by décades suggest that the linear shoals superposed on the
profile do show small but real shifts in position. (Moody, 1964, p. 143.)
Charts giving depths on the continental shelves may include soundings
that differ by décades in date.
Plotted profiles usually use vertical exaggeration or distorted
scales to bring out characteristic features. This exaggeration may lead
to a false impression of the actual slopes. As plotted, the three profiles in Figure 4-18 hâve roughly the same shape, but this sameness has
been obtained by vertical exaggerations of 2x, lOx, and 50x.
Sand level changes in the beach and nearshore zone may be measured
quite accurately from pipes imbedded in the sand. (Inman and Rusnak, 1956;
Urban and Galvin, 1969; and Gonzales, 1970.)
4.52 ONSHORE-OFFSHORE TRANSPORT
4-60
4.521 Sédiment Effects. Properties of individual particles which hâve
been considered important in littoral transport include: size, shape,
immersed spécifie gravity, and durability. Collections of particles
hâve the additional properties of size distribution, permeability, and
porosity. These properties détermine the forces necessary to initiate
and maintain sédiment motion.
For typical beach sédiment, size is the only property that varies
greatly. However, quantitative évaluation of the size effect is usually
lacking. A gross indication of a size effect is the accumulation of
coarse sédiment in zones of maximum wave energy dissipation, and déposition of fine sédiment in areas sheltered from wave action. (e.g. King,
197.., pp. 302 , 307, 426.) Sorting by size is common over ripples (Inman,
1957) and large longshore bars (Saylor and Hands, 1970). Field work on
size effects in littoral transport does not permit definite conclusions,
in??’ I.’ P* * 483’ Inman> Komar, and Bowen, 1969; Castanho, 1970; Ingle,
1966, Figure 112; Yasso, 1962; and Zenkovich, 1967a.)
pie shape of most littoral materials is approximately spherical;
departures from spherical are usually too slight to affect littoral
transport.
• F. I^rfed
ravity (spécifie gravity of sédiment minus specthp
° «.-U,d rS theoreticai 17 an important physical property of
snecifir
Particle. (Bagnold, 1963.) However, the variation in immersed
^st beach sedîL 7 tyPÎCal littoral sériais in water is small since
most of tL d
? are qUartz (immersed spécifie gravity = 1.65), and
“ 1 9)
Thus61"?1?
are.calcium carbonate (immersed spécifie gravity
variation in im 1
u variation in littoral transport is expected from
variation in immersed spécifie gravity.
less critical than the accuracy of beach and nearshore profiles. Generally, observed depth changes between successive surveys of the shelf do
not exceed the error inhérent in the measurement. However, soundings
separated by décades suggest that the linear shoals superposed on the
profile do show small but real shifts in position. (Moody, 1964, p. 143.)
Charts giving depths on the continental shelves may include soundings
that differ by décades in date.
Plotted profiles usually use vertical exaggeration or distorted
scales to bring out characteristic features. This exaggeration may lead
to a false impression of the actual slopes. As plotted, the three profiles in Figure 4-18 hâve roughly the same shape, but this sameness has
been obtained by vertical exaggerations of 2x, lOx, and 50x.
Sand level changes in the beach and nearshore zone may be measured
quite accurately from pipes imbedded in the sand. (Inman and Rusnak, 1956;
Urban and Galvin, 1969; and Gonzales, 1970.)
4.52 ONSHORE-OFFSHORE TRANSPORT
4-60
4.521 Sédiment Effects. Properties of individual particles which hâve
been considered important in littoral transport include: size, shape,
immersed spécifie gravity, and durability. Collections of particles
hâve the additional properties of size distribution, permeability, and
porosity. These properties détermine the forces necessary to initiate
and maintain sédiment motion.
For typical beach sédiment, size is the only property that varies
greatly. However, quantitative évaluation of the size effect is usually
lacking. A gross indication of a size effect is the accumulation of
coarse sédiment in zones of maximum wave energy dissipation, and déposition of fine sédiment in areas sheltered from wave action. (e.g. King,
197.., pp. 302 , 307, 426.) Sorting by size is common over ripples (Inman,
1957) and large longshore bars (Saylor and Hands, 1970). Field work on
size effects in littoral transport does not permit definite conclusions,
in??’ I.’ P* * 483’ Inman> Komar, and Bowen, 1969; Castanho, 1970; Ingle,
1966, Figure 112; Yasso, 1962; and Zenkovich, 1967a.)
pie shape of most littoral materials is approximately spherical;
departures from spherical are usually too slight to affect littoral
transport.
• F. I^rfed
ravity (spécifie gravity of sédiment minus specthp
° «.-U,d rS theoreticai 17 an important physical property of
snecifir
Particle. (Bagnold, 1963.) However, the variation in immersed
^st beach sedîL 7 tyPÎCal littoral sériais in water is small since
most of tL d
? are qUartz (immersed spécifie gravity = 1.65), and
“ 1 9)
Thus61"?1?
are.calcium carbonate (immersed spécifie gravity
variation in im 1
u variation in littoral transport is expected from
variation in immersed spécifie gravity.