Durability (résistance to abrasion, crushing, and solution) is usually not a factor within the lifetime of an engineering project. (Kuenen,
1956; Rusnak, Stockman, and Hofmann, 1966; and Thiel, 1940.) Possible
exceptions may include basaltic sands on Hawaiian beaches (Moberly, 1968),
some fragile carbonate sands which may be crushed to finer sizes when subject to traffic, (Duane and Meisburger, 1969, p. 44), and carbonate sands
which may be soluble under some conditions. (Bricker, 1971.) In general,
recent information lends further support to the conclusion of Mason (1942)
that, "On sandy beaches the loss of material ascribable to abrasion . . .
occurs at rates so low as to be of no practical importance in shore protection problems.”
Size distribution and its relation to sédiment sorting may be important for design of beach fills. (See Sections 5.3 and 6.3.) Permeability
and porosity affect energy dissipation (Bretschneider and Reid, 1954; Bretschneider, 1954) and wave runup. (See Section 7.21; and Savage, 195 8.)
Sédiment properties are physically most important in determining fall
velocity and the hydraulic roughness of the sédiment boundary. Fall velocity effects are important in onshore-offshore transport. Hydraulic roughness effects hâve been insufficiently studied, but they appear to affect
initiation of sédiment transport and energy dissipation. This may be particularly true for flow of the swash on the plane surface of the foreshore.
(Everts, 1972.)
4.522 Initiation of Sédiment Motion. Considérable hydraulic and coastal
engineering research has been devoted to the initiation of sédiment motion
under moving water. From this research has corne general agreement (Graf,
1971, Chapter 6; Hjulstrom, 1939; and Everts, 1972) that the initiation of
motion on a level bed of fine or medium sand requires less shear (lower
velocities) than the initiation of motion on a level bed of silt or grave 1
(Figure 4-7 for size classes). It is also generally agreed that cntical
ontraining velocities for sand are usually less than 1 foot per secon
• the offshore zone can be
Velocities of wave-induced water mo^°gmall_ampiitude theory. (See
estimated fairly well from the équation
2-13 which can be transformed
Chapter 2.) This theory leads to Equat
sand sur£ace (z = -d)
into a dimensionless expression for ve o
T _
J
H
sinh
(4-19)
4-20 and for common values
«hich is plotted in dimensionless ,fo™ ^.^and 4-21 give maximum h°”om
of wave period in Figure 4-21.
1|Ufunction of depth,“a”ePoffshire «ne,
particle velocity, vmax(-d) ». * _ hv linear theory for
breaklocal wave height. This prédiction by 1 in
for the I0ne near or
md the related results from solitary
field. (Inman an
*|» agréé fairly well with "æ^rem
5 and 6.).
1956; and Cook and Gorsline, 1972,
4-61
1956; Rusnak, Stockman, and Hofmann, 1966; and Thiel, 1940.) Possible
exceptions may include basaltic sands on Hawaiian beaches (Moberly, 1968),
some fragile carbonate sands which may be crushed to finer sizes when subject to traffic, (Duane and Meisburger, 1969, p. 44), and carbonate sands
which may be soluble under some conditions. (Bricker, 1971.) In general,
recent information lends further support to the conclusion of Mason (1942)
that, "On sandy beaches the loss of material ascribable to abrasion . . .
occurs at rates so low as to be of no practical importance in shore protection problems.”
Size distribution and its relation to sédiment sorting may be important for design of beach fills. (See Sections 5.3 and 6.3.) Permeability
and porosity affect energy dissipation (Bretschneider and Reid, 1954; Bretschneider, 1954) and wave runup. (See Section 7.21; and Savage, 195 8.)
Sédiment properties are physically most important in determining fall
velocity and the hydraulic roughness of the sédiment boundary. Fall velocity effects are important in onshore-offshore transport. Hydraulic roughness effects hâve been insufficiently studied, but they appear to affect
initiation of sédiment transport and energy dissipation. This may be particularly true for flow of the swash on the plane surface of the foreshore.
(Everts, 1972.)
4.522 Initiation of Sédiment Motion. Considérable hydraulic and coastal
engineering research has been devoted to the initiation of sédiment motion
under moving water. From this research has corne general agreement (Graf,
1971, Chapter 6; Hjulstrom, 1939; and Everts, 1972) that the initiation of
motion on a level bed of fine or medium sand requires less shear (lower
velocities) than the initiation of motion on a level bed of silt or grave 1
(Figure 4-7 for size classes). It is also generally agreed that cntical
ontraining velocities for sand are usually less than 1 foot per secon
• the offshore zone can be
Velocities of wave-induced water mo^°gmall_ampiitude theory. (See
estimated fairly well from the équation
2-13 which can be transformed
Chapter 2.) This theory leads to Equat
sand sur£ace (z = -d)
into a dimensionless expression for ve o
T _
J
H
sinh
(4-19)
4-20 and for common values
«hich is plotted in dimensionless ,fo™ ^.^and 4-21 give maximum h°”om
of wave period in Figure 4-21.
1|Ufunction of depth,“a”ePoffshire «ne,
particle velocity, vmax(-d) ». * _ hv linear theory for
breaklocal wave height. This prédiction by 1 in
for the I0ne near or
md the related results from solitary
field. (Inman an
*|» agréé fairly well with "æ^rem
5 and 6.).
1956; and Cook and Gorsline, 1972,
4-61