6.3. BEDLOAD-DOMINATED TRANSPORT MODELS
255
long wave total shear stress scale ratio must be the same as the long wave
bottom shear stress. Equating Eqns. 6.19 and 6.18 and rearranging gives
the horizontal velocity scale (for a geometrically distorted model) as
(6.22)
Assuming a flat bed (Nk = Nd) and an undistorted Froude model (Nx =
Nz — Nl), the Inshore Model horizontal velocity scale reduces to
W'8
7Kamphuis (1975) also included specification of a model using prototype-sized sand,
and a “nothing model” that satisfied none of the criteria. These two models are not
included here.
(6.23)
The Inshore Model neglects short-wave-induced bottom shear stress in its
formulation; hence, it is intended for use with long-wave tidal models.
Finally, Kamphuis (1975) considered the Waves Only Model (WOM)
and stated that the necessary horizontal velocity scale is given as
Nu. = x/ÂÇiVz
(6-24)
for both the Offshore and Inshore Models.
Although these velocity scales for different hydrodynamic regimes may
seem puzzling at the moment, they may become more clear when evaluated
in the context of various proposed movable-bed scaling criteria.
6.3.2 Bedload Model Scale Requirements
Provided that sediment movement by the bedload mode of transport is
a function only of the five dimensionless parameters given in Eqn. 6.4,
perfect similitude could be obtained if the prototype-to-model ratios of all
parameters are unity, i.e,
Nr, = Nf, = Np'/p = N\/d = Nvu = 1
(6.25)
and the hydrodynamics are scaled according to undistorted Froude criterion.
Unfortunately, perfect similitude is impossible, and we must be willing
to accept something less. Based on work that took place primarily between
1971-1973, Kamphuis (1974, 1975) proposed several imperfect similitudes
in which two or more of the scale ratios are not maintained. Table 6.1
lists the proposed scale requirements and indicates which parameters are
preserved between prototype and model7. None of the proposed bedload
models attempt to satisfy the relative fall speed parameter criterion.
255
long wave total shear stress scale ratio must be the same as the long wave
bottom shear stress. Equating Eqns. 6.19 and 6.18 and rearranging gives
the horizontal velocity scale (for a geometrically distorted model) as
(6.22)
Assuming a flat bed (Nk = Nd) and an undistorted Froude model (Nx =
Nz — Nl), the Inshore Model horizontal velocity scale reduces to
W'8
7Kamphuis (1975) also included specification of a model using prototype-sized sand,
and a “nothing model” that satisfied none of the criteria. These two models are not
included here.
(6.23)
The Inshore Model neglects short-wave-induced bottom shear stress in its
formulation; hence, it is intended for use with long-wave tidal models.
Finally, Kamphuis (1975) considered the Waves Only Model (WOM)
and stated that the necessary horizontal velocity scale is given as
Nu. = x/ÂÇiVz
(6-24)
for both the Offshore and Inshore Models.
Although these velocity scales for different hydrodynamic regimes may
seem puzzling at the moment, they may become more clear when evaluated
in the context of various proposed movable-bed scaling criteria.
6.3.2 Bedload Model Scale Requirements
Provided that sediment movement by the bedload mode of transport is
a function only of the five dimensionless parameters given in Eqn. 6.4,
perfect similitude could be obtained if the prototype-to-model ratios of all
parameters are unity, i.e,
Nr, = Nf, = Np'/p = N\/d = Nvu = 1
(6.25)
and the hydrodynamics are scaled according to undistorted Froude criterion.
Unfortunately, perfect similitude is impossible, and we must be willing
to accept something less. Based on work that took place primarily between
1971-1973, Kamphuis (1974, 1975) proposed several imperfect similitudes
in which two or more of the scale ratios are not maintained. Table 6.1
lists the proposed scale requirements and indicates which parameters are
preserved between prototype and model7. None of the proposed bedload
models attempt to satisfy the relative fall speed parameter criterion.