SED TEST1 CASE

Suspended Sediment Test in Channel

This case provides a fundamental check of the ability of a model to 1) represent a simple flow, 2) flux material from the bed, and 3) develop a suspended-sediment profile.

This case provides a fundamental check of the ability of a model to 1) represent a simple flow, 2) flux material from the bed, and 3) develop a suspended-sediment profile.

Model Parameters

The following parameters were used for the Suspended Sediment Test in Channel test case.

Model Parameter	Variable	Value
length, width, depth	Xsize, Esize, depth	10000 m, 100 m, 10 m
number of grid spacings	Lm, Mm, Nm	100, 10, 20 (+variable)
bottom roughness	Zob	0.0053 m
time step	dt	30 s
simulation steps	Ntimes	5000
settle velocity	ws	1.0 mm s-1
erosion rate	E0	5x10-5 kg m-2 s-1
critical stresses	τce	0.05 N m-2
porosity	ϕ	0.90
bed slope	S0	4x10-5
Inflow/Outflow boundary condition	u	1 m s-1

Channel Initial Conditions

Channel initial conditions: The test channel was modeled by establishing a grid parameterized with dx = 100 m , dy=100 m, f0 = 0, and h = 10 m (flat bottom). Initial conditions set a vertical logarithmic velocity profile for u (not required but provided reasonable starting values), v = 0, zeta (water surface height) = 0, SSC in the water column = 0, and bed thickness = 1 m (to provide unlimited supply). The model was forced with 2 methods :

—Simulation 1: Imposing a constant flow of 10 m³/s/m of width. This simulation allowed that water surface elevation to vary. Radiation boundary conditions were imposed for the water level along with a constant flow imposed by a depth averaged velocity ubar = 1.0 m/s at the upstream and downstream boundaries.

—Simulation 2: Imposing a constant bed slope and water surface slope of 4x10-5 m/m. This simulation forced the water surface elevation and hence the bottom stress. Radiation boundary conditions were imposed for the depth-averaged velocity along with a clamped water surface condition at each boundary. The bed slope of 4x10-5 was selected to produce a depth-averaged velocity of 1m/s (similar to simulation 1) with a Z0 = 0.005.

For both simulations, vertical mixing was parameterized using six different closure schemes: MY25, KKLpara, KKLmin, KE, KW88, and ANA MY25 = Mellor Yamada Level 2.5 Closure, parabolic wall proximity function KKLpara = Generic Length Scale parameterized as Mellor Yamada Level 2.5 with a parabolic wall proximity function KKLmin = Generic Length Scale parameterized as Mellor Yamada Level 2.5 with a linear wall proximity function (minimum distance to each surface) KE = Generic Length Scale parameterized as k-epsilon closure KW88 = Generic Length Scale parameterized as k-omega closure ANA = analytical expression of a parabolic vertical eddy diffusivity and viscosity profile:

Kz = k u* z (1 - z/D) where Kz = vertical eddy viscosity, m²/s z = height above the bottom, m D = depth of flow, m, = 10 m and u* = friction velocity which was calculated according to the logarithmic profile.