FLOOD01902

• County: Pitkin
• Community: Aspen
• Title: Drainage Facility Capacity Analysis of City of Aspen
• Date: 9/1/1998
• Prepared For: Aspen
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Project

relatively steep (i,e, alluvial fans), In this study the diffusive wave equations were
used by FLO-2D:
dh
~=~-- ~
dx

and

dh
StY = Soy--
dy

(5)

Flow depth, velocities, and discharges between adjacent nodes are calculated every
time step. The model makes a single sweep of the grid system, explicitly solving for
flow depth one node at a time for each time step, and storage volumes at each node
for both water and sediment are .computed. The inflow, outflow, and change in
storage across the entire grid system are assessed at the end of each time step to
ensure that volume is conserved within tolerance levels, If the volume is not
conserved sufficiently, the model will automatically reduce the time step and resolve
for flow depth at each node,

The rheological behavior of hyperconcentrated sediment flows involves the
interaction of several complex physical processes, including turbulence, fluid-
particle interaction, particle-particle interaction, and fluid viscosity, The total shear
stress in hyperconcentrated sediment flows, including mud floods and mudflows, can
be calculated from the summation of five shear stress components:

'='e+'me+'v+"M;d (6)
Where: , = Total Shear Stress
'e = Cohesive yield stress
'me = Mohr - Columb Shear Stress
'v = Viscous shear stress
" = Turbulent shear stress
'd = Dispersive shear stress

! ..

The following quadratic equation was developed by the authors ofFLO- 2D and used
in FLO-2D to account for the various shear stresses.

( )'
dV dv
't='ty+ll-+C -
dy dy

't'y
TJ
dV
dy
C

(7)

Where:

=

~fnii~"viscosity
Rate of Shear

=

Inertial Shear Stress Coefficient

The first two tenus in Equation 7 are referred to as the Bingham shear stresses and

12

, .-