FLOOD08201

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: The NWS Dambrk Model Quick Users Guide
• Date: 6/20/1988
• Prepared By: National Weather Service
• Floodplain - Doc Type: Educational/Technical/Reference Information

Appendix A-13

QLL

computations during the initial run; it is required
only when QLL is non-zero.
Maximum lateral outflow (cfs/ft) producing the volume
losses experienced by the passage of the dam-break
flood wave through the downstream valley; QLL has a
negative sign and is computed by Eq. (91) in paper;
QLL may be left blank if losses are assumed
negligible.
Initial llt time step size (hr); if 0.0 is read in,
the value of DTHM is computed by the program; if
DTHM<O.O, DTHM represents the divisor MDT for
determining the time step (DTHzTFH/MDT) and DTHM is
reset to zero. See note on page A-24,
Parameter for type of downstream boundary. If
channel control exists at this location, enter
0.0; if YDN=O,25, a single value rating curve of
water surface elevation (ft m,s.l.) vs. discharge
exists at downstream end; if YDN = 0,5, critical
flow such as a waterfall or rapids exists at
downstream end; if YDN=O,75, a specified water
surface elevation (m.s.l.) such as a tide exists at
the end, When the downstream end of a routing
reach is a dam as in options 4, 5, 6, 9, 10, then
YDN is read-in as the initial water (pool)
elevation just upstream of the dam,
Slope of downstream channel (ft/mi) for first mile
below dam. It is used to compute tail water via the
Manning equation. If left blank, model assumes it
is equal to (HS(l,l) - HS(l ,NS/3))/[XS(1) -
XS(NS/3)) x 5280] in which HS is the invert
elevation and XS is the mileage location of
sections 1 and NS/3 where NS, XS, HS are defined in
cards (20, 24, 25), respectively.
Theta (8) weighting factor in finite difference
solution; if left blank, a value of 0,60 is used in
program; if 0.5 is used, 8 is set internally to~
0.60 and the model is capable of allowing negative
flows or any flows less than the initial flow (t=O)
to occur by omitting the low-flow filter; if 0.51
is used, 8 is set internally to 0.60 and the
routing is done by the diffusion routing method
(first two inertial terms in momentum Eq. (9) are
omitted) instead of dynamic routing.
Convergence criterion for stage (ft) in Newton-
Raph50n iterative solution of finite difference
unsteady flow equations; varies from 0.001 to
.1 ft; if left blank, program use 0.01 fto Also,
can be used to specify the exponent me used in Eq.
(93) in the paper; if EPSy.s.0.50, me=4; if EPSY>0.5,
me=EPSY and then EPSY is automatically set to 0.01.
Time (hr) when time step changes from DTHM to
TFH/MDT. See time step note on page A-24.

DTHM

YDN

I

SOM

I

I

F11

I

I

r
I

EPSY

I

TF!

I

I