FLOOD06918

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: The NWS Simplified Dam Break-Flood Forecasting Model
• Date: 5/16/1986
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

-------- -
e h
CASE I: If (Qb < Qv)' then D max (21)
=
max c m+l
h
CASE II: If (Qb > Qv)' then D = e h - h + ...:!.- (22)
max c max v m+l

The average velocity in the reach is given by the Manning equation, i.e.:

v
c

1.49 1/2
=-S
n

2/3
(D )
c

(23)

where S is the slope of the channel from the dam to the routing point.

The average velocity
Eq. (24) to determine the

(V ) and hydraulic depth (D ) are substituted into
c c
average Froude number (F ) in the reach as follows:
c

F
c

=

V
c

(24 )

./gD
c
where: g = 32.2 ft/sec2 (acceleration of gravity)

*
The dimensionless volume parameter (V ) that identifies the specific
member of the curve family for the computed Froude number is the ratio of the
reservoir storage volume to the average flow volume within the X reach. The
c
average cross sectional area of flow (A ) is given by Eq. (25) or (26) as
c

follows:

CASE I:

if (Qb < Q ), then
max v

A
c

K(eh )m D
Max c

(25)

CASE II: if (Qb > Qv)' then
max

A =ihmD
c v c

(26 )

.

*
The volume parameter (V ) is determined by

volume (AcXc) into the reservoir storage volume

dividing the average flow
(VOL ), i.e.:
r

1-16