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

Routing Curves

*
Knowing the value of Fc and V , the user may consult the specific curve

(see Appendix Ia) defined for these values (interpolation may be necessary)

and check the original estimate of the value of e used in Eq. (21)-(27).

*
The ordinate of the routing curve at X = 1 is the ratio of the peak flow

(Q ) at X to Qb . Knowing Q , the user may determine the stage (h ) at
p c max p x

X using Eq. (8) or (11) with the average channel fitting coefficients. The
c

value of e is checked by rearranging Eq. (20), i.e.:

o =

h + h
Max x

2 h
max

(28)

If there is a significant difference in the new value of e from the

initial estimate of e (e.g., t5%), Eqs. (21)-(27) should be recalculated and

the new value of e rechecked. Generally, within two passes the value for e

will converge.

Knowing the proper routing curve for predicting peak flow attenuation,

the user may then non-dimensionalize the distance(s) downstream to the

forecast point(s) using the relation.

* = Xi
Xi X
c

(29)

where Xi is the downstream distance to the ith forecast point, i

1,2,3,...

,;;

routing

To find the peak flow at Xi' the
curves and finds the ordinate

user consults the proper
*
of the specific V curve at

family of
*
Xi .

produces the peak flow (Qp)

Multiplying the value of this ordinate by Qb
max

at Xi miles downstream of the dam.

The time of travel for the floodwave to Xi is computed by first

calculating the reference flow velocity at the midpoint between the dam and

Xi' The user must determine, from the routing curve, the peak flow (Qx/2)

1-19