FLOOD03608

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Procedure for Hazard Determination
• Date: 8/31/1984
• Prepared By: Colorado Office of the Engineer
• Floodplain - Doc Type: Educational/Technical/Reference Information

Worksheet W-2 is designed to determine the flow depth (D) by iteration for the

given charmel configuration. Values K and D 8/3 are available for

trapezoidal charmel cross-sections in HANDBOOK OF HYDRAULICS by King and

Brader, tables 7-10 and 7-19 respectively. Once the flow depth (D) is

determined, travel time can easily be calculated in the manner shown on

Worksheet W-2.

/' .' -....--.."
~_l'qu:~ion 2 asslIII8s. ~t_ t~_ t~ical_~_~~..~ross-section is trapezoi~tJ~- ---( 7
c~_ .!ille 51 'VI Jte nlRIN" tll," innr to one (4: W For other conditions, the_/--j t ~
-~,..._.-, ". ..." "... ", ---f'

reader may use any method to calculate flow cross sectional area (Example:
Equation 3), and subsequently, the travel time.

Returning to the example of Worksheet W-2, a flow depth of ten feet resulted

for a Qp of 13,400 cfs. This requires a flow cross sectional area of 700

square feet and an average velocity of approximately 19 feet per second (i.e"

V = ~ ). However, th:.!'ve!_age flow ye1o.city would probably not be achieved,

since the floodwave would transport large boulders and other debris and more

likely be in the subcritical flow regiem.[4] A maximum average velocity of

12 feet per second was selected and travel time calculated as 0.69 hours.

The term "fRouting Steps" defines the degree of the polynomial which will be
- ----

expanded for routing the original failure hydrograph. The greater the number
- "-

of routing steps, the more reduced the peak of the original hydrograph will be.
,

-~,-----<--........_'"-_.~..

.' _.,~~~- .,."~....----~._-,,~. -"'-"-'--~'~ '-'<

fRouting Steps = (Travel Time) (tSlices) (2)
T

Equation 4

12