FLOOD05940

• Designation Number: 325
• County: Teller
• Community: Cripple Creek
• Stream Name: Pony Gulch, Poverty Gulch
• Basin: Arkansas
• Title: Drainage Master Plan - Cripple Creek, Final Report
• Date: 4/1/1992
• Designation Date: 7/1/1992
• Floodplain - Doc Type: Floodplain Report/Masterplan

overland flow. The velocity of overland flow can vary with surface cover and
tillage characteristics. If the slope and land use of the overland flow reach
are knO\l,11,travel time can be calculated using the followingequatio n:

T, '" 1.12 (1.1 - CIO) LM S~_lJ

Whcre:

ClO '" adjusted runoff coefficient for 10-
year flow;

L '" lengthofover1and flow in feet;

S" slope of flow path lfi
percent;

T '" travel time in minutes or
,
time of concentration

Traveltime through a storm ~cwcr, road gutter systcm or open channel is the
Slim of travel times in each individual eompOnelll of the drainage system. In
most cases. average velocities can be used without a significant loss of
accuracy. Times of concentration, calculated for fully developed land use,
should not be less than 5 minutes to avoid oversizing of inlets, storm ~ewers
and opcn channels to unrealistic level~.

Given a time of concentration, determination ufthe average int ensityofthe
precipitation for the period is made from a graph constructed for
depth/duration VCfSUS time. A graph for the Cripple Creek area is shown a~
Figure 2 in Appendix A, 'Time . Intensity - Frequency Curves.'

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5.

Peak Runoff Rates

It is realized that the Rational Method of predicting pcakstorm wate rrunoff
rates may not be as precise a.~ other analytical methods. However, it is felt
that mis method does result in reasonable estimates of peak runoff rate~.
Considering me assumptions which must be made with regard to land use,
proposed development patterns and soil types. the use of more sophistieated
analytical techniques probably do not materially improve the precision of the
peak storm water runoff quantities which have been developed.

Major drainage in the City of Cripple Creek oceurs through numerous n atural
drainage channels and manmadestructures. In utilizing the Rational Method
for determining storm water runoff quantities, the City of Cripple Creek was
divided into 19 drainage basin~ and 99 subhasins. De,ign points were
established at specific points of interest to detennine accumulated peak flow
for the hydraulic analysis of existing structures and preliminary design of
propo>ed stroctures. E>;hihit 1, 'Drainage Map", outlines the suhba,ins and
indicates design point locations. Peak flow data at each design point for each
storm event (IO-year, lOO-year) is presented in Appendix B, Table 3,
"Hydrology: Pony Gulch. Future Development," and Table 4, "Hydrology;
Cripple Creek - Future Development:

A schematic flow diagram of the Pony Gldch and Cripple Creek watersheds
depicting basins. subbasins, design points, and existing structures is shown as
Fi/(ure 3 in Appendix A, "Subbasin Schematic.' Basic information relating to
cach subhasin, including drainage area, runoff coefficients. and time of
concentration, isprovi(]ed in Tables 3 and 4 of Appcndix B.

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