FLOOD09180

• County: Denver
• County: Adams
• Stream Name: Cherry Creek Basin
• Basin: South Platte
• Title: Paleoflood Investigations for Cherry Creek Basin
• Date: 8/1/2000
• Prepared For: Eastern Colorado
• Prepared By: USGS
• Floodplain - Doc Type: Flood Documentation Report

16
14
e 12
"
':G
"
>- 10
~
~
.a
.e. 8
e
c 6
0
.,
..
>
..
Ui 4

NI~surface &
scoured colluvium

/ange of 1933 flood & Max PSI 2 1ft boulders
850-1,250 m3/s II

------*---------------- ------

NI-surface &
scoured cQlluvium

------t-~~~~:~------- -
5_0.032 m/m

Figure 2, Channel cross section for Cherry Creek near Franktown streamflow-gaging station
(0671200), which is located about 4 km south of Franktown, The highest paleostage indicator is
constrained by uneroded, old colluvium (non-inundation, NI, surface) and a flood-deposited boulder
bar (-215 x 100 x >3 m) deposited by the 1933 dam-failure flood.

This factor likely would be larger if paleoflood data were available for other eastern Colorado
streams, For example, Jarrett and Tomlinson (in press) noted the addition of paleoflood data
increased the contemporary envelope curve of flooding by about 20 to 25 percent for northwestern
Colorado streams,

Local extreme rainfall (fig, 1) and flood data defining this eastern Colorado envelope curve appear
to be associated with areas of high topographic relief (Jarrett, 1990), PMF values for selected streams
in eastern Colorado, including Chcrry Creek basin (Bullard, 1986; U,S, Army Corps of Enginecrs,
written commun., 1997) with an enveloping curve are shown on figure 4, Generally, PMF values
exceed the envelope curve of maximum contemporary floods in eastern Colorado by a factor of
about 2,6, PMF values exceed the envelope curve for Cherry Creek by a faclor of about six to eight
for Cherry Creek basin, which suggests different flood-producing mechanisms,

Flood-Frequellcy Atudysis

Flood-frequency relations for Chcrry Creek developed using the recorded annual peak-flow data
near Franklown (06712000) and near Melvin (06712500) are shown in figures 5 and 6. A second
run incorporaled paleoflood data in the frequency analyses; rectangles (figs, 5 and 6) bracket the
estimated ranges of uncertainty of discharge and relative age (P) of a paleoflood, Although
extrapolations of flood-frequency relations have uncertainties, they can be used to estimate the
probability of eXlremely large floods when paleoflood data are available (Baker, 1987; Jarrett and
Costa, 1988; Ostenaa and Levish, 1995),

5