FLOOD02026

• County: Fremont
• Community: Florence, Canon City
• Stream Name: Arkansas River
• Title: Floodplain Information Report
• Date: 6/1/1982
• Prepared For: Fremont County
• Prepared By: CWCB
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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HYDROLOGIC AND HYDRAULIC DETERMINATIONS

Flood Characteristics

Floods in the study area are usually caused by general rainstorms and
cloudburst storms during the period May through September. Floods re-
sulting frorn prolonged heavy rainfall over the watershed are characterized
by moderate peak floVl of moderate volume and duration, The cloudburst type
is a high-intensity, short duration rainstorm which produces a flood of
high pNk flOVl, short duration and small volume of runoff.
Flood potenthl also exists from rapid melting of heavy snow cover in late
spring and sumner. Flood flows resulting from sno\<tllelt are characterized
by moderate peaks, 1arge volume and long duration. Arkansas River peak flow
from snD\<I11elt occurs in June and July. This p~ak flow in combination with
rainfall can cause severe flooding.

Hydrologic AnalYSis
Hydrologic analyses >lE're carried
frequency relationShips for floods
the Arkansas River and to compare
Engineers report (Reference 11,
herein.

out to establish the peak dischargeM
of the selected recurrence intervals for
resu1tsbetween the U,S, Army Corps of
for the flooding sour<:es under study

A regional relationship of basin area to peak discharge was used for the
Arkansas River. Gaging stations locat('d within the ~pper Arkansas basin
wer(,lIS('dtoestablishthisregional relationship. Thefrlethod developed by
the U.S. l<Iater Resources Cou~cil (Reference 6) was used to detenl'line the
floodflow~frequency rel ationship based on a Log-Pearson Type I II di strj.
bution for eaCh sel ected gaging station. The ann~al peak di scharges were
obtained from U.S. Geological Survey l<Iater-SupplyPaper Nos. 1681, 1921,
and 2121 (References 2,3, and 4, respectivelyl and from l<Iater Reso~r<:es
Gata tor Colorado (Reference5l. Regional relationships of basin area to
peak discharge were determined for the 10-, 50-, 100-, and50D-yearfloods.
These discharges >lE're then compared to the discharges obtained by the Corp
of Engineers' 1n their study at Florence, Colorado (Reference I). The
Corps of Engineers computed frequency-discharge curves from gage station
analyses of the USGS gages on the Arkansas River at P~eblo and Cano~ City.
An area proportion was then appl ied betwee~ the Pueblo and Canon City
station results to obtain the peak floVls in the town of Florence and in
FremontCOllnty. The diSCharges obtained in CDM'sregional analysis fell
within the 90% confidence limits of the Corps of Engineers' Canon City gage
station analysis discharges in Reference 1 and therefore the hydrologic
anlaysisas presented by the Corps of Engineers in the FlorenceFl oodplain
Information Report was adopted for use in estimating the flood boundaries
for the Arkansas River.

The peak diSCharges for the Arkansds River at Canon City and Florence are
presented tn Tahle 3 and Figure 4.

19