FLOOD06672

• County: Logan
• Community: Crook
• Stream Name: South Platte River
• Basin: South Platte
• Title: South Platte River at Crook
• Date: 10/1/1993
• Prepared For: Crook
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

attenuation, can be evaluated frOI~ rate c,f rise and s1:age data.

2.3.3 Rate of Rise at Warning sites
Rates of ris,e were cc)mputr~d using a HEC-l model of the
South Platte Rive:t'. Those rate.s of rise were applied to the
hydraulic ratings computed for both gage sites. The initial
alarm stages for each qagl~ were established based upon site
hydraulics and local conditions. The proposed initial settings
are listed in Table 2.

TABU: 2.
INITIAL ~'LOOD ALARM S'1'AGES
Stages in I'eet of Elevati.on above Mean Sea Level
Discharges in CUbic Feet P,ar Second

WARNING GAGE

Highway 6
(Sterling gage)

Uppl~r
* Middle
LoWlar

STAGE
(msl)

:3928.8

DISCHARGE
(cfs)

18000

WARNING l:.EVEL

3926.3

3000

*

The middle float stage is flexible,
set so ciS not to interfere with the
floats.

but it must be
upper or lower

The rates of rise between the lo'wer and upper warning
levels, which are characteristic of the rising limbs of floods
of 10, 50, 100 and 500 year intenl;ity, are listed in Table 3.

TABLll 3.
RISE TIMES :eN HOURS BETWE~;N LOWER AND UPPER FLOATS
DURING MODllI.ED FLOOD

WARNING.GAGE

Highway 6
(Sterling gage)

10-YEAR

50-YEAR

100-YEAR

SOO-YEAR

3.8

O.I~

0.6

0.4

The gage at Crook is located too far downstream 'to be used
in any calculations regarding t:he arrival of the flood wave.
By the time water levels Ibegin 'to riSE. sufficiently at this
site, it will be too late to del anything about it. Only the
flood warning gage at the upstream site in Sterling can be used
to provide the necessary amount o:f lead warning time.

2.4 Hydrology and. Hydraulics Dis'~ussion
A complete discussion of the hydrology and hydraulics work
that was performed. for this proje,~t is contained in Appendix A.

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