FLOOD10502 ‎(2)‎

• County: Statewide
• Basin: Statewide
• Title: State of Colorado - 2007 Flood Documentation Reports
• Date: 8/1/2007
• Prepared For: CWCB
• Prepared By: ICON Engineering
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Site Visits and Survey Information

^ lield visit was conducted for this event which included talking directly to citizens and
public oflicials regarding the characteristics of this stonn and the resulting llooding. The
personnel and dates of the site visits arc listed below in Table 2.1.

Table 2.1 - Field visit dates and personnel.

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natc of Site Visit
June 19.2007

Entit\' ({enresented
ICON Engineerinl'

Personnel
Justen Ilamann

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No field surveying was perfonned for this event.

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lIydrolo~ie ulld lIydruulie IIIYesti~utiolls

Ilydrologie analyses were perfonned using available baseline data from NO^^ Atlas 2
in order to generate Intensity Duration Frequency, or IDF. curves for rainfall events
within the Ilolyoke and eastern Phillips County area. Using the varying amounts or
rainfall mentioned in the Storm Characteristics section or this chapter, and the duration of
the storm. one could estimate the frequency of the specilic events.

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According to the data collected by the CoCoRallS network. the storm on Monday June
11th fell anywhere in the range of an event which was less than the 2.year frequency to an
event greater than the IOO-year storm depending on which point rainfall was analyzed.
The precipitation amounts reported by 7-News also seem to concur with the CoCoRaHS
data indicating the event exceeded the IOO-year stornl in areas of eastern Phillips County
The measured raint:111 for the next day, June 1th, indicates that the Tuesday stornl also
fell in the less than 2-year frequency in the western to central portions of the county but
the eastern portion of the county, particularly along the Nebraska state line, exrerienced
rainfall amounts which exceeded the IOO-year event. On Wednesday June 131 . the area
experienced yet another day of rain however, this day's storm was estimated to be less
than the 2-year event throughout the county.

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Estimated Flood Ilamu~es & AllY S"ecial Factors Affeetill~ Ihe Flood

As stated before, several state highways and various county roads in Phillips County had
to be closed due to standing water. 7-News reported that watcr lip to 5-fcet deep in
places forced the closure of Colorado Ilighway 23 between Ilolyoke and Amherst and
U.S. Highway 6 between Holyoke ,!nd the Nebraska slate line. Additionally, a private
railroad crossing near Amherst along County Road 51 was washed out as the existing
culverts at that location were overwhelmed. At least one home in the region sustained
llooding damage as the owner reported as much as 16-inches of standing water in her
unfinished basemcnt.

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ICON Englr"eerlng, Inc

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June 2007