FLOOD00265

• County: Weld
• Community: Evans
• Title: FIS - Evans
• Date: 10/1/1978
• Prepared For: Evans
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Date

Discharges
(Cubic Feet per Second)

J'>.pproxirnate
Frequency (Years)

June 7, 1921
September 4, 1938
April 25, 1942
June 15, 1949
. June 18, 1965
'lay 8, 1969
May 8, 1973

31,000
18,500
19,200
17,800
23,500
21,800
31,500

100
30
30
25
50
50
100

Photographs of the 1969 flood in Evans are shown in Figures 2
through 6 (Reference 6).

2.4 Flood Protection Heasures

Two significant flood protection m~asures have been taken in the City
of Evans. One was to replace the destroyed 37th Street bridge after
the 1969 flood with a much higher, arch-type bridge. The old 37th
Street bridge was unable to pass the 1969 flood, causing its destruc-
tion and considerable backwater flooding into the eastern section of
Evans. ~he new bridge was able to pass most of the 1973 flood without
causing much backwater flooding in Evans, even though the discharge
was higher in 1973 than in 1969. The other significant flood pro-
tection measure was the construction of a levee along the north bank
of the South Platte River from u.s. Highway 85 to 37th Street. A
larger area of Evans would have been flooded in 1973 if it was not
for this levee. The levee will contain a lOa-year flood.

3.0 ENGINEERING METHODS

For flooding sources studied in detail in the cOInPlunity, standard hydro-
logic and hydraulic study methods were used to determine the flood
hazard data required for this study. Floods having recurrence intervals
of 10, SO, 100, and 500 years llave been selected as having special sig-
nificance for flood plain management and for flood insurance premium
rates. The analyses reported here reflect current conditions in the
watersheds of the flooding sources.

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak discharge-
frequency relationships for floods of the selected rccurrrence
intervals for each stream studied in detail in the community.

The U.S. Army Corps of Engineers, Omaha District, provided the flood
discharges for the 10-, 50-, 100-, and SOO-year discharges for the
South Platte ~iver through Evans (Reference 5).

4