FLOOD04744

• County: Weld
• Community: Weld County
• Stream Name: First Creek
• Basin: South Platte
• Title: Lost Creek Flood, February 10, 1980
• Date: 5/1/1981
• Prepared By: CWCB
• Floodplain - Doc Type: Flood Documentation Report

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FIG. 6

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The flood began to enter Lord Reservoir at about 1:25 p.m. on
Sunday. and the water level was reported to have risen initially
at a rate of about 10.5 inches per hour. Water began to flow
through the central service spillway at about 2:15 p.m.. and
through the emergency spillway at 3:45 p.m. The outlet works were
opened to increase discharge capacity.

At approximately 10:15 Sunday night. the rate of release from
Lord Reservoir equalled the rate of inflow. and the water level
slowly began to drop. The combined peak discharge from the three
release points was 1.200 cubic feet per second. based on a series
of water level measurements taken at the service spillway. The
water stopped flowing over the emergency spillway at about 10:00
a.m. on Tuesday. February 12. 1980. The volume of water that
passed through Lord Reservoir is estimated to be approximately
2.230 acre-feet.

Flood hydrographs were developed from observations and
available information for the stream reaches immediately
downstream of both Lord and Prospect Valley Reservoirs. These
hydrographs are shown in Figure 4. The peak discharge from the
Prospect Valley Reservoir breach is estimated to be approximately
4,100 cfs. which occurred at about 12:00 p.m. Sunday. The flood
hydrograph below Lord Reservoir had an estimated peak discharge of
approximately 1,200 cfs. occurring at about 10:15 p.m. Sunday.

The flood continued below Lord Reservoir and generally
followed the Lost Creek channel north, toward 1-76. The peak
discharge had been attenuated by Lord Reservoir. The rate of tra-
vel in the 7-mile reach below Lord Reservoir averaged about 0.3
miles per hour ( 0.4 feet per second. see Figure 5). The width of
the flooded area in this reach ranged from a maximum of about 3.100
feet. at Weld County Road 16, to as narrow as 30 feet in the chan-
nel above Weld County Road 20.

As the flood approached 1-76. the water spread out and flowed
in an irregular pattern over primarily uncultivated land. The