FLOOD10353

• County: Larimer
• Community: Fort Collins
• Stream Name: Big Thompson River
• Basin: South Platte
• Title: Twenty Years Later, What We Have Learned Since the Big Thompson Flood - Proceedings of a Meeting Held in Fort Collins - July 13-15, 1996
• Date: 7/13/1996
• Floodplain - Doc Type: Educational/Technical/Reference Information

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to the EWS in its effectiveness in reducing the potential for loss
the dam to store the entire flood. This alternative is
since it would cause the inundation of the town of
flood event, nor is it technically or economically

Fisher

equivalent
of life would be to raise
not politically feasible,
Estes Park during the

feasible
Another reason for selecting a warning system as the preferred corrective
action alternative is the need to warn downstream populations of high releases
from the dam. The safe channel capacity below Olympus Dam is approxi-
mately 1,000 ft3/S. At this level, the amusement park immediately down-
stream from the dam begins to be inundated. Releases of approximately 1,500
ff/s will begin to flood permanent residences in the Big Thompson Canyon.
Most of the structures in Big Thompson Canyon are inundated at flows of
5,000 ft3/s. This is less than one-fourth of the- present release capacity of
Olympus Dam spillway. Therefore, it is imperative that the downstream
population receive adequate warning of impending high releases from
Olympus Dam

Early Warning System Description

The Early Warning System (EWS) hardware and software were installed
in the fall of 1993. The EWS hardware consists of eleven sites with multiple
sensors as follows: 10 tipping bucket rain gauges, nine stream gauges, two
weather stations, two reservoir level sensors, four temperature sensors, and
a repeater site. These sites transmit data via line-of-site VHF radio to the

repeater site that splits a
area office microwave

microwave signal placed into the eastern Colorado
system. The data are received at three independent
that located at the eastern Colorado area office
Plant (VHF), and the Reclamation-Western
(WAPA) Joint Operations Center (JOe)

are
Power

EWS base stations
(microwave), the Estes
Area Power Administration
(microwave and VHF)

Reservoir Elevation Information

The Olympus Dam reservoir elevation gauge is an important source of
information when making decisions concerning evacuation of the population
at risk (PAR) located downstream from the dam. However, there will not be
adequate time to carry out a successful evacuation during a severe thunder-
storm event based on the rate of rise in the reservoir alone. Streamflow data
from the Big Thompson River gauge located just upstream from the dam will
provide accurate inflow data for flows up to the top of the flume (approxi-
mately 1,700 ff/s). This information is available both on the EWS and from