WSP07449

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 7/1/1985
• Author: Resource Consultants
• Title: Droughts and Their Effect on the Water Supplies for the City of Fort Collins Colorado
• Water Supply Pro - Doc Type: Report/Study

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EXECUTIVE SUMMARY
DROUGHTS fu1D THEIR EFFECT ON THE WATER SUPPLIES
FOR THE CITY OF FORT COLLINS, COLOPAnO

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The drought study for the City of Fort Collins involved three major
tasks:

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1.

Determination of prolonged drought characteristics for the Cache
la Poudre River.

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2.

Evaluation of drought effects on the City's water supply for both
present and future conditions.

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3. Identification and analysis of various water supply strategies

that could be adopted by the City for dealing with extreme

droughts.

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Historic data were gathered on the Poudre River and four adjacent

river basins. Using the statistics of these data, a long-term synthetic

record of river flows was generated and analyzed. The average annual flow

of the Poudre River was determined to be 289,000 ac-ft per year. Drought

periods were defined as consecu~ive years which were all below the mean

flow of the Poudre River. The characteristics of droughts for selected

return frequencies were as follows:

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Drought
frequency

Cumulative deficit of
consecutive drought
(ac-ft)

Corresponding approximate
duration of drou~ht
(yrs)

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1-in- 20
1-in- 50
1-in-100
1-in-500

370,000
520,000
630,000
890,000

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Tree-ring data were obtained from the Laboratory of Tree-Ring Research

to help verify long-term patterns and severities of historic droughts.

Statistics from the tree-ring data matched quite closely with the historic

data and the synthetically generated data.

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Four droughts corresponding to the 1-in-20, 1-in-50, I-in-IOO, and

l-in-500 frequencies were selected for computer model simulation of the

Poudre Basin supplies and the City's water supply system. A model known as

MODSIM was used to simulate several water demand and supply scenarios. One

scenario was with the City's existing supply, two scenarios were with

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RE.:c;OURCE.: CONc;UlTt>.NTc; INC