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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Table 8
Comparisons of Generated Data to Historical
Record for Annual Poudre River Virgin Flows

50,000 years of 393 years of 100 years of
stochastically data generated historical
generated data from tree rings data
(1572 to 1964) (1884 to 1983)
Long-term mean 289,000 288,000 288,000Y
Std deviation about mean 106,000 98,000 105,000
l-in-20 Droughts
Avg RL (yrs) 4.7 4.2 4.2
m 375,000 349,000 303,000
Avg RS (ac-ft)
m 112,000 114,000 109,000
Avg RI (ac-ft!yr)
m
l-in-50 Droughts 4.01J
Avg RL (yrs) 6.5 6.1
m 516,000 491,000 334,000
Avg RS (ac-ft)
m 130.000 141,000 126,000
Avg RI (ac-ft!yr)
m
l-in-100 Droughts 8.al!
Avg RL (yrs) 7.8 7.3
m 628,000 573,000 535,000
Avg RS (ac-ft)
m 142,000 158,000 138,000
Avg RI (ac-ft!yr)
m
1-1n-500 Droughts 9.0!!} NA~./
Avg RL (yrs) 10.8
m 890,000 777,000
Avg RS (ac-ft) NA
m 166,000 218,000
Avg RI (ac-ft!yr) NA
m

l! The historical mean and standard deviation are based on the 73-year
record, 1911 to 1983, as opposed to the 100-yr record.

2! The historical 100-yr record was split into two 50-yr increments
covering the years 1884-1933 and 1934-1983. This caused the 8-yr
drought of 1930-1937 to be considered as two 4-yr droughts, resulting in
a significant reduction in the average run length and run sum for the
historical l-in-50 droughts. Hence, the discrepancy between the average
run length and run sum for the historical I-in-50 data and the other two
data sets is not significant.

3! The historical record contains only one 100-yr drought.

4! The data set generated from tree rings contains only one 500-yr drought.

l! The historical record too short for estimating even one 500-yr drought.

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RESOURCE: CON<;Ull~NT<; INC