PROJ00441

• Contract/PO #: C153459
• Contractor Name: Loveland, City of
• Water District: 0
• County: Larimer
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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4.3.2 Augmentation Results

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The correlation coefficient is a measure of the consistency of the
relationship between two sets of data. A correlation coefficient of :1.0
indicates a constant, "ideal" relationship. (In hydrology studies, this
occurs only in examples such as that presented earlier.) A previous study
for the City of Fort Collins, Colorado revealed that the annual native
flows of the Cache La Poudre River were highly correlated with those of the
Big Thompson River, with a correlation coefficient of 0.925 (RCI 1985).
Monthly native flow values for the Cache La Poudre were provided to CDM by
the City of Fort Collins for the period from 1936 to 1983 and were used in
this analysis to estimate streamflow values in the Big Thompson River as
part of the augmentation process.

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Correlation analyses of native flows in both rivers revealed that the
monthly correlation ranged from a low of 0.26 in March to a high of 0.94 in
July. The annual correlation coefficient weighted by the average monthly
native flows of the Big Thompson was 0.82; this value indicates a good
statistical agreement between the two sets of streamflow data.

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Precipitation data were available from 1907 to 1984. However, evaluation
of the augmentation analysis indicated that use of the precipitation data
would not satisfactorily preserve the serial correlation of monthly flows.
The serial correlation indicates the tendency for a "dry" June to be
followed by a "dry" July, etc. Consequently, precipitation data for the
three weather stations were used primarily to augment the record during the
period from 1927 to 1984 for months in which gauge data were missing or in
which Cache La Poudre native flows were unavailable. Correlation between
monthly precipitation at the various stations and monthly streamflow was
rather low; the maximum monthly correlation coefficient was 0.21.

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Table 4-2 summarizes the monthly statistics of the historic and augmented
flow records. The standard deviation represents the dispersion of the data
around the mean values. The larger the standard deviation, the more

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