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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water supply to a nearby City and the City wishes to estimate the 10-year
average flow and 10-year low flow, Examination of those records with
concurrent data indicates that the streamflow in Stream #1 is always equal
to 20 times the measured rainfall; similarily, the streamflow in Stream #2
is always equal to 5 times the measured rainfall, or 25 percent of the
streamflow in Stream #2.

Using these relationships, the missing years of data for Stream #2 can be
determined as follows:

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0 For year #1, streamflow #2 = 0.25 x streamflow #1 0.25 x 200 =
50 ac-ft
0 For year #2, streamflow #2 0.25 x streamflow #1 = 0.25 x 300 =
75 ac-ft
0 For year #8, streamflow #2 = 5 x precipitation = 5 x 20
100 ac- ft
0 For year #9, streamflow #2 = 5 x precipitation = 5 x 5
25 ac- ft

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In this way, the historic streamflow record can be extended over a longer
period to provide important information. In this example, for instance,
the procedure used above showed that the streamflow in year #9 for stream
#2 was only 25 ac-ft. If only the data available from the direct
measurements at stream #2 had been considered the actual flow during year
#9 would remain unknown and the minimum flow would appear to be 75 ac-ft.
Use of this procedure is referred to as "augmentation" of a historic
record.

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It is also possible to use statistical and stochastic techniques to
generate a much longer (many hundreds or thousands of years) period of
record than is historically available. These techniques rely on examining
the serial (i.e., year-to-year or month-to-month) relationships evident in
an existing historic record in conjunction with annual (and/or monthly)
average and extreme values. This procedure is called "generation of
synthetic streamflow". Both augmentation and synthetic generation

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