PROJ00318

• Contract/PO #: C153618
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 87-15
• Loan Projects - Doc Type: Feasibility Study

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

The only gagi ng stati on on the Cache 1 a Poudre Ri ver, whi ch covers the enti re
period, is at the mouth of the canYon near Fort Collins. The gage on the
South Fork Cache 1 a Poudre Ri ver near Rustic has streamflow records from
August 1956 through September 1979. These data sets were correlated with each
other to extend the records for the gage near Rustic.

For Peterson lake Reservoir, the streamflow records for Fall Creek near Rustic
were correlated with the South Fork Cache 1a Poudre River near Rustic, to
extend the peri od of record. Si nee the drai nage areas di ffered by a 1 arge
percentage, the streamf10ws were adjUsted by the square root of the ratio of
their drainage areas--about 85 percent. The adjusted annual flows were used
as Peterson lake inflows.

Discussions with the Water Commissioner for the Cache la Poudre River provided
i nsi ght for detenni ni ng storabl e flows. Reservoi rs in the Cache 1 a Poudre
system nonnal1y fill in April and JUhe from spring runoff. The remainder of
the year, senior ditches divert the e~tire supply for irrigation and municipal
purposes. For thi s investigation, only the percentage of the annual flows
whi ch occurred in Apri 1 and June wel'e consi dered storab1 e in the reservoi r.
For Peterson lake Reservoi r, the stol'ab1 e flows were estimated as 37 percent
of the annual inflows.

Under the current restri cted operati ng conditi ons, Peterson lake Reservoi r
could fill to the restricted level every year. If the dam is repaired and its
seepage problem corrected, the reservoir will fill 88 percent of the time.

Table IV.7 shows the historic water levels in the reservoir, based on the gage
hei ght. Thi s i nfonnati on was obtai ned from the Cache 18 Poudre Ri ver Water
Commi ssi oner. Records were not avail ab1 e for every year, and in some cases
are mi sl eadi ng. Whether or not the reservoi r fi 11 ed in a gi ven year was not
always a function of the availability of water. The City's water needs were
balanced against the potential liability associated with reservoir storage
each year. Thi s detenni ned the desi red storage and the maximum water 1 evel s
for much of the peri od of record. Some of the zero storage years were a
result of construction activities for rehabilitation of the dam, spillway, and
outlet works.

~27-