PROJ00147

• Contract/PO #: C153637
• Contractor Name: North Poudre Irrigation Company
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 92-87
• Loan Projects - Doc Type: Feasibility Study

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The maximum flJl level for Reservoir No. 6 during the years 1940 to 1990 is Gage
Height 34.0 feet. The reservoir has been filled to Gage Height 29 feet or above
in 16 of the 42 years of record studied; to Gage Height 25 feet or above 23 of
the 42 years; to Gage height 20 feet or above 31 of the 42 years; and, to Gage
height 15 or above in 36 of the 42 years of record. The lowest flJl level of
record for Reservoir No. 6 is 7.0 feet in 1955 disregarding the zero storage levels
since the storage restriction in 1984. The average storage level for the dry
years of 1954 through 1956 is 11.3 feet for an average capacity of 1221 acre-
feet.

The safe yield of the reservoirs could be considered to be the storage for the
years 1955 through 1956 of 1,221 acre-feet which is the minimum storage of
record from 1940 to 1991. However, things have changed since that time which
wouid alter the future minimum storage under a drought similar to that from
1953 to 1956. The North Poudre Irrigation Company now has shares of CBT
(Colorado-Big Thompson) water that can be introduced into the system and wouid
alter the results of a drought as seen in the 1950's. It is not certain what the
safe yield would now be with the present makeup of the system and could not be
determined without analyzing the whole Cache La Poudre system. If the water
storage record is studied for the years from 1960 on and disregarding the years
1977 and 1978 the results would indicate a minimum storage for No. 5 at Gage
Height 20 feet for a capacity of 4364 acre-feet. For Reservoir No.6, from 1960
to 1980 when restrictions started lowering the level, the normal fill level was in
excess of Gage Height 25 feet most years for a capacity of 4936 acre-feet.
These values could be indicative of the firm yield for both reservoirs for a total
of 9300 acre-feet.

The records may be misleading as to the safe yield of both reservoirs due to
external forces on the system. The land irrigated under Reservoir No. 5 and 6
is only 640 acres. Based on this low demand, it is possible the reservoirs have
not been filled to capacity because the need has not been there. This is
somewhat indicated by a review of the minimum storage levels on Figures IV-l
and IV-2. These plots Indicate that during most years the reservoirs have not
been emptied but usually are at a water level only 5 to 10 feet lower than the
maximum level for any particular year. Their was no need for North Poudre to
try to maintain maximum storage in No. 5 and No. 6 and short other reservoirs of
needed storage in dry years. As outlined above, the North Poudre system Is
treated as one reservoir by the Water Commissioner and in dry years it would be
expected that higher reservoirs would be filied rather than No. 5 and 6 where
the water could more effectively be managed. Even with this in effect, Reservoir
No. 5 was filled to a capacity of 2555 acre-feet or above 80% of the years and
Reservoir No.6 was filled to 3189 acre-feet 74% of the years on record.

Based on the water records as indicated above and the changes In the water
situation in Northern Colorado over the past 50 years, it is estimated the firm
yield for both Reservoir No. 5 and 6 would be in excess of 6,000 acre-feet.

D. Water Quality. The water quality of Reservoir No. 6 is not expected to be a
problem. Due to the expected turnover of the reservoir each year a build up of
salts and other minerals is not expected. The water supplying Reservoir No. 6 Is
runoff from the mountains and from the plains and should be of good quality.

PAGB 6
Chapter IV - No. 6 Feulbillty