WSP03901

• File Number: 8446
• Description: Cache La Poudre Platte Project
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 11/1/1962
• Author: BOR, DoI
• Title: Reconnaissance Report, cache La Poudre Unit, Colorado Peak Division, Missouri
• Water Supply Pro - Doc Type: Report/Study

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were not made for this reconnaissance report. However, it was
assumed the necessary detailed studies wouJ.d be performed during the
feasibility investigations to indicate the required operations for
maintaining the recommended w.l,nter fish :f:l.ows in the river below
Grey Mountain.

O}leration Studies

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The reservoir operation studies for the plan of development
were prepared in three parts: (1) conservation functions; (2)
power regulation; and (3) combined power and conservation functions.

The study of conservation functions combined the a.na.lysis of
plains reservoir consolidation, municipal supplies, unappropriated
:f:l.ows, fish releases and reservoir evaporation. Release of the new
irrigation supply was patterned after the shortages found in the
basin depletion a.na.lysis (note Tables 3 and 4). The required active
capacity for these functions wouJ.d be 220,000 acre~feet.

Maximum utilization of the Id;ylwilde site capacity (maximum
possible development of site is 180,000 acre~feet) with a practical
minimum capacity at Grey Mountain Reservoir was favored because of:
(1) cheaper unit cost of storage; (2) increa.sed regulation and head
for power; and (3) lower surface losses. Power operation studies
of the unit were controlled by the desired generation to meet the
load curve at the Oache la Poudre P~Terplant. Studies indicated
76,000 acre-feet of capacity in Idylwilde shouJ.d be reserved for
boosting generation in years of low runoff while the remaining active
capacity wouJ.d be necessary to regulate power relea.ses in a normal
year.

The Grey Mountain active capacity of 200,000 acre-feet was
determined by combining of the conservation functions of the unit
as . reservoir outflow and the regulated power :f:l.ow and unregulated
:f:l.ow be10lf Rustic diversion dam as an in:f:l.ow. In this manner all
possibilities of combined use of capacity were considered.

The operation studies showed a minimum of 90,000 acre-feet
wouJ.d be needed in the system at all times for tuJ.l-scale operations.
This operational pool couJ.d well be gained initially by a transfer
of Horsetooth Reservoir water (Colorado-Big Thompson) into the
system by exchange and kept until sufficient water is developed in
the Oache la Poudre Unit to replace it.

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The operational budget for the Cache la Poudre Unit is presented
in Table 8 and the operation of the principal reservoirs is presented
in Exhibit 3. Also presented in Exhibit 3 is the unit's effect on
corrected streamflow at the "mouth of canyon" gage due to the
regula:tion of surp1.us f'lOWEr and the plains reservoir transfer.

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