WSP08419

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 3/1/1993
• Author: Hydrosphere
• Title: Yampa River Basin - Alternatives Feasibility Study - Final Report
• Water Supply Pro - Doc Type: Report/Study

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Executive Summary

summer months. This corresponded to minimum storage of 35,000 af during June, July and
August. A recreation pool of 16,400 af was defined at Stagecoach to be consistent with
historical operating criteria,

Although there is not a minimum release requirement below the existing Elkhead Dam, a
minimum release of 10 cfs or inflow was defined in this Study for the enlarged reservoir. An
existing release requirement below Stagecoach of the minimum of 40 cfs or the reservoir
inflow was also represented. This Study defined the Juniper Project contemplated draft
(adjusted to consider the drafts of existing reservoirs) as an instream flow right at Juniper
Canyon.

Water Supply

Several model revisions and sensitivity tests were made which were designed to test the
effects of various reservoir operating criteria imposed on the recommended enlargements. The
final results of the revised model runs are presented in Tables S-6 through S-8. Table S-5
shows the shortages to demands under the 2015 and2040 demand conditions with only the
development of the 46,500 af Elkhead Reservoir. As shown in Table S-8, with the
development of the Stagecoach Reservoir enlargement to 52,000 af, most of the 2040 demand
shortages were eliminated, Table S-6 compares the water delivery shortages in these final
model runs with those generated in Scenarios III and IV. As can be seen, the imposition of
more specific minimum release and recreation pool operations at Elkhead had relatively little
effect on modeled shortages.

Table 8-6

Comparison or Delivery Shortages Between Initial and Final Model Runs
Assuming Phased Enlargement or Reservoirs

Demand Catel!OI:Y

Scenario III

Scenario IV

Final Runs

Potential 1989
Maximum
Average

5,841 *
1,955*

n.a.

6,595*
1,368*

Projected 2015
Maximum
Average

6,413*
2,084*

n.a.

7,167*
1,532*

Projected 2040
Maximum
Average

* = With near-term project only

n.a,

6,629
247

7,153
255

Reservoir Water Levels

Figures S-4 and S-5 show modeled reservoir contents over the study period for the 2015
and 2040 demand conditions, respectively, Under 2015 demand conditions with only the
enlargement of Elkhead Reservoir, Elkhead was drawn down an average of approximately
10,000 af each year; this drawdown typically occurred in the month of February. Stagecoach

S-26