NorthPlatteBasinWaterSupplyandNeedsReport

• Basin Roundtable: North Platte
• Title: Water Supply & Needs Report for the North Platte Basin
• Date: 6/1/2006
• Author: CDM
• Basin Roundtables - Doc Type: Needs Assessment Documents

Section 8
Options for the North Platte Basin

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7,000

6.000

Average Annual Available Flow = 14,600 AF

5.000

;2
~ 4,000

"C
]1
~ 3.000

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2,000

1,000

o
o

2.000

4.000

6.000

8.000

10.000

12.000

14.000

reservoir size (AF)
1-0% minimum storage pool - - 30% minimum storage pool I

Figure 8-7
Example Storage to Yield Curve for Environmental and Recreational Options: Minimum Pool
Leroux Creek Reservoir - Gunnison River Basin: Agricultural Use

The model simulations show that to achieve a firm yield
of 4,000 AFY, for example, without minimum reservoir
capacity considerations (Alternative A), approximately
8,000 AF of storage is required. Alternatively, for the
same system but with a minimum permanent pool
requirement of 30 percent (Alternative B), approximately
12,000 AF of storage is required. The additional storage
requirement (4,000 AF) for Alternative B would allow for
the capture and storage of a greater percentage of the
legally available flows, which can then provide the
minimum pool. The acquisition of additional water rights
may be required for the implementation of Alternative B.
Costing of the two reservoir options could then be
performed and assessed relative to the recreational
benefits gained from maintaining the minimum pool.

As a second example, Figure 8-8 shows model
simulations for a hypothetical reservoir located on Little
Bear Creek in the Yampa River basin. Predicted yield
curves are again a function of legally available flows for
the location, as predicted by the Yampa River basin
CDSS. For this analysis, the two curves shown on the
figure correspond to:

CONI

8-14

Alternative A - A management alternative in which no
minimum release requirements are maintained.

Alternative B - A management alternative that follows
the approach outlined by The Nature Conservancy in the
paper "How much water does a river need?" This
approach maintains average historical monthly flows,
minus 1 standard deviation, downstream of the reservoir.

Minimum release flow values for Alternative B were
calculated using legally available flows captured by the
reservoir. Model simulations show that, for the
environmental Alternative B, significantly larger
reservoirs are needed to provide the same firm yield
when compared to the alternative without environmental
considerations (A). For example, to provide 2,000 AF per
year of firm yield, Alternative A requires approximately
2,000 AF of storage, while Alternative B requires
approximately 17,000 to 18,000 AF of storage. It is
possible for releases from the reservoir for downstream
uses can serve a dual purpose and provide for the target
environmental flows. This is a site specific issue and is
determined by the location of the diversion from the
reservoir for the water use.

S:\1177\Basin Reports\North Platte\SB_North Platte.doc