BOARD02105

• Board Meeting Date: 5/23/2005
• Description: ISF Section - MOA Between the Eagle River Water & Sanitation District and the Colorado Department of Natural Resources
• Board Meetings - Doc Type: Memo

Proposal to Enlarge Black Lake No, 1

March 2005
Page 2

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dated March 1990, that revised and improved the operating procedures for Black Lakes
for a ten-year period, Under the revised operating plan, all 300 acre-feet of available
storage was to be used to augment streamflows in Gore Creek during the winter months
of December through March, This operating plan was implemented in 1993 upon
completion of the fIrst enlargement and has now expired,

RESERVOIR ENLARGEMENT PROPOSAL

The District is proposing a second enlargement of Black Lake No, I that would involve
raising the reservoir surface elevation by approximately 4 feet, increasing the capacity of
the spillway, and utilizing about 18 acre-feet of storage below the currently established
minimum pool. These changes would increase the total active storage capacity of Black
Lakes Nos, 1 and 2 from the current 300 acre-feetto 425 acre-feet. The proposed project
would involve the following actions:

[J The dam spillway would be enlarged from a 20-foot bottom width to a 40-foot
bottom width;

[J A 4-foot high weir would be installed in the widened section of the spillway to
raise the surface elevation of the reservoir to 10,494.5 feet;

[J The danl crest would be raised by about 2 feet to an elevation of 10,502,5 feet,
using material removed from the spillway enlargement;

[J The wheel house for control of the outlet valve, the handicap accessible fIshing
pier and path, piezometers and other appurtenances would be modifIed as
necessary to accommodate the increases in water surface and dam crest
elevations; and

[J A new operating plan for the reservoir would be implemented to make storage
water available to the District for other uses in addition to augmentation of
instream flows in Gore Creek during the fall and winter,

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Table 1 summarizes the changes in the physical characteristics of the dam, reservoir and
spillway associated with the structural modifIcations listed above, Figure I provides a
preliminary site plan showing the proposed spillway enlargement area and the post-
project change in the reservoir surface area.

Table 1: Proposed Changes in Black Lake No.1 Dam and Reservoir Characteristics.

, Parameter Existine: reservoir Cban.e Proposed reservoir
Maximum reservoir water surface area 25.7 acres +1.7 acres 27.4 acres
Maximum dam spillway elevation 10,490.5 feet +4 feet 10,494.5 feet
Embankment crest elevation 10,500,5 +2 feet 10,502,5 feet
Maximum outlet discharge 22,3 cfs +2,7 ef, 25,0 ef,
Maximum storaee canacitv 362 AF +107 AF 469 AF
Minimum storage capacity 135 AF -18AF 117 AF
Active capacity 227 AF +125 AF 352 AF

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