BOARD02052

• Board Meeting Date: 8/15/1995
• Description: Notice of Board Meeting
• Board Meetings - Doc Type: Meeting

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STATE OF COLORI\DO

OFFICE OF THE STATE ENGINEER
');\I;5;on of \-Vater Resources
Jepartment of Natural Resources
1313 Sherman Screet. Room 818
Denver. Colorado 80203
~~"",eIJ03)866-3S81
FA.~ 13031866-3589

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June 30, 1994

Water Supply and Storage
Post Office box 1584
Ft. Collins,. Colorado 80522

Gentlemen:

Roy Romer
Governor

James S. Lod'lr.ead
Executive OirectlJr

HalO. Simp5<)n
State Engineer

The purpose of this letter is to address the dam safety issues associated with small
releases of water (e,g" about 2-1/2 cfs) throughout the winter at Long Draw Dam, The flow
will vary with reservoir head, and since the gate setting will probably not be able to be
adjusted over the winter period due to the inaccessibility of the structure, some estimates will
be necessary to obtain the flows required, In fact, the remoteness of the structure and the
inaccessibility to it during the winter causes concern for the overall safety of the dam under
this mode of operation,

The primary concern is that the small releases are subject to freezing either in the
conduit or at the downstream end of the conduit. The extent of freezing depends on
reservoir levels and temperatures. We feel that the flow of water form the reservoir during
the winter would create a flow of cold air through the shaft below the gatehouse which will
increase the potential of freezing in the outlet conduit. Blockage from snow and ice are .
greatly influenced by snow drift conditions on the ciani. The ice in conduits can cause
damage over the long term and can potentially cause critical problems in one season. The
conduits are not subject to this risk under your current operation. Besides jeopardizing the
release structure, winter operations jeopardize the safety of the dam by potentially making
the outlet unusable.

A second concern is the potential damage to the trash rack from ice action at times
when the reservoir is at low levels at the beginning of the winter period. Damage to the
trash rack can lead to damage or malfunction of the outlet works.

A third concern is that small releases have been found to be damaging to the outlet
gates, even under normal conditions. Past operations have been limited to greater than 20
cfs because of this limitation. Small releases can lead to undesirable gate wear and ca,vitation
of the conduit.