BOARD02509

• Board Meeting Date: 7/9/1992
• Description: Agenda or Table of Contents, Minutes, Memos. Partial.
• Board Meetings - Doc Type: Meeting

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A Blaney-criddle analysis was performed to estimate the amount
of water that would need to be carved-out to provide for irrigation
of these lands (Tables 2 and 3). The consumptive use requirement
for pasture grass or turf in the Piedra area is 15.33 inches or
1.28 acre-feet of water per acre per year. This assumes no carry-
over moisture at the beginning and the end of the growing season
and effective precipitation of 6.80 inches (80 percent chance of
exceedence). Therefore, the dry year water requirement for the
2,940 acres of additional lands would be 3,758 acre-feet of
consumption per year. Table 4 displays the amounts and
distribution of the consumptive use during the irrigation season,
the maximum consumptive use occurs during July and amounts to 16.5
cfs.

The next step in the analysis was to incorporate the carve-out
into the USFS recommended flow levels. Piedra River hydrologic
data were obtained from the USGS gage located near the present
Highway 160 bridge. This gage was operated from 1938 through 1973.
The flow recorded at this gage reflects the natural flow minus all
upstream consumptive uses from present diversions (Figure 1). The
USFS flow recommendations are presented in Aooendix A.

Based on historic gage records, it appears that the carve-out
would reduce the USFS recommended flow amounts under two scenarios.
When the flow in the piedra River was greater than or equal to
1,615 cfs, the USFS has requested the entire flow of the river for
wilderness purposes. Under the carve-out proposal, the USFS
recommendation would be reduced by the amounts set forth in Table
. 4. The max reduction would be 16.5 cfs in July (Figures 2-4).

The other occasion when the carve-out would reduce the USFS
flows would be times when the natural flow of the Piedra is not
sufficient to meet both the USFS recommendation and the carve-out
requirement. This occurs when the natural flow approaches the USFS
QLl and QL2 flow amounts.

The proposed Piedra Wilderness Area instream flow would be a
new junior water right and would have no effect on the existing
di version practices in the Piedra Valley. Therefore, present
irrigation requirements are protected by the priority system. The
proposed wilderness instream flow would, however, affect subsequent
water rights as does the Board's existing 70 cfs, summer, and 40
cfs, winter, instream flow right (appropriation date March 16,
1978). The proposed carve-out amount would provide protection for
future water users as against the USFS right. The Board I s existing
instream flow right would not be affected by the carve-out and
would be senior to future uses.

Summary
The staff has made the following conclusions:

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There are 2,940 acres of private land that could be irrigated
in the future;

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