ISFAPPC00132

• Case Number: 80CW0092
• Stream Name: Slate River
• Watershed: East River
• Water Division: 4
• Water District: 59
• County: Gunnison
• Instream Flow App - Doc Type: Supplemental Data

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mean flow in 1971-80 to the mean flow in 1941-50 was determined.
'l'hese ratios were then applied to the Slate River data to estimate
the 1971-80 flows (Table 2). The CWCB filings exceed the mean
flows in November, January, and February. If the additional
impact of 42.55 cfs conditional rights (excluding those on
Washington Gulch) is considered, with perhaps 15% consumptive use,
the whole period from September to March could be below the
instream flow.

TABLE 2
SLATE RIVER RATIO ESTIMATED FLOWS MEAN AMOUNT
MONTH 1941-50 (CFS) 1971-80 TO 1941-50 1971-80 ABOVE CWCB FILINC
0 26.9 .940 25.3 2.3
N 21.0 .915 19.2 -3.8
D 14.3 .953 13.6 1.6
J 10.6 .957 10.1 -1.9
F 9.5 .944 9.0 -2.0
M 12.7 1.115 14.2 2.2
A 122 .789 96.3 73.3
M 536 .817 438 415
J 621 1.027 638 615
J 204 1.180 241 217
A 47.2 1. 009 55.7 32.7
S 22.3 1.039 23.2 0.2

Alternatively, consider the effects on the Slate River flows
if all irrigation rights since 1942 were developed fully and if
all non-irrigation rights (conditional and absolute since 1942)
are developed at different levels of consumptive use. Rights on
Washington Gulch are excluded since the gage was located upstream
of Washington Gulch, but Slate river rights downstream from the
gage are included. The resulting figures show the maximum effect
at the mouth of the Slate, assuming no tributary inflow below Coal
Creek. '

~ne irrigation rights since 1942 total 73.70 cfs. If return
flow is estimated at 35%, then the maximum depletion would be 47.9
cfs. Assume that depletions are proportional to consumptive use
for pasture grass in Gunnison, and that there is sufficient water
to cover the maximum depletion (Table 3).

TABLE 3
CONS. USE % OF
MONTH IN INCHES MAX DEPLETION (CFS)
A .29 .09 4.3
M 1. 74 .52 24.9
MEMORANDUM -2- April 22, 1985