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Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4)<br />

and Stewart et al. (2005) found that stream runoff steadily advanced during the latter half of the twentieth<br />

century and now occurs 1 to 3 weeks earlier, due largely to concurrent decreases in snowpack and earlier<br />

spring melt (Mote et al. 2005). These changes diminished recharge of subsurface aquifers that support<br />

summer baseflows (Hamlet et al. 2005). Luce and Holden (2009) found that three-fourths of the 43 gauge<br />

records they examined from the Pacific Northwest exhibited statistically significant declines in summer<br />

low flows. Luce and Holden (2009) also found that the driest 25% of years are becoming drier across the<br />

majority of the Pacific Northwest sites, with most streams showing decreases exceeding 29% and some<br />

showing decreases approaching 50% between 1948 and 2006. Sites on or near the Sawtooth National<br />

Forest showed similar declines in mean annual flow (Table 3).<br />

Site Name<br />

13139510<br />

13186000<br />

13302500<br />

Big Wood River at<br />

Hailey<br />

SF Boise River NF<br />

Featherville<br />

Salmon River at<br />

Salmon<br />

Table 3. Mean annual flow from 1948-2006<br />

Average<br />

Annual Flow<br />

(mm)<br />

25 th<br />

Percentile<br />

Change<br />

170 Assessing the Vulnerability of Watersheds to Climate Change<br />

Median<br />

Change<br />

75 th Percentile<br />

Change<br />

Mean<br />

Change<br />

257 -31% -13% -6% -7%<br />

411 -43% -30% 1% -21%<br />

182 -42% -29% -11% -26%<br />

In the upper Salmon River drainage, there are numerous irrigation diversions on federal and private land<br />

within the Sawtooth NRA. There are nine subwatersheds (Champion, Elk, Fisher, Huckleberry, Iron-<br />

Goat, Park-Hanna, Pole, Slate, and Smiley Creeks) at risk from declining baseflows and water diversion<br />

(Table 4). Future decreases in summer baseflows in these subwatersheds are likely to have severe<br />

consequences for aquatic ecosystems where there are already high water demands from diversions.<br />

HUC-6 Name<br />

% Decrease in MeanSummer<br />

Baseflows from Current<br />

2040 2080 Overall Influence<br />

Water Diversions<br />

Miles of Stream<br />

Impacted<br />

Alturas Lake 24 39 None --<br />

Beaver Creek 30 42 Low 1.21<br />

Beaver-Peach 14 25 Low 3.88<br />

Big Boulder Creek 109 15 Low 0.58<br />

Big Casino Creek 10 14 Moderate 1.06<br />

Big Lake Creek 11 20 None --<br />

Bluett-Baker 10 22 Low 3.96<br />

Boundary-Cleveland 15 28 Low 5.25<br />

Cabin-Vat 22 34 Low 1.99<br />

Champion Creek 17 33 Mod/High 3.13<br />

East Basin-Kelly 24 30 None --<br />

Elk Creek 25 53 Moderate 0.30<br />

Fisher Creek 24 27 High 1.95<br />

Fishhook Creek 25 37 None --<br />

Fourth of July Creek 122 21 Low/Mod 4.52<br />

French-Spring 13 24 Low 5.16<br />

Germania Creek 13 27 None --

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