watervulnerability

Sawtooth National Forest Watershed Vulnerability Assessment, Intermountain Region (R4)
Figure 18. Amount of infrastructure within the Sawtooth NRA.
Red shaded subwatersheds have high amounts of
infrastructure; yellow moderate amounts, and green low
amounts.
178 Assessing the Vulnerability of Watersheds to Climate Change
Forty-six subwatersheds were evaluated for
potential impacts to infrastructure on the
Sawtooth NRA. Of these, 19 (41%)
subwatersheds had low amounts, 22 (48%) had
moderate amounts, and 5 (11%) had high
amounts of infrastructure (Figure 18).
Subwatersheds with the most infrastructure
included Cabin-Vat, Fourth of July Creek, Nip
and Tuck Sunny, Pole Creek, and Slate Creek.
As discussed, VIC projects the risk from midwinter
peak flows triggered by rain-on-snow
events increases substantially by 2080.
Specifically, the highest 5% winter peak flows
average 0.88 days under current conditions
(1977-97), but increase to 2.6 days in 2040 and
4.44 days in 2080 in under the A1B emission
scenario. Currently there are 18 (39%)
subwatersheds at low risk, 24 (52%) at
moderate risk, and 4 (9%) from winter peak
flows (Table 7). These numbers change
substantially as risk from winter peak flows
increases into the future.
By 2080, only one (2%) subwatershed (Yellowbelly Lake Creek) continues to have a low infrastructure risk,
while 19 (41%) subwatersheds are at moderate risk and 26 (57%) are at high risk (Table 7).
Although the Sawtooth NRA has been actively upgrading and removing facilities from riparian areas for
many years, these efforts may not be enough to address projected increases in winter peak flows. There are
also substantial implications to public safety, emergency access, and impacts to aquatic ecosystems. This
new disturbance regime may be unlike anything we have faced before and will certainly challenge the
limited resources the Forest has to repair and move facilities. If these projected changes occur, this analysis
will provide a road map for further assessment of subwatershed infrastructure and incremental improvement.