watervulnerability

Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10)
Historically, wildfires have been infrequent and of low intensity in the Resurrection Creek watershed, but
predicted increased temperatures and higher evapotranspiration rates may dry fuels and increase the
number of hazardous fire days on the peninsula as a whole (Haufler et al. 2010). Earlier snowmelt dates
could also extend the period during which grasses and other dead vegetation can dry and provide
flammable material, before the spring green-up, thus extending the fire season (Ecology and Environment
Inc. 2006).
Hydrologic/Geomorphic Risks
The predicted annual increase in precipitation is relatively small at 2 to 3 inches, so unlike rainier areas of
the Chugach National Forest, flooding may not be seen as a great concern. High initial infiltration rates
also reduce the risk (Kalli and Blanchet 2001). An increased risk of floods from rain-on-snow events may
not be likely. Hamlet and Lettenmaier (2007) state that cold systems where snow processes dominate the
hydrologic cycle may be less prone to flooding. Even though winter temperatures are expected to increase
by 4 °C, mean temperatures at sea level are still predicted to be below freezing. The usual rain-on-snow
events in the fall and spring may occur, but not throughout the winter, as they would in a warmer area.
The town of Hope and the infrastructure in the Resurrection Creek valley are unlikely to be affected by
floods. Most of the town straddles a low ridge between two watersheds. The town’s buildings are set on
higher areas away from where the creek enters the ocean. The buildings, roads, and the airstrip in the
valley are also on relatively high ground. There are only 20 developed parcels within the 100-yr
floodplain (Kenai Peninsula Borough 2011). Despite frequent extreme weather in recent years, which has
caused flooding in other areas of the Kenai Peninsula, no flood damage was reported for the Hope area
(Kenai Peninsula Borough 2011).
A later freeze date and earlier spring melt would change flow timing, however. The current peak
discharge is in mid-June and would be expected to occur earlier. Reduced flows from July to September
could be partially offset by increases in precipitation ranging roughly from one-half to one inch of rain
per month. Also, given the high mean elevation of the watershed and the predicted increase in winter
precipitation, there could be an increased snowpack at the higher elevations that would last longer into the
summer.
In warmer, rainier areas, erosion and sediment transport are expected to increase because of higher
precipitation, rain on snow events, increased freeze/thaw cycles, avalanches, and exposed glacial
moraines. The Resurrection Creek watershed, however, should be less exposed to these factors because of
the low predicted increases in precipitation, low winter temperatures even with warming, and limited area
of glaciers and icefields. Thus, the risk of increased filling and shifting of channels is not expected to be
much higher than existing levels.
Biological Risks
Although the Kenai Peninsula is a relatively dry area for Alaska, low flows are not expected to be a major
concern for fish. As discussed earlier, the changes in the hydrograph may be offset by increases in
summer precipitation and an increased snowpack at high elevations. The lowest flows are in the winter,
and given the warmer temperatures, precipitation falling as rain in early winter could increase flows then.
The risk is also lessened by the fact that most fish habitat is in the low gradient channels near the valley
floor, rather than small headwater streams. These lower elevation streams drain larger areas and are less
likely to dry up.
Higher precipitation is not likely to increase the risk of salmon redds and juveniles being scoured by high
flows, given the moderate increases. This risk is probably more dependent on other factors, such as the
292 Assessing the Vulnerability of Watersheds to Climate Change