watervulnerability

Chugach National Forest Watershed Vulnerability Assessment, Alaska Region (R10)
Bakke (2008) advises, “Passive restoration techniques, such as establishment of wider riparian buffers,
may be a more sustainable alternative in light of increased geomorphic instability caused by global
warming.” This may well be the case in the Power Creek delta, where sediment from landslides and
exposed glacial moraines will be deposited and where channels can be expected to fill and shift
frequently.
Thus, it may be best, and less costly, not to alter naturally functioning channels. Maintaining the current
floodplain connectivity may do the most to protect fish habitat from floods and scouring of redds.
Keeping the upland vegetation and slide-prone slopes undisturbed should be the key methods for
minimizing runoff, landslides, and transport of material to the streams.
If development projects are proposed, managers would obviously need to be aware of the increased
potential for avalanches, landslides, and flooding in project areas. There will also be a need for more
appropriate road construction standards, such as more frequent cross drainage, larger culvert size, and
more consideration of slope stability.
Cooperative Efforts
Flooding
The most likely adverse effect of climate change will be the increased frequency of floods, which will
affect residences, small businesses, and other development along Eyak River, as well as areas around the
lake. Flood mitigation measures will require cooperative efforts among government agencies, private
landowners, and Native corporations. Assuming that the uplands will be managed properly, the question
becomes what other actions can be taken to prevent flooding or to mitigate the effects.
One project that has been proposed over the past 25 years is to build a dike separating Eyak River and the
glacial Scott River. As mentioned above, the Scott River can deposit sediment in lower Eyak River,
reducing the Eyak channel’s drainage capacity. The project has never been implemented, due to the high
construction and maintenance costs. Project investigators for the U.S. Army Corps of Engineers stated in
2000 that the dike would cost $5 million to $8 million, and given their hydrologic data at the time, the
value of the property and houses that might be flooded was only $2 million (Hodges 2000).
Given the predictions of more frequent flooding, possible higher flood levels, and the increased
development and property value in the area since that time, it would be reasonable to study the situation
and cost/benefit analysis once again. One specific action that is needed is to develop a “water budget” for
the watershed, as proposed by Rothwell and Bidlack (2011). At the present time, there is no way to
correlate streamflows, precipitation, etc., with lake and river levels and, in turn, flood levels. Once a water
budget is developed, predicted increases in precipitation and other climate change information can also be
incorporated for determining flood risks in the future.
One other flood issue is the potential water pollution from fuel and other substances stored in flood-prone
areas. Almost all of the residences rely on fuel oil for heating, and the tanks are susceptible to damage or
inundation. Through its Million Dollar Eyak Lake program, the Copper River Watershed Project is
looking into ways to get homeowners to elevate fuel tanks above flood levels and to adequately secure
tanks so they are not washed away. Public education and possible grant opportunities for implementation
are being considered. Many landowners have already begun raising their tanks and houses, as well.
285 Assessing the Vulnerability of Watersheds to Climate Change