Table 4 (online only). Projected climate change effects and adaptation options in the context of road management at
Olympic National Forest and Olympic National Park. Projected effects on physical watershed processes are based on
projected climate change effects on Olympic Peninsula, including increased winter air temperatures/fluctuation above and
below freezing; more precipitation falling as rain rather than snow; increased winter and spring streamflows in some types
of watersheds; decreased summer streamflows in some types of watersheds; increased winter precipitation and runoff;
increased storm intensity; increased flood frequency and magnitude in some types of watersheds; and elevation shifts in
transition (rain on snow) zones.
Program
Road
maintenance
Project
Planning
Implementation
Road operations
Design
- water crossing
- fish passage
Design
- bank protection
Design
- reconstruction
- drainage upgrades
- stabilization
- storm-proofing
Projected effects on
physical watershed
processes
 Increased flow
volume
 Increased mass
wasting and
avalanches
 Increased sediment
delivery
 Increased
floodplain
inundation
 Increased channel
migration
 Increased flow
volume
 Increased mass
wasting/debris
flows
 Increased sediment
delivery to culvert
inlets and ditches
 Increased rate and
volume of water
delivery to
channels
 Increased flow
volume
 Increased sediment
and wood transport
 Increased channel
migration
 Increased flow
volume
 Increased erosion
and scour
 Increased channel
migration
 Increased mass
wasting and/or
avalanches
 Increased flow
volume
 Increased rate and
volume of water
delivery to
channels
 Increased sediment
and wood transport
 Increased mass
wasting/debris
Current and expected
sensitivities
 Culvert capacity
 Water diversion
 Fill slope failures
 Stream-adjacent road
failure
Adaptation management
options and strategies
 Prioritize road treatment
by watershed risk and
road risk (the roads with
the most sensitivities
and that are most
connected to streams)





 Increased maintenance
(preparation and
response), including:
 culvert cleaning
 armoring outlets and
ditches
 installing water bars
and drivable dips
Culvert capacity
Culvert plugging
Water diversion
Fill slope failures
Extension of channel
network (development
of first order channels)
 Culvert capacity
 Foundation scour
 Lateral channel
adjustments
 Design more resilient
structures (e.g., design
resilient bridges and
larger structures)
 Stream-adjacent road
failure
 Cut-bank failures on
montane and
subalpine roads
 Either relocate road
segment, decommission
road segment, or accept
higher maintenance
costs
 Install retaining walls or
other cut-bank
stabilization
 Culvert capacity
 Culvert plugging;
water diversion
 Fill slope failures
 Extension of channel
network (development
of first order channels
 Implement more
conservative design
elements (more
intensive treatments
such as larger diameter
culverts, closer spacing
between ditch relief
culverts and/or
waterbars
 Increase maintenance
flows
 Increased sediment
delivery to culvert
inlets and ditches
frequency of drainage
features