Olis, M. and Veldhuisen, C., 2007. Suiattle Forest Road Sediment Reduction Assessment Phase 1 – Northern Suiattle Basin. Skagit River System Cooperative, La Conner, WA. pp. 42.

The Suiattle Basin Forest Road Sediment Reduction Assessment is an ongoing cooperative project
sponsored by the Skagit River System Cooperative (SRSC) and the Mt. Baker-Snoqualmie National
Forest (MBSNF). The Skagit River System Cooperative is a fisheries management consortium for the
Sauk-Suiattle Indian Tribe and Swinomish Indian Tribal Community. The project was designed to
identify opportunities to reduce sediment-related impacts to fish and aquatic resources from federal forest
roads within the Suiattle basin. Forest Service lands within the Suiattle basin are entirely within the
Usual and Accustomed Fishing area of the SRSC member tribes and are managed by the Forest Service.
The objective of this project is to identify opportunities to reduce sediment from forest roads that can
negatively affect aquatic resources. The project determined the present condition of forest roads, the
scale of ongoing and future sediment impacts and the portions of each road that pose the greatest threat to
fisheries resources. Other aspects of road management, such as fish passage barriers, wildlife effects, and
access for timber harvest, recreation or tribal cultural activities, were beyond the scope of this study, but
should be considered before road treatments are chosen.
We collected information needed to estimate the effects of a range of possible road treatments, including:
1. Maintenance – e.g. grading, ditch clearing and brushing, 2. Upgrades – e.g. replacing culverts, fill
removal, 3. Deactivation – i.e. making the road undrivable so it is less erodible and requires minimal
maintenance, and/or 4. No action – i.e. probable consequences of non-treatment. This study stopped short
of designing road treatments, in part because such decisions would require consideration of broader
landowner and stakeholder concerns listed in the previous paragraph. However, this study does
characterize possible aquatic damage considerations that will be useful for prioritizing which road
segments pose the greatest threat to aquatic resources and provides detailed data that can be used to help
develop specific road treatments. Although the focus of this report is at the road-segment scale to provide
an overview, the site-scale notes can be consulted to help evaluate specific sites and treatments.
Further, we also hope that the methodologies developed for this study can provide a model for similar
road sediment reduction projects in other watersheds.
Sediment Concerns in the Suiattle Basin
The Suiattle River basin was chosen for this project for a variety of reasons including: 1. The presence of
important fisheries resources (federally threatened Chinook salmon and Bull trout plus other salmonids of
commercial and recreational importance), 2. Chronically high fine sediment levels in the Suiattle
mainstem, and 3. Interest from MBSNF. Because the Suiattle mainstem receives large inputs of fine
sediment, primarily from natural sources, habitat in the non-glacial “clear-water” tributaries located
downstream of roads in this study is critical to threatened fish species (Mt. Baker-Snoqualmie National
Forest, 2004). For this reason, it is particularly important to minimize management-related sediment
inputs to tributaries.
As in many other steep forested basins, forest management (logging and roads) has contributed to
elevated sediment inputs to the Suiattle and its tributaries (Mt. Baker-Snoqualmie National Forest, 2004),
largely through the acceleration of landsliding. In comparison to other sediment input processes, such as
soil creep and surface erosion from roads and clearcuts, contributions from landsliding are far larger
(Paulson, 1997). For this reason, landsliding is perceived to be the prevalent source of managementrelated
sedimentation and thus a major focus of this assessment. Increased landsliding from logged areas
generally declines over one-to-two decades following harvest with forest regrowth (Sidle, 1985).