The Suiattle River is located within the Skagit River watershed and enters the right bank of the Sauk River, the largest tributary to the Skagit River, just downstream from the Town of Darrington, WA. The Suiattle River watershed drains approximately 343 square miles, the majority of which (94%) falls within the jurisdiction of the United States Forest Service (USFS) Mt. Baker-Snoqualmie National Forest (Mt. Baker-Snoqualmie National Forest 2004). The remainder of the land ownership is primarily private and state timber interests, along with a few recreational parcels, tribal holdings, and parcels managed for conservation purposes. Designated by Congress as a National Wild and Scenic River, the Suiattle River supports runs of Chinook, coho, chum, and pink salmon, steelhead trout, cutthroat trout, and native char. It also supports a genetically distinct population of Spring Chinook (SRSC and WDFW 2005).
The Suiattle River watershed is largely undeveloped and long stretches of the river undergo active and dynamic river channel migration. The main road that accesses the Suiattle River watershed is Forest Road 26 (FR26), also known as the Suiattle River Road. FR26 runs parallel to the Suiattle River for approximately 23 miles from State Route 530 to about a half mile past Sulphur Creek. The road runs in close proximity to the river along the majority of its length, in some places along a high terrace above the river and in other places along the edge of the floodplain. Active channel migration has impacted FR26 in several locations in the past, creating a road maintenance and management problem for the USFS. In addition, emergency road repairs that include rip-rap bank protection can negatively impact fish habitat by reducing edge habitat complexity (Beamer and Henderson 1998) and limiting the natural process of channel migration that can create side channels, sloughs, and other important habitats (SRSC and WDFW 2005). Over the past several decades, the river has continually eroded road embankments and bridge approaches. Information provided by the USFS (Doyle 2005) show that from 1980-2003, eight sites along FR26 that were damaged during Suiattle River flood events were funded by the Western Federal Lands Emergency Relief for Federally Owned Roads (ERFO) Program, just one of the funding sources for road repairs. Most recently, several road washouts occurred during the floods of 2003 and 2006, and the road is currently closed near milepost 12.
The USFS contracted Skagit River System Cooperative (SRSC) to assess the impact of river channel movement on FR26. The purpose of this analysis is to evaluate historic river channel movement and development in the Suiattle River in order to help identify potential future erosion risks to FR26. Eight sets of historic aerial photographs dating from 1942 to 2007 were collected and analyzed to determine rates of historic channel movement and historic areas of erosion.
Ramsden, K. and Smith, D., 2010. Suiattle River Channel Mapping and Forest Road 26 Erosion Risk Analysis. Skagit River System Cooperative, La Conner, WA. pp. 45.
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