About the South Santiam Watershed
The South Santiam Watershed has its headwaters in the central Cascades mountain range and flows into the Willamette River Valley. The watershed covers approximately 1,040 square miles within Linn County, including three communities: Sweet Home, Lebanon, and Scio.
From steep, mountainous terrain in the east to low floodplain in the west, the South Santiam watershed varies greatly in elevation, land use, and ecology.
What is a Watershed?
A watershed is defined as the area of land where all precipitation drains to a common water body. The boundaries of a watershed are determined by the contours of the land around it (buttes and mountain ranges), much as the walls of a funnel guide water into a spout. Because a river and the land around it are intimately connected, healthy lands mean healthy streams.
Key Issues in the South Santiam Watershed
Riparian areas in the upper watershed are generally intact and have wide buffers of conifer and hardwood stands. Conifers are primarily second-growth (<80 years), so potential for large woody debris (LWD) delivery is currently moderate. The majority of low elevation lands have been developed for agricultural and residential land use, and as a result are characterized by narrow, discontinuous riparian areas in poor to fair condition, dominated primarily by grass/shrub vegetation.
Large Woody Debris
The South Santiam Watershed lacks large wood in some places due to past timber management and stream cleaning practices, and torrential flows that removed woody debris in the 1970’s and 1996. Large wood provides critical in-stream benefits. It:
- Dissipates streamflow energy and prevent erosion
- Retains spawning gravel and nutrients
- Creates and maintains instream habitat complexity
The lack of large wood is most striking in the lower reaches of the basin, but the upper reaches would also benefit from greater habitat complexity that comes with the presence of large wood.
With the exception of alpine wetlands in the Cascade Mountain range, wetland habitats in the watershed have largely been converted to agriculture and rural residential. Most remaining wetlands are disconnected from each other and from the mainstem river or its tributaries. Wetlands in the Willamette valley provide important habitat for birds and other wildlife. Wetlands also act as filters for pollutants and buffer impacts from flooding by absorbing excess water.
There are 11 stream segments in 8 subwatersheds that exceed the Department of Environmental Quality's upper threshold for temperature. Elevated temperatures are inhospitable for the salmon and trout that rear and migrate in South Santiam Watershed. Shading streams is one way in which landowners and managers can help cool the water in the summers.
Many reaches in the lower watershed have a high rate of actively eroding streambank due to a variety of land use practices. Erosion, compacted soils and high road densities all lead to elevated levels of in-stream sedimentation and turbidity. This can reduce water quality, raise temperatures and reduce food production. Changing certain land use practices, installing fences and plantings along stream sides and increasing channel complexity can all help reduce erosion and sedimentation.
The watershed sustains populations of federally listed Upper Willamette River Chinook Salmon and Upper Willamette River steelhead. Hatchery stocks of salmon and steelhead have long been released in the basin, providing valuable recreational opportunities, while potentially contributing to the decline of wild runs through competition and hybridization. The watershed is also home to coastal cutthroat trout and Pacific lamprey, both considered sensitive species by state management agencies.
Besides these high-profile species, the South Santiam is home to abundant native fishes, which are usually not subject to recreational fisheries, and provide invaluable ecosystem services.
Snowpack in the Cascades supplies the mainstem South Santiam River with ample flow from November to March. Several tributaries have water rights that, combined with seasonal flows, can cause dewatering at times that are important for fish.
Foster and Green Peter dams provide water storage and can help provide flood relief. The US Army Corps of Engineers operates the dams and regulates the water releases to mitigate the effects of water withdrawal. However, the dams impair floodplain function by preventing significant re-charging of the water table and regular interaction between mainstem, wetland and riparian habitats. In addition, the flow regime created by the dams has altered historic seasonal water temperatures, which may decrease egg-to-smolt survival for spring Chinook that spawn naturally in the mainstem South Santiam River.
The floodplain is further constrained by urban and rural development that seeks to channelize and the natural meandering pattern of the river and tributaries. Channelization, streambank erosion, increased peak flows and decreased base flows reduce habitat complexity, diversity and abundance. Some areas in the watershed, particularly headwater reaches, are targeted for protection while others are identified as having high restoration potential.