Basic information and facts about the South Santiam Watershed
That area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community.
—John Wesley Powell, scientist, geographer
The South Santiam Watershed is situated in the Central Cascades and flows into the Willamette Valley. It drains approximately 1,040 square miles in area. With steep, mountainous terrain in the east and a low floodplain to the west, the watershed is characterized by much variation in elevation, ecoregions, and land use practices. The watershed supports three communities (Sweet Home, Lebanon, and Scio), and is located in Linn County, Oregon.
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 in generally good condition with wide buffers of conifer and hardwood stands. Conifers stands 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 is deficient in LWD due to past timber management, stream cleaning practices, and torrential flows that removed woody debris in the 1970’s and 1996. This deficiency limits the ability of the watershed to dissipate streamflow energy and prevent erosion, retain spawning gravel and nutrients, or to create and maintain instream habitat complexity. LWD is severely lacking in lower reaches of the basin, but even upper reaches have low habitat complexity and would benefit from increased LWD.
With the exception of alpine wetlands in the Cascade Range, wetland habitats in the watershed have been converted to agriculture and rural residential areas. Most remaining lowland wetlands are scattered and disconnected, and little to no wetlands remain connected to the mainstem river or its tributaries. Wetlands in the Willamette Valley are an important habitat for birds and other wildlife. Wetlands also help filter out pollutants and act as a sponge and lessen the impacts of floods.
The South Santiam Watershed has 11 stream segments (8 subwatersheds) that exceed the 18° C temperature criterion for salmon and trout rearing and migration, and are listed by the Department of Environmental Quality (DEQ) on the state’s 303(d) list of impaired water bodies. These water bodies include Crabtree Creek, Hamilton Creek, Middle Santiam River, Quartzville Creek, lower South Santiam River, upper South Santiam River, Thomas Creek, and Wiley Creek. Shading streams is one way in which landowners and managers can help cool the water in the summers.
Sedimentation and turbidity are high on lower reaches of the mainstem river and tributaries. Lower reaches have a high percentage of actively eroding streambank due to removal of vegetation as a result of agriculture/residential land use practices. High road densities (average 4 miles of road/sq. mile) and highly compacted soils throughout the watershed contribute significantly to surface erosion.
The watershed sustains populations of native spring chinook and winter steelhead, listed as threatened under the ESA. Planting of hatchery stocks has been significant in the past, which has probably been detrimental to native runs due to competition and hybridization. The watershed is also home to Coastal cutthroat trout (Upper Willamette River ESU) and Pacific lamprey, listed as “sensitive.”
Construction of Foster and Green Peter Dams in the late 1960’s adversely affected the ability of salmonids to migrate successfully to and from prime spawning and rearing habitat in the upper reaches of the basin. Green Peter Dam completely prevents fish passage to the Quartzville Creek and Middle Santiam River Watersheds. Foster Dam is located on the mainstem South Santiam river 37 miles above its confluence with the Willamette River. Upstream passage systems at Foster allow adult migration to spawning habitat in the upper South Santiam basin, but create a host of problems for smolts migrating downstream. Slow water velocities in Foster reservoir impede migration, and predators including bass and northern pikeminnow feed heavily on the juveniles. Since Foster is a low head dam, juveniles must use the turbines or spillway gates to migrate past the dam. Passing through this system results in significant mortality for juveniles.
Snowpack in the Cascades supplies the mainstem South Santiam River with ample flow from November to March, however, dewatering potential is high (above 30% water withdrawal) for the following tributaries: Neal Creek, Thomas Creek, Crabtree, Creek, and Ames Creek. Foster and Green Peter dams reduce flooding and regulate the release of water to mitigate the effects of water withdrawal, but essentially impair the function of the floodplain by preventing significant re-charging of the water table and regular interaction with wetland and riparian habitats. In addition, the flow regime created by the dams has changed seasonal water temperatures, which is thought to have decreased egg to smolt survival of spring chinook naturally spawning in the mainstem South Santiam River.
The encroachment of urban and rural development on the floodplain has constrained the natural meandering pattern of the river and its tributaries, and resulted in increased channelization, streambank erosion, increased peak flows and reduced base flows, and reduced habitat complexity and diversity. Subwatersheds identified as priority watersheds for habitat restoration include Thomas, Crabtree, Ames, Wiley, Little Wiley, the lower mainstem South Santiam, Hamilton, and McDowell subwatersheds. Upper reaches of the watershed including Canyon Creek, Moose Creek, and Soda Fork subwatersheds have been identified by ODF&W as vital refugia and spawning areas for anadromous fish, and are priority areas for protection.