Off-Channel Aquatic Zones
The Willamette River has historically shifted course within the valley floor and abandoned sections of channel, which became exbow lakes and linear ponds [Figure 3 shows abandoned channel remnants to the west of the 1850s channel]. Local examples include Horseshoe and Colorado Lakes and the "Little Willamette" [Figure 15]. Human-created channel cut-offs have also formed off-channel aquatic areas.
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These lakes and ponds are generally surrounded by woodland, and provide habitat for animals such as the Western pond turtle, amphibians, and waterfowl. Many of these separated wooded channel sections have been converted to farmland, though the soils often remain saturated with water from winter into late spring [Figure 16].
Figure 15. Colorado Lake to the north-east of Corvallis, a remnant of an abandoned river channel [U.S. Geological Survey map, 1975.]
Figure 16. McBee Slough [at Peoria], was a wooded remnant channel in 1956, but was later cleared to be farmed. Standing water generally collects on the land in the winter [Benner and Sedell, 1997].
The East Channel of the Willamette
The section of the river known as the "East Channel" was once the main course of the river, and made an "S" turn above Corvallis [Figue 14]. In the 1880s and 1890s the community and the U.S. Army Corps of Engineers feared that the river might change course and the channel travel to the east of what is now the O.S.U. golf course. Since the town was dependent on river travel for commerce, it was felt that something had to be done to:
...prevent a threatened change in the channel of the river, by which that city would be left high at a considerable distance from it and the navigation of the river greatly impaired [Corps, 1887].
Figure 13. Construction of the second section of the bank-stabilizing wall on the outside bend of the East Channel . The first section was built in 1888-1889.
Figure 14. "Threatened cut-off of the Willamette River" at Corvallis. The U.S. Army Corps of Engineers discussed either enlarging a flood channel [stippled A to B] to alter the river's course, or building a bank-stabilizing wall along the outside bank of the East Channel bend [stippled C]. The Corps decided to build the wall. By 1917, the river had changed course to roughly the flood channel location [U.S. Army Corps of Engineers map].
The winter floods usually cover this alluvial bottom [across from Corvallis]... Below the concave bend, where the cutoff is threatened, the winter floods [are] to a depth of 4 to 8 feet. The flood velocities probably reach as high as 7 miles per hours ... [U.S. Army Corps of Engineers, 1887].
River-Transported Sediment and Channel Dynamics
River water carrying suspended sediment is often looked at as dirty, and erosion in rivers is often thought to be ecologically detrimental. Some human activities and natural events have created erosion and channel sedimentation problems in river systems, but the Willamette has probably always transported tremendous amounts of sediment during higher flows. And, physical disturbances that cause ongoing changes to the river are important for a dynamic, healthy river system that has evolved within these processes.
The process of erosion and deposition is evidenced by the quality floodplain farmland soils. The river is in a never-ending cycle of eroding materials from one section of the river, and moving it on downriver to be used as building blocks at another location.
An 1875 quote by the U.S. Army Corps gives a sense of the amount of sediment that might have been naturally found in the river water during higher winter flows. Though some of the floodplain land was in farmland by this time, most of the timber remained on the river bottomlands:
The Willamette River had risen...so high as to render it unsafe and risky to venture with boat into the channel, owing to the number of floating logs and large trees displaced from the banks. The water was so thick with mud as to render it impossible to discern the positions of snags below its surface
[U.S. Army Corps of Engineers, 1875].
Figure 17. The Willamette River at Corvallis in 1939, looking east-southeast. The old East Channel location is still clearly visible, but now a part of East Muddy Creek. The Calapooia River is in the distance, and Oak Creek is at the bottom of photograph [U.S. Army Corps of Engineers, 1939].
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