21.8' - expect major and widespread flooding in Philomath and Corvallis and rural areas along the lower Marys River. Grange Hall Road, Fern Road, Chapel Drive, and Bellfountain Road will likely be impassable. The flow at this level is about 15,000 cfs and has a 2 percent chance of happening in a given year (aka 50-year flood).
21.4' - expect major and widespread flooding in Philomath and Corvallis and rural areas along the lower Marys River. Grange Hall Road, Fern Road, Chapel Drive, and Bellfountain Road will likely be impassable. The flow at this level is about 10,900 cfs, which has a 10 percent chance of happening in a given year (aka 10-year flood).
21.25' - expect major and widespread flooding in Philomath and Corvallis and rural areas along the lower Marys River. Grange Hall Road, Fern Road, Chapel Drive, and Bellfountain Road will likely be flooded. The flow at this level is about 9,000 cfs and has a 20 percent chance of happening in a given year (aka 5-year flood)
21' - expect major and widespread flooding along the Marys River from Philomath to Corvallis, with numerous homes and farms affected. Several roads will likely be flooded, including Grange Hall Road, 13th Street / Fern Road, Chapel Drive, and Bellfountain Road.
20.8' - expect widespread flooding in Philomath, especially on the south side in the vicinity of Chapel drive and Grange Hall Road, in central Benton County, and portions of Corvallis.
20.7' - expect road flooding in Philomath, especially the south part of town in the vicinity of Chapel Drive, Fern Road, Grange Hall Road and Bellfountain Road. Portions of Highway 99W in Corvallis have historically been flooded at this level. If the Willamette River stage at Corvallis is at 28 ft or higher, expect additional flooding of county roads due to backing up of the Marys.
20.5' - expect flooding of some homes in the southern part of Corvallis to begin, especially when the Willamette is also running high. In south Corvallis, a trailer park and light industrial areas begin to flood. Flooding may begin in the vicinity of Chapel Drive and Grange Hall Road on the south side of Philomath. Problems with the sewers have historically begun in Philomath at this and higher stages.
20' - expect widespread low land and agricultural flooding. Numerous roads along the Marys are affected, and some structures near the river may begin to flood.