Corvallis sits along the Willamette River in the heart of Oregon's wet western valley, and Mary's River flows through the city before joining the Willamette, creating two distinct flood corridors. The city receives approximately 46 inches of rain annually with October through March accounting for 70% of precipitation, producing extended saturated soil conditions that promote foundation seepage. Benton County's silty river-bottom soils retain water poorly after heavy rain, contributing to downstream flooding in low-lying residential areas.