There are about 27 miles of open stream channel in the Tryon Creek Watershed. An additional three miles of streams are in culverts or pipes. The physiographic characteristics of the watershed and its soil types have had severe impacts on the stream systems in terms of channel incision, undercutting of stream banks, landslides, and exposed sewer pipes.
Impervious surfaces include streets, parking lots, and buildings. Impervious surfaces comprise about 990 acres, or 24 percent, of the Tryon Creek Watershed. Impervious surface coverage is highest in the upper portions of Tryon Creek, particularly along Interstate 5 and SW Barbur Boulevard.
Tryon Creek mainstem is a perennial stream that originates in the West Hills of Portland and flows southeast from Multnomah Village, through Tryon Creek State Natural Area, to its confluence with the Willamette River at the Highway 43 crossing in Lake Oswego. It is one of the major remaining free-flowing tributaries that descend from Portland’s West Hills. Tryon Creek is primarily a high-gradient, open-stream system, with the exception of culverts at road crossings (Map 9-Tryon Creek Contour Map, Map Atlas).
Tryon Creek’s tributaries include Arnold Creek, Falling Creek, Oak Creek, Park Creek, and Nettle Creek.