Johnson Creek is a tributary of the Willamette River in the Portland metropolitan area of the U.S. state of Oregon. Part of the drainage basin of the Columbia River, its catchment consists of of mostly urban land occupied by about 180,000 people as of 2012. Passing through the cities of Gresham, Portland, and Milwaukie, the creek flows generally west from the foothills of the Cascade Range through sediments deposited by glacial floods on a substrate of basalt. Though polluted, it is free-flowing along its main stem and provides habitat for salmon and other migrating fish.
Prior to European settlement, the watershed was heavily forested and was used by Native Americans of the Chinook band for fishing and hunting. In the 19th century, non-Native American settlers cleared much of the land for farming, and the stream is named for one of these newcomers, William Johnson, who in 1846 built a water-powered sawmill along the creek. By the early 20th century, a rail line parallel to the stream encouraged further residential and commercial development. As urban density increased in the floodplain, seasonal floods grew more damaging. In the 1930s the Works Progress Administration of the federal government lined the lower of Johnson Creek with rock to control the floods. Despite this, the creek flooded 37 times between 1941 and 2006. Since the 1990s, regional planners have tried to reduce flooding by controlling stormwater runoff, creating stream meanders, reducing erosion, replacing impervious surfaces, and protecting riparian buffers.
The Johnson Creek watershed includes the subwatersheds of Badger Creek, Sunshine Creek, Kelley Creek, Mitchell Creek, Veterans Creek, Crystal Springs Creek, and smaller streams. Parks along the creek and its tributaries include natural areas, a wildlife refuge, a rhododendron garden, a botanical garden, and a bicycle and pedestrian rail trail that follows the creek for much of its length.
Course Johnson Creek begins near the unincorporated community of Cottrell in Clackamas County, Oregon, southeast of Gresham in the foothills of the Cascade Range, and flows generally westward about to its confluence with the Willamette River, a major tributary of the Columbia River. The creek passes through the cities of Gresham, Portland, and Milwaukie and crosses the border between Clackamas County and Multnomah County eight times.
For much of its course, the creek flows at almost right angles to the numbered avenues of southeast Portland and its eastern suburbs. As the creek descends, so do the avenue numbers. The creek begins in uplands in Clackamas County east of Southeast 362nd Avenue and flows swiftly to the west for about , crisscrossing the border between Clackamas County and Multnomah County 5 times in this upstream stretch, and passing under U.S. Route 26, the Mount Hood Highway, in Multnomah County at about from the mouth. Shortly thereafter, it receives Badger Creek and Sunshine Creek from the left and the North Fork of Johnson Creek from the right.
Turning sharply, Johnson Creek flows swiftly northwest for about , entering Gresham and shortly thereafter passing the United States Geological Survey (USGS) gauge at Regner Road, from the mouth. Soon the creek enters Main City Park in Gresham, where it again turns sharply and flows slightly south of west. Here the slope flattens, and the stream runs more slowly for the next third of its course. Slightly west of Main City Park, it passes the Gresham Pioneer Cemetery. Just beyond the cemetery, it receives Butler Creek on the left, enters Portland at about from the mouth, and receives Kelley Creek on the left shortly thereafter. Mitchell Creek, a major tributary of Kelley Creek, enters Kelley Creek about south of Johnson Creek. Shortly thereafter, Johnson Creek passes the USGS gauge station at Sycamore, from the mouth, and flows under Cedar Crossing Bridge.
Meandering slowly through the Lents neighborhood of Portland, Johnson Creek receives Veterans Creek, which enters on the left from its headwaters in Happy Valley in Clackamas County. Johnson Creek passes under Interstate 205, and shortly thereafter begins to flow more swiftly again at Southeast 82nd Avenue, about from the mouth. It then makes its sixth and seventh county-border crossings, dipping briefly into Clackamas County and back north into Multnomah County, and then runs near the border between Portland and Milwaukie along Johnson Creek Boulevard for about . After passing under Oregon Route 99E (Southeast McLoughlin Boulevard) in Portland's Sellwood neighborhood, the creek turns sharply south about from the mouth.
At Southeast 21st Avenue, it receives Crystal Springs Creek, which enters on the right. This tributary, long, begins on the Reed College campus, flows under the Blue Bridge in Reed Canyon, through the Crystal Springs Rhododendron Garden, and generally south to Johnson Creek. From its confluence with Crystal Springs Creek, Johnson Creek flows south about , crossing the county border for the eighth and final time. After re-entering Clackamas County, it passes the USGS gauge station at Milwaukie, from the mouth. Shortly thereafter, Johnson Creek empties into the Willamette River above its confluence with the Columbia River, which in turn flows about another to the Pacific Ocean at Astoria.
Watershed
Geology and topography The floodplain of Johnson Creek is a remnant of large glacial floods known as the Missoula Floods that deposited thick sediments between 18,000 and 13,000 years ago in the Columbia River Basin, including much of the Willamette Valley. Underlying the sediments are substantial thicknesses of basalt lavas from the Columbia River Basalt Group. The lava, exposed mainly in the uplands, has been folded and faulted to form a series of sub-basins, including the Johnson Creek watershed.
The watershed is a roughly rectangular area of about . The topography of the watershed varies greatly from the high point of about above sea level in the Boring Hills near the creek's source to the low point of where the creek meets the Willamette River.
Slopes in the watershed range generally between 1 and 25 percent. Mount Scott and Powell Butte rise to about and have slopes ranging from 10 to 30 percent. Gresham Butte and Hogan Butte, in Gresham, have the steepest slopes, including a few around 50 percent. The Boring Hills, of volcanic origin, rise more than higher than the terraces to the north and west. The Kelso Slope, a northwest-sloping dissected surface west of the canyon of the Sandy River, tilts down from about above sea level near Sandy to about above sea level east of Gresham.
Formed by the ancestral Columbia and Willamette Rivers, the terraces north of Johnson Creek are generally underlain by permeable sand and gravel. Three isolated hills—Rocky Butte, Mount Tabor, and Kelly Butte—rise about above the surrounding terraces. Except for Powell Butte, the terrain on the creek's north side is less steep than on the south side, which includes Mount Scott and the Boring Lava Domes.
The eastern half of the watershed is more open and rural than the urban western half, which consists largely of residential areas with pockets of commerce and industry. An estimated 180,000 people lived in the watershed as of 2012.
Soils The potential for soil erosion varies throughout the watershed. Erosion is not a big threat in the northwestern part of the watershed, where the land is flat and developed, or in the northeast, dominated by low-erosion soils. In the southeast, soils have a medium risk of erosion, and soils around Powell Butte and the Boring Lava Domes have "an extremely high erodibility factor and are sensitive to ground disturbance".
The watershed's soils vary in their permeability and ability to retain water. Clays that do not absorb much water dominate the eastern end of the watershed and the lands south of the creek. Northern areas of the watershed tend to be porous and less prone to rapid runoff.
Hydrology
The watershed can be divided into two hydrologic areas with different infiltration rates. The northern area, comprising about 40 percent of the watershed, consists of the Portland Terraces, and the southern consists of the Boring Hills and the Kelso Slope. Most of the rain that falls on the northern area percolates into the ground, and most of the rain that falls on the southern area runs quickly into the creek or its tributaries. Rain that falls on the north generally has a more gradual, longer-lasting effect, sustaining the base flow of the creek during dry periods.
About 40 percent of the tributaries that originally flowed over the surface of the watershed were piped or relocated during urban development, especially on the north side of the main stem. Generally, the remaining free-flowing tributaries begin south of the main stem and run north; the major exception is Crystal Springs Creek, which begins as a groundwater discharge and flows south. The other major tributaries are Hogan, Kelley, Butler, Sunshine, and Badger creeks. Crystal Springs and Kelley creeks contribute more flow to the main stem than the other tributaries.
Fill at Foster Road and Southeast 111th Avenue usually prevents stormwater runoff from a area of the watershed in the Lents and Powellhurst-Gilbert neighborhoods from flowing directly into the creek. Instead, runoff is routed to sumps, where it percolates into the ground. Normal drainage patterns have also been altered further downstream in the Sellwood, Eastmoreland, Westmoreland, and Woodstock neighborhoods, where runoff flows into the Portland sewer system instead of into the creek.
Jurisdiction Six local political jurisdictions overlap with the Johnson Creek watershed. In 2000, 38 percent of the watershed was in Portland's city limits, 24 percent in unincorporated Clackamas County, 23 percent in Gresham, 11 percent in unincorporated Multnomah County, 4 percent in Milwaukie, and 0.1 percent in Happy Valley. None of the cities lies entirely within the watershed. In 2000, Johnson Creek and its tributaries drained 53 percent of Gresham, 42 percent of Milwaukie, 19 percent of Happy Valley, and 14 percent of Portland. The watershed covered only 1.2 percent of unincorporated Multnomah County and less than 1 percent of unincorporated Clackamas County.
Neighboring watersheds on the east side of the Willamette River include Mount Scott Creek and Kellogg Creek, which flow through Milwaukie and drain directly into the Willamette; the Clackamas River, which drains the southeast suburbs and empties into the Willamette near Oregon City; the Sandy River, which drains the eastern suburbs and empties into the Columbia; and Fairview Creek and the Columbia Slough, which drain north Portland and Gresham, emptying into the Columbia.
19th-century maps also show numerous springs and small streams flowing into a wetland that covered an area of today's southeast Portland between Powell Boulevard (U.S. Route 26) and Johnson Creek, a distance of . Though most of the wetland complex has been filled in and built upon, remnants exist at the Crystal Springs Rhododendron Garden on Crystal Springs Creek. Old maps also show two streams flowing into a slough that drained part of the wetland. One flowed through the Clinton Street neighborhood, about six city blocks north of Powell Boulevard, and the other drained the Colonial Heights neighborhood, slightly further north near Ladd's Addition. These streams and most others in this area were diverted into the city sewer system and no longer appear on the surface. A Johnson Creek near Hoyt Arboretum on the west side of the Willamette River in Portland has no relationship to the Johnson Creek on the east side.
Volunteer group