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Elevation derived from Google Earth search using GNIS source coordinates.〕 | source_length_imperial = | source_lat_d = 45 | source_lat_m = 26 | source_lat_s = 51 | source_lat_NS = N | source_long_d = 122 | source_long_m = 17 | source_long_s = 18 | source_long_EW = W | source_coordinates_note = 〔 | mouth_name = Willamette River | mouth_location = Milwaukie | mouth_district = | mouth_region = Clackamas County | mouth_state = Oregon | mouth_note = | mouth_lat_d = 45 | mouth_lat_m = 26 | mouth_lat_s = 39 | mouth_lat_NS = N | mouth_long_d = 122 | mouth_long_m = 38 | mouth_long_s = 36 | mouth_long_EW = W | mouth_coordinates_note = | mouth_elevation_imperial = 26 | mouth_elevation_note = 〔 | length_imperial = 25 | length_round = 0 | length_note = | watershed_imperial = 54 | watershed_round = 0 | watershed_note = | discharge_location = Milwaukie, from mouth | discharge_round = 2 | discharge_imperial = 77.5 | discharge_note = | discharge_max_imperial = 2170 | discharge_min_imperial = 9.3 | discharge1_location = Gresham | discharge1_imperial = 27 | discharge1_note = 〔Note: Average discharge rate was calculated by adding average annual discharge rates for the 7 calendar years 1999–2005 and dividing by 7. 〕 | map = Johnson Creek watershed map.png | map_size = 300 | map_caption = Johnson Creek watershed | map_alt = Johnson Creek flows through Clackamas and Multnomah counties from near Cottrell, Oregon, on the east to Milwaukie, Oregon, on the west. Much of its watershed lies in Gresham and Portland, both in Multnomah County. | map1 = Oregon Locator Map.PNG | map1_size = 300 | map1_caption = Location of the mouth of Johnson Creek in Oregon | map1_alt = Johnson Creek is in northwestern Oregon. | map1_locator = Oregon | commons = }} Johnson Creek is a 25-mile (40 km) 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 watershed 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, white 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.〔〔 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Johnson Creek (Willamette River)」の詳細全文を読む スポンサード リンク
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