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The Columbia Slough is a narrow waterway, about long, in the floodplain of the Columbia River in the U.S. state of Oregon. From its source in the Portland suburb of Fairview, the Columbia Slough meanders west through Gresham and Portland to the Willamette River, about from the Willamette's confluence with the Columbia. It is a remnant of the historic between the mouths of the Sandy River to the east and the Willamette River to the west. surround much of the main slough as well as many side sloughs, detached sloughs, and nearby lakes. Drainage district employees control Fluid dynamics with pumps and floodgates. Tide fluctuations cause reverse flow on the lower slough.
The Columbia floodplain, formed by geologic processes including lava flows, volcanic eruptions, and the Missoula Floods, is part of the Portland Basin, which extends across the Columbia River from Multnomah County, Oregon, into Clark County, Washington. Five percent of Oregon's population, about 158,000 people, live in the slough drainage basin of about . Municipal wells near the upper slough provide supplemental drinking water to Portland and nearby cities. The cities, the drainage districts, the county, and a regional government, Metro, have overlapping jurisdictions in the watershed. A regional agency operates Portland International Airport along the middle slough and marine terminals near the lower slough. The Oregon Department of Environmental Quality (DEQ) and the city's Bureau of Environmental Services (BES) deal with environmental issues.
Long before non-indigenous people explored the region, tribes of Native Americans fished and hunted along the slough. In the early 19th century fur trappers and explorers including Lewis and Clark visited the area before large migrations of settlers began arriving from the east. The newcomers farmed, cut timber, built houses, and by the early 20th century established cities, shipping ports, roads, rail lines and industries near the slough. Increased investment in the floodplain led to larger losses during floods, and these losses prompted levee building that greatly altered the area. A flood pouring through a levee break in 1948 destroyed the city of Vanport, which was never rebuilt.
Used as a waste repository during the first half of the 20th century and cut off from the Columbia River by levees, the slough became one of Oregon's most water pollution waterways. Early attempts to mitigate the pollution, which included raw sewage and industrial waste, were unsuccessful. However, in 1952 Portland began sewage treatment, and over the next six decades the federal Clean Water Act and similar legislation mandated further cleanup. State and local governments, often assisted by community volunteers, undertook projects related to public health, natural resources, and recreation in a region with many homes, industries, businesses, and roads. The businesses and industries in the watershed employ about 57,000 people, which is also frequented by more than 150 bird species and 26 fish species and animals including otters, beaver, and . One of the nation's largest freshwater urban wetlands, Smith and Bybee Wetlands Natural Area, shares the lower slough watershed with a sewage treatment plant, marine terminals, a golf course, and a car racetrack. Watercraft able to portage over and levees can travel the entire length of the slough. The 40-Mile Loop and other hiking and biking trails follow the waterways and connect the parks.
Running slightly north of and parallel to U.S. Route 30 (Sandy Boulevard), the slough flows by Zimmerman Heritage Farm on the (south) about from the mouth, Big Four Corners Wetlands on the shortly thereafter, and receives Wilkes Creek on the left shortly after that. At about river mile (RM) 15.5 or river kilometer (RK) 24.9, it passes through a gated levee that separates the upper slough from the middle slough. Soon it passes Prison Pond Wetlands near Inverness Jail and connects to Johnson Lake Slough, all on the left. Shortly thereafter, it flows under Interstate 205. From here and for most of the rest of its course, the slough runs parallel to and slightly north of Columbia Boulevard. Passing Johnson Lake on the left, it crosses the Colwood National Golf Course and flows by Portland International Airport and an Oregon Air National Guard base on the right. On the left is Whitaker Ponds Natural Area. Shortly thereafter, it receives Whitaker Slough on the left and crosses the Broadmoor Golf Course. Between from the mouth, it receives Buffalo Slough from the left and passes by the defunct Peninsula Drainage Canal (City Canal), which lies to the slough's right. At this point, it passes through a second gated levee that separates the middle slough from the lower slough and its tidal flow reversals.
In the next stretch, the Columbia Slough crosses under Interstate 5 at about RM 7 (RK 11). Beyond the interstate, to the slough's north lies Delta Park, Portland International Raceway, and the Heron Lakes Golf Course. Until flooding destroyed it in 1948, the city of Vanport occupied this site. To the south is the Columbia Boulevard Wastewater Treatment Plant.
The slough flows through the Wapato Wetland and by the Smith and Bybee Wetlands Natural Area, including the former St. Johns Landfill, on the right at about RM 3 (RK 4.8) from the Willamette River, and by Pier Park on the left. Shortly thereafter, it turns sharply north for the rest of its course. It receives North Slough, connected to Bybee Lake, on the right, and passes through the Ramsey Lake Wetlands and Kelley Point Park before entering the Willamette River about from its confluence with the Columbia River. The mouth of the Columbia River is about further downstream at Astoria on the Pacific Ocean.
The watershed includes residential neighborhoods, agriculture, the airport, open spaces, 54 schools, interstate highways, railways, commercial businesses, and heavy and light industry. In general, the northern part is industrial and commercial; the southern part is residential, and agricultural areas lie to the east. As of 2001, single-family residential zoning covered 33 percent of the watershed, and mixed-use zones accounted for another 33 percent. The other zones were 12 percent industrial, 12 percent parks or open space; 6 percent multi-family residential, 3 percent commercial, and 2 percent were for farming or forests. As of 2005, about 3,900 businesses operated in the watershed and employed about 57,000 people.
Adjacent to the Columbia Slough basin are the watersheds of the Sandy River to the east, Johnson Creek to the south, the Willamette to the south and west, and the Columbia to the north. Lying slightly north of the watershed, large islands in the Columbia River include, from east to west, McGuire Island, Government Island, Lemon Island, and Tomahawk Island, which is connected to Hayden Island. Bordered by the Columbia and two arms of the Willamette, Sauvie Island lies just west of the mouth of the slough.
The Portland Basin is being pulled slowly apart between faults in the Tualatin Mountains (West Hills) on the west side of Portland, the East Bank fault along the east side of the Willamette River, and other fault systems near Gresham further east. About 3 million years ago, many small volcanoes and cinder cones erupted through the thin, stretched crust of the basin and in the Cascade foothills to the southeast. Ash, cinders, and debris from these Boring Lava Field volcanoes added another layer of sediment to the Troutdale formation.
About 15,000 years ago, cataclysmic ice age events known as the Missoula Floods or Bretz Floods originating in the Clark Fork region of northern Idaho inundated the Columbia River basin many times. These floods deposited huge amounts of debris and sediment. Water filled the entire Columbia Gorge to overflowing and turned the Willamette Valley into a lake long, wide and deep. The floodwaters ripped the face off Rocky Butte in Portland and deposited a gravel bar, Alameda Ridge, that runs parallel to and slightly south of the Columbia Slough.
Faults associated with the expanding Portland Basin are capable of producing significant earthquakes. More than a thousand earthquakes, many too small to be felt, have been recorded in the basin since 1841. The stronger ones reached about magnitude 5 on the Richter scale. In 1892, one estimated at magnitude 5 shook downtown Portland for about 30 seconds. In 1962, one centered about north of Portland was estimated at between magnitude 4.9 and 5.2.
Historically, most rain falling on the watershed was taken up by vegetation, flowed into wetlands, soaked into the ground, or evaporated. Heavy rain in the winter months recharged the groundwater and provided to the slough during dry summers. Urban development, which replaced vegetation and water-absorbing soils with airport runways, house roofs, highways, warehouses, parking lots, and other hard surfaces, interrupted this cycle. In 1999, a study estimated that impervious surfaces covered 54 percent of the watershed. Storm surface runoff that might have taken days to reach the historic slough reaches the developed slough in hours.
upper slough extends from the slough's source at Fairview Lake, roughly from the mouth, to a gated levee known as the mid-dike levee about downstream. This sector, managed by MCDD, covers completely surrounded by levees. A northern side channel extends from the mid-dike levee to MCDD Pump Station No. 4 on the Columbia River (Marine Drive) levee near Big Four Corners. Water usually exits this sector through the open gates of the mid-dike levee, but to control threatening flows the MCDD can close the gate and pump water from the northern side channel directly into the Columbia. The pump's maximum capacity is .
The middle slough, also managed by MCDD, lies between the mid-dike levee and the Pen 2 levee, from the mouth. This sector covers , is completely surrounded by levees, and contains many side sloughs, ponds, small lakes, and springs. Pump Station No. 1 rests on the Pen 2 levee, which is gated across the course of the slough. To control flows, MCDD can open or close the gates, and it can pump water from the middle slough to the lower slough when its flow is reversed by the tide or when gravity flow is insufficient. The pump's capacity is .
Water levels in the lower slough, managed by Pen 2 and Pen 1, depend more on Willamette River conditions than on pumping by MCDD. Incoming tides cause a variation in water surface elevation of between roughly twice per day along the entire lower slough. Flow direction varies with the tide. Pen 2 and Pen 1, separated by Interstate 5, border the north side of the lower slough. Pen 2 manages east of the highway, and Pen 1 manages to the west (downstream). Multiple pump stations move water from lesser sloughs in both districts into the main slough. Parts of this subwatershed are unprotected by levees and are vulnerable to 100-year floods.
With one exception, the streams feeding Fairview Lake are the watershed's only remaining creeks, although springs also reach the surface. Wilkes Creek, the slough's only free flowing tributary, is about long and enters the upper slough from the south. Dozens of similar streams that once flowed into the slough from the south have all been piped or filled. Many bodies of water in addition to the main slough channel lie within the drainage basin. The area around the middle slough contains several slough arms and small lakes, including Buffalo Slough, Whitaker Slough, Johnson Lake, Whitaker Ponds, and Prison Pond. In the lower slough, Smith and Bybee Wetlands Natural Area at is one of the largest urban freshwater wetlands in the United States. A side slough called North Slough connects Bybee Lake and the main slough channel. A water control structure at the outlet from Bybee Lake to the North Slough regulates the lakes' levels.
In 1792, Lieutenant William Broughton, a British explorer, led the first trip by non-natives as far up the Columbia River as the mouth of the Sandy River. He and his men camped on Sauvie Island, which lies between the Willamette and Columbia rivers directly opposite the mouth of the slough. Broughton encountered many Chinookans while exploring and mapping geographic features including Hayden Island and other islands in the Columbia just north of the slough. When Lewis and Clark visited the area in 1806, the Clackamas tribe consisted of about 1,800 people living in 11 villages. The explorers estimated that 800 people of the Multnomah tribe of Chinookans lived in five villages on Sauvie Island.
In 1825, the Hudson's Bay Company established its western administrative headquarters at Fort Vancouver, across the Columbia River from the slough. The British fort became the center for fur trading and other commerce throughout the Pacific Northwest, including what would later become the state of Oregon. By the 1830s, smallpox, malaria, measles and other diseases carried by non-indigenous explorers and traders had reduced the native population by up to 90 percent throughout the lower Columbia basin. The United States gained control over the Oregon Territory—including Fort Vancouver, the Portland Basin, and the slough—by treaty with Great Britain in 1846. By 1851, the Clackamas tribe's population had fallen to 88, and in 1855 the tribe signed a treaty surrendering its lands to the U.S.
Nature has been more than lavish in her gifts to St. Johns. Travel as many miles as you like and go where you will, it is highly improbable that you will find a spot with so many magnificent nature advantages as has St. Johns. The fine stretch of level land on which the city is located, the deep water of the two rivers, the navigable sloughs and the superb scenery which nature has painted with a master hand, makes the location an ideal one in every respect either for industries or residences.
Over the next 30 years, more lumber and wood products companies opened along the slough, and tugboats moved log rafts up and down the waterway. Truck freight and other transportation companies built in the watershed. The city created the St. Johns Landfill on wetlands and small channels off the lower slough and built a new Portland Airport on land along the middle slough. Activists and civic leaders, concerned about pollution on the Willamette River, led cleanup campaigns, but voters declined to pay for sewage treatment. Pollution eventually grew so bad on the slough that mill workers refused to handle logs that had been stored in its water.
In 1942, Kaiser Shipyards began making ships for the war at three huge installations near the lower slough, one in St. Johns, one on Swan Island in Portland's Overlook neighborhood, and one in Vancouver, Washington. St. Johns and Vancouver made , while Swan Island made tankers. The St. Johns shipyard became the nation's leading producer of Liberty ships. To house shipyard workers and their families, Henry J. Kaiser bought of former marsh, pasture, and farmland in the lower slough watershed surrounded on all sides by dikes between high. Here he built a new city, at first called Kaiserville and later Vanport. By 1943, Vanport's population of 39,000 made it the second largest city in Oregon and the largest wartime housing project in the U.S. After the war, the population fell to about 18,500. This was roughly the number of people living there on May 30, 1948, when a flood broke through Vanport's western levee. The break occurred during the afternoon of a day with mild weather. The first rush of water soon became a "creeping inundation", slowed in its advance for 35 to 40 minutes by water-absorbing sloughs. The water's gradual rise within the city allowed most of the residents to escape drowning. The county coroner's official list of bodies recovered was set at fifteen, and seven people on a list of missing people were never found. The flood destroyed the city, which was never rebuilt.
The Vanport flood induced changes to the slough's system of levees, which were rebuilt and in some cases fortified to withstand a 100-year flood. Instead of repairing the levee along the Peninsula Canal, the city plugged it at both ends. The disaster also affected Oregon's system of higher education. After floodwaters destroyed the Vanport Extension Center, set up in 1946, the Oregon Board of Higher Education reestablished the school in downtown Portland, where it eventually became Portland State University.
pushes a barge from the Willamette River into the Columbia River around Kelley Point Park at the tip of the peninsula through which the slough flows.]]Debate about how to use the slough and its watershed continued through the rest of the century. In 1964, the Port of Portland, interested in industrial development, began to fill Smith, Bybee, and Ramsey lakes with dredging sands from the Columbia. In the 1970s, the Oregon Legislature passed a law against filling Smith or Bybee lakes below a contour line above mean sea level except to enhance fish and wildlife habitat. Plans for a Willamette River Greenway project proposed by Oregon Governor Tom McCall in the late 1960s called for park and recreation areas along the Willamette and many of its tributaries but ignored the slough. Some planners argued that the slough was so filthy that more industry was all it was good for. They portrayed cleanup as a lofty but impractical goal.
At Oregon's request, the U.S. Congress stripped the slough of its navigable status in 1978. This ended channel dredging on the slough, which could then be used for recreation. Other laws affecting the slough in the 1970s and beyond were the federal Clean Water Act and the Oregon Comprehensive Land Use Planning Act. In 1986, a business association began promoting commercial development along the upper slough, and the city later used urban renewal funds to support industrial projects near the airport. In 1996 the city acquired the Whitaker Ponds Natural Area, where it began a slough watershed education program for children.
The city closed the St. Johns Landfill, adjacent to the lower slough, in 1991. Pressed by citizen action groups, it agreed in 1993 to establish a environmental conservation zone along the slough. In response to a threatened lawsuit, the city began a comprehensive cleanup of the slough in 1994, and a year later it received a $10 million grant from the EPA for the purpose.
Of the streams monitored in the lower Willamette basin by the Oregon Department of Environmental Quality (DEQ) between 1986 and 1995, the Columbia Slough had the worst pollution scores. DEQ's measurements came from the slough at Landfill Road, from the mouth. On the Oregon Water Quality Index (OWQI) used by DEQ, water quality scores can vary from 10 (worst) to 100 (ideal). The average for the Columbia Slough was 22, or "very poor". By comparison, the average in the Willamette River at the Hawthorne Bridge in downtown Portland was 74 during the same years. Measurements of water quality at the Landfill Road site during the years covered by the DEQ report showed high concentrations of , ammonia and , Fecal coliforms, and suspended solids, and a high biochemical oxygen demand. High temperatures enhanced extreme eutrophication in the summer.
The Port of Portland began efforts in 1997 to reduce the flow of aircraft deicing chemicals from the airport into the waterway, though it still diverted concentrated chemicals (mostly glycol) directly into the slough during rare times of reservoir overflow. By 2012, the Port had completed work on an enhanced system that collects, stores, and treats the chemicals, and is more likely to direct runoff to the Columbia River than the slough.
By 2000 the City of Portland had spent about $200 million to nearly eliminate CSOs from entering the slough. It also replaced septic tank and cesspit systems near the middle and upper slough with . BES analysis of water samples taken between 1995 and 2002 showed that by the end of this period DEQ water quality standards for Escherichia coli, the indicator organism for fecal contamination, were nearly always being met in the upper and middle sloughs and generally being met in the lower slough. Despite these and other improvements in water quality, the slough is not a safe source of edible fish. The Multnomah County Health Department and other agencies have advised people to avoid or greatly reduce consumption of fish and crayfish from the slough because they contain polychlorinated biphenyls (PCB) and .
In 2002 the city, the MCDD, and the U.S. Army Corps of Engineers began a project to improve habitat by creating of stream and wetland terraces along the slough. Through its Watershed Revegetation Program, begun in 1996, the city worked with property owners to plant native vegetation and to remove invasive weeds. Through 2005, participants had replanted more than along nearly of riparian corridors in the slough watershed. Other strategies pursued by the city, Metro, and other interest groups include connecting separated habitats with a continuous riparian corridor, removing wildlife corridor barriers, restoring hydrological connections to the slough, and restoring the floodplain where feasible.
Big Four Corners Wetlands, managed by the Portland Parks & Recreation Department (PPR), includes about of wetlands and forests about from the slough's confluence with the Willamette River. Providing habitat for deer, , and river otter as well as birds and amphibians, it is the fourth largest natural area in the city. Further downstream, a consortium of interest groups is restoring a natural area of about at Johnson Lake. Whitaker Ponds Nature Park, at about RM 10 (RK 16), is a site with a walking trail, canoe launch, garden, and wildflower meadow. West of Whitaker Ponds, the Columbia Children's Arboretum, with every state tree, lies on a property managed by PPR.
Delta Park is a large municipal park complex that straddles Interstate 5 between the slough and the Columbia River at the former Vanport site. East Delta Park, covering about , has a sports complex and a street-tree arboretum. Portland International Raceway, for car, motorcycle, and bicycle racing, occupies about of West Delta Park. Adjacent to the raceway is the Heron Lakes Golf Course, . The grounds include wetlands and interpretive signs about Vanport. Smith and Bybee Wetlands Natural Area, a public park and nature reserve managed by Metro, lies just west of Delta Park. At about , it is one of the largest urban freshwater wetlands in the United States. Kelley Point Park covers at the tip of the peninsula between the Willamette and Columbia rivers.
Along the east side of the slough watershed, the City of Gresham has opened a segment of the Gresham-Fairview Trail, a planned , north–south hiking and biking route between the Springwater Corridor along Johnson Creek and the 40 Mile Loop along the Columbia River. On the west side of the watershed, the Peninsula Crossing Trail connects Willamette Cove on the Willamette River in St. Johns with the 40 Mile Loop along the Columbia River. This linear hiking and biking trail crosses the lower slough and passes between Smith Lake and Heron Lakes Golf Course. The trail is level and accessible by wheelchair. Amenities include a picnic area, seats carved from basalt, and art installations.
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