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140-587: 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 watershed of about 51 square miles (130 km). Municipal wells near

280-403: A booster publication called The Peninsula , said: 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

420-706: 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, 2.6 miles (4.2 km) 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

560-500: A Willamette River port. In 1902, the U.S. Congress passed a Reclamation Act that encouraged irrigation, flood control, and wetland development in places like the peninsula. In 1907, the Spokane, Portland and Seattle Railway began work on a rail line across the peninsula. The railway and the port improvements led to high expectations. "St. Johns, the City of Destiny", a 1909 editorial appearing in

700-510: A comment on the Komatsu analysis, Brian Atwater and colleagues observed substantial evidence for multiple large floods, including mud cracks and animal burrows in lower layers, which were filled by sediment from later floods. Further, evidence for multiple flood flows up sidearms of Glacial Lake Columbia spread over many centuries has been found. They also pointed out that the discharge point from Lake Columbia varied with time, originally flowing across

840-663: A continuous riparian corridor, removing wildlife corridor barriers, restoring hydrological connections to the slough, and restoring the floodplain where feasible. Although reduced and altered, habitats in the watershed support a wide range of wildlife, some of which is found nowhere else in Portland. Many species that used the slough in 1850 still use it. This includes more than 150 species of birds, 26 species of fish of which 12 species are native several kinds of amphibians , western pond turtles , beaver , muskrat , river otter , and black-tailed deer . Juvenile salmon enter

980-461: A cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred several times over the 2,000 years between 15,000 and 13,000 years ago. U.S. Geological Survey hydrologist Jim O'Connor and Spain 's Museo Nacional de Ciencias Naturales scientist Gerardo Benito have found evidence of at least twenty-five massive floods, the largest discharging about 10 cubic kilometers per hour (2.7 million m³/s, 13 times that of

1120-409: A defined barometric pressure . Generally, the pressure used to set the altimeter is the barometric pressure that would exist at MSL in the region being flown over. This pressure is referred to as either QNH or "altimeter" and is transmitted to the pilot by radio from air traffic control (ATC) or an automatic terminal information service (ATIS). Since the terrain elevation is also referenced to MSL,

1260-650: A dozen species of ducks, geese, swans, and raptors , as well as Neotropical shorebirds and songbirds. Invasive species adapted to the slough include the nutria , common carp , bullfrog , and European starling . The slough watershed lies in the Portland/Vancouver Basin ecoregion, part of the Willamette Valley ecoregion designated by the U.S. Environmental Protection Agency (EPA). Black cottonwood , red osier dogwood , willow , Oregon white oak , and Oregon ash grow in scattered locations throughout

1400-457: A drainage area of undetermined size. The maximum flow was 2,400 cubic feet per second (68 m/s) on December 5, 1995, and the minimum flow (biggest reverse flow) was −6,700 cubic feet per second (−190 m/s) on February 7, 1996, which coincided with a flood on the Columbia and Willamette rivers. Draining about 51 square miles (130 km), the Columbia Slough watershed lies in the floodplain of

1540-432: A few metres, in timeframes ranging from minutes to months: Between 1901 and 2018, the average sea level rose by 15–25 cm (6–10 in), with an increase of 2.3 mm (0.091 in) per year since the 1970s. This was faster than the sea level had ever risen over at least the past 3,000 years. The rate accelerated to 4.62 mm (0.182 in)/yr for the decade 2013–2022. Climate change due to human activities

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1680-399: 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

1820-588: 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

1960-506: 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. After the start of the war with Japan, President Franklin D. Roosevelt signed an order for internment of all

2100-587: A place of deep mud or mire , a swamp, a river inlet or backwater, or a creek in a marsh or tide flat . The Columbia Slough is classified as a "stream" in the Geographic Names Information System (GNIS) of the United States Geological Survey (USGS). The slough takes its name from the Columbia River, of which it was historically a side channel or anabranch . Robert Gray , a Boston fur trader and whaler who sailed partway up

2240-438: A reference datum for mean sea level (MSL). It is also used in aviation, where some heights are recorded and reported with respect to mean sea level (contrast with flight level ), and in the atmospheric sciences , and in land surveying . An alternative is to base height measurements on a reference ellipsoid approximating the entire Earth, which is what systems such as GPS do. In aviation, the reference ellipsoid known as WGS84

2380-417: 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 coyotes . One of the nation's largest freshwater urban wetlands, Smith and Bybee Wetlands Natural Area , shares the lower slough watershed with

2520-493: A sewage treatment plant, marine terminals, a golf course, and a car racetrack. Watercraft able to portage over culverts 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. Slough usually rhymes with shoe in the U.S. except in New England, where it usually rhymes with now , the preferred British pronunciation. Slough may mean

2660-463: A sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century. Local factors like tidal range or land subsidence will greatly affect the severity of impacts. For instance, sea level rise in the United States is likely to be two to three times greater than the global average by the end of the century. Yet, of the 20 countries with

2800-469: A shipping route to downtown Portland. Other settlers logged the forests near the slough and built sawmills, fished, and farmed. In 1852, James John operated a ferry based on the peninsula of land between the Columbia and the Willamette River. The community of St. Johns , platted in the same year on the peninsula, is named after him. Legislation creating the Port of Portland in 1891 improved St. Johns' prospects as

2940-464: A study estimated that impervious surfaces covered 54 percent of the watershed. Storm runoff that might have taken days to reach the historic slough reaches the developed slough in hours. Until the 20th century, the slough and its side channels and associated ponds and lakes were part of the active Columbia River floodplain. When the historic river was high, the slough received water from it near Big Four Corners, about 17 miles (27 km) from

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3080-453: 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 7 miles (11 km) north of Portland was estimated at between magnitude 4.9 and 5.2. Based on records from 1961 to 1990,

3220-464: A wetland near Grant Butte and flows north for 5 miles (8 km) through the cities of Gresham and Fairview to reach the lake. Fairview Creek has two named tributaries, No Name Creek, and Clear Creek. A smaller stream, Osborn Creek, also flows into the lake, which empties through a weir and culvert system into the upper slough. With one exception, the streams feeding Fairview Lake are the watershed's only remaining creeks, although springs also reach

3360-405: Is a type of vertical datum  – a standardised geodetic datum  – that is used, for example, as a chart datum in cartography and marine navigation , or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels . A common and relatively straightforward mean sea-level standard

3500-635: Is an aquifer that is the primary source of drinking water for Vancouver in Washington and an auxiliary source for Portland. 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

3640-488: Is because the sea is in constant motion, affected by the tides, wind , atmospheric pressure, local gravitational differences, temperature, salinity , and so forth. The mean sea level at a particular location may be calculated over an extended time period and used as a datum . For example, hourly measurements may be averaged over a full Metonic 19-year lunar cycle to determine the mean sea level at an official tide gauge . Still-water level or still-water sea level (SWL)

3780-460: 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. Many governmental entities share responsibility for the slough and its drainage basin. Decisions by the municipal governments of Portland, Fairview, Gresham, Maywood Park, and Wood Village, and the government of Multnomah County affect the slough. Metro ,

3920-427: Is due to change in either the volume of water in the world's oceans or the volume of the oceanic basins . Two major mechanisms are currently causing eustatic sea level rise. First, shrinking land ice, such as mountain glaciers and polar ice sheets, is releasing water into the oceans. Second, as ocean temperatures rise, the warmer water expands. Many factors can produce short-term changes in sea level, typically within

4060-483: Is increasingly used to define heights; however, differences up to 100 metres (328 feet) exist between this ellipsoid height and local mean sea level. Another alternative is to use a geoid -based vertical datum such as NAVD88 and the global EGM96 (part of WGS84). Details vary in different countries. When referring to geographic features such as mountains, on a topographic map variations in elevation are shown by contour lines . A mountain's highest point or summit

4200-408: Is instead a long-term average of tide gauge readings at a particular reference location. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales . Current sea level rise is mainly caused by human-induced climate change . When temperatures rise, mountain glaciers and polar ice sheets melt, increasing the amount of water in the oceans, while

4340-447: Is the level of the sea with motions such as wind waves averaged out. Then MSL implies the SWL further averaged over a period of time such that changes due to, e.g., the tides , also have zero mean. Global MSL refers to a spatial average over the entire ocean area, typically using large sets of tide gauges and/or satellite measurements. One often measures the values of MSL with respect to

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4480-723: Is the main cause. Between 1993 and 2018, melting ice sheets and glaciers accounted for 44% of sea level rise , with another 42% resulting from thermal expansion of water . Sea level rise lags behind changes in the Earth 's temperature by many decades, and sea level rise will therefore continue to accelerate between now and 2050 in response to warming that has already happened. What happens after that depends on human greenhouse gas emissions . If there are very deep cuts in emissions, sea level rise would slow between 2050 and 2100. It could then reach by 2100 slightly over 30 cm (1 ft) from now and approximately 60 cm (2 ft) from

4620-527: Is typically illustrated with the AMSL height in metres, feet or both. In unusual cases where a land location is below sea level, such as Death Valley, California , the elevation AMSL is negative. It is often necessary to compare the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called the geoid . In the absence of external forces, the local mean sea level would coincide with this geoid surface, being an equipotential surface of

4760-682: The Amazon River ). Alternate estimates for the peak flow rate of the largest flood range up to 17 cubic kilometers per hour. The maximum flow speed approached 36 meters/second (130 km/h or 80 mph). Within the Columbia River drainage basin , detailed investigation of the Missoula floods' glaciofluvial deposits , informally known as the Hanford formation , has documented the presence of Middle and Early Pleistocene Missoula flood deposits within

4900-632: The Clackamas River , which empties into the Willamette River about 25 miles (40 km) south of the slough. The Clackamas tribe was a subgroup of the Chinookan speakers who lived in the Columbia River Valley from Celilo Falls to the Pacific Ocean. Clackamas lands included the lower Willamette River from Willamette Falls , at what later became Oregon City , to the Willamette's confluence with

5040-617: The Oregon Department of Environmental Quality (DEQ) to regulate the slough under provisions of the federal Clean Water Act . The Port of Portland , a regional agency run by commissioners appointed by the Oregon governor, owns and manages about 11 percent of the land in the slough watershed. Three drainage districts that manage water flows in the slough floodplain overlap parts of these other jurisdictions. In 2015, Portland's Bureau of Environmental Services (BES) began issuing annual "report cards" for watersheds or fractions thereof that lie within

5180-636: The Potholes Cataract . Bretz coined the term Channeled Scablands in 1923 to refer to the area near the Grand Coulee , where massive erosion had cut through basalt deposits. Bretz published a paper in 1923 arguing that the Channeled Scablands in Eastern Washington were caused by massive flooding in the distant past. Bretz's view, which was seen as arguing for a catastrophic explanation of

5320-465: The Spokane Valley – Rathdrum Prairie immediately downstream of Glacial Lake Missoula, for which several previous estimates had placed the maximum discharge of 17 × 10 m /s and the total amount of water discharged equal to the maximum estimated volume of Lake Missoula (2184 km ). Neglecting erosion effects, their simulated water flow was based on modern-day topography. Their major findings were that

5460-596: The Spokane floods , in the 1920s. He was researching the Channeled Scablands in Eastern Washington , the Columbia Gorge , and the Willamette Valley of Oregon . Beginning In the summer of 1922, Bretz conducted field research on the Columbia River Plateau for the next seven years. He had been interested in unusual erosion features in the area since 1910 after seeing a newly published topographic map of

5600-612: The geoid of the Earth, which approximates the local mean sea level for locations in the open ocean. The geoid includes a significant depression in the Indian Ocean , whose surface dips as much as 106 m (348 ft) below the global mean sea level (excluding minor effects such as tides and currents). Precise determination of a "mean sea level" is difficult because of the many factors that affect sea level. Instantaneous sea level varies substantially on several scales of time and space. This

5740-418: The height above mean sea level (AMSL). The term APSL means above present sea level, comparing sea levels in the past with the level today. Earth's radius at sea level is 6,378.137 km (3,963.191 mi) at the equator. It is 6,356.752 km (3,949.903 mi) at the poles and 6,371.001 km (3,958.756 mi) on average. This flattened spheroid , combined with local gravity anomalies , defines

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5880-544: The 1690s. Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES , TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008. Height above mean sea level ( AMSL ) is the elevation (on the ground) or altitude (in the air) of an object, relative to

6020-973: The 19th century. With high emissions it would instead accelerate further, and could rise by 1.0 m ( 3 + 1 ⁄ 3  ft) or even 1.6 m ( 5 + 1 ⁄ 3  ft) by 2100. In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming stays to its current 1.5 °C (2.7 °F) over the pre-industrial past. It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F). Rising seas affect every coastal and island population on Earth. This can be through flooding, higher storm surges , king tides , and tsunamis . There are many knock-on effects. They lead to loss of coastal ecosystems like mangroves . Crop yields may reduce because of increasing salt levels in irrigation water. Damage to ports disrupts sea trade. The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without

6160-576: The Channeled Scabland landforms were formed mainly by multiple periodic floods or by a single grand-scale cataclysmic flood from late Pleistocene Glacial Lake Missoula or an unidentified Canadian source continued through 1999. Shaw's team of geologists reviewed the sedimentary sequences of the Touchet beds and concluded that the sequences do not automatically imply multiple floods separated by decades or centuries. Rather, they proposed that sedimentation in

6300-466: The City of Fairview have also drilled three wells near the upper slough. Archeological evidence suggests that Native Americans lived along the lower Columbia River as early as 10,000 years ago, including near what later became The Dalles , on the Columbia River about 70 miles (110 km) east of the Columbia Slough. By 2,000 to 3,000 years ago, the Clackamas Indians had settled along

6440-476: The Columbia Gorge would be expected to produce higher flow resistance and correspondingly higher floods. The dating for Waitt's proposed separation of layers into sequential floods has been supported by subsequent paleomagnetism studies, which support a 30–40 year interval between depositions of Mount St. Helens' ash, and hence flood events, but do not preclude an up to 60-year interval. Offshore deposits on

6580-467: The Columbia River between the mouths of the Sandy River to the east and the Willamette River. Parts of Portland, Fairview, Gresham, Maywood Park , Wood Village , and unincorporated Multnomah County lie within the drainage basin (watershed). As of 2005, about 158,000 people, 5 percent of Oregon's population, lived in the basin. The watershed includes residential neighborhoods, agriculture,

6720-469: The Columbia River gorge, it backed up again at the 1 mile (1.6 km) wide narrows near Kalama, Washington . Some temporary lakes rose to an elevation of more than 400 ft (120 m), flooding the Willamette Valley to Eugene, Oregon and beyond. Iceberg-rafted glacial erratics and erosion features are evidence of these events. Lake-bottom sediments deposited by the floods have contributed to

6860-479: The Columbia River in 1792, named the river after his ship, Columbia Rediviva . The Columbia part of the ship's name belonged to the tradition of naming things after explorer Christopher Columbus . The Columbia Slough flows roughly parallel to and about 0.4 to 1.7 miles (0.6 to 2.7 km) south of the Columbia River in Multnomah County. It begins at Fairview Lake in the city of Fairview and immediately enters

7000-412: 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 cesspool systems near the middle and upper slough with sanitary sewers . 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 ,

7140-485: The Columbia River through a wetlands slightly upstream of Big Four Corners. In the early 20th century, water managers dug an artificial channel connecting the Fairview Creek wetlands to the slough. In 1960, they built a dam on the west side of the wetlands to create Fairview Lake for water storage and recreation. It covers about 100 acres (40 ha) and is 5 to 6 feet (1.5 to 1.8 m) deep. Fairview Creek forms in

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7280-648: The Columbia River. Missoula Floods The Missoula floods (also known as the Spokane floods , the Bretz floods , or Bretz's floods ) were cataclysmic glacial lake outburst floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age . These floods were the result of periodic sudden ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula . After each ice dam rupture,

7420-409: The Columbia River. The Columbia River floodplain near the mouth of the Willamette contained many stream channels, lakes, and wetlands that flooded annually. Chinookan tribes hunted and fished there and traveled between the two big rivers via the protected waters of the slough. Their main food sources were salmon, sturgeon , and camas . In 1792, Lieutenant William Broughton , a British explorer, led

7560-644: 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 phosphates , ammonia and nitrates , fecal coliform bacteria , and suspended solids, and a high biochemical oxygen demand . High temperatures enhanced extreme eutrophication in

7700-588: The Columbia South Shore Well Field that taps the deeper aquifers. As of 2004, 25 active wells drawing from depths ranging from 60 to 600 feet (18 to 183 m) could produce up to 100 million US gallons (380,000 m) a day from the field. These were drilled between 1976 and 2003 to supplement the city's main water supply from the Bull Run Watershed during droughts or emergencies. The Rockwood Water People's Utility District (PUD) and

7840-476: The Columbia. In the 1970s, the Oregon Legislature passed a law against filling Smith or Bybee lakes below a contour line 11 feet (3.4 m) 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

7980-448: The Earth's gravitational field which, in itself, does not conform to a simple sphere or ellipsoid and exhibits gravity anomalies such as those measured by NASA's GRACE satellites . In reality, the geoid surface is not directly observed, even as a long-term average, due to ocean currents, air pressure variations, temperature and salinity variations, etc. The location-dependent but time-persistent separation between local mean sea level and

8120-606: The Glacial Lake Missoula basin resulted from jökulhlaups draining into Lake Missoula from British Columbia to the north. Further, Shaw's team proposed the scabland flooding might have partially originated from an enormous subglacial reservoir that extended over much of central British Columbia, particularly including the Rocky Mountain Trench , which may have discharged by several paths, including one through Lake Missoula. This discharge, if occurring concurrently with

8260-672: The Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collated data about the sea level. It is used for a part of continental Europe and the main part of Africa as the official sea level. Spain uses the reference to measure heights below or above sea level at Alicante , while the European Vertical Reference System is calibrated to the Amsterdam Peil elevation, which dates back to

8400-635: The Othello Channels, Columbia River Gorge, Channeled Scabland , Quincy Basin, Pasco Basin, and the Walla Walla Valley . Based on the presence of multiple interglacial calcretes interbedded with flood deposits, magnetostratigraphy , optically stimulated luminescence dating, and unconformity truncated clastic dikes , it has been estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago. Because of

8540-519: 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. By 1850, White settlers established donation land claims in the Columbia Slough watershed. One settler, Lewis Love, became wealthy by cutting timber in the watershed and using the slough as part of

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8680-591: 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 . 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 dredge sands from

8820-603: 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

8960-680: The Waterville Plateau into Moses Coulee, but later, when the Okanagan lobe blocked that route, eroding the Grand Coulee to discharge there as a substantially lower outlet. The Komatsu analysis does not evaluate the impact of the considerable erosion observed in this basin during the flood or floods. However, the assumption that flood hydraulics can be modeled using modern-day topography is an area that warrants further consideration. Earlier narrower constrictions at places such as Wallula Gap and through

9100-475: The Willamette River about 1 mile (1.6 km) from its confluence with the Columbia River. The mouth of the Columbia River is about 101 miles (163 km) further downstream at Astoria on the Pacific Ocean. Since 1989, the USGS has monitored the flow of the Columbia Slough at a stream gauge 0.6 miles (1.0 km) from the mouth. The average flow recorded at this gauge is 93.8 cubic feet per second (3 m/s) from

9240-460: The agricultural richness of the Willamette and Columbia Valleys. Glacial deposits overlaid with centuries of windblown sediments ( loess ) have scattered steep, southerly sloping dunes throughout the Columbia Valley, ideal conditions for orchard and vineyard development at higher latitudes. After analysis and controversy, geologists now believe that there were 40 or more separate floods, although

9380-663: 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 zones 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

9520-504: 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

9660-660: The bed of the Pacific at the mouth of the Columbia River include 120 meters of material deposited over a several thousand-year period corresponding to multiple scabland floods seen in the Touchet Beds. Based on Waitt's identification of 40 floods, this would give an average separation between floods of 50 years. Sea level Mean sea level ( MSL , often shortened to sea level ) is an average surface level of one or more among Earth 's coastal bodies of water from which heights such as elevation may be measured. The global MSL

9800-467: The breach of the Lake Missoula ice dam, would have provided significantly larger volumes of water. Further, Shaw and the team proposed that the rhythmic Touchet beds result from multiple pulses or surges within a larger flood. In 2000, a team led by Komatsu simulated the floods numerically with a 3-dimensional hydraulic model. They based the Glacial Lake Missoula discharge rate on the rate predicted for

9940-567: The calculated water depth in each flooded location except for the Spokane Valley–Rathdrum Prairie was shallower than the field evidence showed. For example, their calculated water depth at the Pasco Basin–Wallula Gap transition zone is about 190 m, significantly less than the 280–300 m flood depth indicated by high-water marks. They concluded that a flood of ~10 m /s could not have made the observed high-water marks. In

10080-550: 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,

10220-433: The city of Gresham. Less than 1 mile (1.6 km) later, it enters the city of Portland and continues generally westward for about another 18 miles (29 km) to its confluence with the Willamette River. Throughout its course, the slough is nearly level, 10 feet (3.0 m) above sea level at the source and 9 feet (2.7 m) at the mouth. Semidiurnal tides cause reverse currents on the lower 8.5 miles (13.7 km) of

10360-429: 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

10500-482: The city. BES assigns grades for each of four categories: hydrology, water quality, habitat, and fish and wildlife. Hydrology grades depend on the amount of pavement and other impervious surfaces in the watershed and to what degree its streams flow freely, not dammed or diverted. Water-quality grades are based on measurements of dissolved oxygen , E-coli bacteria, temperature, suspended solids , and substances such as mercury and phosphorus . Habitat ranking depends on

10640-479: The condition of stream banks and floodplains, riparian zones , tree canopies , and other variables. The fish and wildlife assessment includes birds, fish, and macroinvertebrates . In 2015, the BES grades for the Columbia Slough are hydrology, B− ; water quality, B− ; habitat, D− , and fish and wildlife, F. The Columbia Slough is part of the roughly 770-square-mile (2,000 km) Portland Basin, which lies at

10780-406: The cracks, generating more heat, allowing even more water to flow through the cracks. This feedback cycle eventually weakened the ice dam so much that it could no longer support the pressure of the water behind it. It failed catastrophically. This process is known as a glacial lake outburst flood , and there is evidence that many such events occurred in the distant past. As the water emerged from

10920-462: The districts maintained 30 miles (48 km) of levees as well as water pumps, floodgates and other water control devices. The upper slough extends from the slough's source at Fairview Lake, roughly 18.5 miles (30 km) from the mouth, to a gated levee known as the mid-dike levee about 3 miles (5 km) downstream. This sector, managed by MCDD, covers 2,650 acres (1,070 ha) completely surrounded by levees. A northern side channel extends from

11060-400: 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

11200-573: The east sent flows of mud, ash, and eroded volcanic debris into the Columbia, which was powerful enough to carry the material downstream. Deposited above the basalt during the Miocene and early Pliocene , these loose sands and gravels formed part of what is known as the Troutdale Formation. Extending to the Tualatin River Valley to the south and into Clark County on the north, the formation

11340-479: The entire Columbia Gorge to overflowing and turned the Willamette Valley into a lake 100 miles (160 km) long, 60 miles (100 km) wide and 300 feet (90 m) deep. The floodwaters ripped the face off Rocky Butte in Portland and deposited a 5-mile (8 km) 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

11480-529: 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 1,475 acres (597 ha) east of the highway, and Pen 1 manages 901 acres (365 ha) 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 . Historically Fairview Creek flowed north into

11620-408: The exact source of the water is still being debated. The peak flow of the floods is estimated to be 27 cubic kilometers per hour (6.5 cubic miles per hour). The maximum flow speed approached 36 meters/second (130 km/h or 80 mph). Up to 1.9×10 joules of potential energy were released by each flood (the equivalent of 4,500 megatons of TNT ). For comparison, this is 90 times more powerful than

11760-415: The existing seawater also expands with heat. Because most of human settlement and infrastructure was built in response to a more-normalized sea level with limited expected change, populations affected by sea level rise will need to invest in climate adaptation to mitigate the worst effects or, when populations are at extreme risk, a process of managed retreat . The term above sea level generally refers to

11900-600: 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. After years of piping raw sewage directly into

12040-569: The first half of the 20th century and cut off from the Columbia River by levees, the slough became one of Oregon's most polluted 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

12180-435: 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

12320-525: The fragmentary nature of older glaciofluvial deposits, which have been largely removed by subsequent Missoula floods, within the Hanford formation, the exact number of older Missoula floods, which are known as ancient cataclysmic floods , that occurred during the Pleistocene cannot be estimated with any confidence. Geologist J Harlen Bretz first recognized evidence of the catastrophic floods, which he called

12460-482: The geoid is referred to as (mean) ocean surface topography . It varies globally in a typical range of ±1 m (3 ft). Several terms are used to describe the changing relationships between sea level and dry land. The melting of glaciers at the end of ice ages results in isostatic post-glacial rebound , when land rises after the weight of ice is removed. Conversely, older volcanic islands experience relative sea level rise, due to isostatic subsidence from

12600-561: The geology, ran against the prevailing view of uniformitarianism , and Bretz's views were initially disregarded. The Geological Society of Washington, D.C , invited the young Bretz to present his previously published research at a January 12, 1927, meeting where several other geologists presented competing theories. Another geologist at the meeting, J.T. Pardee , had worked with Bretz and had evidence of an ancient glacial lake that lent credence to Bretz's theories. Bretz defended his theories, which kicked off an acrimonious 40-year debate over

12740-624: The greatest exposure to sea level rise, twelve are in Asia , including Indonesia , Bangladesh and the Philippines. The resilience and adaptive capacity of ecosystems and countries also varies, which will result in more or less pronounced impacts. The greatest impact on human populations in the near term will occur in the low-lying Caribbean and Pacific islands . Sea level rise will make many of them uninhabitable later this century. Pilots can estimate height above sea level with an altimeter set to

12880-551: The height of planetary features. Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time long enough that fluctuations caused by waves and tides are smoothed out, typically a year or more. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can occur at rates similar to sea level changes (millimetres per year). Some land movements occur because of isostatic adjustment to

13020-401: 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

13160-576: The land; hence a change in relative MSL or ( relative sea level ) can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates, or both. In the UK, the ordnance datum (the 0 metres height on UK maps) is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Before 1921, the vertical datum was MSL at the Victoria Dock, Liverpool . Since

13300-425: The largest of the boulders moved by the flood. He estimated the water flow was 9 cubic miles per hour (38 km /h), more than the combined flow of every river in the world. More recent estimates place the flow rate at ten times the flow of all current rivers combined. The Missoula floods have also been referred to as the Bretz floods in honor of Bretz. As the depth of the water in Lake Missoula increased,

13440-470: The lower slough as well as Smith and Bybee Lakes. Coastal cutthroat trout inhabit Fairview Creek and Osborn Creek. Three species of native freshwater mussel live in the slough and in Smith and Bybee Lakes. Crayfish have been found throughout the slough. Bald eagles are among the resident birds, and great blue herons have established rookeries in the watershed. Migrants that visit the slough include more than

13580-439: The lower slough watershed surrounded on all sides by dikes between 15 and 25 feet (5 and 8 m) 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

13720-468: The lower slough, Smith and Bybee Wetlands Natural Area at 2,000 acres (810 ha) is one of the largest urban freshwater wetlands in the United States. A 1-mile (1.6 km) 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. Groundwater discharges from an aquifer near

13860-481: The melting of ice sheets at the end of the last ice age . The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds . Changes in ground-based ice volume also affect local and regional sea levels by the readjustment of the geoid and true polar wander . Atmospheric pressure , ocean currents and local ocean temperature changes can affect LMSL as well. Eustatic sea level change (global as opposed to local change)

14000-519: The mid-dike levee and the Pen ;2 levee , 8.5 miles (13.7 km) from the mouth. This sector covers 6,848 acres (2,771 ha), 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

14140-514: 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 275,000 U.S. gallons per minute (17,300 L/s). The middle slough, also managed by MCDD, lies between

14280-630: 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

14420-472: 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 250,000 US gallons per minute (16 m/s). 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 12 inches (30 cm) and 24 inches (61 cm) roughly twice per day along

14560-440: The most powerful nuclear weapon ever detonated, the 50-megaton " Tsar Bomba ". The cumulative effect of the floods was to excavate 210 cubic kilometres (50 cu mi) of loess, sediment, and basalt from the Channeled Scablands of eastern Washington and to transport it downstream. The multiple flood hypothesis was first proposed by R.B. Waitt Jr. in 1980. Waitt argued for a sequence of 40 or more floods. Waitt's proposal

14700-513: The northern end of the Willamette Valley of Oregon and extends north into Clark County in the state of Washington . The region is underlain by solidified lavas of the Columbia River Basalt Group that are up to 16 million years old. Covered by later alluvial deposits, the basalts lie more than 1,000 feet (300 m) below the surface within the basin. About 10 million years ago, eruptions of Cascade Range volcanoes to

14840-565: The origin of the Scablands. Both Pardee and Bretz continued their research over the next 30 years, collecting and analyzing evidence that led them to identify Lake Missoula as the source of the Spokane flood and creator of the channeled scablands. After Pardee studied the canyon of the Flathead River , he estimated that flood waters above 45 miles per hour (72 km/h) would be required to roll

14980-638: The people of Japanese ancestry who lived on the West Coast . About 1,700 of them lived in Portland, and some had farms or businesses near the slough. When the government removed them from their homes in 1942, it housed them temporarily in the Livestock Exposition Center (Expo Center) in Kenton before sending them to internment camps further inland. They were not allowed to return until 1945. In 1942, Kaiser Shipbuilding Company began making ships for

15120-410: The pressure at the bottom of the ice dam increased enough to lower the freezing point of water below the temperature of the ice forming the dam. This allowed liquid water to seep into minuscule cracks present in the ice dam. Over a period of time, the friction from water flowing through these cracks generated enough heat to melt the ice walls and enlarge the cracks. This allowed more water to flow through

15260-482: The regional governmental agency for the Oregon portion of the Portland metropolitan area , is involved in acquiring and protecting wildlife habitat in places like Big Four Corners Wetlands and Smith and Bybee Wetlands Natural Area, acquiring property to close gaps in the 40-Mile Loop and other trails, and creating additional water access along the slough. The United States Environmental Protection Agency (EPA) has designated

15400-484: 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 9 and 8 miles (14 and 13 km) 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

15540-483: The slough because they contain polychlorinated biphenyls (PCB) and pesticides . Development since 1850 has greatly altered the places in the watershed where plants and animals can thrive. In a report published in 2005, the Portland Bureau of Environmental Services (BES), using data from an early United States General Land Office survey, compared the watershed of 1851 with that of 2003. The study showed that all of

15680-459: The slough from combined sewer overflows (CSO)s at 13 outfalls. 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 50-foot (15 m) 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

15820-406: The slough had formed three drainage districts to control floods. They dug ditches, deepened existing water channels, and built levees to keep the rivers and the slough from flooding agricultural, industrial, and commercial property. Hoping to flush the slough with clean water from the river, city engineers created the crosscutting Peninsula Canal. The project largely failed because daily tides reversed

15960-413: The slough's flow and because both ends of the canal were at nearly the same elevation. 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

16100-544: The slough's mouth. In 1917, landowners formed three drainage districts—Peninsula Drainage District No. 1 (Pen 1), Peninsula Drainage District No. 2 (Pen 2), and Multnomah County Drainage District No. 1 (MCDD)—to control flooding. A fourth district, the Sandy Drainage Improvement Company (SDIC), manages water flow at the upper end of the slough's basin in Fairview and Troutdale. By 2008,

16240-467: The slough, and by 1911 Portland had become the main livestock market for the Pacific Northwest . These and other early 20th century businesses, including stockyards, a dairy farm, a shingle company, and a lumber mill, flushed waste products into the slough. Starting in 1910, north Portland's residential sewage also poured into the slough through pipes laid for the purpose. In 1917, landowners along

16380-425: The slough. Running slightly north of and parallel to U.S. Route 30 (Sandy Boulevard), the slough flows by Zimmerman Heritage Farm on the left bank (south) about 17.5 miles (28.2 km) from the mouth, Big Four Corners Wetlands on the right bank 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

16520-405: 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

16660-435: 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 500 acres (200 ha) along nearly 40 miles (64 km) of riparian corridors in the slough watershed. Other strategies pursued by the city, Metro, and other interest groups include connecting separated habitats with

16800-420: 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

16940-525: 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. As Portland grew, it annexed St. Johns and expanded into the peninsula and other parts of the watershed. East of St. Johns, the Swift Meatpacking Company bought 3,400 acres (1,400 ha) in 1906 and established the community of Kenton . Other companies built packing plants and slaughterhouses along

17080-408: The surface supply an estimated flow between 50 and 100 cubic feet per second (1.4 and 2.8 m/s) to the middle and upper sloughs. Rain infiltration and artificial sumps recharge this shallow aquifer. Geologists have identified four other major aquifers separated by relatively impermeable clays or other strata at various levels below the surface aquifer. The City of Portland's water bureau manages

17220-515: The surface. Wilkes Creek, the slough's only free flowing tributary, is about 2 miles (3 km) 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

17360-651: 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

17500-507: The times of the Russian Empire , in Russia and its other former parts, now independent states, the sea level is measured from the zero level of Kronstadt Sea-Gauge. In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 0.146 m (5.7 in) above chart datum and 1.304 m (4 ft 3.3 in) below the average sea level. In France,

17640-426: The top of the Touchet beds. The two layers of volcanic ash are separated by 1–10 centimetres (0.4–3.9 in) of airborne nonvolcanic silt. The tephra is Mount St. Helens ash that fell in Eastern Washington. By analogy, since there were 40 layers with comparable characteristics at Burlingame Canyon, Waitt argued they all could be considered to have similar separation in deposition time. The controversy about whether

17780-437: The upper end of the slough, the City of Fairview manages Lakeshore Park, 5.2 acres (2.1 ha) on the south edge of Fairview Lake. Slightly further north is Blue Lake Regional Park , a 101-acre (41 ha) recreational park with a 64-acre (26 ha) lake, both managed by Metro . To the northeast is Chinook Landing Marine Park, also managed by Metro. At about 67 acres (27 ha), it is Oregon's largest public boating park on

17920-403: 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

18060-517: 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 Liberty ships , 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 650 acres (260 ha) of former marsh, pasture, and farmland in

18200-525: The waters of the lake would rush down the Clark Fork and the Columbia River , flooding much of eastern Washington and the Willamette Valley in western Oregon . After the lake drained, the ice would reform, creating Glacial Lake Missoula again. These floods have been researched since the 1920s. During the last deglaciation that followed the end of the Last Glacial Maximum , geologists estimate that

18340-477: 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

18480-459: The watershed provided plant and wildlife habitat in 1851, but by 2003 only 33 percent provided habitat. In 1851, water covered 10 percent of the watershed but that had been cut in half by 2003. Marshes and other wetlands that had comprised 22 percent of the earlier watershed dwindled to 1 percent by 2003, while the percentage of land devoted to industry, commerce, and homes rose from 0 to 34. In addition, habitat remaining in 2003

18620-421: 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 baseflows 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,

18760-431: The watershed's average annual precipitation, as measured at Portland International Airport, is about 36 inches (910 mm). About 21 inches (530 mm) falls from November through February and only about 4 inches (100 mm) from June through September. Since temperatures are normally below freezing fewer than 30 days a year, most of this precipitation reaches the ground as rain. Historically, most rain falling on

18900-561: The watershed, while wapato and Columbia sedge thrive in a few places. In the slough itself, macrophytes and algae sometimes restrict water flow and reduce water quality. Golf courses and athletic fields near the slough consist mainly of non-native grasses. Developed plots with houses or businesses often have deciduous street trees, grasses, occasional conifers , and a variety of native and non-native shrubs . Invasive plants include Himalayan blackberry , English ivy , reed canarygrass , purple loosestrife , and Japanese knotweed . At

19040-400: The waterway, Portland built its first sewage treatment plant next to the lower slough in 1952. The Columbia Boulevard Wastewater Treatment Plant handled a combination of raw sewage and storm runoff that flowed into the sanitary sewer system from all over the city and piped the treated water into the Columbia River. When runoff exceeded the plant's capacity during heavy rains, sewage still entered

19180-411: The weight of cooling volcanos. The subsidence of land due to the withdrawal of groundwater is another isostatic cause of relative sea level rise. On planets that lack a liquid ocean, planetologists can calculate a "mean altitude" by averaging the heights of all points on the surface. This altitude, sometimes referred to as a "sea level" or zero-level elevation , serves equivalently as a reference for

19320-610: Was based mainly on analysis from glacial lake bottom deposits in Ninemile Creek and the flood deposits in Burlingame Canyon. His most compelling argument for separate floods was that the Touchet bed deposits from two successive floods were found to be separated by two layers of volcanic ash ( tephra ), with the ash separated by a fine layer of windblown dust deposits, located in a thin layer between sediment layers ten rhythmites below

19460-440: Was greatly disturbed, dominated by Himalayan blackberry and other invasive species and fragmented by roads. The riparian zone along the slough was generally narrow or nonexistent and devoid of trees and shrubs in places, including along the levees. In 2002 the city, the MCDD, and the U.S. Army Corps of Engineers began a project to improve habitat by creating 7 miles (11 km) of stream meanders and wetland terraces along

19600-529: 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

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