Editing Willamette River (section)

==Course==
{{Main|Course of the Willamette River}}
[[File:Pan Voyager moored in the Williamette.jpg|thumb|alt=Pan Voyager moored in the Willamette|Ocean-going cargo ship anchored at the mouth of the Willamette]]
The upper tributaries of the Willamette originate in the mountains south and southeast of [[Eugene, Oregon]]. Formed by the confluence of the [[Middle Fork Willamette River]] and the [[Coast Fork Willamette River]] near [[Springfield, Oregon|Springfield]], the [[main stem]] Willamette meanders generally north for {{convert|187|mi|km}} to the [[Columbia River]]. The river's two most significant course deviations occur at [[Newberg, Oregon|Newberg]], where it turns sharply east, and about {{convert|18|mi|km}} downstream from Newberg, where it turns north again. Near its mouth north of downtown [[Portland, Oregon|Portland]], the river splits into two channels that flow around [[Sauvie Island]]. Used for navigation purposes, these channels are managed by the [[Federal government of the United States|U.S. federal government]]. The main channel, which is the primary navigational conduit for Portland's harbor and riverside industrial areas, is {{convert|40|ft|m}} deep and varies in width from {{convert|600|to|1900|ft|m}}, although the river broadens to {{convert|2000|ft|m}} in some of its lower reaches.<ref name="DeLorme"/><ref name="channel plan"/> This channel enters the Columbia about {{convert|101|mi|km}} from the Columbia's mouth on the Pacific Ocean. The smaller [[Multnomah Channel]], a [[distributary]], is {{convert|21|mi|km}} long, about {{convert|600|ft|m}} wide, and {{convert|40|ft|m}} deep. It ends about {{convert|14.5|mi|km}} farther downstream on the Columbia, near [[St. Helens, Oregon|St. Helens]] in [[Columbia County, Oregon|Columbia County]].<ref name="DeLorme">{{cite map |publisher=DeLorme Mapping |title=Oregon Atlas & Gazetteer |edition=1991 |section=41–43, 47–48, 53, 59–60, 66 |isbn=0-89933-235-8}}</ref><ref name="channel plan">{{cite web |url=http://www.portlandoregon.gov/bps/article/145503 |title=Willamette River Dredged Material Management Plan Project |publisher=City of Portland |author=Bureau of Planning and Sustainability |archive-url=https://web.archive.org/web/20161117144851/http://www.portlandoregon.gov/bps/article/145503 |archive-date=November 17, 2016}}</ref><ref name="topoquest multiple quads">{{cite web |author=U.S. Geological Survey |title=United States Geological Survey Topographic Map |publisher=TopoQuest |url=http://www.topoquest.com/map.php?lat=44.03988&lon=-123.02511&datum=nad83&zoom=4&map=auto&coord=d&mode=zoomin&size=m |access-date=June 29, 2010 |archive-date=October 13, 2012 |archive-url=https://web.archive.org/web/20121013014728/http://www.topoquest.com/map.php?lat=44.03988&lon=-123.02511&datum=nad83&zoom=4&map=auto&coord=d&mode=zoomin&size=m |url-status=dead}} Relevant map quadrangles include Eugene East, Coburg, Junction City, Harrisburg, Peoria, Riverside, Lewisburg, Albany, Monmouth, Salem West, Mission Bottom, Dayton, St. Paul, Newberg, Sherwood, Canby, Lake Oswego, Portland, Linnton, Sauvie Island, and Saint Helens.</ref><ref name="Multnomah Channel">{{cite web |title=Multnomah Channel |url=http://www.oregon.gov/OSMB/library/docs/WillametteRiverGuide-07/WillametteRiverGuidePDF-MultnomahChannel.pdf?ga=t |publisher=Oregon State Marine Board; Oregon State Parks Department |archive-url=https://web.archive.org/web/20140529052638/http://www.oregon.gov/OSMB/library/docs/WillametteRiverGuide-07/WillametteRiverGuidePDF-MultnomahChannel.pdf?ga=t |archive-date=May 29, 2014 |page=30 |url-status=dead}}</ref><ref name="Columbia project">{{cite web |url=http://www.sei.org/columbia/background_project.html |title=Background&nbsp;– Project |publisher=Sustainable Ecosystems Institute |work=Columbia River Project—Columbia River Channel Improvement Reconsultation Project |date=February 28, 2001 |url-status=dead |archive-url=https://web.archive.org/web/20111005050610/http://www.sei.org/columbia/background_project.html |archive-date=October 5, 2011}}</ref>

Proposals have been made for deepening the Multnomah Channel to {{convert|43|ft|m}} in conjunction with roughly {{convert|103.5|mi|km}} of tandem-maintained navigation on the Columbia River.<ref name="Columbia project" /> Between the 1850s and the 1960s, channel-straightening and flood control projects, as well as agricultural and urban encroachment, cut the length of the river between the McKenzie River confluence and Harrisburg by 65&nbsp;percent. Similarly, the river was shortened by 40&nbsp;percent in the stretch between Harrisburg and Albany.<ref>Laenen and Dunnette, p. 24</ref>

[[File:Multnomah Channel (Multnomah County, Oregon scenic images) (mulDA0081a).jpg|thumb|left|alt=The Multnomah Channel|The Multnomah Channel from the Sauvie Island Bridge]]

[[Interstate 5 in Oregon|Interstate 5]] and three branches of [[Oregon Route 99]] are the two major highways that follow the river for its entire length. Communities along the main stem include Springfield and Eugene in [[Lane County, Oregon|Lane County]]; [[Harrisburg, Oregon|Harrisburg]] in [[Linn County, Oregon|Linn County]]; [[Corvallis, Oregon|Corvallis]] in [[Benton County, Oregon|Benton County]]; [[Albany, Oregon|Albany]] in Linn and Benton counties; [[Independence, Oregon|Independence]] in [[Polk County, Oregon|Polk County]]; [[Salem, Oregon|Salem]] in [[Marion County, Oregon|Marion County]]; Newberg in [[Yamhill County, Oregon|Yamhill County]]; [[Oregon City, Oregon|Oregon City]], [[West Linn, Oregon|West Linn]], [[Milwaukie, Oregon|Milwaukie]], and [[Lake Oswego, Oregon|Lake Oswego]] in [[Clackamas County, Oregon|Clackamas County]]; and Portland in Multnomah and [[Washington County, Oregon|Washington]] counties. Significant tributaries from source to mouth include the Middle and Coast forks and the [[McKenzie River (Oregon)|McKenzie]], [[Long Tom River|Long Tom]], [[Marys River (Oregon)|Marys]], [[Calapooia River|Calapooia]], [[Santiam River|Santiam]], [[Luckiamute River|Luckiamute]], [[Yamhill River|Yamhill]], [[Molalla River|Molalla]], [[Tualatin River|Tualatin]], and [[Clackamas River|Clackamas]] rivers.<ref name="DeLorme"/><ref name="topoquest multiple quads"/>

Beginning at {{convert|438|ft|m}} above sea level, the main stem descends {{convert|428|ft|m}} between source and mouth, or about 2.3&nbsp;feet per mile (0.4&nbsp;m per km).<ref name="gnis">{{cite web |url={{GNIS 3|1158060}} |date=November 28, 1980 |title=Willamette River |work=Geographic Names Information System |publisher=U.S. Geological Survey |access-date=June 25, 2010}} Source and mouth elevation derived from [[Google Earth]] search using GNIS source and mouth coordinates.</ref> The gradient is slightly steeper from the source to Albany than it is from Albany to Oregon City.<ref name = "Benke 617">Benke, ''et al.'', p. 617</ref> At [[Willamette Falls]], between West Linn and Oregon City, the river plunges about {{convert|40|ft|m}}.<ref name = "Benke 617"/> For the rest of its course, the river is extremely low-gradient and is affected by Pacific Ocean tidal effects from the Columbia.<ref name = "Benke 617"/> The main stem of the Willamette varies in width from about {{convert|330|to|660|ft|m}}.<ref name = "Benke 617"/>

===Discharge===
{{Main|Course of the Willamette River#Discharge|l1=Discharge of the Willamette}}
With an average flow at the mouth of about {{convert|37400|cuft/s|m3/s}}, the Willamette ranks 19th in volume among rivers in the United States<ref name="USGSrivers">{{cite web |first=J.C. |last=Kammerer |url=http://pubs.usgs.gov/of/1987/ofr87-242/ |title=Largest Rivers in the United States |publisher=U.S. Geological Survey |date=May 1990 |access-date=July 2, 2010}}</ref> and contributes 12 to 15&nbsp;percent of the total flow of the Columbia River.<ref name="Benke 616"/> The Willamette's flow varies considerably season to season, averaging about {{convert|8200|cuft/s|m3/s}} in August to more than {{convert|79000|cuft/s|m3/s}} in December.<ref name = "Benke 617"/>

[[File:Oregon_Route_34_1717.JPG|thumb|alt=The Willamette at Corvallis|The Oregon Route 34 bridge across the Willamette River at Corvallis is a mid-valley highway crossing.]]

The [[United States Geological Survey|U.S. Geological Survey]] (USGS) operates five [[stream gauge]]s along the river, at Harrisburg, Corvallis, Albany, Salem, and Portland. The average discharge at the lowermost gauge, near the Morrison Bridge in Portland, was {{convert|33220|cuft/s|m3/s|0}} between 1972 and 2013. Located at [[river mile]] (RM)&nbsp;12.8 or river kilometer (RK)&nbsp;20.6, the gauge measures the flow from an area of {{convert|11200|sqmi|km2}}, roughly 97&nbsp;percent of the Willamette basin.<ref name= "Morrison Bridge gauge">{{cite web |title=Water-Year Summary for Site USGS 14211720 |publisher=U.S. Geological Survey |url=https://waterdata.usgs.gov/nwis/wys_rpt?dv_ts_ids=114384&wys_water_yr=2015&site_no=14211720&agency_cd=USGS&adr_water_years=2006%2C2007%2C2008%2C2009%2C2010%2C2011%2C2012%2C2013%2C2014%2C2015%2C2016&referred_module= |access-date=January 8, 2017}}</ref> The highest flow recorded at this station was {{convert|420000|cuft/s|m3/s|0}} on February&nbsp;9, 1996, during the [[Willamette Valley Flood of 1996]], and the minimum was {{convert|4200|cuft/s|m3/s}} on July&nbsp;10, 1978.<ref name="Morrison Bridge gauge"/> The highest recorded flow of {{convert|635000|cuft/s|m3/s}} for the Willamette at a different gauge in Portland occurred during a [[Great Flood of 1862|flood in 1861]]. This and many other large flows preceded the [[Flood Control Act of 1936]] and dam construction on the Willamette's major tributaries.<ref name="Flooding">{{cite web |url=http://140.194.76.129/publications/misc/un24/c-8.pdf |title=Willamette River Multi-Purpose Development in the 1930s |publisher=U.S. Army Corps of Engineers |work=Army Engineers and the Development of Oregon: A History of the Portland District U.S. Army Corps of Engineers |year=1983 |page=107 |archive-url=https://web.archive.org/web/20140221174430/http://140.194.76.129/publications/misc/un24/c-8.pdf |archive-date=February 21, 2014}}</ref>

The river below Willamette Falls, {{convert|26.5|mi|km}} from the mouth, is affected by [[tide|semidiurnal tides]],<ref>{{cite web |url=http://www.oregon.gov/DSL/NAV/Pages/tidally.aspx |title=Tidally-Influenced Waterways |work=Waterway Authorizations |publisher=Oregon Department of State Lands |url-status=dead |archive-url=https://web.archive.org/web/20121008131154/http://www.oregon.gov/DSL/NAV/Pages/tidally.aspx |archive-date=October 8, 2012}}</ref> and gauges have detected reverse flows (backwards river flows) below [[Ross Island (Oregon)|Ross Island]] at RM&nbsp;15 (RK&nbsp;24).<ref>{{cite journal |first=James M. |last=Caldwell |author2=Doyle, Micelis C |title=Sediment Oxygen Demand in the Lower Willamette River, Oregon, 1994 |year=1995 |journal=Water-Resources Investigations Report 95-4196 |publisher=U.S. Geological Survey |page=2 |doi=10.3133/WRI954196 |s2cid=129065743 |doi-access=free |hdl=2027/uc1.31210026451912 |hdl-access=free}}</ref> The [[National Weather Service]] issues tide forecasts for the river at the [[Morrison Bridge]].<ref>{{cite web |author=National Weather Service Forecast Office |location=Portland, Oregon |title=Local Tide Predictions and Water Levels |publisher=U.S. Department of Commerce |url=http://www.wrh.noaa.gov/pqr/tides.php |access-date=July 2, 2010}}</ref>