Editing Willamette River (section)

===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>