In what month is the flow of the WIllamette the lowest?
With an average flow at the mouth of about 37,400 cubic feet per second (1,060 m3/s), the Willamette ranks 19th in volume among rivers in the United States and contributes 12 to 15 percent of the total flow of the Columbia River. The Willamette's flow varies considerably season to season, averaging about 8,200 cubic feet per second (230 m3/s) in August to more than 79,000 cubic feet per second (2,200 m3/s) in December.
The U.S. Geological Survey (USGS) operates five stream gauges along the river, at Harrisburg, Corvallis, Albany, Salem, and Portland. The average discharge at the lowermost gauge, near the Morrison Bridge in Portland, was 33,220 cubic feet per second (941 m3/s) between 1972 and 2013. Located at river mile (RM) 12.8 or river kilometer (RK) 20.6, the gauge measures the flow from an area of 11,200 square miles (29,000 km2), roughly 97 percent of the Willamette basin. The highest flow recorded at this station was 420,000 cubic feet per second (11,893 m3/s) on February 9, 1996, during the Willamette Valley Flood of 1996, and the minimum was 4,200 cubic feet per second (120 m3/s) on July 10, 1978. The highest recorded flow of 635,000 cubic feet per second (18,000 m3/s) for the Willamette at a different gauge in Portland occurred during a 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.The river below Willamette Falls, 26.5 miles (42.6 km) from the mouth, is affected by semidiurnal tides, and gauges have detected reverse flows (backwards river flows) upstream from Ross Island at RM 15 (RK 24). The National Weather Service issues tide forecasts for the river at the Morrison Bridge.
August