| OSMB News |
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| Date: Thursday, July 5, 2007 |
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Outlook for Portland/Vancouver Harbor Levels This Summer and Fall
For Immediate Release
With the summer boating season licking into high gear this week, the National Weather Service wants boaters to be aware of the possibility of very low river levels on the Columbia and Willamette Rivers in the Portland/Vancouver area this summer and fall. Boaters whould use caution to avoid sand bars and shallow areas, especially during low tide.
The main cause for low flows on the Columbia and Willamette is the below-normal snowpack this past winter throughout most of the Columbia basin, which encompasses much of the Washington, Oregon, Idaho, western Montana, and southern British Columbia. The snow melted off several weeks earlier than normal, and some areas also had a relatively dry sprint, especially western Oregon. Due to these factors, flows on most tributary rivers are much lower than they would normally be this time of year. This impacts flows on the Columbia through the summer and fall, and it is likely that some of the lowest levels in the Portland/Vancouver areas seen in recent years will be reached this summer and fall.
Generally, the lowest levels at Portland and Vancouver occur on weekends,when releases from Bonneville dam are typically reduced. Low levels are also linked to times of less variation between high and low tides. Considering these factors, NOAA's Northwest River Foewcast Center has identified the following dates as being most likely for extremely low levels: September 22-24, October 6-8, October 20-22, and November 3-5. Levels at the river gauges on the Columbia at the I-5 Bridge and on the Willamette at the Morrison Bridge could get as low as -0/5 feet. For comparison, the lowest reading in recent years was -0.7 feet in July of 2001 and September 2003.
Levels this low would likely impact large deep-draft vessels, smaller boats navigating shallow waters, marinas, and houseboat owners. Note that these dates and levels are only projections, and low levels are possible throughout the summer and fall. Forecasts for the Portland/Vancouver area are updated daily and can be viewed online at either www.nwrfc.noaa.gov or weather.gov/portland. People with activities sensitive to low river levels should monitor these websites closely throughout the summer and fall.
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