05A105 - S. F. Stillaguamish River at Jordan Road Bridge Technical Notes: 2007 Water Year Don Watt Introduction The gage is located on the left bank of the S.F. Stillaguamish River at the south end of the Jordan Road Bridge on the west side of the road. The gage house is at roughly the same elevation as the roadway and the slant-pipe drops abruptly about 30 vertical feet over a steep embankment to the river. The terminal end of the pipe drops into the deepest portion of the channel a few feet offshore. The gage was telemetered and used a combination of Campbell Scientific and Hydrological Services equipment for recording and transmitting data throughout the water year. The period of record for this station is from July 29, 2004 until the present. Discharge Statistics cubic feet per second (cfs) Mean Annual Discharge = 1,630 cfs Median Annual Discharge = 1,100 cfs Maximum Daily Mean Discharge = 18,200 cfs Minimum Daily Mean Discharge = 130 cfs Maximum Instantaneous Discharge = 21,700 cfs Minimum Instantaneous Discharge = 129 cfs Discharge Equaled or Exceeded 10 % of Recorded Time = 3,230 cfs Discharge Equaled or Exceeded 90 % of Recorded Time = 199 cfs Note: Statistics displayed above exclude values for any day in which a predicted instantaneous discharge was greater than twice the highest measured discharge or less than half the lowest measured discharge. Number of Days with Instantaneous Flows Greater Than Twice the Highest Measured Discharge = 1 day Number of Days with Instantaneous Flow Less Than Half the Lowest Measured Discharge = None Events of Note Flows remained below 150 cfs through the first two weeks of October and then made small rises through the first of November. Heavy rain brought a sharp rise on November 3 and produced a peak stage of 18.64 ft on November 6 which was the highest for the water year. Three other events between January and March produced water levels around 14 ft or 21,000 cfs. Dry weather returned in the summer and flows dropped below 170 cfs in mid September. Another rain event returned flows above 2500 cfs on September 30. Rating Curve The incised channel at this site remained stable throughout Water Year (WY) 2007. Rating Table No. 1 covered all of WY 2007 and continued in effect well into WY 2011. This rating curve employs more than 30 measured flows ranging from 134 cfs to 21,400 cfs. The curve is generally defined by a Johnson’s Log Offset of 3.72 feet. Four discharge measurements were made in WY 2007 ranging from 176 cfs at a gage height of 5.11 ft. to 1570 cfs at a gage height of 7.15 ft. During WY 2007 discharge was above two times Table No. 1’s highest measured flow less than 1% of the time. Flows were below the lowest measured flow 1% of the time. Flows remained above one-half of the lowest measured flow throughout the year. Stage Record There were no data gaps longer than 45 minutes during the water year. The high flow event of November 6 damaged the slant pipe for the automated gage and destroyed the staff gages for the station. Following that event, the logged gage height value was found to be about 0.60 ft lower than the water level estimated from tapedown measurements. Primary gage index water level observations were estimated from tapedown measurements until the installation of a wire weight gage on March 27. Error Assessments Calculated potential error due to rating uncertainty for Table No.1 ±11.3% Calculated potential discharge error due to logger drift ± 4.9% The calculated combined potential discharge error for WY 2007 ±16.2% Future Efforts At the end of WY 2007 more frequent discharge measurements were needed, especially at the higher water levels. Accurate cross-sectional and longitudinal surveys were also needed to improve high-flow modeling.