01A140 – Nooksack R. abv the Middle Fork
Water Year 2004 Review
Chuck Springer

The telemetered streamgaging station on the Nooksack River above the Middle Fork 
operated throughout water year 2004.  A series of very large storm events in October and 
November caused extensive flooding throughout the Nooksack basin.  At this stations 
these events washed the staff gage away and changed the channel geometry at the site, 
necessitating mid-water year shifts in the rating curve.  Snowmelt began early (early 
March), and peaked in late-June, with the onset of summer low flows in mid-July.  
Several small storm events from late-August through mid-September 2004 resulted in 
minimum flows that were 120 cfs higher than the minimum flows for water year 2003.

Data Record and Quality Assurance:
The station logged continuously throughout the water year with the exception of a one-
day period in June.  The cause for this interruption is unknown, but data from an 
upstream USGS station (1125000 – N.F. Nooksack R. below Cascade Creek) was used to 
fill the gap.  Due to the washout of the staff gage at this site in October, tape down 
readings from a reference point on the Mosquito Lake Road bridge were used to 
approximate staff gage values from October through July.  During this time, logger 
readings fluctuated wildly, compounded by the inherent error in the tape down readings.  
Corrective adjustments were necessary for every weekly visit to the station.  The 
differences between the instrument readings and the manual tape down readings differed 
by amounts sufficient to result in a difference in predicted flow ranging from -13.2% to 
+42.5%.  A wire weight gage was then installed on the Mosquito Lake Road bridge in 
August, and the logger was recalibrated.  Corrective adjustments were made to the data 
set, and are documented in the Hydstra Data Workbench.  No noise filtering was 
conducted on data for this station.

Rating Curve:
The rating curve for the station covers a range of stage from 4.7 ft. to 12.9 ft.  The range 
of stage encountered during the water year ranged from 5.1 ft. to 12.8 ft.  The measured 
range of flows for the station covers only 20% of the range of flows encountered at the 
site, with measurements ranging from 917 cfs to 5,260 cfs.  However, flows exceeded the 
rating curve less than 5% of the time during the water year.  Flows greater than 5,260 cfs 
were modeled using the established relationship between stage and velocity during the 
highest measured flows, along with a surveyed high flow cross-section.  The accuracy of 
flows derived from this model is estimated to be within 25%.

cws