01A140 – Nooksack River above the Middle Fork
Technical notes:  2006 Water Year 
Chuck Springer

The telemetered streamgaging station on the Nooksack River above the Middle Fork 
operated throughout water year 2006.  A moderately large storm event at the beginning of 
the water year caused channel fill that was relatively minor, but significant enough to 
warrant a shift in the rating curve.   Snowmelt began in late-March, marked by rising 
river stage in the absence of rainfall, and rising air, and water temperatures.  Several 
small rainfall events temporarily replenished flows in the Nooksack River, however flows 
still dropped to 440 cfs, which is less than half the average minimum summer flow for 
the first two years of operation.  Flows did not drop as low as water year 2005 (<430 cfs).

Rating Curve

Water year 2006 started amidst a transition from rating table 4 to rating table 5, during a 
channel fill event.  Rating table 5 covers a range of discharge from 345 cfs to 20,900 cfs.  
The range of stage encountered during the water year was 4.8 feet.  The range of 
discharge encountered during the water year was from 439 cfs in September 2006 to 
7,110 cfs in December 2005.  The measured discharge, ranging from 373 cfs to 3,540 cfs, 
covers only 47% of the magnitude of flows encountered during the water year.  However, 
discharge exceeded the measured range of flows only 5% of the time during the water 
year.  Flows greater than 3,540 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%.  During a series of rainfall events in late-May 2006, the rating shifted 
again.  This time the channel was scoured back out, and the stage-discharge relationship 
resembled that of rating table 4.  A discharge measurement was made at the site on June 
6, 2006.  The shift was prorated from the beginning of the storm event on May 15, 2006 
to this measurement, and saved as rating table 6, which covers the same range of 
discharge as rating table 5.

Stage Record

The station logged continuously throughout the water year without interruption.  Due to 
the turbulence of the stream channel, high substrate mobility, and the inherent difficulty 
in taking manual stage readings of any kind, variation between manual wire weight gage 
readings and logged stage values was sometimes high.  Differences between measured 
and logged stage values were as high as 0.32 feet.  Time-weighted corrective adjustments 
were made to the continuous stage record whenever the difference between logged and 
measured stage values resulted in a 5% or more difference in discharge.  All adjustments 
are documented in the Hydstra Data Workbench.  The turbulence present at this site also 
causes a great deal of “noise” in the continuous stage data.  At times during the water 
year, the “bounce” in the stage data was as much as 0.06 feet.  However, this variability 
generally amounted to relatively little in terms of discharge (2-3%).  The station is 
permanently set to average stage readings over a 20 second period, which alleviates some 
of the variability.  One period of data, from October 13 to November 16, 2005 was 
qualified as estimates due to the severity and variability of the instrument drift.

Future Efforts

More high flow measurements are needed at this station to augment both the high and 
low ends of the rating curve.  More cross-sectional and longitudinal data collection 
efforts are also needed to improve high flow models for this site.