01A140 – Nooksack R. abv the Middle Fork
Technical notes:  2005 Water Year 
Chuck Springer

The telemetered streamgaging station on the Nooksack R. above the Middle Fork 
operated throughout water year 2005.  A series of storm events in October and November 
caused fairly extensive flooding in the Nooksack basin, mainly in the agricultural 
lowlands.  At this station, these events caused noticeable changes to channel geometry 
both upstream and downstream of the station, however the relationship between stage and 
discharge at the site was not impacted significantly.  A large rain on snow event in mid-
January effectively marked the beginning of spring snowmelt.  However, abundant spring 
rainfall kept flows from dropping dramatically until mid-July.  With insufficient 
snowpack to maintain summer flows, minimum summer flow at this station was 428 cfs 
in September; less than half the minimum flow for the previous two years of record.

Rating Curve
The rating curve for the station for water year 2005 covers a range of discharge from 428 
cfs to 17,300 cfs.  The range of stage encountered during the water year was 10.7 feet.  
The range of discharge encountered during the water year was from 428 cfs in September 
2005 to 17,200 cfs in November 2004.  The measured discharge, ranging from 856 cfs to 
5,260 cfs, covers only 26% of the magnitude of flows encountered during the water year.  
However, discharge exceeded the measured range of flows less than 10% of the time 
during the water year; discharge was above the measured range 2% of the time, and 
below the measured range 8% 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%.

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 0.78 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.  The station is permanently set 
to average stage readings over a 20 second period, which alleviates some of the 
variability.  The most extreme periods of noise during water year 2005 have been 
smoothed using a moving 5-point mean filter.

Future Efforts
More high flow measurements are needed at this station to augment both the high and 
low ends of the rating curve. 

cws