01F070 – S.F.  Nooksack River @ Potter Road
Technical Notes:  2006 Water Year
Chuck Springer

The telemetered streamgaging station on the South Fork Nooksack River at Potter Road 
operated throughout water year 2006 without interruption.  During the water year, three 
discharge measurements were made and 39 discrete manual stage readings were taken at 
this station.

Rating Curve

This station operated throughout water year 2006 on rating table 6.  The rating table 
covers a range of discharge from 47 cubic feet per second (cfs) to 26,700 cfs.  Three of 
the nine discharge measurements used to develop this rating were taken during water year 
2006.  The measured flows for this rating, ranging from 97.5 cfs to 11,740 cfs, cover only 
44% of the rating curve.  However, flows did not exceed the rating curve at all during the 
water year.  Johnson’s method (e = 5.6) was used to temporarily straighten the log: log 
rating curve and extrapolate low flows below the measured range, and to interpolate 
between discharge measurements throughout the measured range.  Flows greater than 
7,730 cfs had been modeled as part of the water year 2005 review.  These model results 
were considered to still be valid, and were applied to rating table 6.  See the water year 
2005 technical notes for details on this flow model.

The calculated potential error for flows derived from the rating curve used during water 
year 2006 for this station is ±11%.

Stage Record

The station logged continuously throughout water year 2006 without interruption.  The 
staff gage at this site is generally readable to within 0.02 ft, and conditions surrounding 
the terminal end of the bubbler orifice are fairly still, particularly at low flow conditions.  
However, despite these factors, the stage height readings from the bubbler often differed 
from manual staff gage readings by 0.03-0.06 ft, and were as high as 0.19 ft.  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.  During one period from mid-July to mid-August 2006, the instrument drift 
was particularly unstable, such that the difference in predicted average daily discharge 
between raw and adjusted stage values differed by 20% or more.  Continuous data for 
this time period was flagged as an estimate.  All adjustments are documented in the 
Hydstra Data Workbench.

The calculated potential error of the continuous stage data for this station is ±8%.




Future Efforts

Longitudinal and cross-sectional surveys are needed at this site to facilitate updated high 
flow modeling.  Also, flows at this station have occasionally exceeded the measured 
range of flows by as much as 125%.  High flow measurements are needed to verify the 
upper end of the rating curve.