01D100 - Sumas River @ Telegraph Rd.
Technical Notes:  2009 Water Year
Chuck Springer

The instantaneous stream gaging station on the Sumas River at Telegraph Road was monitored 
throughout water year 2009.  During the water year, nine discharge measurements were made 
and 12 discrete stage readings were taken at this station.

Rating Curve

This station started water year 2009 on Rating Table 8.  Flows encountered while Table 8 was in 
effect during water year 2009 range from 13.9 to 307 cubic feet per second (cfs).  Seven of the 
17 discharge measurements used to develop this rating were taken during water year 2009.  The 
measured flows for this rating, ranging from 11.8 to 307 cfs, cover the full range-of-flows 
encountered while Table 8 was in effect during water year 2009.  Johnson’s method was used  
(e = -14.7) to temporarily straighten the stage-discharge relationship.  Interpolations between 
discharge measurements and extrapolations to half the lowest measured flow and twice the 
highest measured flow were then performed.  The calculated potential error for flows derived 
from this rating table is ±14%.

Over the course of summer 2009, reed-canary grass growth in the channel gradually impeded 
flow, trapping sediment and causing a low-end “fill” in the rating, shifting the stage-discharge 
relationship back to Rating Table 9.  Flows encountered while Rating Table 9 was in effect 
during water year 2009 range from 9.8 to 14.7 cfs.  Three of the ten discharge measurements 
used to develop this rating were taken during water year 2009.  The measured flows for this 
rating, ranging from 9.8 to 307 cfs cover the full range-of-flows encountered while Rating  
Table 9 was in effect during water year 2009.  Johnson’s method was used (e = -38.8) to 
temporarily straighten the stage-discharge relationship.  Interpolations between discharge 
measurements and extrapolations to half the lowest measured flow and twice the highest 
measured flow were then performed.  The calculated potential error for flows derived from this 
rating table is ±12%.

Stage Record

The stage record for this station is comprised of discrete (instantaneous) staff gage readings 
taken during weekly visits.  A linear regression of staff gage readings versus depth-to-water 
surface, or “tape down” readings taken from a reference point on the Telegraph Road Bridge had 
an r2 of 0.999, and a standard deviation of 0.06.  The regression revealed one obvious outlier 
during water year 2009, which was caused by a mis-entered tape down reading.  There were also 
three minor outliers, all of which deviated from the regression by more than  
0.10 feet; however, none of these could be reconciled, and were all qualified as estimates.

Future Efforts

Monitoring at this station was permanently discontinued at the end of water year 2009.