01D100 - Sumas R. @ Telegraph Rd.
Technical Notes:  2008 Water Year
Chuck Springer

The instantaneous stream gaging station on the Sumas River at Telegraph Road was monitored 
throughout water year 2008.  During the water year, eight discharge measurements were made 
and 18 discrete stage readings were taken at this station.

Rating Curve

This station started water year 2008 on Rating Table 9.  Flows encountered while Table 9 was in 
effect during water year 2008 range from 23.0 cubic feet per second (cfs) to 156 cfs.  Five of the 
nine discharge measurements used to develop this rating were taken during water year 2008.  The 
measured flows for this rating table, ranging from 10.5 to 307 cfs, cover the entire range of flows 
encountered.  Johnson’s method was used (e = -38.8) to temporarily straighten the stage-
discharge relationship.  Interpolations between discharge measurements and extrapolations to 
half of the lowest measured flow and twice the highest measured flow were then performed.  
The calculated potential error for flows derived from Rating Table 9 is ±15%.

In March 2008, several storm events swept through the region, scouring the low flow channel 
back to the stage-discharge relationship represented by Table 8.  Flows encountered while Table 
8 was in effect during water year 2008 range from 11.8 cfs to 111 cfs.  Four of the 17 discharge 
measurements used to develop this rating were taken during water year 2008.  The measured 
flows for this rating table, ranging from 11.8 to 307, cover the entire range of flows encountered.  
Johnson’s method was used (e = -14.7) to temporarily straighten the stage-discharge relationship.  
Interpolations between discharge measurements and extrapolations to half of the lowest 
measured flow and twice the high4est measured flow were then performed.  The calculated 
potential error for flows derived from Rating Table 8 is ±14%.

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 did 
not yield any outliers during water year 2008.  The standard deviation from the linear regression 
was 0.02 ft, so even small errors in readings were relatively easy to detect.  At several times 
during the water year, the staff gage was submerged, or was too muddy to read, at the time of 
observations.  The stage height for these observations was estimated based on the regression 
between staff gage readings and tape down readings.  

Future Efforts

The stage-discharge relationship at this site changes frequently, and often does so in unorthodox 
ways.  Ongoing frequent discharge measurements will be needed to maintain an accurate rating.