01D100 - Sumas R. at Telegraph Road
Technical Notes:  2007 Water Year
Chuck Springer

The instantaneous stream gaging station on the Sumas River at Telegraph Road was monitored 
throughout water year 2007.  During the water year, eight discharge measurements were made 
and 29 discrete stage readings were taken at this station.

Rating Curve

This station started water year 2007 on Rating Table 6; however, there were no flows measured 
or observed while this rating table was in effect during water year 2007.   On October 5, a large 
storm event caused substantial channel filling at this station, changing the stage-discharge 
relationship at low to moderate flows.  This shift is reflected in Rating Table 7.

Flows encountered while Table 7 was in effect during water year 2007 range from 7.9 cubic feet 
per second (cfs) to 284 cfs.  Five of the 16 discharge measurements used to develop this rating 
were taken during water year 2007.  The measured flows for this rating table, ranging from 7.9 to 
307 cfs, cover the entire range of flows encountered.  Johnson’s method was used (e = -5.2) 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 7 is ±15%.

In March 2007, several storm events swept through the region, scouring the low flow channel, 
while at the same time causing sloughing on the steep banks.  The resulting shift, represented by 
Table 8, shows a low-end scour and a slight mid-range fill.  Flows encountered while Table 8 was 
in effect during water year 2007 range from 10.5 to 168 cfs.  Five of the 17 discharge 
measurements used to develop this rating were taken during water year 2007.  The measured 
flows for this rating table, ranging from 11.8 to 307, cover nearly the entire range of flows 
encountered.  Three of the flows derived from the discrete staff gage observations are below the 
lowest measured flow.  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 highest measured flow were then performed.  
The calculated potential error for flows derived from Rating Table 8 is ±14%.

During August and September 2007, aquatic weed growth began to impede flows, shifting the 
stage-discharge relationship.  This shift is represented by Table 9.  Flows encountered while Table 
9 was in effect during water year 2007 range from 10.5 to 11.8 cfs.  Two of the nine discharge 
measurements used to develop this rating were taken during water year 2007.  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 ±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 did 
not yield any outliers during water year 2007.  The standard deviation from the linear regression 
was 0.03 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 unusual 
ways.  Ongoing frequent discharge measurements will be needed to maintain an accurate rating.