01D100 – Sumas River @ Telegraph Road
Technical Notes:  2005 Water Year
Chuck Springer

The instantaneous streamgaging station on the Sumas River at Telegraph Road was 
monitored throughout water year 2005.  During the water year, four discharge 
measurements were made and 41 instantaneous stage readings were taken at this station, 
at stages ranging from 2.01 feet to 12.10 feet.

Rating Curve

This station started water year 2005 on rating table 4.  The rating table covers a range of 
discharge from 3.3 cfs to 1,430 cfs.  Two of the five measurements used to develop this 
rating were taken during water year 2005.  The measured flows for this rating, ranging 
from 6.7 cfs to 140 cfs, cover only 9% of the rating curve.  During water year 2005, 
12 of the instantaneous stage readings fell outside the measured range of flows.  Seven 
readings were lower than the lowest measured flow, and five readings were higher than 
the highest measured flow.

A storm event in mid-January 2005 caused substantial channel scour at this site.  The 
rating was shifted to reflect higher discharges at stages below 5.9 feet, and the shifted 
rating was saved as rating table 5.  The transition from table 4 to table 5 was pro-rated 
over the rising limb of the storm event.  Three discharge measurements were made 
confirming table 5 during the remainder of water year 2005, ranging from 10.6 cfs to 
165 cfs.  Johnson’s method (e = -3.4) was used to temporarily straighten the log: log 
rating curve and extrapolate low flows below the measured range.  The resolution of 
rating table 5 at flows below 32 cfs is extremely poor.  Rating curve segments below  
32 cfs are qualified as estimates.  The calculated potential error for flows derived from 
the rating curves used during water year 2005 for this station is ±14%.

One high flow measurement taken during water year 2006 (219 cfs) was used to “anchor” 
the upper end of the rating curve.  Flows greater than 219 cfs were modeled using 
Manning’s equation to estimate velocities and a surveyed high flow cross-section to 
estimate channel geometry.  A longitudinal survey had also been conducted to estimate 
channel slope.  The calculated potential error for high flows derived from this model is 
±36%.  This represents only the potential error in modeling the measured discharges, and 
not the total error of the modeled flows.  


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 readings taken from a reference point on the Telegraph Road 
Bridge yielded no outliers during water year 2005.  Confidence is high that there were no 
erroneous readings during the water year.

Future Efforts

Due to fine-grained substrate, coupled with rampant algae and grass growth during the 
summer months, the discharge rating for this station shifts frequently.  Ongoing discharge 
measurements at frequent and regular intervals will be necessary at this site.