01N060 – Bertrand Cr. nr mouth
Technical Notes: 2006 Water Year
Chuck Springer

The telemetered stream gaging station on Bertrand Creek near the mouth operated throughout 
water year 2006 without interruption.  During this time, nine discharge measurements were made 
and 33 discrete manual stage readings were taken at this station.

Rating Curve

This station began water year 2006 in transition from Table 4 to Table 5 during a fill event, which 
was captured in progress by a discharge measurement taken on October 5, 2005.  The timing of 
the shift from Table 4 to Table 5 was set such that the discharge predicted by the rating curve on 
October 5 matched the discharge measured on that date.  Also reflected in the shift from Table 4 
to Table 5 is the implementation by Whatcom County of flood control measures upstream of the 
station during summer 2005, which substantially altered the behavior of the creek at high flows.  
Table 5 covers a range of discharge from 1.1 cubic feet per second (cfs) to 1,260 cfs.  Seven of 
the eight discharge measurements used to develop this rating were taken during water year 2006.  
The measured flows for this rating, ranging from 2.2 to 633 cfs, covers only 50% of the rating 
curve: however, flows exceeded the measured range of flows only 9% of the time during water 
year 2006.  Eight percent of flows were less than the lowest measured flow, and 1% of the flows 
were greater than the highest measured flow.  Flows greater than  
633 cfs were extrapolated using Johnson’s method to temporarily straighten the rating curve 
using log offsets (e=1.2 for GH<3.0, e=-4.0 for GH>3.0) calculated from the stage-discharge 
relationship.
 
A series of small storm events between mid-April and early-June 2006 caused a substantial 
amount of sand to accumulate on the banks at this station, shifting the mid-range of the rating 
curve by as much as a foot.  This shift is reflected by Table 6.  The specific event that caused the 
shift could not be identified, so the shift was prorated between discharge measurements taken on 
April 17 and June 5, 2006.  Since high and low flows were not affected by this fill on the banks, 
statistics cited above for Table 5 also apply to Table 6.

As part of the rating curve review process for water year 2006 for this station, historic rating 
curves for water years 2003-2005 were recalculated using current methods, resulting in changes 
to the previously reported discharge record for those years.

The calculated potential error for flows derived from rating curve used during water year 2006 
for this station is ±13% for Rating Table 5, and ±14% for Rating Table 6.

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 throughout the range of flows.  Conditions 
surrounding the terminal end of the bubbler orifice are similar to those around the staff gage.  
The stage height readings during the high-flow season typically differed from manual staff gage 
readings by 0.01-0.03 ft, and were as high as 0.09 ft.  During the summer 2006, the differences 
were only as high as 0.01 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.  All adjustments are documented in the Hydstra Data 
Workbench.

The calculated potential error of the continuous stage data for this station is ±1%.

Future Efforts

This station has experienced changes to the upper end of the rating curve in recent water years.  
New high-flow modeling should be conducted, including new cross-sectional and longitudinal 
surveys of the station.