01N060 – Bertrand Creek near mouth
Technical Notes: 2007 Water Year
Chuck Springer

The telemetered stream gaging station on Bertrand Creek near the mouth operated throughout 
Water Year (WY) 2007 without interruption.  During this time, nine discharge measurements 
were made and 30 discrete manual stage readings were taken at this station.  Cumulative 
potential error for this station for WY 2007 was ±16%.

Rating Curve

This station began WY 2007 on Rating Table 6.  Table 6 covers a range of discharge from 1.1 
cubic feet per second (cfs) to 1,260 cfs.  One of the seven discharge measurements used to 
develop this rating was taken during WY 2007.  The measured flows for this rating ranging from 
2.2 to 633 cfs cover only 50% of the rating curve; however, flows exceeded the highest 
measured flows only 3% of the time during WY 2007.  Flows greater than  
633 cfs were extrapolated using the same log offset as for Table 5 (e = -4.0 for GH > 3.0).
 
A series of small storm events during the fall of 2006 caused a substantial amount of scouring on 
the sand banks at this station, shifting the mid-range of the rating curve by more than a foot.  
This shift is reflected by Table 7.  The specific event that caused the shift could not be identified, 
so the shift was pro-rated between discharge measurements taken on November 9, 2006 and 
January 10, 2007.  Since high and low flows were not affected by this fill on the banks, statistics 
cited above for Table 6 also apply to Table 7.  Eight of the 16 discharge measurements used to 
develop this rating were taken during WY 2007.

Sometime between mid August and late September 2007, the channel scoured.  No distinct event 
could be identified as a cause for this shift; it was pro-rated between discharge measurements 
taken on August 14 and September 26.  This shift is represented by Table 12, which covers a 
range of flows from 0 to 1,250 cfs.  Two of the 15 discharge measurements used to develop this 
rating were taken during WY 2007.  The measured flows for this rating, ranging from 4.3 to 633 
cfs cover only 50% of the rating curve; however, flows did not exceed the rating curve during 
the month and a half that Table 12 was in effect during WY 2007.  Flows greater than 633 cfs 
were extrapolated using a log offset (e = 1.1) to temporarily straighten the rating curve in log 
space.

The calculated potential error for flows derived from rating curves used during WY 2007 for this 
station is ±12%.

Stage Record

The station logged continuously throughout WY 2007 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 differed from manual staff gage readings by variable amounts, as much 
as 0.24 ft.  Time-weighted corrective adjustments were made to the continuous stage record 
whenever the logged and measured stage values differed.  All adjustments are documented in 
the Hydstra Data Workbench.

The calculated potential error of the continuous stage data for this station is ±4%.

Future Efforts

This station experiences frequent rating shifts.  Ongoing frequent discharge measurements are 
necessary at this station to ensure accuracy.