01N060 – Bertrand Creek near mouth
Technical Notes: 2009 Water Year
Chuck Springer

The telemetered stream gaging station on Bertrand Creek near the mouth operated throughout 
Water Year (WY) 2009 without interruption.  During this time, ten discharge measurements were 
made and 12 discrete manual stage readings were taken at this station.  Cumulative potential 
error for this station for water year 2007 was ±21%.

Rating Curve

This station began WY 2009 on Rating Table 9.  Table 9 covers a range of discharge from 0 to 
1,260 cubic feet per second (cfs).  Five of the 16 discharge measurements used to develop this 
rating were taken during WY 2009.  The measured flows for this rating, ranging from 18.5 to 633 
cfs, covers less than 50% of the rating curve.  Flows exceeded the lowest measured flows 80% of 
the time during the 15 days that Table 9 was in effect during WY 2009.  Flows greater than 633 
cfs were extrapolated using a log offset (e = 1.1) to temporarily straighten the rating curve in log 
space.
 
In the fall of 2008, large woody debris downstream of the gaging station began causing repeated 
debris pileups that would elevate the stage height during channel control conditions (high flows), 
which are represented by Table 10.  These pileups would periodically get washed away by high 
flows resulting in multiple occurrences of Table 10 during WY 2009 and 2010.  A total of five of 
the 12 discharge measurements used to develop this rating were taken during WY 2009.  Table 
10 covers a range of discharge from 0 to 112 cfs.  The measured flows for this rating, ranging 
from 0 to 56 cfs, cover 50% of the rating curve.   
 
Flows exceeded the highest measured flows 47% of the time during the month Table 10 was in 
effect during the fall of 2008.  Flows between 56 and 112 cfs were extrapolated using a log 
offset (e = 1.4) to temporarily straighten the rating curve in log space.  Since this rating table had 
high flows that were unique from any other rating for this station and the rating occurred during 
two distinct and relatively short time periods, the field survey data to support a high flow 
modeling effort could be collected.  Thus flows greater than 112 cfs (twice the highest measured 
flow) are not reported.

A pair of large storm events in November 2008 washed away the debris pileup that had formed 
downstream of the gaging station, shifting the stage-discharge relationship back to that of Table 
9 (this occurrence of Table 9 is labeled Table 901).  See the description of Table 9 above for 
discharge range statistics.  Flows exceeded the highest measured flows 1% of the time that Table 
901 was in effect during winter/spring 2009.  

A series of storm events in April/May 2009 caused another debris pileup downstream of the 
gaging station; elevating the stage-discharge relationship back to that of Table 10 (this recurrence 
of Table 10 is labeled Table 101).  See the description of Table 10 above for discharge range 
statistics.  Flows did not exceed the measured range while Table 101 was in effect during the 
spring/summer 2009.
The calculated potential error for flows derived from rating curves used during water year 2009 
for this station is ±15%.

Stage Record

The station logged continuously throughout WY 2009 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 0.21 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 ±6%.

Future Efforts

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