01M090 – Kamm Slough @ Northwood Rd.
Technical Notes:  2006 Water Year
Chuck Springer

The instantaneous stream gaging station on Kamm Slough at the mouth was monitored 
throughout water year 2006.  During the water year, six discharge measurements were made and 
34 discrete stage readings were taken at this station.  

Rating Curve

This station started water year 2006 on rating Table 2, which remained valid until January 2006.  
Flows encountered during this time period cover a range of discharge from 3.1 cfs to 27.1 cfs.  
All three measurements used to develop this rating were taken during water year 2006.  The 
measured flows for this rating, ranging from 3.5 cfs to 20.1 cfs, cover nearly 70% of the flows 
encountered while rating Table 2 was in effect during water year 2006.  Two of the discrete stage 
readings taken during this time period exceeded the highest measured flow, and five exceeded 
the lowest measured flow.  A Manning’s slope-conveyance high flow model was developed for 
this rating as part of the water year 2005 review.

During winter 2006, the reed-canary grass in the channel died off, gradually reducing impedance 
to flow at this site.  The rating was shifted to reflect higher discharges at stages below 3.85 feet, 
and this shift was prorated from January 18 to March 22.  Flows encountered during this time 
period cover a range of discharge from 4.3 cfs to 10.6 cfs.  Two of the eight measurements used 
to develop this rating were taken during water year 2006.  The measured flows for this rating, 
ranging from 3.0 cfs to 20.1 cfs, cover the full range of flows encountered while rating Table 3 
was in effect during water year 2006.  

Again during summer 2006, reed-canary grass growth impeded flow at this station, elevating the 
stage and shifting the stage-discharge relationship.  The rating was shifted to reflect lower 
discharges at stages below 3.85 feet, and the shift was prorated from June 6 to October 6.  A 
measurement taken on September 20 captured the transition to this new rating (Rating Table 4), 
and the transition was timed such that predicted flows for September 20 match this 
measurement.

The calculated potential error for flows derived from the rating curves used during water year 
2006 for this station is ±14%.  Due to high variability throughout the measured range, coupled 
with frequent shifting of the stage-discharge relationship, the rating curves for this station are 
considered estimates.




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 Northwood Road bridge 
revealed one erroneous tape down reading, which was corrected in Hydstra.  The regression also 
revealed one outlier that could not be reconciled, so both the staff gage and tape down readings 
were qualified as estimates in Hydstra.  

Future Efforts

Due to a narrow, low-gradient channel, and extensive vegetation growth at this site, flows are 
often impeded.  Frequent and regular flow measurements, and frequent maintenance of the 
measurement cross-section to keep it clear of vegetation growth will be necessary at this site.