01M090 – Kamm Slough @ Northwood Rd.
Technical Notes:  2005 Water Year
Chuck Springer

The instantaneous stream gaging station on Kamm Slough at the mouth was monitored 
throughout water year 2005.  During the water year, three discharge measurements were made 
and 37 discrete stage readings were taken at this station.  Due to low velocities created by 
extreme vegetation growth downstream of this station, discharge measurements were not 
possible using standard current meter instrumentation.  Acquisition of a RD Instruments 
StreamPro Acoustic Doppler Current Profiler (ADCP)  in 2005 enabled the first discharge 
measurements to be made, and a rating curve to be developed at this station.

Rating Curve

This station started water year 2005 on rating Table 1, which remained valid until June 21, 2005.  
Flows encountered during this time period cover a range of discharge from 3.4 cfs to 50.9 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 3.4 cfs to 20.1 cfs, cover only 35% of the flows 
encountered while rating Table 1 was in effect.  However, only one of the discrete stage readings 
taken during this time period exceeded the highest measured flow.  Flows greater than 20.1 cfs 
were modeled using a Manning’s slope-conveyance model developed for this station, and 
Johnson’s method (e = 2.6) was used interpolate between measurements and to extrapolate to 
half the lowest measured flow.

Reed-canary grass growth during the summer 2005 gradually impeded flow.  The rating was 
shifted to reflect lower discharges at stages below 3.8 feet, and this shift was prorated from June 
21 to September 20.  A flow measurement taken on July 26, 2005 captured the transition from 
Table 1 to Table 2, and the transitional period was set based on this measurement.  Flows 
encountered during this time period cover a range of discharge from 3.3 cfs to 9.2 cfs.  None of 
the three measurements used to develop this rating were taken during water year 2005.  The 
measured flows for this rating, ranging from 3.8 cfs to 20.1 cfs, covered nearly the full range of 
flows encountered while rating Table 2 was in effect during water year 2005.  One of the 
discrete stage readings taken during this time period exceeded the lowest measured flow.  
Johnson’s interpolations were not developed for this rating curve, as the measurements already 
fell within a linear segment.

The calculated potential error for flows derived from the rating curves used during water year 
2005 for this station is ±12%.  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.  Flows above the measured range are qualified as “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, or “tape down” readings taken from a reference point on the Northwood Road bridge 
yielded one erroneous staff gage readings and one erroneous tape down reading.  Both these 
readings were corrected in the Hydstra database, and the resulting values were qualified as 
estimates.

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.