01L050 – Anderson Cr. at mouth
Technical Notes:  2006 Water Year
Chuck Springer

The instantaneous stream gaging station on Anderson Creek at the mouth was monitored 
throughout water year 2006.  During the water year, seven discharge measurements were made 
and 31 discrete stage readings were taken at this station.

Rating Curve

This station started water year 2006 on rating Table 5, which remained valid until June 27, 2006.  
Flows encountered during this time period cover a range of discharge from 2.8 cfs to 
161 cfs.  Five of the 11 measurements used to develop this rating were taken during water year 
2006.  The measured flows for this rating, ranging from 0.44 cfs to 144 cfs, cover 91% of the 
flows encountered while rating Table 5 was in effect during water year 2006.  Only two of the 
discrete stage readings taken during this time period exceeded the highest measured flow.  
Johnson’s interpolations and Manning’s slope-conveyance high flow modeling were developed 
for this rating table as part of the water year 2005 review.

A storm event in mid-June 2006 caused moderate channel fill. The rating was shifted to reflect 
lower discharges at stages below 1.54 feet, and the shifted rating was saved as rating Table 6.  
The transition from Table 4 to Table 5 was set at a flow measurement on June 27.  The transition 
was not prorated as there were no discrete stage readings taken during the transitional timeframe.  
Flows encountered during this time period cover a range of discharge from 0.01 cfs to 1.7 cfs.  
Two of the 14 measurements used to develop this rating were taken during water year 2006.  The 
measured flows for this rating, ranging from point of zero flow (PZF) to 144 cfs, cover the full 
range of flows encountered while rating Table 6 was in effect during water year 2006.  Johnson’s 
interpolations were not developed for this rating curve, as there were several closely-spaced 
discharge measurements within the shifted range.  The resolution of rating  
Table 6 at flows below 8 cfs is rather poor.  Rating curve segments below 8 cfs are qualified as 
estimates.

The calculated potential error for flows derived from the rating curves used during water year 
2005 for this station is ±19%.

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 Roberts Road bridge 
yielded no outliers during water year 2006.  Confidence is high that there were no erroneous 
readings during the water year.

Future Efforts

Due to high substrate and woody debris mobility, the discharge rating for this station can shift 
frequently.  Ongoing discharge measurements at frequent and regular intervals will be necessary 
to maintain an accurate rating at this site.