01L050 – Anderson Cr. at mouth
Technical Notes:  2005 Water Year
Chuck Springer  

The instantaneous stream gaging station on Anderson Creek at the mouth was monitored 
throughout water year 2005.  During the water year, seven discharge measurements were made 
and 37 discrete stage readings were taken at this station.

Rating Curve

This station started water year 2005 on rating Table 4.  Flows encountered at this station during 
water year 2005 cover a range of discharge from 0.2 cfs to 246 cfs.  Five of the ten 
measurements used to develop this rating were taken during water year 2005.  The measured 
flows for this rating, ranging from 0.07 cfs to 144 cfs, cover only 58% of the flows encountered 
during the water year.  However, only one of the discrete stage readings taken during water year 
2005 exceeded the highest measured flow.  Johnson’s method (e = 0.26) was used to temporarily 
straighten the rating curve in logarithmic space and interpolate between discharge measurements.  
Flows greater than 144 cfs were modeled using a slope-conveyance model developed for this 
station based on the characteristic of measured discharges.

A storm event between mid-April and mid-May 2005 caused substantial 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 5.  The transition from Table 4 to Table 5 was prorated between a flow 
measurement taken on April 19 and a discrete stage reading taken on May 12.  Like with Table 4, 
Johnson’s method (e = 0.6 for GH < 1.27, e = 0.95 for GH > 1.27) was used to interpolate 
between discharge measurements.

The calculated potential error for flows derived from the rating curves used during water year 
2005 for this station is ±11%.

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 2005.  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.