01R090 - California Creek @ Valley View Rd.
Technical Notes: 2008 Water Year
Chuck Springer

The instantaneous stream gaging station on California Creek at Valley View Road was upgraded 
to continuous monitoring as part of the Drayton Harbor TMDL in November 2007.  The 
continuous stream gaging station operated throughout water year 2008.  During the water year, 
eight discharge measurements were made and 20 discrete manual stage readings were taken at 
this station.

Rating Curve

This station began water year 2008 on Rating Table 5.  Flows encountered while Rating Table 5 
was in effect during water year 2008 range from 2.3 to 66.4 cfs.  The measured flows for this 
rating, ranging from 4.7 to 118 cfs, cover all but the lowest 8% of the range of flows 
encountered.  Three of the 12 discrete stage observations exceeded the lowest measured flow.  
Johnson’s method was used (e = 2.0) to temporarily straighten the stage-discharge relationship.  
Interpolations between discharge measurements and extrapolations to half the lowest measured 
flow and twice the highest measured flow were then performed.  The calculated potential error 
for flows derived from this rating table is ±21%.
 
During winter 2008, several storm events passed through the area.  The channel at this station 
scoured substantially during one of these events.  This shift is represented by Rating Table 6.  
The exact timing of the shift is unknown, so the shift is phased between December 2007 and 
February 2008 measurements.  Table 6 covers a range of discharge from 0.9 to 240 cfs.  Five of 
the six discharge measurements used to develop this rating were taken during water year 2008.  
The measured flows for this rating, ranging from 1.8 to 118 cfs, cover less than 50% of the rating 
curve.  However, flows exceeded the measured range of flows less than 10% of the time while 
Table 6 was in effect during water year 2008.  Eight percent of flows exceeded the lowest 
measured flow, and 1% of flows exceeded the highest measured flow.  The rating curve was 
interpolated between discharge measurements and extrapolated to half the lowest measured flow 
using Johnson’s method to temporarily straighten the rating curve using a log offset (e=1.4 for 
GH<3.8, and e=-9.0 for GH>3.8) calculated from the stage-discharge relationship.  The potential 
error for flows derived from this rating curve is ±12%.

During spring 2008, a local weed control campaign began, and bank vegetation along this reach 
of the creek was sprayed to control weed growth.  This greatly altered the geometry of the 
channel at this site, allowing greater conveyance at high flows.  However, the lack of vegetation 
on the banks resulted in sloughing downstream of the station, impounding low flows.  The 
resulting shift, represented by Rating Table 7, shows a “scour” at high flows, but a “fill” at low 
flows.  The major slough that impacted low flows occurred on August 9, 2008, so the shift was 
implemented at that time.  Table 7 covers a range of discharge from 1.3 to 183 cfs.  One of the 
six discharge measurements used to develop this rating was taken during water year 2008.  The 
measured flows for this rating, ranging from 2.6 to 91.6 cfs, cover less than 50% of the rating.  
Flows exceeded the lowest measured flow 70% of the time while Table 7 was in effect during 
water year 2008.  The rating curve was interpolated between discharge measurements and 
extrapolated to half the lowest measured flow using Johnson’s method to temporarily straighten 
the rating curve using a log offset (e=1.4 for GH<3.8, and e=-9.0 for GH>3.8) calculated from 
the stage-discharge relationship.  The potential error for flows derived from this rating curve is 
±13%.

Stage Record

This station was upgraded to collect continuous stage data in November 2007.  The station 
logged continuously throughout water year 2008 with no interruptions.  However, in June 2008, 
a PDA containing six weeks of downloaded data for this station was stolen during a vehicle 
prowl at a Bellingham hotel.  The resulting data gap was filled using correlated data from station 
01P080 - Tenmile Creek above Barrett Lake.  

The staff gage at this site is generally readable to within 0.01 ft during all flow conditions.  
Conditions surrounding the terminal pressure transducer are similar to those around the staff 
gage.  The stage height readings typically differed from manual staff gage readings by 0.02 to 
0.03 ft, and were as much as 0.05 ft.  Time-weighted corrective adjustments were made to the 
continuous stage record whenever the staff gage observations and datalogger readings differed.  
All adjustments are documented in the Hydstra database.

Quality control measures were also taken to identify potentially erroneous staff gage 
observations.  A linear regression of staff gage observations versus tape down observations had 
an r2 of 0.998, with a standard deviation of 0.05 ft.  The regression did not identify any obvious 
outliers, indicating that the staff gage and tape down observations made during water year 2008 
are at least reasonably accurate.

The calculated potential error of the continuous stage data for this station is ±4%.  

Future Efforts

The Drayton Harbor TMDL study culminated in October 2009, eliminating the need for 
continuous data collection at this site.  Further, overall monitoring at this station was indefinitely 
discontinued in October 2009 due to budget cuts.