01S070 - Squalicum Cr. @ West St.
Technical Notes:  2005 Water Year
Chuck Springer

The instantaneous stream gaging station on Squalicum Creek at Valley View Road was 
monitored throughout water year 2005.  During the water year, four discharge measurements 
were made and 35 discrete stage readings were taken at this station.

Rating Curve

This station began water year 2005 on Rating Table 2.  Flows encountered while Rating Table 2 
was in effect during water year 2005 range from 2.3 cubic feet per second (cfs) to 565 cfs.  One 
of the nine discharge measurements used to develop this rating was taken during water year 
2005.  The measured flows for this rating, ranging from 0.7 to 530 cfs, cover 94% of the range of 
flows encountered while Rating Table 2 was in effect during water year 2005.  Only one of the 
discrete stage readings exceeded the highest measured flow.  Johnson’s method was used  
(e = 4.0 for GH < 3.4, e = 3.25 for GH > 3.4) 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 Rating Table 2 is ±13%.

A large storm event in January 2005 caused a moderate amount of channel fill, impacting the 
stage-discharge relationship at low flows.  This shift is represented in Rating Table 3.  Flows 
encountered while Rating Table 3 was in effect during water year 2005 range from 0.9 to  
530 cfs.  Four of the eight discharge measurements used to develop this rating were taken during 
water year 2005.  The measured flows for this rating, ranging from 0.9 to 530 cfs, cover the 
entire range of flows encountered while Rating Table 3 was in effect during water year 2005.  
Johnson’s method was used (e = 3.4) 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 stage-discharge 
relationship for this rating was very difficult to measure accurately at low flows.  The calculated 
potential error for flows derived from Rating Table 3 is ±110% for flows below 5 cfs, and 14% 
for flows above 5 cfs.  Flows less than 5 cfs are qualified as 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 Valley View Road Bridge 
yielded no obvious outliers during water year 2005; however, the relationship between the staff 
gage and tape down readings was somewhat variable.  The standard deviation from the linear 
regression was 0.08 feet - so small errors in readings were difficult to detect.

Future Efforts

High flows have been difficult to obtain at this station due to physical and logistical constraints.  
An ongoing effort to measure high flows is needed.