01S070 - Squalicum Cr. @ West St.
Technical Notes:  2006 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, six discharge measurements were 
made and 24 discrete stage readings were taken at this station.

Rating Curve

At the beginning of water year 2006, Ecology staff began using a staff gage installed by the City 
of Bellingham as the primary gage index for this station, as the stage height of the creek dropped 
below the Ecology staff gage.  This station started water year 2006 on Rating Table 4, which was 
a -2.82 ft. shift from Rating Table 3.   There was only one site visit during the time Rating  
Table 4 was in effect, with an observed discharge of 28 cubic feet per second (cfs).  The 
measured flows for this rating table range from 28 to 162 cfs.  One of the three discharge 
measurements used to develop this rating was taken during water year 2006.  Since this rating 
table was derived using a linear offset from Rating Table 3, no further interpolations or 
extrapolations were performed.  The calculated potential error for flows derived from Rating 
Table 4 is ±9%.

A large storm event in January 2006 caused a substantial amount of channel fill, impacting the 
stage-discharge relationship though most of its range.  This shift is represented in Rating Table 5.  
Flows encountered while Rating Table 5 was in effect during water year 2006 range from 0.5 to 
115 cfs.  Six of the eight discharge measurements used to develop this rating were taken during 
water year 2006.  The measured flows for this rating, ranging from 0.9 to 162 cfs, cover nearly 
the entire range of flows encountered while Rating Table 5 was in effect during water year 2006.  
However, ten of the 29 discrete stage readings exceeded the lowest measured flow.  Johnson’s 
method was used (e = 0.85) to temporarily straighten the stage-discharge relationship.  
Interpolations between discharge measurements and extrapolations to half of 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 ±76% for flows below 5 cfs, and 10% for 
flows above 5 cfs.

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 one outlier during water year 2006.  This outlier was the first reading taken using the 
City of Bellingham’s staff gage, but was also the first reading taken following the City’s 
construction of flood control structures at the box culvert downstream of the station.  It is 
believed that during the fall 2005 and early winter 2006, the relationship between staff gage 
readings and tape down readings was compromised due to the flood control structure.  The staff 
gage reading is believed to be correct.   The relationship between the staff gage and tape down 
readings was somewhat variable overall.  The standard deviation from the linear regression was 
0.09 ft, 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.