01Q070 - Dakota Cr. @ Giles Rd.
Technical Notes:  2005 Water Year
Chuck Springer

The instantaneous stream gaging station on Dakota Creek at Giles 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 started water year 2005 on Rating Table 1.  Flows encountered while Rating Table 1 
was in effect during water year 2005 range from 3.2 to 487 cfs.  Two of the 11 discharge 
measurements used to develop this rating were taken during water year 2005.  The measured 
flows for this rating, ranging from 4.5 to 487 cfs, cover nearly 100% of the flows encountered 
while Rating Table 1 was in effect during water year 2005.  Only two of the discrete stage 
readings exceeded the lowest measured flow.  Johnson’s method was used (e = 2.4) 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.

Beaver activity downstream of this station during summer 2005 temporarily shifted the stage 
discharge relationship, resulting in low flows that occurred at much higher stages than during 
previous months.  This shift is represented by Rating Table 3.  Flows encountered while Rating 
Table 3 was in effect during water year 2005 ranged from 0.7 to 21.8 cfs.  Two of the 12 
discharge measurements used to develop this rating were taken during water year 2005.  The 
measured flows for this rating, ranging from 1.3 to 173 cfs, cover nearly the entire range of flows 
encountered while Rating Table 3 was in effect during water year 2005.  Only one of the discrete 
stage readings exceeded the lowest measured flow.  Johnson’s method was used (e = 2.9) 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 the rating curves used during water year 
2005 for this station is ±13% for Rating Table 1, and ±18% for Rating Table 3.

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 Giles Road Bridge yielded 
two outliers during water year 2005.  In each case, it was determined that the tape down reading 
was most likely erroneous.  Because this could not be determined conclusively, the staff gage 
readings on those dates were flagged as estimates.

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Future Efforts

This station tends to see beaver activity every summer, followed by washouts of those dams 
during winter storm events.  Ongoing frequent discharge measurements and, when possible, point 
of zero flow measurements will be necessary to monitor these shifts.