18P070 McDonald Creek at HWY 101
Technical Notes: 2005 Water Year
Christopher Evans

Introduction

Ecology’s telemetry stream gage on McDonald Creek is located at river mile 4.0 at Hwy 
101.  This gage was operated from October 1, 2004 to September 30, 2005.  Stage 
reference observations were taken from the staff gage located at the station approximately 
one time each week for the period of record.  The cross-section remained stable 
throughout water year 2005.  The mean annual discharge for water year 2005 was 9.5 cfs 
compared to a mean annual discharge of 13.9 cfs during water year 2004.  Discharge 
ranged from a low of 0.8 cfs to a high of 87 cfs for the water year.

Stage Record

The stage record for the water year contains three substantial gaps totaling 72 days due to 
electrical, battery, and replacement part problems.  These gaps in the data were filled 
with data from Ecology station 18N050 Little River nr Mouth.  A linear regression of the 
two stations stage data from the 2004 water year produced a correlation coefficient of  
r = 0.94.  The data set from 18N050 Little River was run through the linear equation used 
to establish the relationship and inserted into the gaps in the McDonald Creek data.  To 
correct for instrument drift, the difference between the logged stage and the observed 
stage, the record has been adjusted to the known individual stage reference observations.  
The recorded range of stage for the period of record was 1.52 ft.  A low of 3.32 ft was 
recorded on September 08, 2005 and a high of 4.84 ft was recorded on December 10, 
2004.  Rapid changes in stage at this station can be attributed to the operation of the 
McDonald Irrigation ditch adjacent to this station.

Rating Curve

Two rating curves were used during water year 2005.  These curve included four new 
discharge measurements.  The lowest discharge measurement taken during the water year 
was 0.92 cfs.  Discharge was below 0.92 cfs for 3% of the period of record.  The 
difference in stage between the lowest measured stage and the lowest recorded stage was 
.04 ft.  The highest measured discharge for the water year was 46 cfs, however the 
highest point used in the rating curve was at 98 cfs.  This measurement, taken in January 
of 2006, was 0.08 ft higher than the highest logged stage of water year 2005.  
Subsequently, the water year 2005 rating encompasses the highest logged stage value for 
the year.