01R090 - California Creek @ Valley View Rd. Technical Notes: 2009 Water Year Chuck Springer The continuous stream gaging station on California Creek at Valley View Road, which was upgraded from instantaneous monitoring in November 2007, operated throughout water year 2009. During the water year, nine discharge measurements were made and 13 discrete manual stage readings were taken at this station. Rating Curve This station started water year 2009 on Rating Table 7. Table 7 covers a range of discharge from 1.3 to 183 cfs. Five of the six discharge measurements used to develop this rating was taken during water year 2009. The measured flows for this rating, ranging from 2.6 to 91.6 cfs, cover less than 50% of the rating. Flows exceeded the measured range of flows over 30% of the time while Table 7 was in effect during water year 2009. A total of 25% of flows exceeded the lowest measured flow, and 7% 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 ±13%. A large storm event in January 2009 caused moderate scour of the control for this gage. This shift is represented by Rating Table 8. Table 8 covers a range of discharge from 0 to 183 cfs. Flows during two storm events in January exceeded 183 cfs, which is twice the highest measured flow. However, since no slope-conveyance modeling had been conducted for this site, these flows are considered “unknown” and do not report publicly. All six discharge measurements used to develop this rating were taken during water year 2009. The measured flows for this rating, ranging from 2.6 to 91.6 cfs, cover less than 50% of the rating curve. Flows exceeded the measured range of flows more than 20% of the time while Table 8 was in effect during water year 2009. Twenty 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 the point of zero flow using Johnson’s method to temporarily straighten the rating curve using a log offset (e=0.97) calculated from the stage-discharge relationship. The potential error for flows derived from this rating curve is ±12%. Substantial aquatic vegetation growth occurred at this site during summer 2009. This caused a major low-end “fill” of the rating curve. This shift is represented by Rating Table 9. Table 9 covers a range of discharge from 0 to 183 cfs. All four discharge measurements used to develop this rating were taken during water year 2009. The measured flows for this rating, ranging from 1.3 to 91.6 cfs, cover less than 50% of the rating curve. Flows exceeded the measured range of flows more than 25% of the time while Table 9 was in effect during water year 2009. Twenty- five percent of flows exceeded the lowest measured flow, and 1% exceeded the highest measured flow. The rating curve was interpolated between discharge measurements and extrapolated to the point of zero flow using Johnson’s method to temporarily straighten the rating curve using a log offset (e=0.4) calculated from the stage-discharge relationship. The potential error for flows derived from this rating curve is ±13%. Stage Record This station, which upgraded to collect continuous stage data in November 2007, logged continuously throughout water year 2009. However, beginning in April 2009, the logger began to malfunction. The symptoms were intermittent at first, materializing as zero spikes and brief periods where the digital display would not function. The logger was replaced in June 2009. This was immediately followed by erratic stage data from the pressure transducer. This is suspected to have been caused by low water, and even brief periods of “dewatering” of the pressure transducer. Stage data from early July to late September are qualified as estimates. 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 0.05 to 0.07 ft, and were as much as 0.25 ft. The large differences are at least partially attributable to the datalogger and pressure transducer malfunctions that were experienced over the course of the water year. 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 0.997, with a standard deviation of 0.06 ft. The regression identified two obvious outliers. Both were determined to be tape down readings that had been misread by 0.10 ft. The calculated potential error of the continuous stage data for this station is ±20%. 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.