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Discharge.-- PLATTE RIVER BASIN 06694920 SOUTH PLATTE RIVER ABOVE SPINNEY RESERVOIR Location.-- Drainage and Period of Record.-- Lat. 38°59'10",Long. 105°40'52" in NE1/4 Sec 21, T. 12S, R. 74W, Park County, 3.3 miles below the confluence of the Middle and South Forks of the South Platte River, and 7 miles southeast of Hartsel, CO. 772 square miles. October 1982 to present. Graphic water-stage recorder and Sutron SatLink 2 Data Collection Platform (DCP) with a Sutron 56-0540 shaft encoder (SE) in a wooden shelter over a concrete well at a 25-foot concrete Parshall flume. The primary reference is an inside Electric Tape Gage (ETG) with a staff gage on the right side at the Ha location. The gage and satellite monitoring equipment are owned and maintained by the City of Aurora. Aurora operates the gage seasonally and it is shut down in the winter. Colorado Division of Water Resources (DWR) operates the gage under a contract with City of Aurora to provide real time data and for record development. A Sutron Stage-discharge recorder (SDR) was installed July 8, 2010 and the graphic water-stage recorder was removed. Equipment.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Flow at gage affected by releases from Antero Reservoir and natural flows from the South and Middle Fork of the South Platte River and Four Mile creek. Releases from Montgomery Reservoir and irrigation diversions also affect flows. The primary record is hourly averages of 15 minute satellite data with chart and SDR back up. The record is complete and reliable, except as follows: November 10, 2009 to April 12, 2010 - DCP and gage were shut down for winter; October 29 to November 2, 2009 - Stage discharge relationship was affected by ice. On two days ( June 9, 2010 - 09:00, July 16, 2010 - 09:00) hourly values were compromised by flushing of the intakes. Onsite observations along with good chart data were used to fill in missing data without loss of accuracy. . On July 31, 2010 an apparent lightning strike near the gage reset the SE to zero at 16:30 hours. The SE was reset to the ETG on August 1, 2010 at 10:45. The primary record agrees with the chart to within 0.02 ft. Good chart data was used to fill in the missing data without loss of accuracy. Thirty visits were made to the gage, one shaft encoder adjustment of -0.01 ft was necessary on September 13, 2010. Levels were last run on August 27, 2008. No corrections were made. The control is a 25-foot Parshall flume with a standard rating. Negative shifting can be caused by moss growth; however this year significant moss growth was not observed. Positive shifting is possibly caused by the approach conditions. An effort was made at spring start up to excavate the weir pool, but it filled early in the year. Shifting was not significantly affected. Observations from levels reveal that the crest is slightly lower than the converging section which could cause reduced gage height and positive shifting. High flows have been observed to by-pass the flume by leaving the channel and crossing the access road. This is believed to occur at gage heights greater than 4.00 ft. and at flows in the 1000 cfs range. The rating is well defined to 493 cfs by measurements made since 2001. Wading measurements are made downstream of the foot bridge (measurement section width 30.5 ft.) while section rod and cable measurements are made on upstream side (measurement section width 32.1 ft.). Bridge is indexed on both sides to obtain accurate section widths. Fourteen measurements (Nos. 289 - 302) were made during the water year ranging in discharge from 21.6 to 493 cfs. The average daily flow was above the highest measurement on the following days: June 8-10, 2010. Using the USBR Water Measurement Manual, Third Edition, Figure 8-9, Page 8-44, the range of accurate (within +/-5%) discharge measurement for a 25 ft Parshall Flume is 15 to 1200 cfs. Anything above or below this range is outside the +/- 5% accuracy range. All flows during the 2010 water year were within this range during the operational period of the gage. The peak flow of 546 cfs occurred at 0800 on June 10, 2010 at a gage height of 2.91 ft.with a shift of 0.08 ft. It exceeded measurement No. 295 made June 8, 2010 by 0.19 ft. in stage. Shifting control method was used all year. Stage dependent shifting was used for the majority of the year with the exception of periods were moss accumulation could be identified and shifts were applied as defined by measurements and were distributed mainly by time with consideration to change in stage. Two variable shift tables, PLASPICOVST1 and PLASPICOVST2, based on measurements made during the water year, were utilized for the record with the exception of winter estimated periods. The range in stage experienced this year was confined to the weir section. Measurements for the entire water year show shifts varying from -0.02 ft. to 0.08 ft. Shifts were distributed as follows: October 1, 2009 to April 22, 2010: PLASPICOVST2 from water year 2009 was used with the addition of measurements 289-291 made during the period. Measurement 290 was adjusted 2% to fit the table. April 22 to May 25, 2010: Measurements 291-293 given full weight and applied by time. The pool in front of the gage was being excavated during this period. The measured shifts covered most of the range in stage, so little accuracy was lost by not considering stage change. May 25, 2010 to July 28, 2010: Variable shift table PLASPICOVST1 developed from measurements Nos. 293 through 298 made during the period, was used. Msmt No. 294 was adjusted 1% and No. 297 by 1% to better fit the stage shift curve. July 28, to September 30, 2010: Variable shift table PLASPICOVST2 developed from Mmts No. 299-302 made during the period and given full weight was applied. September 30, 2010 (12:22 to 23:45): Time distribution. Measurement given full weight. Discharge for estimated days October 29-November 2 and April 12 was based on partial and adjacent record. Gage closure periods were estimated as below except for April 8-11 which was based on temperature trends as the stream opened up. The winter estimates (gage closed) were taken from Aurora’s Spinney Mountain Reservoir accounting; the figures are based on reservoir elevation readings, and tend to show step-wise changes. The frequency of the reservoir elevations readings is daily; however surface ice on the reservoir affects the readings, so the accuracy of daily discharges is questionable. 2010Water Year