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Discharge.-- <br />PLATTE RIVER BASIN <br />SOUTH PLATTE RIVER BELOW ANTERO RESERVOIR <br />Location.-- <br />Drainage and Period of Record.-- <br />Lat. 38°56’53”, Long. 105°41’02”, in the SW ¼ of the NE ¼ Sec.21, T125, R76W, Park County, Hydrologic Unit 10190001, on <br />left bank about 400 ft below the Reservoir. <br />Drainage area approximately 185 square miles; flows regulated by Antero Reservoir outlet works. 1976 to <br />current year. <br />Stevens A-71 graphic water-stage recorder and Sutron SatLink 2 satellite Data Collection Platform (DCP) with a Sutron 56- <br />0540 shaft encoder (SE). The equipment is in a concrete shelter over a 48 inch concrete well with inside electric tape gage <br />on a sharp crested Cipolletti weir with broad-crested concrete overflow walls. Well is connected to channel by two 4-inch <br />intakes located at the same elevation. Gage is owned and maintained by the Denver Water Dept. <br />Equipment.-- <br />Hydrographic Conditions.-- <br />Gage-Height Record.-- <br />Datum Corrections.-- <br />Rating.-- <br />Discharge.-- <br />Special Computations.-- <br />Remarks.-- <br />Recommendations.-- <br />Drainage area approximately 185 square miles; flows regulated by Antero Reservoir outlet works. <br />The primary record is hourly averages of 15 minute data satellite data with chart back up. The primary record agrees with <br />the chart to within +/-0.02 ft. The record is complete and reliable. The gage was visited sixteen times in water year 2009. <br /> Levels were run on October 2, 2009 and the gage was found to be within the ±.02 ft. tolerances. No instrument corrections <br />were made. <br />The control is a 10 ft. sharp-crested Cipolletti weir with a rectangular concrete wall overflow. The overflow has sloped <br />walls. Initially the weir employed a theoretic rating based on compound weirs. However, this proved inaccurate and a new <br />rating, Rating MOD10FTCIP, was developed using the Cipolletti rating to a stage of 3.16 ft. Above 3.16 ft. the rating is <br />defined to 316 cfs by measurements made in 2002 and 2003. This rating was utilized for 2009. No measurements were <br />made in water year 2009. The peak flow of 247 cfs occurred at 0900 May 27, 2009 at a gage height of 3.47 ft with a shift of <br />0 ft. <br />Shifts could be caused by moss growth and approach velocities. Regular visits ensure that the blade of the Cipolletti weir <br />remains clean. No corrections were necessary after cleaning. By agreement with the Denver Water Board, a zero shift is <br />used and any applied measurement shift would need sharp-crested weir accuracy. Flows can drop off during lower flow <br />periods as the slide gates can plug with debris until the caretaker opens the gate to flush the debris out. <br />Peak flow occurred as the larger conduit was placed into service while release was increased. Duration was less than <br />fifteen minutes and taken from chart data. <br />Record is complete and rated good. Record developed by Mike Wild . <br />Due to limitations and / or issues associated with performing conventional current meter measurements at this site, <br />investigation and evaluation of the weir’s rating by use of an Acoustic Doppler Current Profiler (ADCP) should be <br />considered. However, site condition suitability for ADCP use has not been evaluated as of yet, and excessive air <br />entrainment introduced by the baffle structure located in the weir pool may preclude ADCP use. <br />2009Water Year