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Discharge.-- PLATTE RIVER BASIN 06696000 SOUTH PLATTE RIVER NEAR LAKE GEORGE Location.-- Drainage and Period of Record.-- Lat. 38°54'19",Long. 105°28'22". in SW¼ sec. 20, T.13 S., R.72 W., Park County, Hydrologic Unit 10190001, on left bank 700 ft downstream from Elevenmile Canyon Reservoir and 8.2 mi southwest of town of Lake George. 963 mi². October 1929 to current year. Monthly data only for some periods. Graphic water-stage recorder and Sutron SatLink 2 satellite monitoring Data Collection Platform (DCP) with Sutron shaft encoder (SE) in a concrete shelter at a 15-foot concrete Parshall flume. Primary reference is an inside tape gage, and there is an enameled staff gage on the right side of the flume at the Ha location. The gage has power and the shelter is heated during cold weather. The gage is owned and maintained by the Denver Water Department. A 10-foot rectangular bypass channel is located beside the upper right wing wall of the 15-foot Parshall flume. The channel is normally kept closed by log stop (boards). At a gage height of 3.40 ft. in the Parshall flume, water reaches the floor of the bypass channel. A Sutron Stage-discharge recorder (SDR) was installed July 8, 2010. Equipment.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- Natural flow of stream affected by storage variations in Eleven Mile Reservoir (capacity 97,780 acre feet), Spinney Mountain Reservoir releases (capacity 53,651 acre feet), and transmountain diversions from the Homestake pipeline into Spinney Reservoir, Antero Reservoir releases (capacity 22,300 acre feet) and diversions for irrigation and return flow from irrigated areas. Abrupt gage height fluctuations are experienced at this gage when the reservoir is spilling. Prevailing winds cause waves of water to wash over the spillway. The gage is close to the spillway channel and experiences the waves as rises and dips of unpredictable magnitude. The primary record is hourly averages of 15 minute satellite data with chart and SDR back up. The primary record agrees with the chart to within 0.02 ft. The record is complete and reliable without missing values. Instrument calibration was verified by twenty visits made to the gage. One SE adjustment of +0.01 ft was made on May 25, 2010 and was prorated to the last visit. Levels were run on August 8, 2010 using RM4 as a base. The RP was found to be 0.004 ft low (the gage was found to read 0.005 high) which is within the allowable limits of 0.02 ft., no correction to the RP was necessary. The control is a standard 15-foot Parshall flume. Shifting is caused by moss and high approach velocities as weir pool is constricted by width and depth. Rating No. 4, dated October 1, 1971, is a standard Parshall flume table, the expanded version was used for the record. The by-pass was not used this year. A rating for the bypass was developed in 1995 and is included in the record. All flow in water year 2010 passed through the 15 foot Parshall flume. Sixteen measurements (Nos. 1088 - 1103) were made, ranging in discharge from 52.6 to 290 cfs. Using the USBR Water Measurement Manual, Third Edition, Figure 8-9, Page 8-44, the range of accurate (within +/-5%) discharge measurement for a 15 ft Parshall Flume is 8 to 600 cfs. Anything above or below this range is outside the +/- 5% accuracy range. The 15 ft rating for this flume has been further verified by measurements from 3.97 to 837 cfs. All flows during the 2010 water year were within this accuracy range. The peak discharge of 417 cfs occurred at 1630 on August 10, 2010 at a gage height of 3.41 ft. with a shift of +0.03 ft. It exceeded measurement No. 1099, made on June 18, by 0.69 ft. in stage. Shifting control method was used for the entire year. Measured shifts ranged from -0.03 to +0.03 feet. Shifts were applied as defined by measurements and were distributed mainly by time with some consideration to change in stage. Shifts were applied by as follows. October 1, 2009 to April 22, 2010: time distribution with all measurements given full weight. April 22 to May 5, 2010: time distribution with consideration to stage by applying measurement No. 1095 (May 5) back to peak flow event on April 24, 2010. Measurement 1095 was adjusted 3% to smooth distribution. May 5 to June 18, 2010: time distribution with consideration to stage by applying measurement No. 1099 (June 18) back to a peak flow event on June 15, 2010. Measurements 1095 and 1097 made during high wind were adjusted 3% and 1% to smooth time distribution. (Measurement 1097 was a check measurement.) Other measurements were given full weight. June 18 to August 17, 2010: time distribution with consideration to stage by applying measurement No. 1102 (August 17) back to a peak flow event on August 4, 2010. All measurements given full weight. August 17 to September 30, 2010: time distribution with all measurements given full weight. When clean, the flume will often show positive shifting, possibly due to approach velocities. Moss growth causes negative shifting. None. The record is considered good. Station maintained and record developed by Mike Wild. Approach conditions to the flume cause velocities greater than 0.5 ft/s in weir pool. Weir pool needs work to slow velocities. 2010Water Year