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Discharge.-- <br />PLATTE RIVER BASIN <br />06696000 SOUTH PLATTE RIVER NEAR LAKE GEORGE <br />Location.-- <br />Drainage and Period of Record.-- <br />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 <br />ft downstream from Elevenmile Canyon Reservoir and 8.2 mi southwest of town of Lake George. <br />963 mi². October 1929 to current year. Monthly data only for some periods. <br />Stevens A-71 graphic water-stage recorder and Sutron SatLink 2 satellite monitoring Data Collection Platform (DCP) with <br />Sutron 56-0540 shaft encoder (SE) in a concrete shelter, at a 15-foot concrete Parshall flume. Primary reference is an <br />inside tape gage, and there is an enameled staff gage on the right side of the flume at the Ha location. The gage has <br />power, and the shelter is heated during cold weather. The gage is owned and maintained by the Denver Water Department. <br />A 10-foot rectangular bypass channel is located beside the upper right wing wall of the 15-foot Parshall. The channel is <br />normally kept closed by boards. At a gage height of 3.40 ft. in the Parshall, water reaches the floor of the bypass channel. <br />Equipment.-- <br />Hydrographic Conditions.-- <br />Gage-Height Record.-- <br />Datum Corrections.-- <br />Rating.-- <br />Discharge.-- <br />Special Computations.-- <br />Remarks.-- <br />Recommendations.-- <br />Natural flow of stream affected by storage variations in Eleven Mile Reservoir (capacity 97,780 acre feet), Spinney <br />Mountain Reservoir releases (capacity 53,651 acre feet), transmountain diversions from the Homestake pipeline into <br />Spinney Reservoir, Antero Reservoir releases (capacity 22,300 acre feet) and diversions for irrigation and return flow from <br />irrigated areas. Abrupt gage height fluctuations are experienced at this gage when the reservoir is spilling. Prevailing <br />winds cause waves of water to wash over the spillway. The gage is close to the spillway channel and experiences the <br />waves as rises and dips of unpredictable magnitude. <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. Instrument calibration was verified by seventeen visits made <br />to the gage. Two SE adjustments were made on January 15, 2008 (- 0.06 ft) and September 28, 2009 (0.015 ft). <br />Levels were run on September 28, 2009 using RM4 as a base. Gage was found reading 0.015 ft. low. Tape length was <br />adjusted from 8.39 to 8.405 ft and an instrument correction of +0.015 ft was made. A measurement was made the <br />following day and the shift was applied back to the SE correction made on September 28, 2009 at 13:50 hours when the <br />tape was adjusted. Measurement GH’s and shifts prior to September 28 were not adjusted. <br />The control is a standard 15-foot Parshall flume. Rating No. 4, dated October 1, 1971, a standard Parshall flume table was <br />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 <br />the record. All flow in water year 2009 passed through the 15 foot Parshall flume. Fifteen measurements (Nos. 1073 - <br />1087) were made, ranging in discharge 53.5 to 317 cfs. The USBR "Water Measurement Manual" Third Edition shows a <br />15 ft Parshall Flume range of accurate discharge measurement is 8 cfs to 600 cfs. Anything above or below this range is <br />outside the +/- 5% accuracy. All flows during the 2009 water year were within this accuracy range. Average daily flow was <br />above the highest measurement of 317 cfs on June 3-11, June 29-July 7, 2009. The peak flow of 504 cfs occurred at <br />1615 July 2, 2009 at a gage height of 3.82 ft with a shift of 0.05 ft. It exceeded measurement No. 1081, made on June 3, <br />by 0.98 ft. in stage. <br />Shifting control method was used for the entire year. Shifts are caused by moss growth and approach conditions. <br />Unadjusted shifts ranged from 0.01 to 0.05 feet. Shifts were applied by as follows: October 1 , 2008 to June 3, 2009: Time <br />distribution with all measurements given full weight. June 3 to July 13, 2009: Stage distribution, using the measurements <br />made during the period, Nos. 1081-1083. All were given full weight. July 13 to September 30, 2009: Time distribution with <br />all measurements given full weight. A +0.015 ft correction was made to the tape length when levels were run on <br />September 28, 2009, and this correction was taken up in the shifts as follows: the +0.03 shift measured on September 15 <br />was run to 13:50 on September 28. After this time the +0.01 shift measured on September 29 was used. When clean, the <br />flume will often show positive shifting, possibly due to approach velocities. Moss growth causes negative shifting. <br />On December 12, 2008 a Denver Water Board (DWB) employee replaced a light bulb on a fixture in the stilling well and <br />caused the float tape to slip on the SE wheel. A -0.06 ft correction was used from December 12, 2008 09:45 to January 15, <br />2009 09:45 when the problem was discovered. As discussed, the levels correction was taken up in the shifts. The amount <br />of the correction represented the exact difference between shifts preceding and following the adjustment. <br />The record is considered good. Station maintained and record developed by Mike Wild . <br />Replace chart recorder with an SDR and set data collection frequency to five minutes to help determine GH’s during <br />measurements. Approach conditions to the flume cause velocities greater than 0.5 ft/s in the weir pool. Weir pool needs <br />work to slow velocities. <br />2009Water Year