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Discharge.-- PLATTE RIVER BASIN 06708000 SOUTH PLATTE RIVER AT WATERTON Location.-- Drainage and Period of Record.-- Lat. 39°29'18",Long. 105°05'32", in NE¼ sec. 34, T.6 S., R.69 W., Jefferson County, Hydrologic Unit 10190002, on left bank 168 ft downstream from bridge on State Highway 221, 0.4 mi south of Waterton, 4.7 mi west of Louviers, and 6 mi upstream from Plum Creek. 2,621 mi²; 1926 to present. Graphic stage recorder, and satellite monitoring DCP with a phone modem (on separate floats)-- in a 54-inch galvanized, corrugated steel shelter and well. The primary reference is an electric drop tape. The gage has power and is equipped with heat lamps to prevent the well from freezing. The DCP is state-owned, but the phone card is owned by the USACOE and maintained by the USGS. The gage is connected to the stream by 2 inlets with flush valves and risers. One of the risers is partially plugged. There is an outside gage that is no longer functional. A bank operated cableway for measuring high flows is located at the gage. Equipment.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- A natural-flow hydrograph is not observed except during periods of extended high runoff when upstream reservoirs are all full. Flow is completely regulated at other times. Between Strontia Springs reservoir and the Waterton gage, Denver Water Department can divert water through Conduit 20, the Highline Canal and the Last Chance Ditch. The Last Chance diversion was new in the 2003 water year. In prior years Denver attempted to maintain a winter flow at Waterton of 30 cfs, but the use of the Last Chance diversion allows Denver’s minimum streamflow at Waterton to drop to 15 cfs. This resulted in lower stream flows than have been historically seen at this gage. With the Last Chance ditch running, the FERC minimum streamflow is 15 cfs between September 16 and May 14, and 45 cfs between May 15 and September 15. The primary record is hourly averages of 15 minute data taken from satellite with chart back up. The record is complete and reliable, except for the following period of ice affect: December 4, 2009 to February 26, 2010. During December 6-16, the well was frozen. From October 29,2009 to November 2, 2009 and for March 24, 2010: DCP data not available and backup chart record used without loss of accuracy. The crest of the control usually stays open, but the channel often freezes over. it is very hard to tell from inspection how much ice-effect is happening at the control. Also, periods when the inlets freeze can be tricky, since the release from Strontia Reservoir is usually constant in the winter. Visit notes, chart inspection, temperature data and the Denver Water Spreadsheets were used to determine ice effects. Without visit notes it is difficult to distinguish between ice effect at the gage and diurnal flow due to ice melting in the canyon. Also, ice affect can occur during a warm-up due to floating ice jamming on the control. Levels were not run this year. Levels were last run to the inside gage on September 23, 2009, using R.M. No. 7 as base. At that time the benchmark elevations were re-established, and the gage was found to read correctly The control is a broad crested weir formed by a pipeline crossing approximately 35 feet below the gage. Rating No. 10 developed for use in 2007 is defined from about 13 to 2000 cfs and was used this entire water year. Shifts, both positive and negative, are generally caused by scour and fill of channel material, vegetative growth, and detritus affecting the velocities of the control area and the channel as a whole. Twenty two measurements (Nos. 929-950) were made this water year ranging in discharge from 18.4 to 843 cfs. They cover the range in discharge experienced, except for lower daily flows of Feb. 7, Mar. 16-18, and the higher daily flows on June 13 and 16. The peak flow of 1280 cfs occurred at 1515 on June 16, 2010 at a gage height of 2.53 ft with a shift of -0.03 ft. It exceeded high measurement No. 941, made on June 14, by 0.44 feet in stage. Shifting control method was used. Shifts were caused by scour and fill of the approach area. This year’s measurements show unadjusted shifts varying between -0.03 and 0.01 feet. Shifts were prorated by time with consideration of stage. Shifts do show a slight trend toward negative as stage increases, but the frequency and timing of measurements was such that time shifting was fully accurate. Stage consideration was used between measurements #936 (April 25) and #937. For purposes of ice estimation, the shift for the first Spring measurement, No. 931, March 12 was applied back through December. Msmt 945 was made with the bank-operated cableway for training purposes and was not used. Msmts 940, 943 and 950 were fair measurements and were adjusted up to 8% to fit distribution. Measurement 934 was made for training and adjusted 4% to match No. 933 made at the same time. Finally, Msmt. 937 was adjusted 3% to fit distribution. Estimated flows during ice affected periods at the Waterton gage were developed from a mass balance spreadsheet. Discharges were used for South Platte River below Strontia Springs Reservoir, with columns subtracted for Denver’s diversions to Conduit 20, the Last Chance Ditch, and the Highline Canal. (Denver’s diversions were available on from their monthly “Chatfield Checksheet” accounting spreadsheets.) The mass balance estimate was found to be about 5 cfs higher than periods of good record, so this offset was incorporated into estimates. These spreadsheet should be used with caution of days of flow change, since Denver’s accounting is based on 8am to 7am rather than calendar day figures like Strontia release and Waterton. The record is rated good, except December 4 to February 26 which is estimated and fair. Station maintained by Jana Ash and Tony Arnett and record developed by Tony Arnett. The chart recorder should be watched closely. The channel and control should be cleared of ice during warm periods in the winter. Levels should be run in the 2011and 2012 water years to verify the stability and elevation of RM 8. 2010Water Year