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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 and shaft encoder 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 gage is owned and maintained by Denver Water Department. 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 located just upstream of the gage is use for high flow measurements using conventional current meter measurements as well as to pull the ADCP unit across the channel. Equipment.-- Hydrographic 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 min data taken from satellite monitoring with chart back up. The record is complete. Missing satellite data on October 9-17, 2008 were filled in with chart data with no loss of accuracy. Record is reliable except for the following periods of ice affect: December 15, 2008 to February 21, 2009; March 26-27, 2009. Some days were estimated, but for the majority of the time, computed record was used. During the period: February 21—March 3, the record had possible ice affect but computed record was used. The levels history indicates that the gage shelter settled 0.03-0.04 ft. sometime between 1998 and 2006, and has been relatively stable since then. Levels were last run to the inside gage on September 23, 2009, using R.M. No. 7 as base. The correction indicated of +0.04 ft was achieved by a one-time reset of the elevations of the benchmarks. This fresh start preserved the current rating, and will allow a smooth transition for any future datum corrections The control is a broad crested weir formed by a pipeline crossing approximately 35 feet below the gage. Rating No. 10, developed in 2007 was used all water year. Rating number 10 is well developed from about 13 to 2000 cfs. Shifts are caused by moss growth on the control and by the amount of stilling of approach velocities provided by the pool behind the control. Fifteen measurements (Nos. 914-928) were made this water year ranging in discharge from 17.2 cfs to 872 cfs. They cover the range in discharge experienced, except for lower daily flows of Dec. 4, 7-8, 11-14, 30-31; Jan. 1-4, 8-10, 12, 14-15; Feb. 5-6; March 31 and April 7-8 and the higher daily flows on June 2-9. The peak flow of 1260 cfs occurred at 0945 June 3, 2009 at a gage height of 2.51 ft with a shift of -0.03 ft. It exceeded high measurement No. 922, made on June 10, by 0.39 feet in stage. Shifting control method was used. Shifts were prorated by time with consideration with stage. This year’s measurements show raw shifts varying between -0.03 and 0.02 feet. Shifts were analyzed and the relationship between stage and gage height correlated very well with time and changes in stage. Shifts between measurements #923 (June 25) and #924 (July 17) were held for stage. Estimated flows for 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 East Slope accounting spreadsheets, using the sheet tab “WT”—“Water Distribution in the South Platte Canyon”. These spreadsheet estimates should be used with caution, since Denver’s accounting is based on 8am to 7am rather than calendar day figures like Strontia release. Discharge for the periods of ice affect and possible ice affect were taken from computed record, except for the following days which were estimated using a mass balance spreadsheet: December 15 to January 16; January 28-30; February 15, 16; March 26, 27. Computed record for these days diverged greatly from spreadsheet estimates, so the spreadsheet was used as a basis for estimates. Other ice-period days used computed record because there was general agreement with spreadsheet estimates. The crest of the control usually stays open, but the channel often freezes over. and it is very hard to tell from inspection of the gage height record how much ice is affecting the control. 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. The record is rated good, excep periods of ice effect which are estimated and poor. The period February 22 to March 3 is considered fair. Station maintained and record developed by Jana Ash. The chart recorder should be watched closely. The channel and control should be cleared of ice during warm periods in the winter. 2009Water Year