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Discharge.--
<br />PLATTE RIVER BASIN
<br />06707500 SOUTH PLATTE RIVER AT SOUTH PLATTE
<br />Location.--
<br />Drainage and Period of Record.--
<br />Lat. 39°24'33",Long. 105°10'10", SE¼ sec. 25, T.7 S., R.70 W., Jefferson County, Hydrologic Unit 10190002, on left bank at
<br />South Platte, 200 ft downstream from bridge on State Highway 75, and 400 ft downstream from North Fork.
<br />2,579 mi²; 1910 to present.
<br />Sutron SatLink 2 Data Collection Platform (DCP) with a Sutron shaft encoder (SE); a Sutron stage-discharge recorder
<br />(SDR) and a tipping bucket rain gage in a concrete shelter with a 60 inch corrugated stilling well on left bank. There is a
<br />105 foot cableway for measurement of flows greater than 350 cfs just upstream of the gage house. The primary gage is an
<br />electric tape gage (ETG) mounted on the equipment shelf. Gage house has 120-volt electricity. The gage is on Denver
<br />Water Board property, and a Denver Water Department (DWD) employee will sometimes visit the gage during high flow
<br />events. Satellite equipment is owned and maintained by Division of Water Resources (DWR).
<br />Equipment.--
<br />Hydrologic Conditions.--
<br />Gage-Height Record.--
<br />Datum Corrections.--
<br />Rating.--
<br />Discharge.--
<br />Special Computations.--
<br />Remarks.--
<br />Recommendations.--
<br />Flow runs through mountainous terrain and is somewhat controlled by releases from Cheesman Reservoir and Robert’s
<br />Tunnel. A large portion of the watershed contains significant burn areas due to the Hayman, Schoonover and Buffalo Creek
<br />fires. However, soil erosion from these fires is stabilizing and turbidity, though still present, is decreasing. Trees and other
<br />organic material migrate down river during heavy precipitation events.
<br />The primary record is hourly averages of 15 minute satellite data with chart and SDR back up. Checks between the primary
<br />and backup record agreed within 0.02 ft. The record is complete and reliable, except November 15, 2009 through February
<br />28, 2010, when there was possible ice affect. Instrument calibration was verified by nineteen visits made to the gage. Two
<br />SE adjustments were made; March 15, 2010 (0.01) and on July 9, 2010 (-0.01). Both were prorated to the last visit. The
<br />SDR was installed August 12, 2010, 3 missing unit values were filled from on site observations without loss of accuracy.
<br />Levels were last run on August 27, 2008 and were found to be within the ±.02 ft. tolerances. No instrument corrections
<br />were made.
<br />The control is a rock channel and bank at medium and high stages. At low flows a slight narrowing of the channel and a
<br />rock riffle downstream (on REW) of the gage act as the control. Channel constriction a quarter mile below the gage may
<br />affect extremely high flows. Rating No. 16 (PLASPLCO16) in use since Oct 1, 2002 was continued in use this year. It is
<br />defined by measurements to 3350 cfs. Positive and negative shifts are caused by movement of gravel and sand past the
<br />gage. Winter ice can also result in shifts at the gage. Eleven measurements (Nos. 822-832) were made this year, ranging
<br />in discharge from 194 to 1190 cfs. The measurements covered the range of discharge experienced during non-ice record
<br />except for the lower mean daily flows of October 12-14, 29-31, November 1-3, 2009, March 10, 11, 2010; and the higher
<br />mean daily flow of June 15, 2010. The peak flow of 1340 cfs occurred at 0530 June 14, 2010 at a gage height of 4.38 ft at
<br />a shift of 0.08 ft. It exceeded measurement No. 827, made on June 16, 2010 by 0.22 ft. in stage.
<br />Shifting control method was used for the entire year. Measurements show shifts varying from 0.00 to 0.13 ft in WY 2010.
<br />Shifts were applied as defined by measurements and were distributed by stage from October 1-26, 2009; and by time with
<br />consideration to change in stage and event for the remainder of the water year. All measurements were given full weight,
<br />except for measurement No. 826 which was adjusted 3% to smooth distribution.
<br />Ice affect is not obvious from the GH record. Ice periods are identified by comparing computed record against DWD
<br />estimates for computed inflow to Strontia Springs Reservoir, about 2 miles downstream. Generally the computed record will
<br />start to greatly exceed the DWD figures shortly after winter cold sets in, and ice record will be considered to begin. Most
<br />years the computed figures will remain high until sustained warm weather. When gage figures and DWD figures get close
<br />again, ice-affect is assumed to be ove. WY2010 had a warmer winter. Temperature information suggested possible ice
<br />from November 15, 2009 to February 28, 2010. A spreadsheet is developed for the ice period displaying computed
<br />record, Strontia estimates, weather data, and tributary inflows from Cheesman Reservoir and the North Fork of the South
<br />Platte at Grant. Ice periods showed up with computed discharges much higher than Strontia inflow and out of line with
<br />trends from tributary gages. The ice periods also correlated to periods of sustained below zero temperatures. Inflows into
<br />Strontia from DWB accounting were used to estimate discharge for Nov. 15-19; Dec. 8-12, 23-31; and Jan. 1-11. Other
<br />days in the ice period used computed discharges rated as Fair.
<br />The record is good, except for days of possible ice which are rated fair to poor. Station maintained and record developed
<br />by Mike Wild.
<br />Winter measurements and visits should continue to be made in order to better determine the ice affected days.
<br />Measurements should also continue to be made twice a month as conditions allow.
<br />2010Water Year
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