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Discharge.-- PLATTE RIVER BASIN 06707500 SOUTH PLATTE RIVER AT SOUTH PLATTE Location.-- Drainage and Period of Record.-- 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 South Platte, 200 ft downstream from bridge on State Highway 75, and 400 ft downstream from North Fork. 2,579 mi²; 1910 to present. Sutron Satlink2 Data Collection Platform (DCP) with Sutron 56-0540 shaft encoder, a Stevens type A graphic water stage recorder and a tipping bucket rain gage, in a concrete shelter over a 60-in CMP well, and cableway. The primary gage is an electric tape gage mounted on the equipment shelf. The gage is on Denver Water Board property, and a Denver Water Department (DWD) employee will sometimes visit the gage during high flow events. Satellite equipment is owned and maintained by Division of Water Resources (DWR). Equipment.-- Hydrographic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- Flow runs through mountainous terrain and is somewhat controlled by releases from Cheesman Reservoir and Robert’s Tunnel. A large portion of the watershed contains significant burn areas due to the Hayman, Schoonover and Buffalo Creek fires. However, soil erosion from these fires is stabilizing and turbidity, though still present, is decreasing. Trees and other organic material migrate down river during heavy precipitation events. The primary record is hourly averages of 15 minute satellite data with chart back up. The primary record agrees with the chart to within +/-0.02 ft. The record is complete and reliable except as follows: October 1, 2008 - 10:15 to 15:30 - Satellite equipment upgraded to Satlink2, data obtained from chart and on site observation; October 28, 2008 - 20:15 to 22:00, data obtained from chart; November 23, 2008 - 08:15 to 09:00, no edits necessary, chart checked; April 18, 2009 – 04:15 to 06:00, data obtained from chart. December 5, 2008 through February 8, 2009, when ice affected the stage-discharge relationship. Levels were run on August 27, 2008 and were found to be within the ±.02 ft. tolerances. No instrument corrections were made. The control is a rock channel and bank at medium and high stages. At low flows a slight narrowing of the channel and a rock riffle downstream of the gage act as the control. Channel constriction a quarter mile below the gage may affect extremely high flows. Rating No. 16 (PLASPLCO16) in use since Oct 1, 2002 was continued in use this year. It is defined by measurements to 3350 cfs. Nineteen measurements (Nos. 803-821) were made this year, ranging in discharge from 216 to 1550 cfs. The measurements covered the range of discharge experienced during non-ice record with the exception of the following days when daily average flows were less than 216 cfs: December 3, 4, 2008, February 10-12, Feb 14 through March 19, 2009; and, days of greater daily average flow on June 3, 2009. The peak discharge of 1590 cfs occurred at 0830 June 3, 2009 at a gage height of 4.79 ft with a shift of 0.00 ft. It exceeded measurement No. 815, made June 4, 2009 by 0.05 feet in stage. Shifting control method and stage dependent shifting was used for the year with the exception of estimated periods. Shifts were distributed as follows: October 1, 2008 to February 24, 2009, shifts distributed by time. The shift defined by measurement number 802 taken September 11, 2008 was prorated to the start of the water year. The shift defined by measurement number 803 was adjusted 3 % and measurement number 804 by 1 % to provide continuity with the 2009 water year record. February 24, 2009 to peak discharge on June 3, 2009, (08:30) stage dependent shifting with consideration to time using variable shift curve PLASPLCOSC1, based on measurements 808 through 815. The following shifts were adjusted to produce a smooth, realistic shift adjusted rating to account for movement of gravel and sands in the controlling section at the gage: Measurement 803, 3%, 0.08 to 0.05; Measurement 813, 5%,-0.02 to 0.05 ;Measurement 814, 1%, 0.05 to 0.04. June 3, 2009 to September 30, 2009 stage dependent shifting by using variable shift curve PLASPLCOSC2, based on measurements 815 through 822. This variable shift curve accounts for the changes in the channel following the peak flow on June 3, 2009. Two shifts measurement were adjusted to provide continuity in the shift curve: Measurement 819, 3%, 0.03 to 0.07. Positive and negative shifts are caused by movement of gravel and sand past the gage. Winter ice can also result in shifts at the gage. Measurements show shifts varying from 0.00 to 0.07 ft. The ice-affected record is not always obvious from the chart. Ice periods are identified by comparing computed record against DWB estimates. A mass balance spreadsheet is included in the record. Strontia Dam temperature data from National Oceanic Atmospheric Association (NOAA) was also examined during periods of below freezing temperatures. Generally the computed record will start to greatly exceed the DWB figures shortly after severe winter cold sets in, and ice record will be considered to begin. The computed figures will remain high until sustained warm weather. When gage figures and DWB figures get close again, ice effect assumed to be over. Usually around December, the computed flows start becoming markedly higher than the Strontia estimates. In February or March the computed daily flows will drop until they again have reasonable agreement with the Strontia computed inflows. The record is good, except for periods of ice affected record, which are estimated and poor. Station maintained and record developed by Mike Wild. Winter measurements and visits should continue to be made in order to better determine the ice affected days. Measurements should also continue to be made twice a month as conditions allow. 2009Water Year