DWR_2668843

• Title: STREAM FLOW DATA FOR COLORADO
• Year: 2009
• Document Type - Publications and Reports: Streamflow Report

Discharge.--
PLATTE RIVER BASIN
06707501 SOUTH PLATTE RIVER BELOW STRONTIA SPRINGS
Location.--
Drainage and Period of Record.--
Lat. 39°26'00",Long. 105°07'30", SW¼SW¼ sec. 16, T.7 S., R.69 W., Douglas County, on right bank 1/4 mi downstream from
Strontia Springs Dam.
2596 sq mi. 1983 to present.
Graphic water stage recorder, satellite monitoring data collection platform with digital shaft encoder installed in a formed
concrete shelter and well. An adjustable reference point with a graduated tape on the float drive for the recorder is used for
referencing. An adjustable reference for a drop tape is located below the floor hatch to the well. An outside staff gage is
used as an additional reference. The gage and well are one-piece cast concrete, set on bedrock. A cableway for high flow
measurements is located 100 ft downstream of the gage.
Equipment.--
Hydrographic Conditions.--
Gage-Height Record.--
Datum Corrections.--
Rating.--
Discharge.--
Special Computations.--
Remarks.--
Recommendations.--
The flow is controlled by reservoir releases most of the time, including flows released from further upstream at Cheeseman
Reservoir and Robert’s Tunnel. The flows will reflect extreme basin conditions when the reservoirs are very low or
completely full. Strontia Dam is approximately 1500 feet upstream. The record usually runs in steps from the releases. A
period of free river occurred in June this year during which Strontia gates were closed and the reservoir spilled all inflow.
Primary record is hourly averages of 15-minute satellite data. Chart data are used for backup. Record is complete and
reliable. The encoder maintained calibration so that no corrections were necessary to the record.
In the past, it was believed that since the gage is cast on bedrock, no RP to BM checks were needed because the most
stable BM sites would be all attached to the gage. Levels were run this year, and three reference marks were established.
No corrections were made.
The control is a boulder and cobble riffle channel. The grade drops approximately 170 feet below the gage (just below the
cableway). The riffle below the cableway is considered to be the major control for flows under approximately 800 cfs. At
flows above approximately 800 cfs the entire channel becomes the control. Rating No. 4, dated March 19, 2008 was
continued for 2009. It is defined by measurements to 1670 cfs. Frequent measurements at high flows are needed since the
channel does change, but additional measurements are particularly desirable around 1000 cfs, as computed flows in this
range sometimes do not balance well with downstream gages. Sixteen measurements (441-456) were made ranging in flow
from 34.9 cfs to 914 cfs. They cover the range in discharge except for lower daily flows on December 3-17, 19, 21-22, and
higher daily flows on June 2-10. The peak flow of 1430 cfs occurred at 1200 on June 3, 2009 at a gage height of 5.72 ft.
with a shift of -0.02 ft. It exceeded the stage of high measurement No.451 (made June 10, 2009) by 0.56 ft.
Shifting control method was used all year. Shifts at low and medium flows are caused by scour and fill through the section
control below the gage. High flow shifts are influenced by downstream channel gradients and impedance factors.
Measurements showed raw shifts ranging from -0.03 to +0.08 feet. Shifts were distributed by time the entire water year with
consideration of stage changes during these periods: November 24 (#444) to January 21 (#445), April 7 (#448) to April 29
(#449), August 4 (#454) to August 31 (#455) . Stage changes occurred due to changes in release rates from the reservoir,
and flushing of Strontia reservoir. Measurements 442, and 447 were discounted -2% and +3% to smooth shift
distribution. Measurement 445 was essentially not used. More water was measured than Denver was thought to be
releasing, so a check measurement (446) was made immediately. The check showed 13% less water so this second
measurement (446) was used. Snow and ice were melting between the gage and the measurement section, so the first
measurement was thought to reflect some transient condition. Using our current HydroApp measurement software, it was
simpler to adjust measurement 445 a -13% to the measurement 446 shift than it was to delete measurement 445.
No ice was observed at the gage this year, as it was a generally warm year. Strontia typically releases constant amounts
for long periods of time and this helped to confirm the record. Also, the Strontia reports show max/min temperatures just
below their Strontia Outflow numbers and this spares the need to examine the chart closely. We just look for cold days
during periods of constant release when our figures are higher than theirs.
The record is considered good. Station maintained by and record developed by Jana Ash.
The Strontia—Chatfield gages need to be measured with the highest possible accuracy. Otherwise the shifts can cause
bad water balances and lots of complaints. These gages need to be operated by very experienced personnel who are
familiar with stage-shift relationships and the diversion flows that are balanced by the gage figures. The description needs
a photo showing the float tape and indicator as the primary reference.
2009Water Year