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Discharge.-- PLATTE RIVER BASIN 06710500 BEAR CREEK AT MORRISON Location.-- Drainage and Period of Record.-- Lat. 39°39'11",Long. 105°11'42, in SE¼SW¼ sec. 35, T.4 S., R.70 W., Jefferson County, Hydrologic Unit 10190002, on left bank at Morrison, 180 ft upstream from bridge on State Highway 8 and 0.2 mi upstream from Mount Vernon Creek. 164 mi². Sporadic, incomplete data Sep. 1881 to Feb. 1902. Good data October 1919 to current year. Monthly data for some periods only. Some early years published as near Morrison, at Starbuck, at Idledale. Graphic stage recorder and satellite monitoring DCP with telephone access in a 60-inch metal shelter and 48 inch well. The float for the encoder resides inside a cylinder tube containing Isopar (an anti-freezing agent). The back-up chart recorder float is in the well itself and prone to freezing. A drop tape within the well referenced to an adjustable RP on the instrument shelf is the primary reference gage. There is no outside gage. Control is a compound weir. A bank-operated cableway at the gage is used for high flow measurements. No equipment changes were made this water year. Equipment.-- Hydrographic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- The Bear Creek drainage is a mix of mountains and urban landscape. It extends from the mountains near Mt. Evans down to the City of Sheridan before entering the S. Platte River. Runoff was light this year due to above average snow pack in the upper and lower basins. Rainfall was also less that average throughout the summer. In the summer of 2005, the Town of Morrison constructed a new bike path along the creek and past the gage. It does not seem to be affecting the gage or nearby creek banks in a negative manner. The primary record is hourly averages of 15-minute satellite data with chart record as back up. Record is complete and reliable except for the following periods : December 5, 15-23 2008; January 4-6, 26, 27, 2009, when the stage discharge relationship was affected by ice; December 5, 2008 to March 6, 2009 when ice was observed in channel resulting in possible ice affect; May 14-28, when the well inlet was partially closed or plugged and there was some GH movement but does not show variation expected; July 22-27, when the inlet valves were left closed and there was no GH record. Missing data values were filled in using the chart on 10/9, 17, 20, 22-24, 11/23, 11/28-30, 12/1, 4, and 3/8/2009 when the DCP was missing transmissions with no loss of accuracy. On April 29, 2009 a log was noted on the weir plate but was not removed. On May 7, 2009 at 16:35 the log was removed and a -0.02 ft gage height correction was noted in the 15-minute transmitted data. This correction was run from April 29 – May 7 as a -0.02 ft debris (Datum) correction. Since the timing on when this log actually was caught was assumed sometime between April 17 (before runoff) and April 29 (runoff), the correction was prorated from April 17 to April 29. The mean gage height for Measurement 979 (4/29) was adjusted -0.02 ft due to a log on the control. Levels were run this year. No corrections were necessary or made . The control is a compound weir consisting of a broad crested concrete wall with a six-foot sharp-crested Cipolletti notch (one-foot deep) for low flows. Rating No. 23 was developed from the standard Cipolletti for the first foot and from measurements made in 2003 above the first foot. The rating shows a break in slope around GH = 6.0 as flow goes above the notch and out over the much wider section of broad crested weir. Rating 23 is defined by measurements to 346 cfs, but it is not well defined around GH = 6.0 ft where the flow transitions out of the Cipolletti. Nineteen measurements (Nos. 970- 988), ranging in discharge from 7.12 to 89.7 cfs were made this year. The peak flow of 159 cfs occurred at 1315 June 2, 2009 at a gage height of 6.91 feet (GH correction of -0.01 ft applied) with a shift of -0.01 ft. It exceeded measurement No. 979, made April 29, 2009 by 0.26 ft. Shifting control method was used this year. Shifts are caused by scour and fill in weir pool, uneven flow when the stage tops the notch and flows over the wall, and by ice-affect in the winter. Shifts generally have been negative at high and low stages and zero in the middle. Measurements show unadjusted shifts varying from –0.07 to + 0.01 ft. Shifts were distributed by time from October 1 to April 29. The ice period December 15-23 was considered to be the point of change for shifts during December. All measurements were given full weight. Shifts were distributed using a stage-shift table from April 29 to September 30. Measurements 979, 982, 986 and 987 were adjusted from -1% to +4% to fit the table. High flow measurements 931 and 935 from 2007 were included in the table to cover the range in stage experienced. Determination of ice affect involves some judgment, since the flow does fluctuate and peaks and bumps in the graphic record do not always mean ice. Also, flows in the winter are often less than 25 cfs, and as such are contained 100% within the Cipolletti notch. When flow is completely through the notch, measurement shifts often show little ice affect even if there is heavy ice in the gage pool behind the weir, The general approach is to examine the graphic record and temperatures to identify periods of likely ice-affect. When the primary GH graph rises at night when the temperature is well below freezing, ice is usually indicated. (The primary GH graph is most reliable here, since the encoder is on an oil cylinder and the chart record is not. Sometimes ice in the well causes the chart and encoder to differ.) Record can sometimes be estimated by chopping off ice peaks and correcting the GH. After editing any suspect GH’s, we examine the computed discharges with temperature trends, and with figures from nearby USGS gages. If discharges rise when temperatures fall or if computed record is out of line with other gages, then some ice-affect is presumed. Estimates are made which are consistent with other gages, temperatures, and climate data. Discharge for December 5, 15-23 and January 4-6, 26, 27 was estimated from adjacent record and temperature trends. July 22-27 was estimated using the upstream USGS gage at Evergreen. The record is good, except for periods of ice effect whcih are esimtated and poor,periods of potential ice effect which are considered fair, period of partially plugged intakes which considered fair to poor, and the period of closed intakes which is estimated and poor. Station maintained and record developed by Jana Ash. 2009Water Year