DWR_2669034 - Laserfiche WebLink

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 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.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- 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. 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. Primary record is hourly averages of 15-minute satellite monitoring data with chart back up. Record is complete and reliable, except for the following periods: December 1, 2009–March 4, 2010, when the stage-discharge relationship was affected by ice and ice was observed in channel and in well. Missing data values were filled in using the chart on Oct 27 and Nov 29-Dec 1, when the DCP was missing transmissions, with no loss of accuracy. A correction of -0.08 ft. occurred on April 26, 2010 when debris was removed from the control. The correction was applied back to the gage height increase found on April 22. Levels were last run in 2008. No corrections were 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 6.00 ft 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 6.00 ft where the flow transitions from the notch to the concrete weir. Fifteen Measurements (Nos. 989-1003), ranging in discharge from 11.5 to 138 cfs were made this year. The peak flow of 180 cfs occurred at 0730 on June 12, 2010 at a gage height of 6.99 ft with a shift of -0.03 ft. It exceeded measurement No. 996, made May 19, 2010 by 0.11 ft in stage. Shifting control method was used this year. Shifts are caused by scour and fill in weir pool 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 –0.09 to 0.00 ft. Measurements 990 and 993 were adjusted 2%, and Measurement 1002, rated fair, was adjusted 7%. Shifts were distributed by time with consideration of stage for the entire water year. 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. Our 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. 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. The -0.08 ft GH adjustment made for debris removal on April 26 was presumed to have occurred on a flow rise on April 22. The amount of uncertainty involved in this correction reduces the record to fair for this period. Light debris and branches accumulated at the weir between measurements during 4/22/2010 and 4/26/2010. Flow was estimated during December 1 – March 4, 2010 by reducing some GH’s for ice affect and using computed record. Ice effect was possible throughout the period. The record is good except for the following periods: December 1, 2009 through March 4, 2010 is poor due to ice; and April 22-26 is fair due to debris on the control. Station maintained by Jana Ash and Tony Arnett and record developed by Tony Arnett. A new rating table may be necessary for higher flows (i.e. flows above 200 cfs). A series of measurements should be focused around gage heights where flow transitions out of the Cipolletti weir notch in order to better define the rating. An outside gage has been installed but needs to be tied in with BM. Also, it would be a good idea to check the highway bridge for a MSL benchmark and tie the control BM back to sea level. Weekly measurements and ice observations with photos would help in evaluating how the ice affects the weir (if possible). 2010Water Year