DWR_2669034 - Laserfiche WebLink

Discharge.-- PLATTE RIVER BASIN 06717000 FALL RIVER NEAR IDAHO SPRINGS, CO. Location.-- Drainage and Period of Record.-- Lat 39°45'20", long 105°33'24”, in SE1/4, Sec. 28, T.3 S., R.73W., Clear Creek County. Gage is located on right upstream bank of the I-70 box culvert,near the Fall River Road Exit (238) approximately 20 ft. past Fall River Road. Not determined. Gage established July 2007 at present site and datum to monitor minimum stream flow reach and aid in the administration of water rights. Sutron Satlink 2 Data Collection Platform (DCP) and Sutron AccuBubble unit in a 12-inch by 30-inch by 36-inch NEMA4 enclosure. A single orifice line in 2-inch conduit extends from the NEMA4 enclosure and terminates in a gravel packed muffler buried in the stream bed approximately 5-feet upstream from the steel sill plate/box culvert control. A staff gage located on the right edge of water is the primary reference with an additional staff gage located on the left edge of water wing wall of the culvert as backup (datum offset is applicable). Equipment.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- Mountainous topography mainly consisting of densely treed slopes with sporadically patches of oak shrubs and grass. Rock outcropping increases with elevation and Saint Mary’s Glacier sits at the headwater of Fall River. The river runs fast and quickly responds to rainfall-runoff events. Flow is partly regulated by several small reservoirs located upstream of the gage near St. Mary’s Glacier. It should be noted that mining activity in this valley has occurred in the past. The primary record is hourly averages of 15-minute telemetered bubbler data with DCP logged data as backup. The record is complete and reliable, except for: November 17, 2009 to April 23, 2010, when the gage was disabled for winter and no gage-height record was collected. On June 12, 2010, an abnormal peak due to sudden backwater or an instrument problem was recorded, which did not fit with diurnal trends and there was no precipitation. For the period, July 15-23, 2010, the record is unstable due to a log on the control. The record “painted” for flows above about 30 cfs, due to hydraulic instability as flow bounced off the bridge wingwalls . Instrument calibration was supported by 16 visits to the gage. The instrument was set once in the spring and followed up with two calibrations throughout the summer. Accurate readings of the staff gage are subject to individual interpretation, duration of stage, and inconsistent and relentless bounce of the water surface. These conditions change frequently as a result of changing river bottom profiles. Lack of stable surface water conditions has affected gage calibration and the accuracy of staff gage measurements. The subjective interpretation of GH level varies widely with individuals and is compounded with increasing stage. Changes in stage also occur rapidly and unexpectently with changes in environmental conditions upstream of the gage. Unstable surface conditions, previously reported as bounce, are easily seen in hydrographs of 15-minute data recordings. Two calibration corrections were made to the record: a +0.05 ft correction was applied from June 23, 2010 and distributed back to June 11, 2010; and a -0.02 ft correction was applied August 26,2010 and distributed back to August 11, 2010. Removal of a log from the control on July 23, was cause for a -0.06 ft calibration between July 15 and July 23, 2010. However, this period was estimated based on adjacent measurement and record. Levels were run August 10, 2010. The gage was found to be reading correctly. The channel is composed primarily of gravel, cobble and small boulders. The control at all stages is a metal sill mounted in front of the box culvert running under I-70 about 5-feet downstream of the gage. Shifts result from material moving into the stilling basin, debris accumulation in the channel and from an incomplete definition of the rating. Cobble fills the weir basin entirely during runoff, so that the bed of the stream is level with the top of the weir. The channel alignment is straight above and below the gage. Rating No. 2, dated June 28, 2008, was used all year and is defined by measurements from 3.66 to 133 cfs. Rating 2 was extrapolated to 336 cfs (GH=2.70 ft) on June 14, 2010 to capture real time flows. Thirteen (Nos. 44-56) measurements were made this year, ranging from 4.12 to 133 cfs. These flows are generally higher than previous years of record. The peak discharge of 241cfs occurred at 0945 on June 09, 2010 at a gage height of 2.36 feet with a shift of 0.07 feet. It exceeded measurement No. 48, 133 cfs made on June 11, 2010 by 0.41 feet of stage and 108 cfs respectively. The peak flow was 180% of the high measurement. Shifting control method was used all year. Measurements show shifts ranging from -0.19 feet to +0.11 feet. The wide range of shifting indicates changing stream bed profiles. Shifts were applied by time, with Msmt 50 being adjusted 4% for smoothing purposes. Consideration to stage was given during June 15-22, by extending the Msmt 49 (June 22) shift back through a period of steady GH to June 15. The large variation in shift between Msmts. 48 and 49 was contained in the interval June 11-15, where wide GH variability and suspected backwater occurred. Following June 12 a period of high shift variability [June 11 (+0.07) , June 22 (-0.15)] occurred. The flows during the period of July 15-23 when a log was in the control, were estimated from adjacent record and measurements, and are considered Poor. The log created unstable GH’s and a high variability in shifts: July 14 (-0.15) to July 23 (+0.11). The record is fair except for the following days which are estimated and poor: June 12-14, 2010, due to instability in the channel and rating, and July 15-23, 2010 due to the effects of a log on the control. The instantaneous peak is of 241 cfs on June 9, 2010 is considered poor since it exceeds 150% of the highest measurement. Station maintained by Jana Ash and Tony Arnett and record developed by Tony Arnett. Additional high flow measurements are needed with good stilling conditions for rating development. Photo of new control is needed for the station description. Cleanout of cobble filling in front of the control should be done when the gage is opened. Enlargement of the stilling area is planned for April, 2011. A structure upstream of the stilling pool for catchment of moving rock material would benefit maintenance of the gaging area and stabilization of flow conditions. 2010Water Year