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Discharge.-- PLATTE RIVER BASIN 06722500 SOUTH SAINT VRAIN NEAR WARD Location.-- Drainage and Period of Record.-- Lat. 40°05'27",Long. 105°30'50" 14.4 mi²; 1925-27,28-31, 54-73, 1992 to present. Graphical water stage recorder, and digital shaft encoder (SE) connected to a Sutron Satlink data collection platform (DCP) in a 42-inch diameter corrugated metal pipe shelter and well. The primary reference is a metal drop tape from an adjustable reference point (RP) located on the equipment shelf of the shelter. No other supplemental references are available. Equipment.-- Hydrographic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- Drainage area is 14.3 sq mi from topographic maps (RMNP quad.). Drainage is virtually uninhabited forested lands up to the continental divide, with no artificial diversions. This site is commonly used for watershed studies. The gage is approximately 3.5 miles downstream from Brainard Lake, a naturally occurring water body. Water passing this gage is diverted into the Lefthand Creek basin about 1/3 mile downstream, at the Lefthand Ditch Diversion (LEFTHDCO). Normally the entire flow is diverted up to the point where it spills over the Lefthand diversion structure. So the two gages report similar, if not identical, discharges. However, the high flow point when water bypasses LEFTHDCO is not well defined. Measurements made at this gage are sometimes also used for flow at the Lefthand gage, when it is observed that 100% is being diverted. The primary record is hourly averages of 15-minute telemetered data with graphical chart record as backup. The record is complete and reliable, except for the following periods: November 5-12, 2008, when the gage was frozen; November 13, 2008 to May 10, 2009, when the gage was closed for winter and no gage-height information is available; May 11, 2009, partial day record. The encoder held calibration all year. No datum corrections were required. One control correction was required as follows: Work on the control was done on September 1, 2009. The channel was cleaned of a few large boulders and the control was fortified with more cobble. The result was a +0.02 ft. rise in gage height. Measurement no. 199 was performed prior to the control work resulting in a -0.03 shift. Measurement no. 200 was performed after the channel work resulting in a -0.05 ft. shift. The shifts compensate for the rise in gage height from the control work. Levels were run on October 14, 2009. RP was found to be 0.014 ft. high. No correction was made. The control for low to moderate flow is a rock riffle composed of embedded river boulders approximately 30-feet downstream from the shelter. The high water control is a sharp bend and gradient change in the stream channel approximately 50-feet downstream of the gaging station. The control is subject to shifting boulders moving into and out of the control area as well as material embedding and being released from the rock riffle. Moss growth and debris accumulation is generally not an issue at this gage; however fill and scour conditions as well as control movement do occur. Rating No. 11 developed in water year 2007 is defined by measurements from 4.74 to 156 cubic feet per second (cfs). The rating was extended this year to 510 cfs to include a 2009 measurement of 317 cfs. Twelve measurements (Nos. 190-201) were performed this year ranging in discharge from 4.68 cfs to 317 cfs. They cover the range of stage experienced except for peak days June 26-27. The peak discharge of 494 cfs occurred at 2315 on June 26, 2009 at a stage of 3.20 feet with a shift of +0.08 ft. It exceeded measurement No. 195 made on June 27, 2009 by 0.24 feet of stage. Shifting control method was used all year. Unadjusted shifts ranged from -0.08 feet to +0.02 feet. All measurements were given full weight unless specified differently below. Shifts were distribured by time and by stage. Shifts were distributed by time as follows: Oct 1-Nov 12, 2008, ( Nov 12, 2008 – May 11, 2009 – Gage off for winter season) , and May 11-26, 2009. Measurement 192 (May 26) was adjusted 3% to smooth transition between time and stage shifting. Shifts were distributed by stage using two variable stage shift relationhsips: SSVWARCOVST01, applied May 26 – Sept 1, 2009 and based on measurements made during the period. Measurement 194 (June 24) was adjusted 8% to better fit with measurement 195. Measurement 194 was made under poor conditions and was rated fair. Measurement 195 (June 27) was also a fair measurement, but was not adjusted as it is the highest measurement ever made at this gage. And, SSVWARCOVST02, applied Sept 1-30, 2009. The second table was necessary to compensate for work done on the control on September 1. Discharges for November 5 thru 12, 2008 were estimated using values from the downstream station, LEFTHDCO. Discharge for May 11, 2009 was estimated from partial day record. This is a partial year record. No record was kept for the winter period (November 13, 2008 to May 10, 2009). The record is good except for periods of no gage height record and ice affected record, which are estimated and poor. The peak is rated as estimated and poor since it is higher than 150% of the highest measurement of 317 cfs. Station maintained and record developed by Patrick Tyler. Defining high flows remains a problem. High water measurements at or above 140 cfs cannot be waded. Crane measurements off the bridge at the gage are difficult and poor due to turbulence caused by a constriction at the bridge abutments, high velocities, and debris firmly lodged in the channel bed at the bridge section. Due to the remoteness of this gage, efforts to find a more suitable measurement location have been unsuccessful. Moreover, under high water conditions measurement at LEFTHDCO is not an option due to diversion practices and supercritical velocities encountered at the only available cabling location due to the LEFTHDCO structure lay out. The cabling section at this gage should be improved prior to high flow and the intakes shortened to avoid possible drawdown effects. 2009Water Year