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Discharge.-- PLATTE RIVER BASIN LEFT HAND DIVERSION NEAR WARD Location.-- Drainage and Period of Record.-- Lat. 40°05'29",Long. 105°30'31", the gage is located ½ mile downstream from gage on S. St. Vrain Creek off Highway 72. Established station on May 21, 1992 at request of Water Commissioner for administration of water rights in District 5, Div. 1. The gage is located one-quarter mile downstream from gage on South Saint Vrain Creek off Highway 72. This station is operated as a partial year record station usually from May to October. Graphic water stage recorder and digital shaft encoder (SE) connected to a Sutron Satlink data collection platform (DCP) in a 36-inch diameter corrugated metal pipe shelter and 42-inch concrete well. The well is connected to the channel with two two-inch polyvinyl conduit (PVC) inlets. The PVC inlets are equipped with ball valves, street keys and flushing risers. 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.-- Semi-regulated diversion point. This gage measures water diverted from the South Saint Vrain Creek into James Creek and thence to Lefthand Creek in the Boulder Creek water shed. Diversions usually encompass the entire flow of the South Saint Vrain Creek at this point. The area listed for the upstream gage (South Saint Vrain Near Ward, CO (SSVWARCO)) is 14.3 sq mi consisting of virtually uninhabited forested lands. The SSVWARCO gage is approximately 3.5 miles below Brainard Lake and approximately 0.4 miles above the Left Hand Diversion at South Saint Vrain Creek (LEFTHDCO) gage. The LEFTHDCO diversion structure is comprised of a concrete diversion dam, and a 10-foot wide radial gate with trash rack located approximately 55-feet upstream from the control. The radial gate is operated in such a way that it is under pressure for a majority of the season creating a somewhat regulated diversion. Due to this operational regime, peaks and troughs encountered by the SSVWARCO gage can be somewhat attenuated at this gage. Some inflow is expected to occur between the SSVWARCO and LEFTHDCO gage during runoff and storm events which accounts for some computational differences. Travel time between gages is approximately 30 min, therefore minimal time lag effect. 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 6-12, 2008, suspected ice effect; November 13, 2008 to May 10, 2009, gage was closed for winter, and no gage-height information is available; Nov 12 and May 11, gage turned off/on for season, partial day records. Missing data from the primary data set due to DCP failure was filled in with graphical chart record and with correlation from the upstream station at SSVWARCO without loss of accuracy on the following days: October 22-31, 2008 and June 6- 9, 2009. Instrument agreement was good (+/- 0.02 feet) between the primary data set and the backup chart record for this period. Flows above approximately 90 cfs cannot be measured at the gage, therefore high water measurements must be made upstream at SSVWARCO and applied to LEFTHDCO. However, the 2009 peak flow measured at the upstream station showed a large positive shift when applied to LEFTHDCO. This calls to question whether the measurement GH at LEFTHDCO could have been affected by gate operation, or adverse hydraulics at the inlets (drawdown, standing wave , etc.). Velocities are high past the gage and inlet drawdown has been speculated as a source of GH irregularity. Levels were last run on October 14, 2009. The RP was found to be 0.008 ft. high, so no correction was needed. The control is a broad crested concrete dam approximately 10 feet below the gage shelter. Moss and debris accumulation is generally not an issue at this gage however; larger debris such as tree limbs can catch on the control. Rating No. 3 in use since October 2005 was used again this water year. It was extended this year to include 2009 Measurement 143, the highest measurement recorded at this gage. Eleven measurements (Nos. 138-148) were performed this year ranging in discharge from 4.68 cfs to 316 cfs. They cover the range experienced. Measurement Nos. 140 and 142-144 were made at the SSVWARCO gage, when flow rates were above wadeable limits at LEFTHDCO, and applied to this gage. The peak flow of 318 cfs occurred at 0915 June 27 at a gage height of 2.33 ft with a shift of +0.37 ft. It exceeded measurement 143, made June 27, by 0.05 ft. Shifting control method was used all year. SSVWARCO and LEFTHDCO are in such close proximity to each other that discharges should be quite consistent. When the gages are individually measured, measurements may be adjusted in order to have a good trend between the two stations. In 2009, Measurement Nos. 139-141 and 146 and 147 were adjusted between -5 and 4%.to achieve this. Measurement 142, made at SSVWARCO, was adjusted for the SSVWARCO record to show more water to be consistent with the high measurement. No 142 was similarly adjusted for the LEFTHDCO record. Shifts were applied by time and stage. Shifts were distributed by time from Oct 1, 2008 - May 11, 2009. Shifts were applied by stage using varaible stage shift relationship LEFTHDCOVST01 from May 12 to the end of the water year. A spreadsheet was used to compare computed discharges with the upstream gage, SSVWARCO. When LEFTHDCO was diverting the entire flow, measurements applied from SSVWARCO were applied to LEFTHDCO, and were confirmed by field observation. Care was taken to adjust measurements applied from SSVWARCO in the same direction and amounts that were used in the development of the SSVWARCO record. Comparison of the final record with that of SSVWARCO revealed that daily discharges diverged 10% or more during the peak days, namely June 22-27, and July 2, 3. 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 periods of ice effect and partial record, which are estimated and fair. June 22-27, and July 2, 3 are fair due to poor rating definition. The instantaneous peak of 318 cfs is considered fair. Station maintained and record developed by Patrick Tyler. 2009Water Year