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Discharge.-- PLATTE RIVER BASIN 06701500 SOUTH PLATTE RIVER BELOW CHEESMAN RESERVOIR Location.-- Drainage and Period of Record.-- Lat. 39°12'33",Long. 105°16'02", in SE¼NW¼ sec.6, T.10 S., R.70 W., Jefferson County, Hydrologic Unit 10190002, on left bank 1,400 ft downstream from toe of Cheesman Dam and 3.8 mi southwest of Deckers. 1,752 mi². Oct.1, 1924-May 13, 1956 at site 370 feet upstream and 0.50 ft. higher. May 14, 1956 to present at current site. Unreliable record from 1909 to 1924 unpublished. Sutron SatLink 2 satellite Data Collection Platform (DCP) with a Sutron 56-0540 shaft encoder (SE); a Sutron Stage- discharge recorder (SDR) in a concrete shelter and concrete well on left bank adjacent to a 30-foot concrete Parshall flume. No outside staff gage is present. The station and flume are owned and maintained by the Denver Water Board (DWB). The satellite equipment is owned and maintained by the Division of Water Resources (DWR). Equipment.-- Hydrologic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Cheesman Reservoir is in the center of the 2002 Hayman burn area. The fire severely damaged the watershed and the Denver Water Board has performed extensive erosion control in the area surrounding the reservoir. Major revegetation efforts were performed in the burn area to reduce erosion and water quality problems. The primary record is hourly averages of 15 minute satellite data with SDR back up. The primary record agrees with SDR data to within 0.02 ft. The record is complete and reliable, except for July 20, 2010 which was missing 7 hours due to shelter replacement. This data was estimated by presuming constant release. The satellite equipment (DCP and SE) were removed from the gage shelter on June 23, 2010 to facilitate installation of a new shelter which was completed on July 20, 2010. In preparation for this, an SDR logger was installed on September 10, 2009 in a weatherproof enclosure below grade in the stilling well. Data from the SDR was used from June 23, to July 20, 2010. Eighteen visits were made to the gage. One SE/SDR adjustment was made on September 14, 2010. Due to the flume’s proximity to the dam, ice accumulation in the approach, flume, and departing sections is normally not an issue and was not this year. However, the flume is subject to moss and algal growth. One flume cleaning correction of -0.04 feet occurred on April 27, 2010. The correction was prorated by time as a datum correction back to flow change event at 1100 April 16, 2010. Two flume cleaning corrections November 24, 2009 and September 14, 2010 were addressed with shifting as measurements were performed before the flume cleanings were made. Levels were run on September 10, 2009 when the SDR was installed in the stilling well in anticipation of the gage house replacement. A temporary reference point (RP) was installed in the well for the SDR calibration during construction. The gage was found to be reading correctly, either from the existing RP or the temporary RP installed in the well. Levels were run after the installation of the new gage house on July 20, 2010. The ETG was reset on the new instrument shelf and a new metal tape was indexed at 13.604 ft. However, levels were not run to temporary RP for the SDR which was used for primary data from June 23 to July 20, 2010. When the RP for the SDR was put into use on June 23, it showed the same GH as the existing RP. On July 20, the RP board for the SDR was observed to be bowed and had footprints on it. It is presumed that contractors had found a need to step on it during the shelter replacement, sometime between June 23 and July 20. A presumptive levels RP correction of 0.03 ft. was arrived at by noting the release was constant on July 20. The GH on the new RP at 1515 was 0.03 ft higher than the GH from the SDR at 0940. This 0.03 ft. correction was taken up in shifts run from July 9 to July 21, 2010. The control is a concrete 30-foot Parshall flume with a modified rating. The flume submerges at flows near the 1000 cfs range due to constrictions in the channel below the gage. Rating No. 11 was developed in 1995 to compensate for submergence and was continued in use for the current year. Submergence seems to begin when the measurement section velocity reaches around 6.6 feet/sec. The rating is well defined except for flows around 1,000 cfs where submergence appears to cause a break point in the slope of the curve. Shifts historically were positive unless moss accumulation occurs which can cause negative shifting. However as the approach pool has filled, shifts have become more positive. Gravel deposition occurred on the left side of the upstream channel and the flume converging section during a precipitation event on July 21, 2009. An effort was made to remove the gravel on LEW on July 7, 2010 but had little effect on shifting; the entire weir pool would have to be excavated to reduce velocities to 0.5 fps. Comparisons of velocities to measurements taken in 1995 show the effects of the approach pool filling with elevated velocities at comparable depths. Using the USBR Water Measurement Manual, Third Edition, Figure 8-9, Page 8-44, the range of accurate (within +/-5%) discharge measurement for a 30 ft Parshall Flume is 15 to 1500 cfs. Anything above or below this range is outside the +/- 5% accuracy range. Given this fact, flows below 15 cfs at gage height 0.38, or above 1500 cfs at gage height of 5.94 the record would be considered fair. All flows in water year 2010 were within the +/- 5% range of accuracy. Sixteen measurements (Nos. 228-244) were made this year, ranging in discharge from 37.9 to 729 cfs. The rating is well defined for the ranges of flow experienced. The measurements covered the range of discharge experienced except the higher mean daily flows on June 16-17, 2010. The peak flow of 777 cfs occurred at 1945 on June 16, 2010 at a gage height of 3.26 feet with a shift of 0.12 ft. It exceeded measurements Nos. 236, made on June 16, 2010, by 0.13 feet in stage. Shifting control method was used all year. Stage dependent shifting was used for the majority of the year with the exception of periods where moss accumulation could be identified and shifts were applied as defined by measurements and were distributed mainly by time with consideration to change in stage. Negative shifts occur when moss accumulates on the crest of the flume. The range in stage experienced this year was confined to the weir section. Measurements for the water year show shifts varying from -0.04 ft. to 0.12 ft. Shifts were distributed as follows. October 1-26, 2009: time distribution with consideration to stage, Msmt No. 227 applied to October 9, 2009 (0.01). Measurements given full weight. October 26 to November 24, 2009: time distribution. Measurements given full weight. November 24 to July 9, 2010: variable shift table PLACHECOVST10-1 developed from Msmt Nos. 230-238 made during the period was used. Msmt Nos. 230 and 235 were discounted 2% and 1%, respectively, to better fit the shift curve. July 9, to July 21, 2010: time distribution including a presumptive levels correction of +0.03 ft. made on July 20. July 9, No. 238 (full weight) shift of +0.06 ft was prorated to +0.04 ft at 0900 on July 20, which marked the end of the use of GH’s from the temporary installation. July 20 (1000) (new shelter, new RP) to July 21 measurement (full weight), a +0.01 ft shift applied straight through. July 21 to August 26, 2010: variable shift table PLACHECOVST10-2 developed from Msmt Nos. 239-241 made during the period was applied. Measurements given full weight. August 26 to September 30, 2010: Time distribution . Measurements given full weight. 2010Water Year