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RESERVOIR CAPACITY DETEFI�'�tATION <br />IDA.�30 SPRINGS RESERVOIR <br />IDAHO SPRINGS, COLORADO <br />I�1i TRODUCTION <br />Parsons Engineering Science, Inc. (Parsons ES) was contracted by the City of Idaho <br />Springs (City) to conduct hi�h-precision global positioni.ng system (GPS) survey <br />investigations to determine the capacity of the Idaho Sprin�s Reservoir. This report <br />presents the results of the investigations. <br />Idaho Springs Reservoir is located in the upper portion of the Chicago Creek <br />watershed at an approximate elevation of 10,600 feet. It is located in Township 5 <br />South, Range 74 West, Section 1 at approximately 39°38'30" latitude and 105°37'00" <br />longitude. <br />The goal of the study was to determi�e, to the nearest tenth of an acre-foot, all <br />potential reservoir volumes based on one-foot changes in water level. The City <br />required this level of accuracy to address water rights issues. <br />It was determined that this level of accuracy could be met with the use of high- <br />precision GPS equipment. A topographic survey of the bottom of the reservoir was <br />conducted by Parsons ES and its sub-contractor, Johnson, Kunkel and Associates, Inc. <br />(7&K). <br />METHODS <br />On November 7 and 8, 1996, the survey was conducted at Idaho Springs Reservoir. <br />The reservoir had previously been drained by the City. Conditions were very cold and <br />windy, with thin slabs of ice covering most of the reservoir bottom. Snow was blown <br />into drifts a few feet deep in places. <br />A high-precision real time kinematic GPS system was used to perform the <br />topographic survey. A Trimble° 4400 system was used, which produces real-time, <br />centimeter-level accuracy. <br />A base station was established at an existing benchmark, located on the top of the <br />dam and marked wi[h flagging and a nail. It is not known who established this <br />benchmark or when it was established (Scott, 1996). The location of the benchmark is <br />shown on Figure 1. <br />Vertical control for the topographic survey was based on the benchmark. An <br />arbitrary elevation of 1,000 feet was assigned to this point, and all stated elevations in <br />the survey are relative to it. Real-world elevations were not assigned because no <br />survey has been conducted to tie that benchmark into any other system (Scott, 1996). <br />The elevations stated in this report could easily be converted to real-world elevations if <br />the benchmark is ever surveyed in. <br />022/730555/ 1. DOC -1- 12/ 12/96 <br />