R2001-120 AUTHORIZING AGREEMENT - Laserfiche WebLink

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Reservoir Sedimentation Records for Lake Decatur Lake Decatur has been surveyed to document sedimentation conditions eight times since 1930. The plan of survey for each of these surveys is shown in figure 2. Five of these survey efforts (1936, 1946, 1956, 1966, and I983) were sufficiently detailed to be termed full lake sedimentation surveys. These surveys, the year of survey, and the a.gency responsible for the survey were: Survey rype Year Agency Reconnaissance survey 1930 Macon County (F.L. Washburn, County Engineer) Benchmark (initial) survey 1931 ISWS � " Re-survey 1936 ISWS, Agricultural Experiment Station Re-survey I946 ISWS Re-survey 1956 ISWS Re-survey 1966 ISWS Re-survey 1983 ISWS Basin 6 re-survey 2000 ISWS The present survey is not considered to be a full lake sedimentation survey. Work for this study was limited to the seven transects immediately upstream of Rea's Bridge as required by the plan of study. Fitzpatrick et al. (1986) present detailed methodologies for the earlier surveys. Prior to initiating the lake depth survey, all surviving monumentation established for previous surveys was recovered and located using a differentially corrected Leica 9600 System Geodetic � Positioning System (GPS}. When all previous monumentatation for a range end was lost, ' relocation ties were used to deternune the location of the range end, and a GPS position was ' deternuned. The 2000 survey was conducted using a marked pole for depth measurement and the differentially corrected Leica 9600 GPS for horizontal control across the transect. All na.vigation and data logging functions were controlled using HYPACK hydrographic survey software. For navigation purposes, the GPS positions determined for the range ends were entered into the HYPACK system, which then provided guidance for positioning each line at pre-deternuned intervals. The GPS positions were differentially corrected using Radio Technical Commission for Maritime Services (RTCIv� correction signals broadcast by the U.S. Coast Guard from St. Louis, Missouri. Water depth measurements were spaced at nominal 50-foot intervals along each transect line. � The GPS position was recorded at each measuring point, using the HYPACK software and the measured water depth was manually entered into the record. All depth measurements were converted to bed elevations using a daily lake level obtained from the main water treatment plant. ' Plots of all surveyed cross sections from 1936, 1946, 1956, 1966, 1983, and 2000 are presented (appendix I). 5