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i provides detailed information on distribution atterns within the lak � p e and defines temporal changes in overall sedimentation rates. � Acknowledgments � The project was funded by the City of Decatur. Keith Alexander, Director of Water Management i was project manager. Views expressed in this report are those of the author and do not necessarily reflect the views of ' the sponsor or the Illinois State Water Survey. This project was conducted by the author as part of his reguiar duties at the Illinois State Water Survey under the administrative guidance of Derek Winstanley, Chie� and Mike Demissie, Head of the Watershed Science Section. James Slowikowski assisted ��ith the field data collection. Yi Han analyzed the sediment samples. Richard Allgire and Shundar Lin provided technical review. Eva Kingston edited the report. Linda Hascall reviewed the graphics. Lake Information Lake Decatur (figure 1) is located in Macon County, northeast of Decatur, Illinois. The location of the dam is 39° 49' 28" north latitude and 88° 57' 30" west longitude in Section 22, T.16N., I R.2W., Macon County, Illinois. The dam impounds the Sangamon River in the Sangamon River I basin. The watershed is a portion of Hydrologic Unit 07130006 as defined by the U.S. Geological Survey (LJSGS, 1974). � � j The lake was constructed in 1922 with a spillway level of 610 feet above mean sea level (feet- I msl). In 1956, a set of hydraulic gates was installed on the original spillway to allow variable lake levels from 610 feet-msl to 615 feet-msl. The operating plan for these gates and the lake levels maintained have been revised several times since 1956. In 2000, the operating plan designated a winter target pool elevation of 612.5 feet National Geodetic Vertical Datum (NGVD) for the period December to April and a summer target pool elevation of 614.4 feet NGVD for the period May to November. � Fitzpatrick et al. (1987) present a more complete review of the history of the Decatur public water supply system and the development of Lake Decatur. The portion of the lake surveyed for the present study was Basin 6 located above Rea's Bridge Road (figure 2). This basin of the lake is the headwater area of the main body of the lake. The Sangamon River enters the lake through this basin. The USGS streamgaging station for the Sangamon R.iver near Oakley is located approximately 6 stream miles above Rea's Bridge. This gaging station has a listed watershed area of 774 square miles (sq. mi.). An additional watershed area of approximately 25 sq. mi. is added to the river between these two sites for a total watershed area of 799 sq. mi, for the study area. 2