| | 1: | | Title: | | | | | Volume/Number: | 1999 | | | | Issuing Agency: | | | | | Description: | The Illinois State Water Survey, in cooperation with the Consumers Illinois Water Company (CIWC), conducted a sedimentation survey of Lake Vermilion during the summer of 1998. The survey was undertaken to provide information on the storage and sedimentation conditions of the lake following a 1991 increase in the operational lake level. Lake Vermilion is owned and operated by the CIWC. The CIWC withdraws water from Lake Vermilion as the sole raw water source for direct distribution of finished water to Danville and Tilton, Illinois. The CIWC also provides finished water to the Catlin and Westville public water supplies. Lake Vermilion is located in Vermilion County, one mile northwest of Danville, Illinois. The operating elevation for the reservoir was increased from 576 feet NGVD to 582.2 feet NGVD in 1991. This modification increased storage capacity of the lake by approximately 4,600 acre-feet (ac-ft). Analysis of sedimentation rates for this larger storage capacity required the introduction of the term potential capacity for the reservoir for 1925-1991. The potential reservoir capacity was defined as the capacity of the reservoir if the basin formed by the valley had been filled to the level of the 1991 spillway. Sedimentation has reduced the potential capacity of Lake Vermilion from 13,209 ac-ft (4,304 million gallons) in 1925 to 7,971 ac-ft (2,597 million gallons) in 1998. The sediment accumulation rates in the lake have averaged 71.8 ac-ft per year from 1925-1998. Annual sedimentation rates for three separate periods, 1925-1963, 1963-1976, and 1976-1998 were 89.5, 50.2, and 53.9 ac-ft, respectively. Earlier lake structures affect the lake as it exists in 1999. These early structures also affected the ability to analyze the present sedimentation rate. The 1914 structure (the old dam) impounded water in what is now the upstream, northern half (lengthwise) of the present lake. This structure caused an undocumented amount of sedimentation in the affected lake segments. This sedimentation is included in the calculated sedimentation volume for the 1925-1963 survey period. On the basis of a 38-year (1925-1963) or a 49-year sedimentation period (1914-1963), the average annual sedimentation rate for the lake would be 89.5 and 69.4 ac-ft per year, respectively. Either rate is considerably higher than subsequent rates. The adjustment of the earlier volumes included an accounting of above water-level deposits for the 1963 and 1976 survey calculations and slightly increased the reported sediment volumes for those surveys. The change in reference capacity also significantly altered the presented sedimentation rates in percent of original volume. | | | | Date Created: | 8 31 2006 | | | | Agency ID: | CR-643 | | | | ISL ID: | 000000000799 Original UID: 999999994049 FIRST WORD: Sedimentation | |
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