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Public Information
2 Dam Features (Stratton) 2 Dam Features (Algonquin) 2 Gate Operations 2 Operation Goals 2 Watershed Map (PDF) 2 Operations 2 High Water Events 2 Boating Restrictions
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Public Information
Stratton and Algonquin Dams
The Operation Guide for the gates at Stratton and Algonquin Dams was
developed by studying historic storm events to determine the maximum
benefits of the gates on the Fox River region. This analysis included
the hinged crest gates before they were constructed. The following
narrative describes the dam facilities and the factors effecting gate
operations.
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Operation of Stratton and Algonquin Dams (15.2 Mb PDF) |
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Stratton Dam
Gates are operated by Illinois Department of Natural Resources, Office of Water Resources. Gate Operations fall into 3 categories: low flows, normal flows, and flood flows. Gate operations are determined by:
The Fox River watershed starts in Waukesha County, Wisconsin. Flows rise on the Fox River because a portion of the rainfall falling on the entire watershed flows overland to a stream and eventually enters the Fox River. As it enters Illinois, the Fox River drains 880 square miles from Wisconsin. The largest tributary to the Fox River is Nippersink Creek which enters the Fox River in Pistakee Lake. The Nippersink Creek watershed area is 200 square miles. The Fox River watershed area at Stratton Dam is 1250 squares miles; at Algonquin Dam it is 1400 square miles; and at Montgomery Dam it is 1732 square miles. Stream gages are used to monitor stream flows throughout the watershed. The gages are operated by the US Geological Survey and reported on the internet in near real time. Several tributaries and the Fox River are monitored. Fox River stream gages are located in Wisconsin at Waukesha, Burlington, and New Munster and in Illinois at Algonquin, Montgomery and Dayton. There are additional gages on the Chain of Lakes and the Fox River at Johnsburg, McHenry Dam, and South Elgin Dam which report river stage only. During normal flow operations, 400 cfs to 1800 cfs, the flows that enter the Chain of Lakes are released at Stratton. The Chain of Lakes elevation is maintained at normal pool (summer at stage of 4.2 on Fox Lake or winter at stage of 2.5 on Fox Lake). If the pool elevation needs to be adjusted, more flow is released if the pool is too high and less flow is released if the pool is too low. Winter Operations Winter drawdown lowers the Chain of Lakes 1.5' to increase the storage by 10,000 acre-feet, almost doubling the storage. Drawdown begins on November 1 and is targeted to be complete by December 1. The lower levels in the Chain need to be reached before an ice cover is formed. This storage is used as warm weather melts the snow and spring rainfall causes higher flows. The Chain of Lakes rises in the spring when the flows increase. To prevent ice jam flooding, flows at Stratton Dam are limited to 1000 cfs after 60 degree freezing days are reached. Limiting flows may require the use of the storage created by winter drawdown. Flood Operations Flood operations begin when predicted peak inflows to the Chain of Lakes exceed 1800 cfs. Gate operations are determined using:
Gates are opened to achieve a specified flow per the operation guide (Operations of Stratton and Algonquin Dams, Fox River in Lake and McHenry Counties). These flows were determined based on analysis of prior storm events and the impacts to the Fox River and Chain of Lakes. Estimating Peak Flows using Hydrologic Modeling Rainfall data is gathered throughout the watershed in Wisconsin and Illinois.
The majority of the rainfall data comes from observers who report measured rainfall
over the previous 24 hour period to the National Weather Service. The NWS makes
this information available around 8:30 every morning. The US Geological Survey operates
four near real time precipitation gages. Data is posted on the internet usually within
2 hours. A
map (PDF)
showing locations where precipitation are recorded is attached.
A
The rainfall data from the watershed is utilized in hydrologic modeling for the Fox River. The precipitation data is entered into the Fox River Operations Hydrologic Model. The hydrologic modeling computes estimates of peak inflows to the Chain of Lakes. The estimated peak inflows to the Chain of Lakes are used with the current stage of Fox Lake to determine the gate flows from Stratton Dam. The National Weather Service makes the official flood predictions at the Fox River at New Munster, Wisconsin and the Fox River at Algonquin, Illinois utilizing their own hydrologic modeling. The NWS prediction is compared with the OWR estimate to investigate the benefits and impacts of alternative gate operations. Operation Guide Development The operation guide criteria for operating the gates were developed with the Illinois State Water Survey. The ISWS developed the hydrologic model. The hydrologic model was calibrated and was utilized with the hydraulic model, Full Equations (FEQ). The hydraulic model was calibrated then verified by the U.S. Geological Survey by making flow measurements and taking water surface elevations during a high water event. These models were used to investigate 10 alternative gate operation scenarios including the use of the proposed hinged crest gates and analyze winter drawdown. The analysis was based on historic storm events. After verifying the benefits of the proposed hinged crest gates, the ISWS developed the refined operation flow chart utilizing predicted peak inflows. This analysis included the hinged crest gates even though the gates were not in place at the time of the analysis. Storage in Chain of Lakes The Chain of Lakes is a natural storage area for the Fox River. As flows increase, the Chain of Lakes rises. During a flood event, not all the flow can be released back into the Fox River at Johnsburg since the Fox River is narrower than the Chain of Lakes. During small flood events, the storage in the Chain of Lakes allows for flow management so the flows on the Fox River can be contained in bank. For these small floods, the Chain of Lakes is not allowed to rise so high that flooding occurs. During large flood events, peak inflows above 5000 cfs, the gates at Stratton Dam and Algonquin Dam are open completely. During large flood events the constraints on the flow capacity out of the Chain of Lakes is the channel geometry and not the setting of the gates at Stratton and Algonquin Dams. Example - June 2008 Event Most of the flood events are a culmination of several rainfall events in a 10 day period. For example, the June 2008 flooding occurred after rainfall from June 5 thru June 10 (PDF) . The largest amounts of rainfall were recorded on the mornings of June 6, 8 and 9. Flows on Nippersink Creek (PDF) near Spring Grove peaked on June 10. Flows on the Fox River near New Munster (PDF) , Wisconsin peaked on June 15. The highest water surface elevation on Fox Lake was reached on June 18. The gates were opened incrementally based on project peak inflows. The gates were opened on June 6, opened further on June 8, and opened completely on June 9. The criteria (projected peak inflows and Fox Lake stage) to completely open the gates were not reached until after the rainfall on June 8. Note that the gates at both dams were opened completely 9 days before the peak water surface elevation was reached in the Chain of Lakes and 6 days before the peak flows on the Fox River at New Munster. Using Forecasted Rainfall for Operation Decisions The ISWS analysis does not recommended using predicted rainfall. Rainfall, especially in the Wisconsin portion of the watershed, takes 1 to 6 days before the runoff enters the Chain of Lakes. Therefore, adequate time exists to open the gates using the recorded rainfall. The Quantitative Precipitation Forecast (QPF), prepared by the NWS, typically over-estimates watershed average rainfall. The largest problem with using the QPF occurs if gates are raised to increase flows above bankfull, i.e. flooding occurs downstream of Stratton Dam based on predicted rainfall. However, the impacts of predicted rainfall are analyzed. Minor changes to gate settings that may be beneficial if the predicted rainfall occurs may be made if these changes will not induce or increase flooding on residences downstream. The gates will not be opened fully unless flooding throughout the entire Fox River and Chain of Lakes is anticipated. Benefits of the Hinged Crest Gates When the hinged crest gates were studied, the analysis showed that the operation of gates would reduce flooding but not eliminate flooding. The ISWS study of alternative operation scenarios showed the use of the hinged crest gates reduced peak water surfaces from the Chain of Lakes to Fox River at Johnsburg by 0.1' to 0.5' during the historic storms. At Stratton Dam the hinged crest gates reduce water surfaces 0.1' to 1.0' for the historic flood events. The hinged crest gate at Algonquin Dam reduces peak water surface elevations immediately upstream of the dam 0.3' to 1.0' for the historic storms. The benefits of the Algonquin hinged crest diminish as you move further upstream. The reduction in peak water surface elevations and flooding justified the economics for construction of the gates. The maximum potential reduction in water surface elevations during a flood event can be analyzed by removing the dam. The ISWS alternative analysis showed that removal of Stratton dam would reduce water surface elevations upstream of the Stratton dam from 0.25' to 0.5' at extremely large flood events and would have no benefits to the Fox River downstream of Stratton Dam. Removal of Stratton Dam would not eliminate flooding. However, removal of the dam would reduce the recreation opportunities in the Chain of Lakes and Fox River upstream of Stratton Dam. Information during High Water Events During flood events, the County Emergency Managers and Stormwater Managers are contacted with daily updates of gate settings and flow at Stratton and Algonquin Dams. The National Weather Service predictions for flows and potential qualitative impacts for the Fox River and Chain of Lakes in Illinois are discussed. This information should be available late morning after decisions for gate operations are made. Gate settings are not available on the internet. The Fox Waterway Agency has the authority to enact no-wake boating restrictions during high water events. Chapter 5 (PDF) of the FWA ordinance specifies the water stages when these restrictions can be enacted. The Illinois Department of Natural Resources does not have authority to implement no-wake restrictions. The Illinois Department of Natural Resources can designate a body of water a "Restricted Boating Area" when conditions make navigation of a body of water significantly dangerous to the public. Title 17 Illinois Administrative Code Section 2030.80 describes the procedure for enacting and rescinding a Restricted Boating Area. The determination to enact and rescind a boating restriction is made on a case by case basis. This determination is made based on the totality of circumstances. Section 2030.15 (c) specifies that restricting boating for the purposes of protecting property is prohibited. The Office of Law Enforcement administers Restricted Boating Areas.
Operation of Stratton and Algonquin Dams (15.2 Mb PDF)
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