The following Myth and Fact Sheet was initiall put together by Supervisor Robin Schmidt to try to help the public understand the complexities of managing the lake levels of the Yahara River Chain of Lakes. Staff from Dane County as well as the DNR reviewed, edited and expanded upon the information.
Myths and Facts:
Water Levels and Management of the Yahara Chain of Lakes
This document addresses various myths about water levels and management on the Yahara chain of lakes (lakes Mendota, Monona, Waubesa and Kegonsa). While water level management and the myths presented involve complex issues, the facts are presented in a concise format. For further explanation, interested parties are encouraged to reference “Dane County Lake Level Management Guide for the Yahara Chain of Lakes.” The management guide provides a comprehensive explanation of how the Yahara chain of lakes are managed as a system.
Myth: Dane County manages lake levels only to minimize flooding on Lake Mendota (or Lake Monona)
Fact: As required by DNR water level orders* the entire chain of lakes is managed as a system.
* The State of Wisconsin’s statutory mandate is to regulate operation of the Yahara River dams in the public interest. Predecessors to the WI DNR established a series of water level orders to address the state’s “public interest.” The WI DNR issued the most recent orders in 1979. The orders seek to balance many competing interests, including navigation, flood control, and fisheries and wildlife.
Myth: The Lock and Dam at Tenney Park are in poor condition and Dane County keeps Lake Mendota lower to protect the dam.
Fact: The lock and dam system has been upgraded over the years and was most recently upgraded in 2006. The lock and dam system is in good condition and can withstand extreme rainfall events.
Myth: Lake Mendota needs to stay high in order to increase flow through the system and eventually lower Lake Monona
Fact: The elevation of Lake Mendota is not the controlling factor in pushing water through the system. When the gradient between Lake Monona to Lake Kegonsa is increased, flow through the chain of lakes is increased.
Myth: Dane County is not taking actions to address flow restrictions that increase the time it takes to for lake levels to recede after storm events.
Fact: There are a number of actions Dane County is taking to address flow restrictions. Efforts include:
· Aquatic Plant Harvesting. The County Board approved funding for additional barges as well as LTE hours to harvest aquatic plants (both native and invasive plants) in all sections of the lake and river system, including smaller more maneuverable barges that can operate in narrow and shallow stretches of the Yahara River;
· Dyreson Fishing Weir. There is a historic fish weir in a stretch of the Yahara River that is thought to restrict flow. Dane County is measuring the impact of the fish weir and will explore options after the weir’s effect on flow in that stretch of the river is better understood.
· Trestles/Bridges. The City of Madison has assessed impacts from the bridges over Highway 113, but at this time there are no plans to make any alterations to those bridges. There are several railroad trestle bridges in the system that may restrict flow, but the WI DNR and Dane County have not been able to quantify the significance of those trestles. Dane County continues to work with the Cities of Madison and Monona, as well as the State Department of Transportation and the Wisconsin & Southern Railroad to evaluate trestles and bridges on the system for possible modification or replacement.
· Monitoring. Dane County continues to contract with the United States Geological Survey (USGS) for flow and lake level monitoring. In addition, UW‐Madison Civil and Environmental Engineering and the City of Madison Engineering and Dane County have gathered survey data, and purchased and installed additional gauging stations to monitor water levels and discharge to better assess flow throughout the Yahara chain of lakes.
Myth: The Stoughton Dam controls lake levels in the Yahara chain of lakes.
Fact: The Stoughton Dam has a direct effect on water levels in Lake Kegonsa, but only an indirect effect on the upper lakes. The dam has the potential to create a backwater condition at the outlet of Lake Kegonsa that would limit how much flow can be released and thus how quickly the lake can be lowered. A higher level on Lake Kegonsa reduces the flow gradient, which in turn limits the rate that the upper lakes can be drawn down.
Myth: The Stoughton dam is operated without any consideration for the chain of lakes above it.
Fact: The City of Stoughton has independent water level orders issued by WI DNR to manage the Stoughton Dam. The Stoughton Dam operator works closely with Dane County to assist with lake level management while operating within Stoughton’s water level orders.
Myth: Groundwater flow into the river system is well understood and is not a contributing factor to water levels.
Fact: Dane County is working with the Wisconsin Geologic and Natural History Survey (WGNHS) and USGS to monitor groundwater flow into the river to determine its effect on the system. Information from that monitoring should be available at the end of 2011.
Myth: Dane County has enough information to best manage the lakes. More studies are not needed.
Fact: There is still a great deal that is not fully understood and additional monitoring and studies will need to be done. Dane County, working with various partners (including WGNHS, USGS, UW–Madison, and municipalities within Dane County) have conducted various studies and monitoring efforts on the Yahara chain of lakes. Each new monitoring activity provides information that enables better decision making and identifies other data needs.
Myth: Recent high water levels on Lake Mendota are the primary cause for wetland loss on Cherokee Marsh
Fact: Water levels on Cherokee Marsh are affected by the restriction at Highway 113 and water levels on Lake Mendota. However, studies conducted by the University of Wisconsin show that water fluctuations (seiches) or wave actions on Lake Mendota are damped out due to the constriction point at Highway 113. Studies have also found many factors affect wetlands. High water levels help preserve the interior peat wetlands on Cherokee Marsh. They also indirectly contribute to the creation of floating of wetland vegetation because of the buoyancy of the peat and the plants. Increased river velocities experienced during flooding events cause loss of wetland on Cherokee Marsh. Waves produced by high wind within the marsh can erode the shore and disturb bottom sediments, which also causes wetland loss.
Myth: Simply dredging to deepen the Yahara River below Lake Waubesa would increase flows during periods of high water levels.
Fact: Deepening the river in any one area alone does not guarantee increased flows. Surveys and initial analyses shows that strategically located dredging has the potential to increase the flow between Lakes Waubesa and Kegonsa by reducing high points in the river bottom and increasing cross sectional channel area. However, more channel data is currently being collected to be used in a river model to determine where dredging will be most effective.
