Introduction
Location and Physical Characteristics
Flooding Problems
Seasonal Fluctuations
Industrial, Commercial & Municipal Users
Hydroelectric Power
Domestic and Industrial Water Supplies
Recreational Users
Fish & Wildlife and Wetland Habitat Concerns
Regulation Plan
Regulation Objectives
Data Collection
Regulation Meetings
Contacts
Introduction
The purpose of this pamphlet is to acquaint the public with basic information on Lake Winnebago and the Fox-Wolf River Drainage Basin as well as to inform them about the U.S. Army Corps of Engineers regulation activities and responsibilities.
Location and Physical Characteristics
The Fox-Wolf River Basin is located in east-central Wisconsin and has an area of 6,430 square miles (16,654 square kilometers). Contained within the basin is the Wolf River, the Upper Fox River, the Lake Winnebago pool, and the Lower Fox River. The Lake Winnebago pool consists of Lakes Winnebago, Poygan, Winneconne, and Butte Des Morts (See Figure 1).
FIGURE 1
The Wolf River originates in the central part of Forest County, Wisconsin, and flows in a southerly direction through Lake Winneconne, Lake Poygan and several smaller lakes, and joins the Upper Fox River 10 miles (16.1 kilometers, km) above Oshkosh, Wisconsin.
The Upper Fox River flows through flat marshy areas often with poor drainage. The higher grounds surrounding the floodplain are generally good quality agricultural lands, chiefly devoted to dairy farming.
Lake Winnebago, located between the Upper and Lower Fox Rivers, is the largest inland lake in the State of Wisconsin. The level of Lake Winnebago is controlled by a federal dam at Menasha and a private dam at Neenah. At the elevation of the crest of the Menasha Dam, Lake Winnebago has a surface area of about 206 square miles (534 square kilometers), a length of about 28 miles (45 km), a width of about 10 miles (16 km) and a depth of about 21 feet (6 meters, m).
The Lower Fox River, connecting Lake Winnebago and Green Bay, is 39 miles (63 km) long, with its width varying from about 500 (152m) to 1,000 feet (305 m). The vertical drop from Lake Winnebago to Green Bay (Lake Michigan) is about 168 feet (51 m). In general, the river flows between high clay banks having frequent reaches of exposed limestone, and an average slope of about 5 feet (1.5 m) per mile. Several cities are located along the Lower Fox River. Most of the land along the river bank has been highly developed for uses such as paper mills, power plants, and other related purposes. The remainder of the drainage basin below Lake Winnebago is well-developed agricultural land.
Flooding Problems
Floods have occurred in the adjacent reaches of the Wolf, Upper and Lower Fox Rivers and along the shores of Lake Winnebago during all seasons of the year, with the most extensive occurring in the spring. Flood stages in the Wolf and Upper Fox Rivers generally require several days to develop. Inflows to Lake Winnebago from these rivers, when at their flood stage, can result in a gradual and sustained rise in the lake level for a week or more. More abrupt rises in the level of Lake Winnebago are primarily due to heavy localized precipitation on the water surface.
Floods may result from rainfall, rainfall accompanied by snowmelt, or snowmelt only. Also, flooding along the shoreline of Lake Winnebago can occur with any of the previously mentioned situations as well as from extensive wind action sweeping the shore from the northeast, east or southeast. Wind actions of these types cause the lake to tilt upward (wind setup) and also create wave action (wave runup) which can cause flooding and erosion.
Seasonal Fluctuations
Seasonal fluctuations reflect variations in groundwater recharge and natural discharge. During the late November to early March period, most of the Wisconsin landscape is snow-covered, with the streams and rivers ice-covered. Water levels usually decline during this period because water continues to flow out of the aquifer. Recharge is negligible when frost is in the ground. The greatest rise in water levels occurs in the spring due to a combination of snowmelt and precipitation. In general, only heavy rains contribute significant recharge with a resultant rise in water levels. Another factor contributing to fluctuations in lake levels is evaporation. About 80 percent of the years total evaporation occurs during the period May through October.
Industrial, Commercial & Municipal Users
The Lower Fox River is part of the most important industrialized region in the basin. Within this area there is the greatest concentration of the pulp and paper industry in Wisconsin. Extensive use is made of the river by these industries for their processes and cooling water supply. The river also provides water for navigation, hydropower, municipalities and other industries along the Lower Fox River. Each user affects the quantity of water available and/or the quality of the water resource.
Hydroelectric Power
The Lower Fox River from Lake Winnebago to De Pere has a fallof 168 feet (51 m) in a distance of 39 miles (63 km), making it a valuable source of water power. Historically, the generation of hydropower at dam sites along the Fox River has been an important factor in the development of the region. However, because of the present marginal dollar value of power generated, the number of hydropower generating stations in operation on the Lower Fox River has been decreasing over the years.
Domestic and Industrial Water Supplies
About 20 percent of the water withdrawn in the basin is used by public water utilities and local governments for domestic water supplies, commercial and industrial uses, and for other purposes such as fire-fighting and street washing. The four communities of Appleton, Oshkosh, Neenah, and Menasha depend on the water supplies from Lake Winnebago; other communities depend primarily on groundwater and wells.
The rivers and lakes within the basin are also used for diluting and removing waste from municipalities and industries. The most intensive use of the regions water resources for these purposes is along the shores of Lake Winnebago and the Lower Fox River. The mean flow of the Lower Fox River is approximately 4,100 cubic feet per second, cfs (116 cubic meters per second, cms), but generally falls to near 2,000 cfs (57 cms) during the warm summer months. In periods of extreme drought, the flows may remain below 1,000 cfs (28 cms) for weeks. The paper companies along the Lower Fox River generate wastewater with a very high biochemical oxygen demand, which requires treatment before being discharged into the river. The degree of treatment required before discharging the wastewater is a function of how much biochemical oxygen demand is permitted to be discharged.
No specific plans exist when flows are insufficient to satisfy the biochemical oxygen demand loading in the Lower Fox River. However, the U.S. Army Corps of Engineers, Detroit District, maintains a working relationship with the Wisconsin Department of Natural Resources, and cooperates with them and industry representatives to minimize such an environmental danger.
Recreational Users
The water resources of the region are also extensively used for year-round recreational activities, particularly fishing, including the sturgeon season in February, hunting and boating. These activities are making increased demands on the regions lakes and streams. The majority of boating use, primarily for fishing, pleasure cruising, and water skiing, is concentrated around those lakes having adequate access and launching facilities. Because of its size and character, Lake Winnebago provides the widest range of boating opportunities. The heavy concentration of boaters will continue to increase in the future, bringing increased demands for mooring facilities and associated services.
Fish & Wildlife and Wetland Habitat Concerns
The increase in recreational activities may also impact the environmentally sensitive areas adjacent to, and in the rivers and lakes of the Lake Winnebago region. The primary causes of wetland habitat loss have been high water levels and nonpoint source pollution due to agricultural practices. The losses have had a direct impact on the abundance and diversity of fish and wildlife.
Regulation Plan
Since the early 1980s, the Corps Great Lakes Hydraulics and Hydrology Branch of the Detroit District has regulated the levels of Lake Winnebago using the Linde Plan as a guide. Arlyn Linde was a Wisconsin Department of Natural Resources research biologist who investigated the causes of wetland losses on the Winnebago pool during the period 1974-1983. The plan is primarily intended to provide water usage for hydropower and navigation, while preserving or enhancing fish, wildlife, wetland habitat, and water quality in the Lower Fox River and the Lake Winnebago pool. The plan requires maintaining a constant lake level during the navigation season and whenever ice is forming or breaking up. A minimum summer flow is mandated, along with winter flow constraints. Water levels on Lake Winnebago follow a seasonal pattern: rising in the spring; declining in the summer; staying level in the autumn; and declining in the winter. Figure 2, shows the various stages of Lake Winnebago during recent years of operation using the Linde Plan.
The regulation plan is based on limits set by the Marshall Order in 1886. Based on this order, the water level on Lake Winnebago is to be retained at or above the crest of the Menasha Dam (1.68 feet (0.51 m)) Oshkosh during the navigation season. The Oshkosh datum is the reference plane to which Lake Winnebago water levels are referred. The navigation season presently extends from about May 1 to early October. During the many years the Corps has regulated the lake, the target level during this period has been 3.0 feet (0.9 m) Oshkosh, which represents a compromise reached between hydropower and navigation interests.
FIGURE 2
The upper limit of regulation of Lake Winnebago (as mandated by the Marshall Order) is 21-1/4 inches (60 centimeters, cm) above the spillway crest of the Menasha Dam (3.45 feet (1.05 m)) Oshkosh. The purpose of establishing this maximum lake stage is to provide for the storage of excess runoff during the spring period, while maintaining the pool at or above the crest of the dams during the dry summer periods.
Thus, the present limits of regulation for Lake Winnebago under the existing laws extend from 21-1/4 inches (60 cm) above the crest of the Menasha Dam down to the crest during the navigation season, plus an additional 18 inches (50 cm) below the crest during the winter.
Regulation Objectives
The regulation period for Lake Winnebago is divided into five segments. They are described as follows:
(1) Winter Drawdown (segment f-a on Figure 3):
After a solid ice cover forms in the upper reaches of the Lake Winnebago pool, the regulator may begin to slowly draw the lake level down. This normally occurs in early December. The upper pool regions of Lakes Poygan, Winneconne, and Butte Des Morts contain the majority of sensitive wetland habitat, which is very susceptible to ice damage. A sudden increase in stage during the winter may damage rooted aquatic plants locked in the ice. In past years, large tracts of marshes were turned into mucky shallows by regulation practices at the time. For the sake of the aquatic and semi-aquatic animals that occupy the shallow-water zone during the fall and winter, the water level can not be drawn down before a solid ice cover develops. It is important to the Lake Winnebago pool environment to avoid stage increases when ice is present, and to draw down after a stable ice cover has formed in the upper regions. The Wisconsin Department of Natural Resources advises the regulator when such a cover exists. If no solid ice cover forms by early January, drawdown must begin regardless.
Lake Winnebago Seasonal Target Changes
FIGURE 3
The drawdown provides storage needed to contain spring flooding. If the storage is insufficient, flooding in the Lake Winnebago pool and/or the Lower Fox River (due to high outflows) is likely during the snow melt. If the lake level is reduced too far, however, spring outflows may have to be severely restricted in order to achieve the required navigation stage when the pool is refilled. Typically, the drawdown commences at a rate designed to achieve a target level by about March 1. The target is usually between 0.80 foot (0.24 m) and 1.30 feet (0.40 m). As winter progresses, the Corps Detroit District office consults the National Weather Service, the Wisconsin Department of Natural Resources and Corps field personnel, to develop an outlook for the spring runoff. The eventual drawdown level may be modified as much as half a foot higher or lower.
Drawdown may require extensive gate changes, especially during mild winters when inflows remain high. Winter outflows can create problems with frazil ice. Frazil ice is formed when fast moving water comes in contact with air below 25 degrees Fahrenheit and develops into a slushy ball which rolls along the river bottom. Frazil ice can clog hydropower and industrial water intakes, causing plants to shut down. This can result in flooding upstream of the problem area, reducing flow downstream. If downstream companies are not alerted in time, their intakes may fail to shut off automatically, drawing the water below the crest of the dam and interrupting flow in the river. To help prevent frazil ice development, experience has shown that flows must be limited to about 4,000 cfs (113 cms) when the air temperature falls below 25 degrees Fahrenheit, until such time as a complete ice cover has developed on the river. Once the river has frozen over, there is no contact with the air, and frazil ice formation is unlikely. There are some sections of the Lower Fox River that rarely freeze over, but in other areas, frazil ice problems are often unavoidable.
(2) Between Drawdown and Ice-out (segment a-b of Figure 3):
Once the drawdown target is achieved, the stage should be held constant until the ice cover in the Lake Winnebago pool breaks upand starts moving out. As before, increases in stage can cause considerable ice damage to the wetlands and to the Lake Winnebago shoreline. Close contact with the Wisconsin Department of Natural Resources is maintained in late March or early April to advise the regulator when the ice has broken up.
(3) After Ice-out (segment b-c of Figure 3):
When the ice cover in the Winnebago pool moves out, the lake can be refilled. The target navigation stage, 3.0 feet (0.9 m) Oshkosh, should be achieved no later than the start of navigation season, which usually occurs near the beginning of May. To achieve this, the pool begins to be filled in early April, regardless of the status of the ice cover, or there will be serious difficulty in achieving the navigation stage. The magnitude of the outflows varies significantly from year to year, depending on inflows and the extent of drawdown.
(4) Navigation Season (segment c-e on Figure 3):
During the navigation season, the level of Lake Winnebago is held as closely as possible to the target stage. Since the years lowest inflows occur during this period, this is not always possible. Streamflow into the Winnebago pool will often fall below 2,000 cfs (57 cms). Evaporation losses, combined with irrigation and municipal water supply diversions, some time result in negative net inflows. Consequently, by the fall, the stage may fall three or four tenths of a foot below the target. Rather than try to regain the original target stage for the remaining month of the navigation season, which may cause environmental instability, the target may be revised to a lower level. This is shown as the dashed line c-d-e on Figure 3. Shoreline wildlife and vegetation which had developed during the summers receding levels could be adversly impacted if an attempt was made to raise the lake to the original target stage. The increase in stage may not necessarily be detrimental, but becomes so because all that much more water eventually has to be removed in a relatively short period of time (before freeze-up).
(5) Between the Navigation Season and Freeze-up (segment e-f on Figure 3):
When the navigation season ends, usually in mid-October, the regulator may begin to lower Lake Winnebago, aiming for a level between 2.00 feet (0.60 m) and 2.50 feet (0.80 m) Oshkosh by December 1. The only outflow constraint is to observe the maximum safe discharge, about 18,000 cfs (510 cms), while allowing only gradual stage changes to minimize impacts on wildlife. Although there is more flexibility during this period with regard to targets and constraints, the unpredictable November weather can complicate the regulation strategy.
Data Collection
Hydrologic and meteorologic data are continuously collected and assessed by the Great Lakes Hydraulics and Hydrology Branch from a reporting network of gages and rainfall stations. Of primary importance in the day-to-day regulation of Lake Winnebago are the nine satellite data collection platforms (See Figure 4) and the acoustic velocity meter at Lutz Park located on the Lower Fox River in Appleton, Wisconsin.
FIGURE 4
These are all equipped to relay real time hydrologic data to the regulator located in Detroit, Michigan. The Corps Fox River Sub-Office at Kaukauna, which performs the actual gate movements at the Menasha Dam, makes the downstream pool adjustments and monitors all the telephone-accessed (telemetered) gages. The acoustic velocity meter provides the regulator with real time outflows from Lake Winnebago. If the acoustic velocity meter data are not available, the regulator must estimate outflows from the Neenahand Menasha Dams and the previous days outflow calculation from Rapide Croche. The lakes stage is taken as the average of the levels at Oshkosh, Stockbridge, Menasha, and Fond Du Lac. The historical daily mean, maximum, and minimum lake levels for the period 1897-1993 as measured at Oshkosh, are shown on Figure 5.
FIGURE 5
Additionally, the four data collection platforms on the upper rivers are used to estimate the current inflow into Lake Winnebago from the upper pool region.
Regulation Meetings
Although use of the Linde plan has proven successful, modifications to the Plans recommendations have been necessary on a year-to-year basis. Representatives of the Corps, Wisconsin Department of Natural Resources, wastewater dischargers and regulators, hydropower users, and other interests meet annually in the spring to discuss problems experienced during the year, and decide on a specific regulation strategy for the next year. Since circumstances change from year to year, and problems occur, the meetings are necessary in order to set the target stages and dates for the next 12 months, and to modify the outflow constraints, if necessary. Since the requirements of each of the regions interests frequently are at variance with those of the others, the meetings allow the local interests and authorities to have a say in how the lake is regulated. This promotes public cooperation, since the parties concerned understand the reasons for regulation practices, and have a chance to agree or object. Cooperation between the Corps, Wisconsin Department of Natural Resources, wastewater dischargers and regulators, hydropowerusers, and other interests is important because Lake Winnebago and the Lower Fox River are integrally related. These meetings are normally organized and hosted by the Corps.
