Simulation of the Effects of Operating Lakes Mendota, Monona, and Waubesa, South-Central Wisconsin, as Multipurpose Reservoirs to Maintain Dry-Weather Flow By William R. Krug U.S. GEOLOGICAL SURVEY Open-File Report 99-67 Prepared in cooperation with the DANE COUNTY REGIONAL PLANNING COMMISSION WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY Middleton, Wisconsin 1999 USGS science for a changing world U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey. For additional information write to: Copies of this report can be purchased from: District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services 8505 Research Way Box 25286 Middleton, Wl 53562-3586 Denver, CO 80225-0286 CONTENTS Abstract................................................................................................................................................................................. 1 Introduction.............................................................................................._^ 1 Purpose and scope....................................................................................................................................................... 2 Physical setting ........................................................................................................................................................... 2 Lake-level and streamflow data............................................................................................................................................ 2 Simulation of reservoir operation ......................................................................................................................................... 3 Model description ....................................................................................................................................................... 3 Regulatory and physical limits.................................................................................................................................... 3 Operating procedures.................................................................................................................................................. 4 Operating alternatives simulated................................................................................................................................. 4 Results of simulation........................................................................................................._^ 4 Summary and conclusions .................................................................................................................................................... 11 References cited.................................................................................................................................................................... 11 Appendix. Operating rules used in lake model..................................................................................................................... 13 FIGURES 1. Map showing location of study area in Wisconsin.................................................................................................... 3 2-5. Graphs showing: 2a. Observed and simulated daily levels of Lakes Mendota and Monona and daily streamflow for the Yahara River at McFarland for 1988, with a minimum outflow of 10 ft3/s................................................... 5 2b. Observed and simulated daily levels of Lakes Mendota and Monona and daily streamflow for the Yahara River at McFarland for 1988, with a minimum outflow of 36 ft3/s........................................... 6 3a. Observed and simulated daily levels of Lakes Mendota and Monona and daily streamflow for the Yahara River at McFarland for 1989, with a minimum outflow of 10 ft3/s................................................... 7 3b. Observed and simulated daily levels of Lakes Mendota and Monona and daily streamflow for the Yahara River at McFarland for 1989, with a minimum outflow of 36 ft3/s................................................... 8 4. Frequency curve of May-October minimum level of Lake Monona for observed and simulated conditions, 1970-93....................................................................................................................................... 9 5. Frequency curves of annual maximum level of Lakes Mendota and Monona for observed and simulated conditions, 1970-94....................................................................................................................... 10 TABLES 1. Annual minimum levels of Lake Monona during May-October for simulated minimum flows of 8.5, 10, 30, and 36 ft3/s compared to observed minimum levels .......................................................................... 9 2. Frequency of annual May-October low level of Lake Monona for various minimum releases for the period 1970-94................................................................................................................................................................. 11 CONTENTS CONVERSION FACTORS AND VERTICAL DATUM Multiply By To Obtain foot (ft) 0.3048 meter square mile (mi2) 2.590 square kilometer cubic foot per second (ft3/s) 0.02832 cubic meter per second Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. IV CONVERSION FACTORS AND VERTICAL DATUM Simulation of the Effects of Operating Lakes Mendota, Monona, and Waubesa, South-Central Wisconsin, as Multipurpose Reservoirs to Maintain Dry-Weather Flow By William R. Krug Abstract merly flowed into streams upstream from the lakes but now is part of the diversion around the lakes. The total A digital reservoir routing model was used to effluent diverted from the metropolitan area averaged simulate the operation of Lakes Mendota, Monona, 68 ft3/s in 1993. The removal of 68 ft3/s of water from and Waubesa, south-central Wisconsin for various the hydrologic system of the lakes by th? wells, and levels of minimum release. Twenty-five years of diversion of this water to a point downstream from the record (1970-94) were used in model simulation. lakes, has resulted in a substantial reduction in the The amount of water available to maintain stream- streamflow leaving the lakes. flow and lake levels during dry periods has Water use, distribution, and the diversion of efflu­ declined because of extensive pumping of ground ent by the metropolitan area has had an appreciable water for municipal use and diversion of the efflu­ effect on the hydrology of the area. The Dane County ent around the lakes. The goal of the simulation Regional Planning Commission, in cooperation with the was to determine whether using the lakes as multi­ Wisconsin Geological and Natural History Survey and purpose reservoirs to maintain flow during periods the U.S. Geological Survey, conducted a multiyear of low flow would appreciably lower the lake lev­ study to better understand the hydrology of the area and els. the effects of ground-water pumpage and effluent diver­ The model results indicated that it would be sion. The main part of the study focused on understand­ possible to maintain a minimum flow of 36 cubic ing the occurrence and movement of ground water and is the subject of separate reports (Krohelski and others, feet per second in all but the driest years simulated in press). The surface-water part of the study was (1970, 1976, 1977, 1981, 1989, and 1991) without directed to determine whether it would H possible to lowering the lake levels more than they have been adjust the management of the dams controlling the lakes lowered from 1970 to 1994 under current operating to mitigate some of the effects of the diversion of water conditions. Maintaining minimum flow would away from the lakes. require detailed computations to guide the opera­ Regulatory limits on allowable variation in lake tion of the dams during the year. levels are included in orders issued by the Wisconsin INTRODUCTION Department of Natural Resources on January 18, 1979 (Douglas Morrissette, Wisconsin Department of Natu­ The Madison metropolitan area in central Dane ral Resources, written commun., 1979). These orders County, Wis. (fig. 1), surrounds a chain of large lakes. established maximum levels for the lakes for the entire The municipalities of the Madison metropolitan area year and two minimum lake levels: a higher minimum obtain their water supply from wells surrounding the lake level "between the first spring runoff occurring lakes. Since 1959, the sewage effluent from the area has after March 1, and October 30," and the lower minimum been diverted around the lakes to Badfish Creek, which lake level "between November 1 and the first spring joins the Yahara River far downstream. This diversion runoff occurring after March 1." These orders limit the was intended to reduce the load of nutrients entering the allowable fluctuations in lake levels to 0.5 ft during the lakes. Since 1959, other communities in the headwaters summer and fall and to 1.9 ft on Lake Mendota and of the Yahara River and in adjacent river basins have 3.0 ft on Lakes Monona and Waubesa during the rest of been