Lake Management Updates

The Land & Water Resources Department is responsible for maintaining lake levels for the four major lakes. For additional information, please visit the links under the Water header on the Dane County Land & Water Resources Department home page.

April 7, 2014

Our current goal is to achieve and maintain summer minimum levels. The locks at Babcock and LaFollette County Parks are now closed to navigation.
 

Links:

Lake Locations and Current and Target Lake Levels*

Dane County Lakes
Mendota  
4/15/2014 Summer Minimum Target max 100-Year**
849.91 849.60 850.10 852.8
Monona  
4/15/2014 Summer Minimum Target max 100-Year**
844.73 844.70 845.20 847.7
Waubesa  
4/15/2014 Summer Minimum Target max 100-Year**
844.55 844.50 845.00 847.0
Kegonsa  
4/15/2014 Summer Minimum Target max 100-Year**
843.31 843.00 843.50 845.2

Readings are updated daily from the United States Geological Survey (USGS) and are expressed in feet above sea level. For additional information, see the USGS web site Real-Time Data for Wisconsin: Yahara River and Lakes or the University of Wisconsin Extension booklet Understanding Lake Data.

To view more lake level readings, check out our Lake Level Search Page.

* Elevations are reported in feet above the National Geodetic Vertical Datum of 1929 (NGVD29). Prior to 1973, this datum was the Sea Level Datum of 1929, commonly referred to as mean sea level (MSL).

More on Vertical Datums

All elevation data is reported in relation to a vertical datum and it is critical to know the vertical datum when evaluating elevation information, such as lake levels and topography. Failure to take vertical datum into account can result in erroneous conclusions about water level impacts on shorelines and shoreland structures.

As of June 2013, there are effectively 4 vertical datums established by the National Geodetic Survey (NGS) in use in the Madison area: the National Geodetic Vertical Datum of 1929 (NGVD 29); and the 1991, 2007 and 2012 adjustments of the North American Vertical Datum of 1988 - NAVD 88(1991), NAVD 88(2007) and NAVD 88(2012). Old references to a U. S. Geological Survey (USGS) datum in the Madison area are generally assumed to mean NGVD 29. According to high-accuracy NGS bench marks in the Madison area, these datums are essentially parallel in the Madison area to within a few hundredths of a foot, with their average separations expressed below as equivalent elevations for a theoretical bench mark at NGVD 29 elevation = 845.60 ft. Note that these equivalencies are averages, only appropriate for a particular point if its elevation has been correctly measured relative to a bench mark with a correct elevation, and if no movement has occurred since measurement.

NGVD 29 = 845.60 ft
NAVD 88(1991) = 845.40 ft = NGVD 29 - 0.2 ft (as predicted by NGS VERTCON 2.0 software)
NAVD 88(2007) = 845.51 ft = NAVD 88(1991) + 0.11 ft
NAVD 88(2012) = 845.57 ft = NAVD 88(2007) + 0.06 ft

The Federal Emergency Management Agency's Flood Insurance Rate Maps use the NAVD88(1991) datum, based on the 0.2 ft shift between NGVD29 and "NAVD88" assumed for Dane County in Flood Insurance Study Number 55025CV001B revised January 2, 2009. The lake level orders for the Yahara Lakes and the USGS gauging station water elevations are reported in NGVD29. Using the conversions above, subtract 0.2 ft from the county/USGS NGVD29 lake levels to compare them to the NAVD88(1991) elevations in the 2009 FEMA flood maps.

Information provided by D. Rodman, Professional Land Surveyor. For more information on Madison-area vertical datums please see here: http://danrodman.tripod.com/

1% Probability of Flooding Every Year (also known as the "100-year floodplain")

Lake NGVD29 NAVD88(1991) NAVD88(2012)
Mendota 852.8' 852.6' 852.77'
Monona 847.7' 847.5' 847.67'
Waubesa 847.0' 846.8' 846.97'
Kegonsa 845.2' 845.0' 845.17'

**100-Year Flood Elevation: the 100-year flood elevation establishes the extent of the 100-year floodplain. The 100-year floodplain is the area that has a 1% probability of flooding every year, and where predicted flood water elevations above mean sea level have been established. Properties in the floodplain are considered to be at high risk of flooding under the National Flood Insurance Program (NFIP). Construction in these areas must meet local floodplain zoning ordinance requirements, including evidence that principle structures are above the 100-year flood elevation as shown on the adopted floodplain maps. For more information on floodplains, please visit Dane County Planning & Development's website.