Flood frequency in Wisconsin

Science Center Objects

Flood-frequency estimates are required at many sites for bridge and culvert design, as well as for flood-plain management and flood-insurance studies. To estimate flood frequency at ungaged locations, a network of approximately 90 crest-stage gages and more than 200 past and current continuous-record gages are used to compute regional flood-frequency equations to estimate floods at ungaged sites.

Historical photo showing Wisconsin River at flood stage near Nekoosa, Wis.

Historical photo showing Wisconsin River at flood stage near Nekoosa, Wis.

Flood-frequency estimates are required at many sites for bridge and culvert design, as well as for flood-plain management and flood-insurance studies. However, most sites for which such estimates are required do not have records of flood peaks. This effort seeks to create flood frequency estimates for ungaged streams based on regional algorithms developed from a state-wide monitoring network.

The objectives of this study are to:

  1. Operate a state-wide network of crest gages to obtain ongoing information on flood peaks
  2. Develop improved regression equations for the state of Wisconsin
  3. Analyze and improve the network of crest-stage gages to obtain better data for developing improved regression equations.

A network of approximately 90 crest-stage gages will be maintained to gather flood peak information, especially on streams with small drainage areas. A crest-stage gage consists of equipment designed to capture maximum gage-heights between visits. The equipment is inexpensive and the gages can be operated at a much lower cost than continuous-record gaging stations. Crest-stage gages can only be used to determine the annual maximum gage height and discharge at a site. The information on annual flood peaks will be used to compute flood-frequency at these sites. Periodically, the expanded information on flood frequency at streams throughout the state will be used to compute regional flood frequency equations to estimate flood-frequency at ungaged sites.

The results and data from the most recent flood-frequency estimates are available online and through a publication.