Probable Maximum Flood Study for Wisconsin River

The Wisconsin River, which runs from Wisconsin’s northern border to the Mississippi River at the southwest edge of the state, has been termed “the nation’s hardest-working river”for its many hydroelectric developments. These projects, many of which evolved from older logging and mill dams, were developed between the late 19th century and the 1950s. In more recent years, many of the dams were found not to have adequate spillway capacity to pass the Probable Maximum Flood (PMF), the standard to which they are regulated by the Federal Energy Regulatory Commission (FERC). Furthermore, due to the use of diverse methods of computing the PMF, estimates at the various projects were not consistent with each other or with the empirical evidence of historic flooding. In 1994 study, a comprehensive model study of the 7,000-square miie basin above the Castie Rock hydroelectric project was conducted to m-evaluate the PMF at 16 hydroelectric projects and storage reservoirs. The study was conducted in accordance with 1994 revisions to the FERCS standards for computing the PMF, using recently deveioped Probabie Maximum Precipitation (PMP) values for Wisconsin, a new method for simulating basin losses, and the UNET dynamic flood wave routing model. The study resuited in a reduction in the estimated PMF at the 16 projects ranging from 24 percent to 60 percent.