Floodplain Restoration for Fish and Wildlife Habitat on the Upper Mississippi River

Over 8 kilometers of islands have been constructed in the floodplain of the Upper Mississippi River near LaCrosse, Wisconsin to restore fish and wildlife habitat. Islands were positioned to alter flow patterns and reduce wind-driven wave action over large areas of the floodplain. The island top elevations varied from the bankfull flood to the 10-year flood. Islands at the bankfull elevation were constructed of rock and allow flood conveyance through floodplain areas that are normally isolated during low flow conditions. Higher islands were constructed of earth, and were stabilized with rock, woody plants, and native grasses. The design of these islands was based on the habitat needs of various species of fish, birds, and animals, and on the desire to create a more riverine sediment transport regime. During low flow conditions, floodplain conveyance had to be low enough so that water velocity, temperature, and dissolved oxygen concentration were at optimum levels for winter fish habitat. During high flow conditions, floodplain conveyance had to be high enough so that erosion occurred in the floodplain. A two-dimensional hydrodynamic model (RMA-2V) was calibrated to prototype data and used to simulate flow exchange between the main channel and the floodplain for various conditions. The design of these islands is discussed in this paper.