Physical History of the Platte River in Nebraska

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Physical History of the Platte River in Nebraska Focusing upon Flow, Sediment Transport, Geomorphology, and Vegetation Delivery Order 114 Simons & Associates 8/11/2000 1. Introduction The Platte River system originates on the eastern slope of the Rocky Mountains and flows in a generally eastward direction from the mountains across the plains until it joins with the Missouri River. The Platte River system, including its principal tributaries (the North Platte and the South Platte), has been affected by numerous water resources projects throughout the basin that include water storage reservoirs, diversions, and groundwater pumping. As a result of these water resources projects and other factors, the river has experienced significant changes over approximately the last century. Streamflows are significantly reduced. Channel morphology has been altered. Riparian vegetation has expanded onto formerly active channel areas. These changes have affected habitat for a variety of species of fish and wildlife, including some threatened or endangered species, that are found in or migrate through the Platte River Basin. One of the principal issues of over -riding concern on the Platte River is the habitat provided by the river to threatened and endangered species as well as other fish and wildlife. The Central Platte River, in what is referred to as the Big Bend Reach (approximately from Lexington to Chapman, Nebraska) has been designated as critical habitat for the whooping crane by the U.S. Fish and Wildlife Service (USFWS). In July 1997, the States of Wyoming, Nebraska, and Colorado signed an agreement with the Department of the Interior to develop a recovery program for four threatened and endangered species which use the Central Platte River.' The four target species of primary concern are the whooping crane, least tern, piping plover, and pallid sturgeon. Focusing exclusively on the riverine environment, habitat consists of the river channel including the river bed below water, sand -bars, islands, and riparian vegetation on the floodplain and on islands. The geomorphology of a river system plays a significant role in many key physical and biological relationships that affect vegetation, hydraulics, fisheries habitat, wildlife habitat, and sediment transport. Historic geomorphology regarding the formation of a river system leading to its current configuration and form, as well as trends and potential geomorphic changes, are critical considerations in evaluating the effects of current operations and other possible operating scenarios along with the feasibility of mitigation and enhancement activities. If it is true (or assumed) that there is a relationship between the quantity of habitat and species population supported by the habitat and that any loss of habitat translates into a decrease in species population; then the maintenance (and possible enhancement of habitat) is of great importance. 1 Cooperative Agreement for Platte River Research and Other Efforts Relating to Endangered Species Habitats Along the Central Platte River, Nebraska. 1997.