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0009i~f\ Need for the Proiect The Platte River is as complex a river system as are the issues surrounding its use. The river itself tends toward a braided configuration of multiple channels that affect and are affected by diversions, returns, wetland interactions, and fill activities. Detailed studies have been made to predict Platte River reaction to changes in flow, sediment, and channel geometry in order to evaluate impacts on river use and wildlife habitat (U.S. Army Corps of Engineers, 1989, Lyons and Randle, 1988). These predictions have relied primarily on computer modeling, and while of some use, no computer model available today can simulate the complex and interacting processes between flow and sediment found in the Platte River. An overlooked resource is the potential for using scaled physical models of the Platte River to lend insight to current policy issues. A scaled physical model is a (usually) smaller version of a real world project, carefull y constructed and tested to reproduce what is observed in nature. Physical models of rivers can span long reaches, as in the model of the Mississippi River from Cairo, Illinois to New Orleans (U.S. Army Corps of Engineers, undated), or short reaches, such as a 1500-foot stretch of the Missouri River near Council Bluffs, Iowa (Nakato, et aI., 1990). Size and scale depend upon purpose. In their recent report, the Platte River Management Joint Study Hydrology Work Group (1989) commented on a possible physical model of the Platte River. They ruled out the possibility of modeling, for example, 325 miles of river, but admitted that modeling a short reach would be possible, Most physical models are built to evaluate the effects of a specific action, such as how an artificial island will affect flows and bank erosion. Because model time scales are reduced, they may also be used to simulate changes over a long period of time. For example, a model may be used to determine the long-term effects of imposed flows, extended droughts, or changes in upstream operating rules. ProDosal It is proposed to use the University of Nebraska Hydraulic Modeling Basin to construct, operate, and evaluate a scaled physical model of miles 205.9 to 207.8 of the Platte River. This section of the Platte River is located downstream from Highway 10 near Kearney, Nebraska, and consists of a relatively wide central channel that carries more than seventy percent of the flow. Waterfowl habitat is rated good in this reach although some island formation in the channel center is beginning to develop. This reach is proposed because I) much of the data necessary for the physical model are available from previous studies, 2) flood marks are available for assuring the physical model can reproduce what has been observed in the field, 3) the reach is typical of a fairly good habitat reach in the Big Bend area of the Platte River, and 4) modifications made in the physical model to show cause-and-effect relationships can be verified later in the field. The University of Nebraska-Lincoln Hydraulic Modeling Basin is located in the Walter Scott Engineering Center. The Basin is over 100 feet long and 25 feet wide. A model scale of approximately I: 100 will accommodate the two-mile reach of the Platte River below Kearney. A lightweight material must be used to simulate the relatively uniform sediment of the Platte River because model flow rates will not be large enough to transport sand. Crushed walnut shells are often used for model sediment (Hotchkiss,