Flood Routing Through A Flat Complex Flood Plain Using A One Dimensional Unsteady Flow Computer Program

The Arkansas River between Pueblo, Colorado, and John Martin Dam, a distance of about 125 river miles, is an alluvial, sand-bed river. It meanders between bluffs in a flood plain about one mile in width. During geologic time the downstream (eastern) portion of this reach has been migrating southward due to heavy sediment loads from northern tributaries. A local flood control project is being planned for the town of La Junta, which is in the downstream one-third of this reach. A study was undertaken to evaluate the future performance of various flood control alternatives with regard to channel stability, sediment movement, and project maintenance. The alternatives considered were various channel and levee configurations. Evaluations were based on both long-term (100-year period) and short-term (single flood event) hydrologic scenarios. The primary tool used in this study was the movable boundary mathematical model HEC-6 entitled 'Scour and Deposition in Rivers and Reservoirs.' The hydrologic and sediment regimes of the study reach are complex due to four tributaries and eleven major irrigation diversions. This paper describes development of representative data for the long-term analysis, operation of the model, calibration and simulation strategies employed, interpretation of model results, and computational aspects of this application.