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<br />Chapter I Introduction <br /> <br />Hydraulic Analysis Components <br /> <br />Stea4y Flow Water Sw:face Profiles. This component of the modeling <br />system is intended for calculating water surface profiles for steady gradually <br />varied flow. The system can handle a full network of channels, a dendritic <br />system, or a single river reach. The steady flow component is capable of <br />modeling subcritical, supercritical, and mixed flow regime water surface <br />profiles. <br /> <br />The basic computational procedure is based on the solution of the one- <br />dimensional energy equation. Energy losses are evaluated by friction <br />(Manning's equation) and contraction/expansion (coefficient multiplied by <br />the change in velocity head). The momentum equation is utilized in <br />situations where the water surface profile is rapidly varied. These situations <br />include mixed flow regime calculations (i.e. hydraulic jumps), hydraulics of <br />bridges, and evaluating profiles at river confluences (stream junctions). <br /> <br />The effects of various obstructions such as bridges, culverts, weirs, and <br />structures in the flood plain may be considered in the computations. The <br />steady flow system is designed for application in flood plain management <br />and flood insurance studies to evaluate floodway encroachments. Also, <br />capabilities are available for assessing the change in water surface profiles <br />due to channel improvements, levees, and ice cover. <br /> <br />Special features of the steady flow component include: multiple plan <br />analyses; multiple profile computations; and multiple bridge and/or culvert <br />opening analysis. <br /> <br />Unsteadv Flow Simulation. This component of the HEC-RAS modeling <br />system is capable of simulating one-dimensional unsteady flow through a full <br />network of open channels. The unsteady flow equation solver has been <br />adapted from Dr. Robert 1. Barkau's UNET model (Barkau, 1992 and HEC, <br />1993). This unsteady flow component was developed primarily for <br />subcritical flow regime calculations. <br /> <br />The hydraulic calculations for cross-sections, bridges, culverts, and other <br />hydraulic structures that were developed for the steady flow component have <br />been incorporated into the unsteady flow module. Additionally, the unsteady <br />flow component has the ability to model storage areas, navigation dams, <br />gated spillways, tunnels, pumping stations, and levee failures. <br /> <br />Sediment Transport/Movable Boundarv ComDUtations. This component of <br />the modeling system is intended for the simulation of one-dimensional <br />sediment transport/movable boundary calculations resulting from scour and <br />deposition over moderate time periods (typically years, although applications <br />to single flood events are possible). <br /> <br />1-3 <br />