The software features a completely integrated work environment including a database, data entry utilities, computation engine, and results reporting tools. A graphical user interface allows the user seamless movement between the different parts of the software. Simulation results are stored in HEC-DSS (Data Storage System) and can be used in conjunction with other software for studies of water availability, urban drainage, flow forecasting, future urbanization impact, reservoir spillway design, flood damage reduction, floodplain regulation, and systems operation. The following is a description of the major features and capabilities of HEC-RAS.

Watershed Physical Description

The physical representation of a watershed is accomplished with a basin model. Hydrologic elements are connected in a dendritic network to simulate runoff processes. Available elements are: subbasin, reach, junction, reservoir, diversion, source, and sink. Computation proceeds from upstream elements in a downstream direction.

Meteorology Description

Meteorologic data analysis is performed by the meteorologic and includes shortwave radiation, precipitation, evapo-transpiration, and snowmelt. Not all of these components are required for all simulations. Simple event simulations require only precipitation, while continuous simulation additionally requires evapo-transpiration. Generally, snowmelt is only required when working with watersheds in cold climates. Selection of the Priestley-Taylor method for evapo-transpiration requires one of the shortwave and longwave radiation methods. Selection of the Penman-Monteith method for evapo-transpiration requires both a shortwave and longwave radiation method.

Hydrologic Simulation

The time span of a simulation is controlled by control specifications. Control specifications include a starting date and time, ending date and time, and a time interval.

A simulation run is created by combining a basin model, meteorologic model, and control specifications. Run options include a precipitation or flow ratio, capability to save all basin state information at a point in time, and ability to begin a simulation run from previously saved state information.

Hydrologic Simulation

A simulation run is created by combining a basin model, meteorologic model, and control specifications. Run options include a precipitation or flow ratio, capability to save all basin state information at a point in time, and ability to begin a simulation run from previously saved state information.

Model Optimization

Two different search methods can be used to minimize the objective function. Constraints can be imposed to restrict the parameter space of the search method.

Forecasting Streamflow

Depth-Area Reduction

Assessing Model Uncertainty

Sediment and Water Quality

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