Cross-section data includes station-elevation data, main channel bank stations, downstream reach lengths, roughness coefficients, and contraction and expansion coefficients. Depicted in Figure 1 is a general example of a river network with cross-section locations.įigure 1 General representation of a river network and floodplain.Ĭhannel cross-section data are used in HEC-RAS to characterize the flow carrying capacity of the river and adjacent floodplain.
A river may be composed of one or more reaches. A reach is defined in HEC-RAS as starting or ending at junctions - locations where two or more streams join together or split apart. A river system is a collection of reaches, all oriented downstream. River networks define the connectivity of the river system. Hydrologic events are represented by flow data.
At Version 2.0, HEC-RAS introduced the capability to use three-dimensional geometry for the description of river networks and cross sections. HEC-RAS requires the input of geometric data to represent river networks, channel cross-section data, and hydraulic structure data such as bridges and culvert data.
#HEC RAS USER MANUAL FULL#
HEC-RAS is capable of modeling a full network of channel, a dendritic system, or a single river reach. The geometric and flow data are used to calculate steady, gradually varied flow water surface profiles from energy loss computations. HEC-RAS model construct requires definition of the land surface to be modeled and flow data for hydrologic events. HEC-RAS is a one-dimensional, steady-flow, water surface profiling program (U.S. HEC-GeoRAS provides a graphical user interface (GUI) that enables the hydraulic engineer to create a HEC-RAS import file containing geometric attribute data from an existing digital terrain model (DTM), process water surface profile data exported from HEC-RAS, and perform floodplain mapping. Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS). The development of HEC-GeoRAS has linked ARC/INFO to the U.S. Providing limited, but logical access to a GIS allows the engineer to concentrate on hydraulic concerns, rather than focusing on the complications of applying the GIS. For the task of river analysis, specific features of a GIS may be made available to the hydraulic engineer through an interface. Data preparation and model interpretation are time-consuming tasks that can be simplified using a GIS for data processing and display. Hydraulic modeling of river systems may be greatly facilitated with a GIS. In the end, the benefits derived by engineers from complex data operations are often dwarfed by the cost of acquiring the knowledge to execute tasks within a GIS. Many engineers have had little or no training working with GIS technology, and to perform even simple tasks within a GIS may prove quite burdensome. Unfortunately, due to GIS complexity, the potential benefits obtained from using a GIS to assist in water-resource analysis are not realized for the inexperienced or infrequent user.
Geographic information systems (GIS) provide a powerful tool for storing, managing, analyzing, and displaying spatially distributed data. The GeoRAS interface provides specific and logical access to ARC/INFO, allowing the engineer to concentrate in hydraulic principles, rather than GIS mechanics, during model development and analysis. GeoRAS allows an engineer with little GIS training to use ARC/INFO to develop geometric data for import in HEC-RAS and view exported water surface profile data. In developing HEC-GeoRAS, the Hydrologic Engineering Center has linked ARC/INFO’s data development and display capabilities to HEC-RAS’s hydraulic analysis capabilities. Brunner, Senior Hydraulic Engineer, Hydrologic Engineering Center, Davis, CA.Īlthough hydraulic analysis can benefit from digital terrain models and other GIS data sets, the complexity and unfamiliarity of GIS programs deters hydraulic engineers from using them. Evans, Senior Hydrologic Engineer, Hydrologic Engineering Center, Davis, CA. Ackerman, Research Hydraulic Engineer, Hydrologic Engineering Center, Davis, CA. HEC-GeoRAS: Linking GIS to Hydraulic Analysis Using ARC/INFO and HEC-RASĬameron T. HEC-GEORAS: LINKING GIS TO HYDRAULIC ANALYSIS USING ARC/INFO AND HEC-RAS