HEC RAS Software - What is It?

The U.S. Army Corps of Engineers (USACE) has developed HEC-RAS . The Hydrologic Engineering Center occasionally make its software available to the general public. Individuals outside of USACE are free to use the application without any use restrictions. 

Non-USACE users will not receive any user support or help from HEC for this product. Downloading this programme signifies your full acceptance of all usage-related responsibilities.

What is HEC-RAS Software?

An integrated software system called HEC-RAS was created for interactive use in a multi-user, multi-tasking network environment. A graphical user interface (GUI), distinct hydraulic analysis components, data storage and administration capabilities, visuals, and reporting tools are all parts of the system. 

Three-dimensional hydraulic analysis components for computations of the steady flow water surface profile, the unsteady flow simulation, and sediment transport across movable boundaries are included in the HEC-RAS system.

The usage of a typical geometric data structure and geometric and hydraulic computation procedures by all three components is crucial.

Along with the three hydraulic analysis components, the system also has several hydraulic design features that can be used once the fundamental water surface profiles have been calculated. These features include computations for bridge scour, computations for uniform flow, stable channel design, and capacity for transporting sediment.

HEC-RAS 5.0 Applications Guide 

HEC-RAS critical depth analysis finds its application in various situations. These are

• Modelling of the floodplain and channels in two dimensions.
• Regions with combined 1D channel flow and 2D floodplain flow.
• Combining sections of 2D flow behind levees with 1D channel and overbank flow.
• Analyses of dam failure or dam breach, ranging from simple to complex.
• Levee failure (i.e., levee breach) assessments, from simple to complex.
• 1D flow with abrupt lateral expansion into the overbank floodplain region.
• Flow outside of a single, clearly defined channel.
• Streams that are intertwined or braided, meanders, and loops.

HEC-RAS File Types 

When working with a model, HEC-RAS automatically generates several inputs and output files. It is crucial to understand the functions of each of these files and how they relate to your project's larger structure. 

It's best practice to keep track of these files in an organised way as your models get bigger and more complex. This post will include an HEC-RAS steady flow analysis and a list of typical HEC-RAS files for projects involving unsteady flow, sediment analysis, water quality, and hydraulic design.

These examples all have the extension "01," and RAS can use more than one copy of each of these files for a single project (except the .prj-only one of those). Numbers are assigned in the order that the files were produced and can go as high as "99."

HEC-RAS Computational Flow Project Example 

1. Project files with the .prj extension contain project descriptions, units, and current plan files. 
2. If the geometry file is g01, it stores cross-sectional data, hydraulic structure data, and modelling technique data.
3. If the Steady Flow file ends with .f01, then this file is about boundary conditions, flow statistics, and profile information.
4. If the flow file extension is u01, then Hydrographs, initial conditions, and user-defined flow options are all saved here.
5. The flow file extension for quasi-unsteady flow (for a sediment study) is.q01.
6. If the Plan file extension is .p01, then it lists all simulation settings as well as a list of the relevant input files.

Since they are all text files, a text editor can read and edit them. Remember that some of these are only RAS's temporary files when performing calculations.

1. If the Output file is .O01, it includes every calculated outcome from the related plan. The only way to read this binary-formatted file is through the user interface.
2. A .dss file is automatically created as an output for Unsteady Flow. Any programme that can read DSS files can view the time series data in this file (typically HEC software).
3. If your model uses .dss files as input data (such as inflow hydrographs, stage hydrographs, observed data, etc.), then those .dss files should be included in the collection of files you send to a reviewer since they are required to run the model.
4. The Run file for steady flow analysis is called r01. It contains all the information required as input for the RAS computation engine. The run file is produced during the model simulation; it is not necessary to view the results.
5. The text file for computational messages is called comp msgs.txt. Note down any notifications related to computation that appear in the computation window. Although not necessary to view the final findings, the messages file can help address issues found by RAS.
6. The resulting file for the Detailed Computational Level is hyd01. This can be activated in the window for unsteady flow analysis.
7. A restart file is.p01.rst (also called a Hot Start File or Initial Conditions File). The user can enable this option in the Output Control Options window. 

These files are classified as "intermediate" for Unsteady Flow analysis, which means that since RAS recreates them during run-time, they are not necessary for running a model or displaying results.

1. The output file for the Geometric Pre-Processor is .c01. It contains the rating curves and tables for hydraulic properties for each cross-section, bridge, culvert, storage area, inline, and lateral structure.

You will only transmit the essential input files if you send your finished model to a client or reviewer. Although sending output files is optional, doing so will save the reviewer from re-running the model. 

For larger models, it might be a good idea to include the .c## files so that RAS can skip the pre-processing stage.

Conclusion 

The hydraulics of water flow across natural rivers and other channels are designed using the modelling programme HEC-RAS.

HEC-RAS, the first software programme from HEC's "Next Generation" (NexGen) line, enables you to carry out one-dimensional steady flow, unsteady flow, computations for sediment transport/mobile beds, and water temperature modelling. 

For more related information on HEC-RAS and its courses, you can reach out to us at Skill-Lync.