Introduction

Welcome to the U.S. Army Corps of Engineers River Analysis System (HEC-RAS) developed by the Hydrologic Engineering Center. This software allows you to perform one-dimensional steady flow, one and two-dimensional unsteady flow calculations, sediment transport/mobile bed computations, and water temperature/water quality modeling.

The HEC-RAS modeling system was developed as a part of the Hydrologic Engineering Center's "Next Generation" (NexGen) of hydrologic engineering software. The NexGen project encompasses several aspects of hydrologic engineering, including: rainfall-runoff analysis (HEC-HMS); river hydraulics (HEC-RAS); reservoir system simulation (HEC-ResSim); flood damage analysis (HEC-FDA and HEC-FIA); and real-time river forecasting for reservoir operations (CWMS).

HEC-RAS Documentation

The HEC-RAS package includes several documents. Each document is designed to help the modeler learn to use a particular aspect of the modeling system.

Documentation	Description
User's Manual	This manual is a guide to using HEC-RAS. The manual provides an introduction and overview of the modeling system, installation instructions, how to get started, a simple example, entering and editing geometric data, detailed descriptions of each of the major modeling components, and how to view graphical and tabular output.
2D User's Manual	This document describes how to use the 2D modeling capabilities that are included in this version of the software. It also describes how to use RAS Mapper in support of 2D modeling (mesh generation) and inundation mapping for models containing 2D flow areas.
HEC-RAS Mapper	This document describes how to use HEC-RAS Mapper to do the following: establish a horizontal coordinate system; develop an HEC-RAS terrain model; layout the geometric data model and extract terrain data; visualize results in the form of maps, plots, and tables.
Sediment Transport User's Manual	This manual describes how to perform sediment transport modeling. The document describes 1D quasi unsteady; 1D unsteady flow, and 2D sediment transport modeling. Additionally sediment impact analysis (SIAM) and bank stability using BSTEM is also described.
Hydraulic Reference Manual	This manual describes the theory and data requirements for the hydraulic calculations performed by HEC-RAS. Equations are presented along with the assumptions used in their derivation. Discussions are provided on how to estimate model parameters, as well as guidelines on various modeling approaches.
Applications Guide	This document contains a series of examples that demonstrate various aspects of HEC-RAS. Each example consists of a problem statement, data requirements, and general outline of solution steps, displays of key input and output screens, and discussions of important modeling aspects.

Overview of this Manual

This Applications Guide contains written descriptions of 24 examples that demonstrate the main features of the HEC-RAS program. The project data files for the examples are contained within the HEC-RAS program distribution Setup package, and will be written to the HEC Data\HEC-RAS\Example Data\Applications Guide directory when the program is installed. The discussions in this manual contain detailed descriptions for the data input and analysis of the output for each example. The examples display and describe the input and output screens used to enter the data and view the output. The user can activate the projects within the HEC-RAS program when reviewing the descriptions for the examples in this manual. All of the projects have been computed, and the user can review the input and output screens that are discussed as they appear in this manual. The user can use the zoom features and options selections (plans, profiles, variables, reaches, etc.) to obtain clearer views of the graphics, as well as viewing additional data screens that may be referenced to in the discussions. The examples are intended as a guide for performing similar analyses. This manual is organized as follows:

Example 1, Critical Creek, demonstrates the procedure to perform a basic flow analysis on a single river reach. This river reach is situated on a steep slope, and the analysis was performed in a mixed flow regime to obtain solutions in both subcritical and supercritical flows. Additionally, the example describes the procedure for cross section interpolation.
Example 2, Beaver Creek - Single Bridge, illustrates an analysis of a single river reach that contains a bridge crossing. The data entry for the bridge and determination for the placement of the cross sections are shown in detail. The hydraulic calculations are performed with both the energy and pressure/weir flow methods for the high flow events. Additionally, the model is calibrated with observed high flow data.
Example 3, Single Culvert (Multiple Identical Barrels), describes the data entry and review of output for a single culvert with two identical barrels. Additionally, a review for the locations of the cross sections in relation to the culvert is presented.
Example 4, Multiple Culverts, is a continuation of Example 3, with the addition of a second culvert at the same cross section. The second culvert also contains two identical barrels, and this example describes the review of the output for multiple culverts.
Example 5, Multiple Openings, presents the analysis of a river reach that contains a culvert opening (single culvert with multiple identical barrels), a main bridge opening, and a relief bridge opening all occurring at the same cross section. The user should be familiar with individual bridge and culvert analyses before reviewing this example.
Example 6, Floodway Determination, illustrates several of the methods for floodplain encroachment analysis. An example procedure for the floodplain encroachment analysis is performed. The user should be aware of the site specific guidelines for a floodplain encroachment analysis to determine which methods and the appropriate procedures to perform.
Example 7, Multiple Plans, describes the file management system used by the HEC-RAS program. The concepts of working with projects and plans to organize geometry, flow, and other files are described. Then, an application is performed to show a typical procedure for organizing a project that contains multiple plans.
Example 8, Looped Network, demonstrates the analysis of a river system that contains a loop. The loop is a split in the main channel that forms two streams which join back together. The example focuses on the procedure for balancing of the flows around the loop.
Example 9, Mixed Flow Analysis, describes the use of a mixed flow regime to analyze a river reach containing a bridge crossing. The bridge crossing constricts the main channel supercritical flow, creating a subcritical backwater effect, requiring the use of the mixed flow regime for the analysis. Results by subcritical and supercritical flow regime analyses are presented to show inconsistencies that developed, and to provide guidance when to perform a mixed flow analysis.
Example 10, Stream Junction, demonstrates the analysis of a river system that contains a junction. This example illustrates a flow combining of two subcritical streams, and both the energy and momentum methods are used for two separate analyses.
Example 11, Bridge Scour, presents the determination of a bridge scour analysis. The user should be familiar with the procedures for modeling bridges before reviewing this example. The scour equations and procedures are based upon the methods outlined in Hydraulic Engineering Circular No. 18 (FHWA 1995).
Example 12, Inline Weir and Gated Spillway, demonstrates the analysis of a river reach that contains an inline weir and a gated spillway. Procedures for entering the data to provide flexibility for the flow analysis are provided.
Example 13, Bogue Chitto - Single Bridge (WSPRO), performs an analysis of a river reach that contains a bridge crossing. The example is similar to Example 2, however, all of the water surface profiles are low flow and are computed using the WSPRO (FHWA, 1990) routines that have been adapted to the HEC-RAS methodology of cross section locations around and through a bridge.
Example 14, Ice-Covered River, is an example of how to model an ice covered river as well as a river ice-jam.
Example 15, Split Flow Junction With Lateral Weir and Spillway, is an example of how to perform a split flow optimization with the steady flow analysis portion of the software. This example has a split of flow at a junction, as well as a lateral weir.
Example 16, Channel Modification. This example demonstrates how to use the channel modification feature within the HEC-RAS Geometric Data Editor. Channel modifications are performed, and existing and modified conditions geometry and output are compared.
Example 17, Unsteady Flow Application. This example demonstrates how to perform an unsteady flow analysis with HEC-RAS. Discussions include: entering storage area information; hydraulic connections; unsteady flow data (boundary conditions and initial conditions); performing the computations; and reviewing the unsteady flow results.
Example 18, Advanced Inline Structure Modeling. This example demonstrates all of the inline structure capabilities within a single structure. This includes: overflow weirs; gates; culverts; user defined rating curves; and a flow time series outlet.
Example 19, Hydrologic Unsteady Flow Routing – Modified Puls. This example demonstrates how to intermix hydrologic routing in the middle of an unsteady flow model. Hydrologic routing can be used for very steep reaches where the full unsteady flow equations may not be applicable or stable.
Example 20, Hager's Lateral Weir Equation. This example demonstrates how to use Hager's Lateral Weir equation for a Lateral Structure.
Example 21, Overflow Gates. This example demonstrates how to use overflow gates in HEC-RAS.
Example 22, Groundwater Interflow. This example demonstrates how to use the groundwater interflow options in HEC-RAS, within a river reach or with storage areas.
Example 23, Urbane Modeling. This example demonstrates how to model pressurized pipe systems within the HEC-RAS unsteady flow modeling capabilities.
Example 24, Manning's n Calibration. This example discusses how to calibrate an unsteady flow model for base Manning's n values, as well as how to use the HEC-RAS automated Manning's n value calibration option.
Appendix A contains a list of references.