HEC-RAS

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HEC-RAS

• Jordan Furnans and Francisco Olivera, Ph.D.
• Center for Research in Water Resources
• University of Texas at Austin

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Channel Hydraulics

• Uniform Flow

• Q flow
• n Mannings coefficient
• A area of cross section
• RH hydraulic radius
• Sf friction slope
• P Wetted perimeter

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Channel Hydraulics

• Energy Equation

• Continuity Equation

• Z elevation of the bottom of the channel
• Y elevation of the water surface
• V flow velocity
• ? coefficient
• g gravity
• he head losses
• A area of cross section

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Channel Hydraulics

• Direct Step Method

• Y elevation of the water surface
• V flow velocity
• ? coefficient
• g gravity
• Sf friction slope
• S0 bottom slope

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Overview

• Entering data
• Viewing results

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Starting a Project

• HEC-RAS (main) Window
• Plan
• Geometry
• Flow
• Open (New) Project window
• Title
• File name (.prj)
• Directory

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Reach Network Data

• Rivers
• Reaches
• X sections at river stations
• Junctions

Within each reach, river station values decrease
downstream. River station values are not a
measure of distance.
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Cross Section Data - Table

• X-section stations
• Elevation of X-section stations
• Distance to next downstream X-section
• Mannings coefficient values
• X-section stations of the main channel banks
• Contraction and expansion coefficients

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Cross Section Data - View

• X-section stations
• Elevation of X-section stations
• Distance to next downstream X-section
• Mannings coefficient values
• X-section stations of the main channel banks
• Contraction and expansion coefficients

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Cross Section Data - Add/Edit

• Copy X-section and paste it at another river
  station
• Adjust X-section station values by multiplying by
  a number, or adding a number
• Adjust X-section station elevations by adding a
  number

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Junction Data

• Length across the junction.
• Computation mode.

L1 and L2 are not defined as part of the cross
section data.
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Steady-Flow Data

• Flows are defined at X-sections.
• Flow does not change between X-sections.
• If flow is not specified at a X-section, then it
  is assumed that it does not change at the
  X-section.

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Boundary Conditions

• Boundary Conditions are specified at
• downstream X-sections for subcritical flow
  (downstream control)
• upstream X-sections for supercritical flow
  (upstream control)

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Plan

• A Plan is a unique combination of
• Geometry File (reach network, X-sections and
  junctions), and
• Steady Flow File (flows and boundary conditions).

15
Overview

• Entering data
• Viewing results

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Results - X-Section

• Cross Section Plots
• Water Surface Elevation
• Energy Grade Line
• Floodplain Extent

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Results - Longitudinal Profile

• Profile Plots
• Water Surface Elevation
• Energy Grade Line

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Results - Reach Rating Curve

• Flow vs. Water Surface Elevation

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Results - Reach Network

• 3D plots of single or multiple reaches showing
• Water Surface Elevation
• Energy Grade Line
• Floodplain Extent
• for single or multiple profiles

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Results - Tabular

• Hydraulic values at different X-sections

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Results - Summary

• Hydraulic values at different reaches