US Army Corps of EngineersBUILDING STRONG ®

General Workflow in HEC -RAS

Jamie G. James, P.E.USACE – Nashville DistrictSeptember 2010

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Discussion Topics

� Data Collection� Data Organization and Evaluation� Data Input� Initial Evaluation and Calibration� Final Analysis

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Data Collection� Data

► Geometry• Existing Models

• Field Run Surveys

• Digital Elevation Models (DEM)

► Flow Data• Gage Records

� Peak Flows� Event Hydrograph

• Rainfall Runoff Models� Single Event� Continuous Simulation

• Regression Equations� Use with Caution (accuracy can vary up to 50%)

► Hydraulic Parameters/Coefficients• Field Visits

• Aerial/Local Photography

► Expense Increases as Accuracy Increases

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Data Organization and Evaluation

� Geometric Data► River station is in order of progression from the stream mouth to

the headwaters• River station zero is nearest the mouth of the stream

• River stations can be in meters or kilometers (feet or miles)

► Cross Section Internal Stationing• Left bank and right bank are determined as if looking downstream (Zero is

always toward the left)

� Discharge Data► Can be gradually varied steady flow, or unsteady flow► Flow change locations/hydrograph locations should be placed at

the headwaters, at tributary confluences and at points of significant change in drainage area

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Data Input

� Project► Data screen that controls the project; identifies the active plan,

geometry, flow

► A single project can have multiple geometries, flows and plans

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Data Input

� Geometry► Contains the cross section and reach information for the project

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Data Input� Flow

► Contains the stream discharge information for the project

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Data Input

� Plan► Combines the geometry and flow into a purposeful unit, contains some

functions such as floodway

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Data Input

� Internal Documentation► HEC-RAS data editors have text blocks for modeler notes (Project,

Geometry, Cross Sections, Plan)► Useful information to include:

• Modeler’s name• Purpose of the model• Date• Changes made to original model• Sources of geometric, flow or other data (field survey, gage analysis, bridge inventory)

► Update this information each time the model is altered

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Initial Evaluation and Calibration

� Check for Errors► Crossing Profiles► Hydraulic Structures► Unusual Results (e.g. adverse water slope)

� Calibration Runs► Based on Available Data

• High water marks – if resources are limited following a flood event, set marks at hydraulic structures

► Adjust Coefficients• Use judgment to determine what adjustments make sense; be consistent

• Adjust sections individually or with universal editor

► Iterative Process

� Does the profile look like you expect water to act?

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Final Analysis

� Based on Calibrated Model (if applicable)� Perform Final Check for Errors or Unusual Results� Document the Process

► Use internal documentation opportunities in the model► Keep good notes, compile a summary at the end of the project► Think like someone looking at your work 20 years from now

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Questions?