1. Processing Geospatial Data with HEC-GeoRAS 3.1
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Good afternoon class, I am Brad Endres and today I will present my project entitled Processing Geospatial Data with HEC-GeoRAS 3.1.
You should be familiar with HEC-GeoRAS from Friday’s presentation by Lim, so I plan to highlight some of the finer points of using this extension.
Brad Endres
CVEN 689
28 April 2003

2. Overview Hydrologic Review Hydraulics Review Applicable Software
Data Requirements
Major Functions of GeoRAS
Demonstration of Capabilities
Application to Area of Interest
Benefits and Drawbacks
Questions
Since we have a variety of engineers in class, I will start by giving you some background knowledge, or review, of hydrology and hydraulics.
I will introduce the leading software packages that can be used in conjunction with ommercial GIS software – specifically ESRI’s ArcView program.
I will cover the digital data that is required to effectively use these programs. A demonstration of GeoRAS using the example data provided by the Hydrologic Engineering Center will showcase the capabilities.
An application to an water resources problem area will depict its analytical capabilities.
I’ll give you my perspective on the benefits and drawbacks of using GeoRAS and I’ll entertain any questions you might have at the end of the briefing.
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3. Hydrologic Review Engineering Hydrology
Occurrence, circulation, & distribution of water
Frequency & magnitude of events (flood/drought) for engineering designs
Gage station
Hyetograph
Hydrograph
Scientific and engineering hydrology are very broad topics, so I just want to cover the basics to help you understand how the software programs incorporate these principle in their modeling abilities.
As engineers, our main objective in studying the waters of the earth is to find out how much we can expect to encounter in a certain area, and how often we expect to encounter it.
We want to protect society from the extreme events of floods and droughts, so we make estimates using proven methods and equations that result in a flood frequency analysis.
Some of the components involved include U.S. Geological Survey gaging stations,, hyetographs that depict rainfall intensity (in/hr or cm/hr) for the 3 major regions of the U.S., and the resulting hydrograph at a water shed outlet that shows discharge (cfs or cms) over time.
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4. Hydraulics Review Hydraulics
Results in design specifications for bridges, culverts, and hydraulic structures
Water Surface profile calculations based on flow data
Energy Equation
Example Floodplain
By closely approximating these hydrologic variables for a give watershed, engineers are able to design effective flood control structures or water supply facilities.
Of particular importance in hydraulics is the calculation of the water surface profile of a stream for the purposes of floodplain management. Using the inputs from hydrologic studies of a watershed, the hydraulic engineering seeks to find out how high the water will rise for a given rainfall event.
The first law of thermodynamics, known as the conservation of energy equation, allows for the computation of a water surface elevation. It basically states that the head energy at a point downstream equals the head energy upstream minus the head loss due to friction between the points. Manning’s equation applies to open channel flow and is used to calculate the discharge rate at a cross section of stream using an estimated value of roughness called Manning’s n.
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5. Hydraulics Review Floodplain Delineation
Conventional Method of quad maps & hand calculations
Digital Method
Digital Terrain Model (DTM) in ArcView 3.2
GeoRAS automates geometry calculations
HEC-RAS models given flow & delineates floodplain
Export back to ArcView for additional grids
One result of applying the energy equation is the water surface elevation, or height above the channel bottom at each calculated cross section. When compared to the elevation of the surrounding terrain, a floodplain can be delineated to indicate the level to which the water will rise.
The old method for doing this called for hand drawing cross sections on topographic, or quadrangle, maps, and recording the contour lines that were crossed. When plotted and connected, these points served as the cross section profile of the stream at a specific point.
With GIS tools, this can now be done using software programs if the appropriate data is available. If a digital terrain model exists, then the GeoRAS extension to ArcView can be applied to automate the previously described channel geometry. This data can be imported to the Hydrologic Engineering Center’s River Analysis System to delineate the floodplain through computer simulation.
Once exported back to ArcView, a floodplain can be delineated on the terrain model, as well as depth and velocity grids that provide further analytical capability to the engineer.
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6. Applicable Software ArcGIS w/ extensions HEC-HMS HEC-RAS
3D & Spatial Analyst
HEC-GeoHMS
HEC-GeoRAS
HEC-HMS
Simulates rainfall-runoff for the watershed
HEC-RAS
Simulates water surface profile of a stream reach

7. Data Requirements Triangular Irregular Network (TIN)
DEM (high resolution)
use stds2dem.exe if downloading from USGS
Land Use / Land Cover
Manning’s Coefficient
See USGS website
CRWR image

8. Major Functions of GeoRAS
Interface between ArcView and HEC-RAS
What does it do?
PreRAS Menu - prepares Geometry Data necessary for HEC-RAS modeling
GeoRAS_Util Menu – creates a table of Manning’s n value from land use shapefile
PostRAS Menu – reads RAS import file; delineates flood plain; creates Velocity and Depth TINs

9. Demonstration of Capabilities
3-D Scene
Load TIN
Create Contour Lines
3-D Scene

10. Demonstration of Capabilities
Create Stream Centerline
Create Banks Theme
Create Flow Path Centerlines
Create Cross Section Cut Lines
Add/Create Land Use Theme
Generate RAS Import File

11. Demonstration of Capabilities
Land Use Theme
Stream Centerline
Right Bank
Flow Path Centerlines
Cross Section Cut Lines

12. Demonstration of Capabilities
Generate RAS GIS import file
Open HEC-RAS and import RAS GIS file
Complete Geometry, Hydraulic, & Flow Data
Run Analysis
Generate RAS Export file

13. Demonstration of Capabilities
RAS GIS import file:

14. Demonstration of Capabilities
RAS GIS export file:

15. Demonstration of Capabilities
New GIS data
PostRAS features
Water Surface TIN
Floodplain Delineation – polygon & grid
Velocity TIN
Velocity Grid

16. Demonstration of Capabilities
Floodplain Delineation (3-D Scene)

17. Demonstration of Capabilities
Depth Grid (Darker = Deeper)
Velocity Grid (Darker = Faster)

18. Application to Area of Interest
Background on Bolinas Lagoon, CA
USGS Map
USACE Map

19. Application to Area of Interest
Bolinas Lagoon, CA
USACE Image
USACE Image

20. Application to Area of Interest
Employing ArcView, GeoRAS, and RAS for Main Channel Depth Analysis (1968)
PreRAS
PostRAS
13.5 ft

21. Application to Area of Interest
Employing ArcView, GeoRAS, and RAS for Main Channel Depth Analysis (1988)
PreRAS
PostRAS
21.0 ft

22. Application to Area of Interest
Analysis of Results
Sensitivity to stream centerline placement
Accuracy improves with more XS cut lines
XS cut lines hard to draw on meandering stream
Possible deepening of the main channel over time
Analysis of area complicated by tidal flows
Validate findings
FEMA floodplain maps
USACE studies
Bolinas watershed

23. Benefits & Drawbacks Overall Benefits
Elevation data is more accurate with TIN files
Better representation of channel bottom
Rapid preparation of geometry data (point and click)
Precision of GIS data increases precision of geometry data
Efficient data transport via import/export files
Velocity grid
Depth grid
Bolinas Lagoon on 10m DEM

24. Benefits & Drawbacks Overall Benefits
Floodplain maps can be made faster
Floodplain maps can include several flow scenarios
HEC-RAS allows steady & unsteady flow analysis
GIS tools aide engineering analysis
Automated calculation of functions (Energy Equation)
Structural validation of hydraulic control features
Voluminous data on World Wide Web
Makes data into visual event – easier for your brain to process!
More GIS!

25. Benefits & Drawbacks Overall Drawbacks
Time required to learn several software packages
Availability of TIN or high resolution data
Estimation of Manning’s Coefficient
Few LU/LC files have this as attribute data
Creating XS cut lines demands attention to detail
Velocity distribution data may not be calculated
HEC-RAS export file without velocity data means no velocity TIN or grid

26. Questions
What are your questions?
New 3-D Viewer in HEC-RAS 3.1