HEC-GeoRAS 8 & Hydraulic Analysis
Temple Williamson
Spring 2004
Texas A&M University
Department of Civil Engineering
CVEN689 Applications of GIS to Civil Engineering
Professor: Dr. Francisco Olivera, Ph.D., P.E.
Abstract
Hydrologic Engineering Center’s River Analysis System (HEC-RAS) is the software
predominately used in the field of hydraulic analysis for floodplain delineation. HEC-RAS,
combined with Hydrologic Engineering Center’s Geographical River Analysis System (HEC-
GeoRAS), offers engineers a powerful tool in the process of hydraulic modeling and analysis.
However, the current version of HEC-GeoRAS is only compatible with ArcGIS 3 and not the
latest version, ArGIS 8. As a result, Environmental Systems Research Institute (ESRI) and
Hydrologic Engineering Center are developing HEC-GeoRAS 8 which will be compatible with
ArcGIS 8. Currently HEC-GeoRAS 8 is only available in a beta version. The following report
outlines the use of the beta version of HEC-GeoRAS 8 for raster data of Langham Creek in
Harris County, Texas.
Introduction
HEC-GeoRAS was developed to provide software which would use digital terrain data
with Geographical Information Systems (GIS) for creating and evaluating hydraulic models. The
current version of HEC-GeoRAS processes geospatial data only from ArcGIS 3.x for use with
HEC-RAS. The programming language for ArcGIS 3.x is Avenue, while the latest version of
ArcGIS’s programming language is Visual Basic. The end result of this difference in
programming language is that the two versions are not compatible. Since HEC-GeoRAS was
developed for ArcGIS 3.x, hydraulic engineers are faced with two options: use the earlier version
of ArGIS for hydraulic modeling or develop an alternative method for hydraulic modeling with
GIS.
Literature Review
To better grasp the role and importance of GIS in hydraulic modeling several articles and
books were reviewed on the topic of hydraulic analysis, especially as it relates to floodplain
mapping. Cameron T. Ackerman reports “GeoRAS provided valuable tools for evaluating
impacts associated with ecosystem restoration and flood damage reduction alternatives.” Peter
Andrysiak’s details in Visual Floodplain Modeling with Geographic Information Systems (GIS),
how the combination of the Hydrologic Engineering Center’s Hydrologic Modeling System
(HEC-HMS) and Hydrologic Engineering Center’s River Analysis System (HEC-RAS) with GIS
was used to develop a model for accurate floodplain representation.
Methodology
In the case of floodplain mapping quite a few steps are involved. The following process
flow diagram for using HEC-GeoRAS was provided by the users’ manual which helps outline
the procedure. The first step is to download the beta version of HEC-GeoRAS 8 from the ESRI
Figure 1 Layer Setup
website (www.esri.com).
Start ArcMap and load the GeoRAS tools. Also load the Spatial Analyst and 3D Analyst
extensions that will be required by the tools. Then, setup the RAS layers that will be used for
geometric data development and extraction.
NEXT, RAS GEOMETRY/ LAYER SETUP Enter Stream Centerline and have Terrain =
Grid
RAS GEOMETRY STREAM CENTERLINE ATTRIBUTES ALL
Create Flow Path Centerlines.
Create Bank Lines (Banks). Personally I offset the centerline by 10 feet to the right and
left of it.
Figure 2 Layout
Now, use the Construct Cross-section Cut Lines tool (green “T” in toolbar) to create. It
should be noted that I selected 600 ft wide XS at 100 ft intervals. However, I received an
error message as seen in figure 2. The proper dialog box should have a unit of feet instead
of degrees for the Interval box.
Figure 3 Error for Cutting Cross-Section
Export HEC-RAS Geometry
o RAS GEOMETRY/EXTRACT GIS DATA
o Manually change extension of export file to .geo, so that HEC-RAS will find it
easier. Note this should not be done in ArcMap, but in Windows Explorer.
Figure 4 HEC-RAS Geometry
Import the geometric data extracted from the ArcMap and complete the necessary
hydraulic calculations. Refer to the HEC-RAS User’s Manual for information regarding
the process involving HEC-RAS. To expedite to process I only did hydraulic analysis for
upper section of Langham Creek.
Figure 5 Upper Section of Langham Creek
Figure 6 XS of Langham Creek with Hydraulic Analysis for 100 CFS
Import HEC-RAS export files into ArcMap by converting it from an ASCII output data
type into XML file. Click on button to execute this function.
Select the Floodplain Mapping/Layer Setup
Figure 7 Setup Dialog
Create the data sets for post processing:
o Floodplain Mapping/Read RAS GIS Export File
Processing Data Results:
o Create inundation data results Floodplain Mapping/WS TIN Generation
o Select the water surface profile
From the User Manual for HEC-GeoRAS:
“One water surface TIN will be created for each selected water surface profile. The TIN
is created based on the water surface elevation at each cross section and the bounding polygon
data specified in the RAS GIS Export File. The water surface TIN is generated without
considering the Terrain TIN. The water surface TINs created will be named as a concatenation of
“ws” and the water surface profile name; and they will be saved into the output directory
specified in the Layer Setup.”
Figure 8 Generated Water Surface
TIN
Now delineate the floodplain for the water surface profile for which a water surface TIN
exists. Scroll through the menu Floodplain Mapping/Floodplain Delineation/GRID-
Intersection
Figure 9 Generated Flooldplain Delineation Grid and Feature Class
Limitation:
o TIN Intersection function for Floodplain Delineation is disabled.
o Tools to generate velocity data sets are currently not available.
Applications, Results, Discussion
The area of study for the GIS project is Langham Creek Basin of Harris County, Texas.
The Digital Elevation Models (DEMs) utilized was collected through the use of Light Detection
And Ranging (LiDAR). The data was acquired from Lockwood, Andrews & Newnam of
Houston, Texas. DEMs have cells of 15-feet X 15-feet and accuracy of better than 6-inch.
Floodplain polygon results are created from intersecting the water surface and terrain
surface. The floodplain delineation procedure converts the water surface GRID and Terrain
GRID to the same cell size and origin. A depth grid is then created with values where the water
surface grid is higher than the terrain grid which gives the final result (see figure 10).
Figure 10 Resulting Polygons
Conclusion
The primary conclusion to be drawn from this project is that HEC-GeoRAS 8 is the
logical next step for engineers who are seeking to stay on the cutting edge of technology. HEC-
GeoRAS 8, because of its compatibility with ArcGIS 8 and user-friendly programming language,
has the potential of becoming the new primary software for the integration of GIS and hydraulic
modeling. It will also greatly streamline the process of hydraulic modeling with GIS. Engineers
will no longer be forced to use the earlier versions of ESRI’s GIS software. However, it should
be noted that anyone seeking to use HEC-GeoRAS 8 at present must use a beta version which
may result in errors and a generally slower processing time.
Developments of technology such as LiDAR and advances in GIS software capability
have not only created the potential for a fast and accurate analysis process for hydraulic
modeling, but also for hydrologic analysis. Thus, it is clear that the technology of water resource
engineering is making rapid advances and that HEC-GeoRAS is an eminent evolution in that
technological march.
References
Cameron Ackerman. (2001)."Hydraulic Modeling of the Salt River, Arizona Using HEC-
GeoRAS" Hydrologic and Hydraulic Modeling Support with GIS.
Environmental Systems Research Institute Hydrologic Engineering Center (2004) "HEC-
GeoRAS Tools Overview Manual".
Hydrologic Engineering Center (2001) "HEC-RAS (Version 3.3.1), River Analysis
System, User's Manual", U.S. Army Corps of Engineers (USACE). Davis, CA.
Richard Kraus.(2000)."Floodplain Determination Using ArcView GIS & HEC-RAS."
Hydrologic and Hydraulic Modeling Support with GIS.