Why would anyone want to purchase GeoHECRAS when HEC‑GeoRAS is free? This is a question we occasionally get asked by clients who have heard of HEC‑GeoRAS. Let’s examine this in detail.
HEC‑GeoRAS enables a user to create a partial HEC‑RAS project using ESRI ArcGIS, ESRI 3D Analyst, and ESRI Spatial Analyst software and required extensions. HEC‑GeoRAS can only work with ESRI TIN (triangulated irregular network) terrain surfaces, and generally there is a fair amount of work necessary to construct a TIN terrain surface by manually swapping TIN edges, refining the TIN, etc. Usage of AutoCAD Civil 3D or Bentley MicroStation drawing files, or ESRI ArcInfo grid terrain surfaces is difficult.
HEC‑GeoRAS will construct only the following elements in a HEC‑RAS model by manually drawing or assigning polylines and polygons within the ArcGIS user interface:
- River centerline
- Channel bank lines
- Flow path lines
- Cross section cut lines
- Manning’s roughness polygons
- Levee lines
- Ineffective flow area polygons
- Storage area polygons
Once the ArcGIS coverages have been created, they need to be exported and then converted into a format that the Army Corps of Engineers HEC‑RAS software can import. However, if the user discovers an error or requires changes in the defined GIS data, the user needs to start back in ArcGIS, make the necessary changes—basically repeating the process over again. Any changes made within the Army Corps of Engineers HEC‑RAS software cannot be reflected back into the ArcGIS model without major data conversion efforts.
After importing the GIS coverages into the Army Corps of Engineers HEC‑RAS software, other elements of the HEC‑RAS model will need to be constructed separately:
- Roadway crossings
- Bridge openings
- Inline structures
- Dam failures
- Lateral structures
- Levee failures
- Storage area connections
- Steady or unsteady flow boundary conditions
- Floodplain encroachments
- Conveyance obstructions
- Cross section lids
After the HEC‑RAS model has been constructed and run within the Army Corps of Engineers HEC‑RAS software, the user needs to export the computed water surface elevations back to ArcGIS in order to generate a flood map. If there were any changes in existing cross section alignments, or additional cross sections inserted, this can cause issues when round-tripping the computed results back to ArcGIS.
Once the HEC‑RAS computed results have been imported into ArcGIS, the user can then generate a flood map. If the user discovers at that time any issues with the completed HEC‑RAS model, the entire process starts again. It is not possible to merge any ArcGIS model changes with an existing HEC‑RAS model.
Another consideration that needs to analyzed is the cost outlay required to get started with HEC‑GeoRAS. Keep in mind that utilizing HEC‑GeoRAS in an efficient manner requires some GIS expertise (or the necessary training or playing around time) to get up to speed.
|Upstream of drop structure:||10 feet|
|Over the drop:||2 feet|
|Inside the stilling basin:||10 feet|
|Downstream of Structure:||10 feet|
In comparision, GeoHECRAS is a fraction of the cost of HEC‑GeoRAS, and includes customized onboard training and toll-free technical support at no additional cost. In addition, special incentives are available to new customers to provide a migration path to GeoHECRAS.
The best way for you to do an effective comparison between HEC‑GeoRAS and GeoHECRAS is to experience GeoHECRAS for yourself. We can point out all of the fantastic functionality that GeoHECRAS provides over other software, but ultimately you need to make that decision—both from a cost perspective, get-up-to-speed perspective, and a technical support perspective.