HEC-RAS 2D Modeling
The software now includes the ability to perform 2D unsteady flow modeling and combined 1D and 2D unsteady flow modeling using the HEC-RAS 2D analysis engine. The 2D flow modeling capabilities of the software can be used for:
- Detailed 2D channel and floodplain modeling
- Combined 1D channels with 2D floodplain areas
- Combined 1D channels and floodplains with 2D flow areas outside of the levees
- Connect 1D reaches into and out of 2D flow areas
- Connect a 2D flow area to 1D storage area with a hydraulic structure
- Multiple 2D flow areas in the same geometry
- Connect multiple 2D flow areas with hydraulic structures
- 2D dam breach analyses
- 2D levee breach analyses
- 2D bridge modeling (without pressure and bridge deck overflow)
- Mixed flow regimes (e.g., subcritical and supercritical regions, hydraulic jumps, etc.)
Adaptive 2D Mesh
In addition to HEC-RAS’ default rectangular (structured) 2D computational mesh, the software can also create an adaptive 2D mesh to better represent more complicated 2D flow conditions and structures. The software will automatically refine the 2D mesh when required, such as at a roadway crossing.
2D Mesh Feature Stamping
The software can stamp bridge piers into the 2D mesh. Supported pier shapes include:
- Circular pier
- Rectangular round nosed pier
- Rectangular sharp nosed pier
- Rectangular square nosed pier
- Square pier
The user can interactively place and rotate the bridge pier relative to the roadway crossing.
2D Ineffective Flow Areas
Ineffective flow areas can be assigned to the 2D mesh using polylines or polygons. Alternatively, the user can draw ineffective flow areas on the Map View. For example, stagnant flow areas at roadway crossings can be stamped into the 2D mesh to account for the ineffective flow area. The software will automatically refine the 2D flow area to incorporate the ineffective flow area shape.
2D Conveyance Obstructions
Conveyance obstructions can be assigned to the 2D mesh using polylines or polygons. Alternatively, the user can draw conveyance obstructions on the Map View. For example, buildings and other structures can be stamped into the 2D mesh as conveyance obstructions to account for flow blockage. The software will automatically refine the 2D flow area to incorporate the conveyance obstruction shape.
Auto Fixing 2D Mesh Bad Elements
The US Army Corps of Engineers HEC-RAS software generates 2D meshes that contain elements that are marked “bad” and that require the user to manually fix. GeoHECRAS will automatically detect and fix these bad elements without requiring any interaction by the user.
Remembering 2D Mesh User Edits
As the user manipulates the 2D mesh by inserting additional elements, moving elements, and other mesh element editing, the software remembers these edits. Then, the next time the 2D mesh is rebuilt, these user-defined changes are automatically incorporated into the mesh.
Assign Land Cover Data as Manning’s Roughness
The software can assign either user-defined land cover polygons or National Land Cover Database (NLCD) data as Manning’s roughness to cross sections and 2D flow areas. The National Land Cover Database provides land cover data for the entire United States. The software can dynamically download a NLCD raster land cover grid for the area being modeled. Each 75ft x 75ft land cover grid cell represents a specific land type. Up to 20 different land types and corresponding Manning’s roughness values are provided.
Flood Hazard Mapping
The software can create a flood hazard map, based upon user-selected criteria. The following analysis result variables can be plotted as a flood hazard map:
- Flood Arrival Time
- Depth x Velocity
- Depth x Velocity²
- Flood Duration
- Flood Recession Time
- % Time Inundated
For the above result variables, the user can define a threshold depth in which the flood hazard map boundary is initiated.
Animated Flood Maps
For unsteady flow models, the flood map can be animated to show how it changes with time. The animation speed can be adjusted, as well as setup to continuously loop. The final animation can be recorded to a video. In addition to animating the flood results, options are available to show the maximum and minimum flood extents.
Velocity Vector Maps
The software can plot velocity vectors on the flood map to represent the flow field for both 1D river reaches and 2D flow areas. The velocity vector length is adjusted to represent the velocity at that point. Velocity vector maps can be created for both steady flow and unsteady flow models.
Particle Tracking Maps
The software can plot moving particles on the flood map to represent the flow field for both 1D river reaches and 2D flow areas. The size and speed of the particle is adjusted to represent the velocity at that point. Particle tracking maps can be created for both steady flow and unsteady flow models.
Google Earth Map Animation
The software can export out the flood map animation to Google Earth. This is helpful for presentations on flood risk assessment and flood management.
Georeference Lateral Structures Command
Additional functionality has been added to the Georeference Lateral Structures command, including the ability to draw a portion of the revised lateral structure alignment polyline and intersect the original lateral structure alignment at two locations to define the change between the points of intersection.
Georeference Storage Areas Command
Additional functionality has been added to the Georeference Storage Areas command, including the ability to draw a portion of the revised storage area boundary polyline and intersect the original storage area boundary polyline at two locations to define the change between the points of intersection.
River Channel Modification Command
The River Channel Modification command allows the user to define a trapezoidal cut into the existing channel geometry. The user can see a profile view of the channel modification along the river, and can either draw the channel bottom, define a channel bottom slope to use, or instruct the software to interpolate the channel bottom between selected cross sections. The user can have the channel modification follow along the existing river centerline, or select a new alignment polyline to use—like when performing stream channel restoration back to a sinuous river path.
After the changes have been added to the river channel, a HEC-RAS analysis can be performed to see what affect these changes have on the computed water surface elevation, depth of flow, velocity, and shear stress. This command can be used by the user in performing stable channel design and for fish waterway and passage design. In addition, bendway weirs and other artificial structures can be easily inserted into the channel to adjust the flow characteristics of the stream, stabilize the channel from horizontal migration, and create habitat areas for fish.
Graphical Editing of Roadway Geometry
The software now allows the user to graphically edit in the Bridge & Culvert Data dialog box the roadway crossing high and low chord geometry. If there is no low chord geometry defined, then the high chord geometry can be moved vertically and horizontally. However, if both high and low geometry are defined, such as at a bridge opening, the high and low geometry can only be moved vertically.
The Process LIDAR command has been extended to allow assignment of a CRS to the processed LIDAR file.
This new command allows the user to select which plans (scenarios), geometry, and flow data to remove from a project. In addition, it automatically compresses the database to shrink the size of the project file.
Additional Map Edit Commands
The following GIS editing commands have been added, allowing the user to manipulate map data:
- Simplify Elements
- Intersect Polylines
- Detach Polylines
- Distribute Vertices
- Simplify Elements
- Intersect Polygons
- Detach Polygons
Layer Transformation and Registration
Surveyors use a NOAA online software program called OPUS that takes measured GPS grid coordinates from a survey data collector and convert them into local ground coordinates that are corrected for the true shape of the Earth (which is not a perfect sphere). AutoCAD Civil3D provides support for the transformation scale factor in its Drawing Settings dialog box. We have implemented support for this transformation scale factor throughout the software, including CAD layers, TIN layers, HEC-RAS layer (and other layers) Properties dialog boxes, allowing the software to support local ground coordinates.
In addition, the user can manually register a layer’s position by providing two coordinate points (i.e., current location and desired location).
Minor Loss Coefficients
Minor losses due to bends, junctions and more can be accounted for in both steady flow and unsteady flow analysis. Minor loss coefficients can vary between 0.0 and 1.0. This loss coefficient gets multiplied by the velocity head at that the cross section it is defined at to compute the minor energy loss. This energy loss gets added to the energy equation for steady flow computations. For unsteady flow computations, the energy loss is converted to an equivalent force and inserted into the momentum equation. In both cases, the energy loss is assumed to act as a force in the upstream direction to slow the flow down.
Internal Changes in WS and EG
Internal boundary conditions can be defined at a cross section, on a profile by profile basis, by defining one of the following:
- Change in water surface elevation
- Change in energy gradeline elevation
- Additional energy head
- Known water surface elevation
- K loss