The Evolution of VO
From HYMO to today's VO, each generation has built on the methods and practical engineering principles established before it, while expanding what engineers can model and analyze.
HYMO | The Foundations
HYMO was developed by Jimmy R. Williams and Roy W. Hann Jr. at the U.S. Department of Agriculture’s Agricultural Research Service in cooperation with Texas A&M University. It provided a practical modeling language for representing rainfall-runoff processes, flood routing, and watershed response.
- Practical hydrologic modeling language
- Watershed runoff analysis
- Flood routing
- Unit hydrograph procedures
- Interconnected hydrologic components
OTTHYMO | Engineering for Urban Growth
Dr. Paul Wisner at the University of Ottawa built on HYMO to develop ‘OTT’HYMO for the growing stormwater management needs associated with urban development. OTTHYMO expanded the original framework for land-use change, urban runoff, and stormwater management applications.
- Urban runoff modeling
- Land-use change analysis
- Stormwater management applications
- Refined watershed modeling methods
Visual OTTHYMO | Making Hydrology Visual
Visual OTTHYMO brought OTTHYMO into a graphical modeling environment. Instead of relying on command-driven model development, engineers could build, edit, and review watershed models visually.
- Graphical user interface & model editing
- Visual watershed schematics
- Single-event modeling
- Simplified model development
VO2–VO4 | Modern, GIS-Driven Modeling
Visual OTTHYMO underwent a major modernization during the VO2–VO4 generations. A redesigned Windows environment was followed by expanded rainfall management, calibration, GIS capabilities, terrain-based model development, and distributed rainfall modeling.
- Modern Windows modeling environment
- Storm Library and rainfall management
- Calibration and batch simulation
- GIS map and spatial data tools
- Watershed parameter extraction
- Distributed Rainfall Modeling Technique (DRMT)
VO5–VO6 | Continuous & Environmental Modeling
VO5 and VO6 expanded Visual OTTHYMO beyond event-based hydrologic modeling with continuous simulation and new tools for evaluating long-term watershed behavior, green infrastructure, water quality, wetlands, and erosion.
- Continuous Simulation Engine
- Expanded Climate Library
- Scenario Comparison
- Wetland and Hydroperiod Modeling
- Eight integrated LID practices
- Water Quality Modeling
- Enhanced Erosion Analysis
- Batch Run Automation
VO6.2 | Hydrology Meets Hydraulics
VO6.2 integrated the EPA SWMM5 engine alongside OTTHYMO, bringing detailed hydraulic modeling into the VO platform. VO now provided two complementary engines within one software environment: VO OTTHYMO for hydrology and VO SWMM for hydraulics.
- EPA SWMM5 integration
- Rural (OTTHYMO) and urban (SWMM) modeling
- RDII analysis
- Major GIS automation
- Automatic catch basin generation
- Enhanced floodplain tools
- Improved LID and scenario reporting
VO6.3 | Connected & Global Modeling
VO6.3 expanded how engineering teams manage and share modeling projects while adding new capabilities for wetland-groundwater analysis, terrain-based modeling, and coordinate systems.
- VO Hub cloud workspace
- Project sharing and version history
- Wetland-Groundwater interaction
- Expanded Coordinate Reference System support
- DEM-based transect extraction
- Enhanced wetland and erosion reporting
More Capability. The Same Commitment to Simplicity.
As engineering needs and modeling capabilities expanded, VO grew with them while maintaining a focus on making models easy to learn, quick to build, and simple to use.
VO has continuously expanded what engineers can model without adding unnecessary complexity to how they model it.