As a I said before, when you need to use a hydraulic model to analyze a problem there are four options, a scaled physical model, three dimensional (3-D) model, two dimensional (2-D) model, or a one dimensional (1-D) model.
Scaled physical models and 3-D models definitely have there place for large complex hydraulic analysis. Though I have observed both I have very little experience with either, and at best can point to other resources. For physical hydraulic modeling studies the best facilities I know of are the CSU, USU, and IU hydraulics labs.
In any river, canal, culvert, stream, creek, etc. all flow is 3-D, but for most hydraulic modeling studies a 1-D or a 2-D model will provide all the information required for an analysis and/or design. Understanding the underlying assumptions of each model is very important when deciding on which type of model to use. The Colorado Floodplain and Stormwater Criteria Manual (Chapter 12) provides a helpful table comparing the differences between 1-D and 2-D modeling.
Because of the differences in how each model computes all of the hydraulic parameters, 2-D models have definite advantages over 1-D models in several situations. These include:
- Complex Floodplain Geometry
- Flow Splits
- Wide Floodplains
- Variations in Channel and Floodplain Flow Paths
- Complex Bridge Crossings
- Multiple Openings
- Roadway Overtopping
- Crossings Near Channel Bends
- Skewed Embankments
- Skewed or Complex Pier Configurations
- Extreme Constriction at Crossing
- Alluvial Fans
- Braided or Anabranched Streams
- Asymmetric Floodplains
- Highly Meandering
In addition to these site characteristics some hydraulic studies depend on additional, more accurate, data provided by 2-D models. These include:
- Bank Protection Design
- Levee Protection Design
- Scour Analysis
- Habitat Analysis
The next time you need to use a hydraulic model make sure you think through your specific site and project characteristics before choosing which tool to use.
For additional reading on this topic please see the resources linked above, and the NCHRP report Criteria for Selecting Hydraulic Models.