If you are interested in learning about the differences between 2D, 1D and 2D-1D modeling with HEC-RAS this post is for you
HEC-RAS is a software program that can perform hydraulic calculations for steady and unsteady flow, sediment transport, water temperature, and water quality in rivers and channels. HEC-RAS can also simulate floodplain inundation, bridge and culvert analysis, dam breach, and levee analysis.
There are three main types of modeling that can be done with HEC-RAS: 2D, 1D, and 2D-1D. Each type has its own advantages and limitations, depending on the complexity and objectives of the study. Here is a brief overview of each type:
2D modeling: This type of modeling uses a two-dimensional grid of cells to represent the geometry and boundary conditions of the study area. Each cell has a depth, velocity, and other hydraulic properties that are calculated by solving the full Saint-Venant equations for conservation of mass and momentum. 2D modeling can capture the spatial variability and interaction of flow patterns, such as eddies, backwater, and lateral flow. 2D modeling is suitable for areas where the flow is highly dynamic, multidirectional, or affected by complex structures or topography. However, 2D modeling also requires more data, computational time, and expertise than 1D modeling.
1D modeling: This type of modeling uses a one-dimensional network of cross-sections to represent the geometry and boundary conditions of the study area. Each cross-section has an elevation, width, and roughness that are used to calculate the average depth and velocity of the flow by solving the simplified Saint-Venant equations for gradually varied flow. 1D modeling can capture the longitudinal variation and profile of the flow, such as water surface elevation, discharge, and velocity. 1D modeling is suitable for areas where the flow is mainly unidirectional, uniform, or controlled by simple structures or features. However, 1D modeling cannot account for the lateral or transverse variation and interaction of the flow, such as floodplain storage, overbank flow, or hydraulic jumps.
2D-1D modeling: This type of modeling combines the 2D and 1D approaches to represent the geometry and boundary conditions of the study area. The 2D and 1D elements are connected by interface elements that allow the exchange of flow and hydraulic properties between them. 2D-1D modeling can take advantage of the strengths of both 2D and 1D modeling while minimizing their weaknesses. 2D-1D modeling is suitable for areas where the flow is a mixture of 2D and 1D characteristics, such as river-floodplain systems, urban drainage networks, or coastal zones. However, 2D-1D modeling also requires more data, computational time, and expertise than 2D or 1D modeling alone.
To illustrate the differences between 2D, 1D, and 2D-1D modeling with HEC-RAS, let us consider a hypothetical example of a river reach with a bridge and a floodplain. The following figure shows the schematic representation of the study area and the possible modeling options:
As you can see, the 2D option uses a rectangular grid of cells to cover the entire study area, including the river, the bridge, and the floodplain. The 1D option uses a series of cross-sections along the river, with additional cross-sections at the bridge and the floodplain boundaries. The 2d-1d option uses a combination of 2D cells and 1D cross-sections, with interface elements at the river-floodplain junctions and the bridge piers.
The following table summarizes the main differences between the 2D, 1D, and 2D-1D modeling options in terms of data requirements, computational time, and output results:
The choice of the modeling option depends on the objectives, scope, and resources of the study. For example, if the main goal is to estimate the water surface elevation and discharge along the river, the 1D option may be sufficient. However, if the main goal is to analyze the flow patterns and inundation extent in the floodplain, the 2D or 2D-1D option may be more appropriate. The 2d-1d option may also be preferred if there are complex structures or features that affect the flow, such as the bridge piers or the floodplain vegetation.
In conclusion, 2D, 1D, and 2D-1D modeling with HEC-RAS are different ways of representing and simulating the hydraulic behavior of rivers and channels. Each type of modeling has its own advantages and limitations, depending on the complexity and objectives of the study. Therefore, it is important to understand the differences between them and choose the most suitable option for each case.
I hope this post has helped you to learn about the differences between 2D, 1D, and 2D-1D modeling with HEC-RAS. If you have any questions or comments, please feel free to share them below. Thank you for reading! 😊
: [HEC-RAS – Hydrologic Engineering Center] : [Two-Dimensional Modeling in HEC-RAS] : [Two-Dimensional Modeling in HEC-RAS – USACE] : [One-Dimensional Modeling in HEC-RAS] : [One-Dimensional Modeling in HEC-RAS – USACE] : [Two-Dimensional and One-Dimensional Coupled Modeling in HEC-RAS] : [Figure 1: Schematic representation of the study area and the possible modeling options] : [Table 1: Summary of the main differences between the 2D, 1D and 2d-1d modeling options]