Use the RAS Mapper viewport to build a simple one-dimensional hydrodynamic model - HEC RAS tips (1)
I. Introduction
After HEC-RAS version 5.0.7 (currently updated to version 6.3.1), the original model workflow has undergone major changes. The new RAS MAP provides a better model data interaction interface. Users can directly plan the river channel in RAS MAP and cut the river channel section through DEM, which greatly improves the efficiency of building a one-dimensional hydrodynamic model. In this section, the author shares some common operations of using HEC-RAS to build models through practical applications.
2. Create new project files
1. Create a new project file
Create a new project in the File-New Project menu bar of the HEC-RAS main interface.
Set the model unit through Options-Unit system in the menu bar of the main interface, as shown in the figure:
2. Set the project coordinate system
Click the RAS Mapper button on the main interface to enter the RAS Mapper window. Set the project coordinate reference system in the menu bar Tools-Set Projection for Project of the RAS Mapper window.
The coordinate reference system information can be read by loading an existing .prj file.
3. Enter geometric information of river network
1. Create new terrain
Create a new terrain in the menu bar Tools-New Terrain of the RAS Mapper window.
2. Add a new geometry database and name it
Add a new geometry database in the data tree on the Messages tab of the RAS Mapper window (right-click Geometry-Add New Geometry). The geometry database records information such as grids and sections. After the data is edited and saved, the edited data will be saved locally in the form of files.
Give the new geometry database a name.
3. Add river channels
Right-click Geometries-youai (geometry library name)-Rivers-Edit Geometry, edit the river geometry, click in the right window to be the starting point of the river, continue to click to be the middle node of the river, double-click the end to be the end point of the river.
Name the river.
4. Add section
Continue to click Geometries-youai (name of the geometry library)-Cross Sections to edit the section geometry. In the right window, add a section where you need to add a river section. Click as the starting point of the section. Continue clicking as the middle node of the section. Double-click The end is the end point of the section (generally, just select the starting point and end point of the section, and note that the section must intersect with the river where it is located). Each time a section is successfully drawn, the software automatically marks the mileage number of the section.
Right-click Geometries-youai (geometry library name)-Cross Sections-Stop Editing to end the editing state. At this time, the software will automatically load the elevation information on the terrain for each cross-section point.
Right-click the section you want to view and click Plot Terrain Profile to view the mileage-elevation map and data table of the river section and terrain profile.
In the editing state, you can view the basic information of the section and manually change the data (Geometries-youai (geometry library name)-Cross Sections-Open Attribute Table). The data that can be changed include the mileage of the section on the river, section name, section description, the distance between the left bank, right bank and the center of the river of the section and the corresponding position of the next section, the left bank mileage, and the right bank mileage.
File-Save saves the edited information.
5. Set the river section roughness
Enter the geometric data window through the View/Edit Geometric data button on the main interface, and load the river channel and river section previously edited through RAS Mapper through File-Open Geometry File in the menu bar.
Open the section roughness setting table in the menu bar Tables-Manning's n or k values (Horizontally varied), and assign values to the roughness of both sides of each section and the river channel.
6. Manually adjust the river cross-section shape
Select the Cross Section button from the vertical buttons on the left side of the geometric data data window to enter the Cross Section Data data window. The data parameters of each section can be viewed and edited.
Enter the Graphic XS Editor window through the Jump to Graphical Cross Section Editor button in the lower row of the Cross Section Data data window menu bar. The river topography can be manually adjusted within this window.
4. Set boundary conditions
The boundary conditions in the constant flow model are set as follows:
View/Edit steady flow data through the main interface to enter the corresponding window.
Upstream boundary conditions: Fill in the flow scenario number of the corresponding section in the Enter/Edit Number of Profiles input box (for example, you need to simulate a 100-year return, a 50-year return, and a 20-year return design flood, The number of scenarios is 3, enter 3 here), and the corresponding column numbers in the corresponding bottom dynamic data table scenario names and frequency flood flow values (Profile Names and Flow Rates) will also be updated.
Downstream boundary conditions: Use the Reach Boundary Conditions button to enter the constant flow boundary conditions page. The average river ratio is reduced to 0.0028. Select the Normal Depth button and enter 0.0028. Other options are Known WS, Critical Depth, and Rating Curve.
5. Run the model
The constant flow operating model is as follows:
Perform a steady flow simulation through the main interface and enter the corresponding window.
The model provides three flow states to choose from: Subcritical, Supercritical, and Mixed. For related introduction, please view the HEC RAS application guide HEC-RAS 5.0.4 Applications Guide.pdf (the file is located in the software installation path C:\Program Files (x86)\HEC\HEC-RAS\5.0.7\Documents).
6. View results
Use the View cross sections button on the main interface to view the cross-section water line.
View the hydraulic elements through the View summary output table by profiles button on the main interface.
View the positional relationship between each river section and the water surface through the main interface (View 3D multiple cross section plot) button.
