The creation of the 1d network layers is described for the GIS packages below:. In this section we define lines where there is flow exchange between the 1D and 2D components of the model. Before we begin creating the link we will spend a bit of time describing how the link works. The 2D water level applied at the 2D boundary cells is calculated in the 1D model. Using a similar naming convention, a HT boundary is a H ead versus T ime boundary, a QT indicates a flow-time hydrograph boundary and a HQ boundary used in the model is a Head versus Flow or stage-discharge boundary.
Depending on the water level in the surrounding 2D cells, flow can either enter or leave the "HX" cells. The volume of water entering or leaving the 2D boundary is added or subtracted from the 1D model to preserve volume. In between 1D nodes a linear interpolation of water level is applied. This is shown in the image below. As the water level in the 2D is calculated at the cell centres, once the water level in the 1D exceeds the elevation in the boundary cell water can enter or leave the model.
If there is a levee, it is important that we use breaklines in the model to ensure that the elevations of the 2D cells are consistent with the levee crest. This will be described in the next section of the tutorial. Often HX lines are located along the top of a levee natural or artificial or flood defence running along the river bank. When carving a 1D channel through a 2D domain, the HX line must be either on the top of the levee or on the inside of the levee closest to the channel.
If the HX line is located on the other side of the levee away from the channel, the effect of the levee on water flow is not modelled. In the sections above, it can be seen that the boundary cell is along the levee and the interaction between the channel and the floodplain 1D and 2D occurs at the correct elevation. This process is described for the various GIS packages in the links below:. As mentioned above, the water level from the 1D is transferred out to the 2D HX cells. Therefore, it is important that the 2D cell elevation reflects the level when water can spill out into the 2D.
The water level computation point for the 2D cells is the cell centre, therefore it is important to use a "thick" breakline. The types of breaklines was discussed further when reviewing the check files for the previous module here.
The black labels are the elevations with no breakline elevation as read from the DEM. At the circled cell, the cell centre elevation is The red line indicates the true top of bank; the labels are elevations along this line. If this is included as a breakline, the elevations are as labelled in yellow. In this case, the level at the circled cell is actually Including breaklines for the top of bank is important, particularly if there is an embankment or levee.
To include breaklines for the top of bank, follow the instructions outlined in your GIS package below. It is important that the area deactivated from the 2D is the same as the area modelled in the 1D solution.
If the 1D cross sections are 20m wide, but a 40m width is removed from the 2D model, the model will be underestimating the conveyance. The opposite would be true if the 1D cross sections were 80m wide but only a 40m width had been deactivated, i. As the HX line was created along the top of bank and was as wide as the cross-sections, we can snap the code polygon which deactivates the 2D cells to the HX line.
To do this please select your GIS package from the list below:. You may have noticed that in addition to extending downstream of the 2D active domain to the north, the 1D network extends slightly upstream from the 2D active domain at the south western edge of the model.
Therefore, we need to adjust the inflow and outflow boundary locations. To do this we need to:. Now that we have made all of the necessary changes to the GIS layers, we need to update our control files to utilise the new GIS layers. Now that the 1D component of the model is becoming more complex we are going to use a separate control file for the 1D inputs. The new 1D control file will have the extension.
Please proceed to Simulation Setup. Follow these steps to Setup the Simulation. The revised boundary data has been provided for this tutorial. This includes the stage-discharge boundary for the weir at the downstream end of the model.
If the model fails to start correctly please refer to the troubleshooting section at the end of this page. Once the model has started we can review the check files to ensure the changes have been correctly applied. In the creek channel we should see that there are channels in the 1D network and that the 2D grid has been deactivated.
If these changes are not visible in your model, ensure that the correct. The model has also been extended further downstream in 1D and a user defined stage-discharge relationship has been adopted. This file can be opened in a text editor and the error is generally located at the end of the file. You can however search for "Error" if you can not see the error. In most cases there is also a spatial location for the error message if the error reported in the log file is prefixed by XY:.
If the model fails to start correctly please refer to the troubleshooting section at the end of this page. While the model is running, now is a good time to open the check files to review the changes to the topography caused by the breaklines.
The layer contains the following information:. The check files should show the changes shown above, if they do not please see the troubleshooting section at the bottom of this page. The 1D and 2D results can be reviewed using the methods outlined in Module 1 and Module 2.
Some suggestions for things to check are:. Point data from survey was provided in text files as x,y,z format data. Check files were used to confirm the changes to the elevation points Zpts. The 2D Z Shape can also be used for more complex modifications, using polygons and TIN lines, these will be introduced in later modules.
In Tutorial Module 4 the setup of 1D open channel will be introduced. This section contains links to some possible issue that may occur when progressing through the second tutorial module. If you experience an issue that is not detailed please detail the issue on the discussion page. This can be opened in a text editor, the error is generally at the end of the file, however you can search for "Error" if you can not see the error.
As such, It will automatically select a timestep to maintain simulation stability. This tutorial discusses this feature. TIP: If you forget any of the steps, the complete input files are provided as part of the download package zip file. The HPC solver uses adaptive timestepping to progress through the simulation.
The three stability criteria Control Numbers are:. These Control Numbers are kept below 1. The console window below highlights the control numbers and resulting simulation timestep value as for the above simulation.
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