FM Tute M01 MI 1D2D Links
- Import in an empty 2d_bc_empty.TAB layer from within the FMT_tutorial\FMT_M01\TUFLOW\model\mi\empty folder.
- Save the layer as 2d_bc_FMT_M01_HX_001.TAB in the FMT_tutorial\FMT_M01\TUFLOW\model\mi folder.
- Open the 1D_2D_HX_Links.TAB GIS layer from Module_Data\Module_01\mi folder. Select all objects from within this layer, copy and paste into 2d_bc_FMT_M01_HX_001.TAB.
- Interrogate one of the lines running along the banks of the watercourse. These lines are the 1D/2D boundary links and have been assigned a type ‘HX’.
- Interrogate one of the lines connecting the x1D node to the HX line. These are the connection or ‘CN’ lines that read the water level from Flood Modeller and transfers this to the HX line. In the figure below, the water level is calculated in Flood Modeller at the nodes FC01.16, FC01.15 and FC01.14. These water levels are linearly interpolated along the lengths of the HX line on each of the left and right banks of the watercourse. When the water level exceeds the ZC elevation of the boundary cell, water is able to flow out onto the TUFLOW 2D floodplain.
- The CN and HX lines between nodes FC02.06 and FC02.01d along the tributary have not been digitised. Digitise these lines to connect the nodes to the 2D domain.
To digitise the CN lines, make the 2d_bc_FMT_M01_HX_001.TAB layer editable. For each node in the 1d_x1d_FMT_M01_nodes_001.TAB layer, draw a line in your GIS pack from the node to the HX line. The line must snap to both the node and the HX line. Draw two lines for each node, one to the left bank and one to the right bank. In the 'Type' attribute of each line, type 'CN'.
The figure below shows how the nodes are connected at the confluence. Note that all Flood Modeller nodes at the junction are present within the 1d_x1D_nodes layer, and are connected to the 2D domain. The HX lines are broken around the junction. - Once all the CN and HX lines have been digitised along the tributary, save the file.
Introduction
In this section we will apply a water level boundary to the 2D cells along the 1D/2D interface. In the 2D boundary condition (2d_bc) GIS layer, we define the location at which this link occurs. The 2D water level applied at the 2D boundary cells is calculated in the 1D Flood Modeller component. The terminology used in TUFLOW is a "HX" type boundary on the 2D cells, with the H indicating that a Head (water level) boundary is used and the X indicating the value is coming from an eXternal model (in this case Flood Modeller). 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 Flood Modeller model to preserve volume. We must connect the HX lines to the 1D Flood Modeller model. This is done using CN type lines in the 2d_bc layer, where a CN line is connected to the HX line, the water level from the 1D Flood Modeller nodes is transferred to the HX line. In between 1D nodes, a linear interpolation of water level is applied.
Method
Note that where there are junctions within the Flood Modeller 1D model (i.e. at structures), both the upstream and downstream nodes are connected to TUFLOW. Refer to the below figure, the Junction nodes are highlighted in red and the upstream and downstream nodes are highlighted in green.
The HX lines must be broken between the nodes. This is a requirement of a linked Flood Modeller – TUFLOW model. In the figure below, the HX lines are broken between FC01.35 and FC01.34 as a culvert is located between these nodes.
900px
Key Tip!
The digitised direction of the HX and CN lines is not important. The CN lines however should be digitised approximately perpendicular to the direction of flow. Two CN lines are digitised for each node and connected to the HX boundary lines along the left and right banks. The HX boundary lines should be digitised along the top of each bank such that the width between the lines approximately correlates to the width of the 1D channel.
Please return to the Flood Modeller Tutorial Model.