FM Tute M01 QGIS 1D2D Links: Difference between revisions
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=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 '''H'''
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. This is shown in the figure below.
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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. <br>
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[[File:FMT 1D-2D Linking QGIS.JPG|600px]]
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Note that where there are junctions within the Flood Modeller 1D model (i.e. at structures), both the nodes immediately upstream and downstream must be connected to TUFLOW. Refer to the below figure where the junctions are circled in
In the example below, the HX lines are broken between FC01.35 and FC01.34 as a culvert is located between these nodes.
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[[File:FM_junction.jpg|900px]]
[[File:FMT 1D-2D Broken HX Line.JPG|900px]]
<li>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.<br>
To digitise the CN lines, make the <b> 2d_bc_FMT_M01_HX_001_L.shp </b> layer editable and ensure snapping has been turned on. For each node in the <b>1d_x1d_FMT_M01_nodes_001_P.shp</b> layer, draw a line 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'. Assign the digitised CN lines an ‘f' attribute’ of ‘1’. This sets the weighting to be applied in distributing the water level from the 1D node to the 2D cell.<br>
<br>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. </li>
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[[File:FMT 1D-2D Linking Junction QGIS.JPG|900px]]
<li>Once all the CN and HX lines have been digitised along the tributary, save the file.</li>
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