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Tute M06 QGIS 2D lfsch Archive: Difference between revisions

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Created page with "In the following steps we will be adjusting the elevations of the road crest as well as using a 2D zsh layer to lower the zpt elevations at the location of the 2D bridge.<br>..."
 
 
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===Lower the 2D Elevations Through the Bridge Opening===
<ol><li>Copy the '''2d_zsh_M06_NorthRd_001_R''' from '''Module_Data\Module_06\M2D_Bridge''' folder into the '''TUFLOW\model\gis''' folder. We will use this layer to remove the road embankment at the 2D Bridge location.</li>
<li>Open the newly saved layer '''2d_zsh_M06_NorthRd_001_R''' in QGIS. Observe the single polygon contained in this shapefile. The polygon intersects the model zpts where we want to modify the elevations and remove the road embankment. We will remove the embankment by creating a GIS layer of point features that instruct TUFLOW to interpolate zpt elevations within the two shapes using the zpt elevations either side of the embankment. Additionally, the GIS layer will be designed such that TUFLOW does not use the zpt elevations intersecting the road embankment. Refer to Sectionthe 4<u>[https://docs.4tuflow.9 and Table 4.8 of the 2010com/classic-hpc/manual/latest/ TUFLOW manualManual]</u> for more information on this procedure.</li>
<li>From the '''model\gis\empty\''' folder, open the '''2d_zsh_empty_P''' shapefile and save a copy called '''2d_zsh_M06_NorthRd_001_P''' into the '''model\gis\''' folder. Add this shapefile to QGIS, and close the '''2d_zsh_empty_P''' shapefile. Right-click, and Toggle Editing on '''2d_zsh_M06_NorthRd_001_P'''.</li>
<li>Enable snapping to the layer '''2d_zsh_M06_NorthRd_001_R''' by selecting ''Settings >>> Snapping Options...''. Select the check-box next to the '''2d_zsh_M06_NorthRd_001_R''' item. Set the tolerance to 5 map units (5 metres) and select apply. Create four points snapped to each of the polygon nodes that are circled in red in the second image below.</li><br>
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Save your edits. The attributes are described fullycompletely in Tablethe 4<u>[https://docs.21 of the 2010tuflow.com/classic-hpc/manual/latest/ TUFLOW manualManual]</u>. Note that L1, L2, and L3 refer to varying layers, as described in Section 4.7.2.3. We are setting:
* Enter an "Invert" value of 99999 to leave the Zpt levels unchanged (iei.e. use the Zpt elevations modified by the 2d_zsh layer above).
* Percentage blockage below the obvert to account for any blockages perpendicular to the direction of flow (in this case 6% to account for the average blockage due to the bridge piers).
* A Form Loss Coefficient (FLC) below the obvert (in this case to account for sub-grid scale losses around piers). Note that the treatment of the FLC is different depending on the object used to define the flow constriction, i.e. a line or a polygon. The reason for this is to permit the flow constriction to be independent of the model cell size. See Tablethe 4<u>[https://docs.19 in thetuflow.com/classic-hpc/manual/latest/ 2010TUFLOW Manual]</u> for more information. In this case, a polygon has been used and the FLC specified is the form loss ''per metre length'' in the predominant direction of flow. FLC values are dependent not on the flow width, but on the length of travel in the direction of flow. Our intention for this study, is to apply a total FLC of 0.3 below the obvert of the bridge. The value entered is therefore 0.3 / 15m which gives a value of 0.02. Refer to latter sections of this tutorial for guidance on how to check the applied FLC.
 
* Blockage from the obvert level to the top of level 2 (in this case 100% to account for the bridge deck).
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</li>[[File:M06_QGIS_2d_Lfcsh_P.png|1000px]]
 
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Add the following attributes to the new points:
{| align="center" class="wikitable" width="25%"
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| L3_Depth || 1 || 1
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</li> '''''Tip:''''' It is helpful to make the nodes along the polygon perimeter visible when snapping nodes along its boundary. Right click on '''2d_lfcsh_M06_bridge_001_R''' in the layers section and select properties. In the ''Style'' tab, select the Add Symbol layer tool [[File:Add Symbol.PNG]]. This adds a second symbol layer for the same file. For the first layer set the following options:
 
It is helpful to make the nodes along the polygon perimeter visible when snapping nodes along its boundary. Right click on '''2d_lfcsh_M06_bridge_001_R''' in the layers section and select properties. In the ''Style'' tab, select the Add Symbol layer tool [[File:Add Symbol.PNG]]. This adds a second symbol layer for the same file. For the first layer set the following options:
* Set the ''Symbol Layer Type'' to '''Outline: Marker Line'''
* Set the ''Marker placement'' to '''On Every Vertex'''
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