FM Tutorial M01 QGIS GPKG Banks

From Tuflow
Jump to navigation Jump to search

    Introduction

    In this section we will define the bank elevations of the watercourse. These are the elevations of the 1D/2D boundary cells that link the 1D Flood Modeller watercourse to the 2D TUFLOW floodplain.
    Note that it is these cell elevations that determine whether water spills from the 1D Flood Modeller domain into the 2D TUFLOW domain. The bank elevations of the Flood Modeller 1D cross-sections do not control the spill. If there is a levee or flood defence, 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.

    The bank elevations are commonly applied using a 2D_bc point layer. The bank (1D/2D boundary) elevations may also be defined using a 2d_zsh layer or other 3D breakline layer. The advantage of using a 2d_bc layer is it ensures the boundary cell elevations are raised and not that of adjacent cells. The 2d_bc point layer is used in conjunction with a 2d_bc line layer with the point layer defining the elevations and the line layer defining where the grid elevations are modified and where the interpolation between known point elevations occur.

    Method

  1. Import in an empty 2d_bc_empty_P.gpkg layer from within the FMT_tutorial\FMT_M01\TUFLOW\model\gis\empty folder.
  2. Save the layer as 2d_bc_FMT_M01_HX_001_P.gpkg in the FMT_tutorial\FMT_M01\TUFLOW\model\gis folder.
  3. Move the empty 2d_bc layer 2d_bc_FMT_M01_HX_001_P.gpkg into the project GeoPackage file M02_5m_002.gpkg in the Browser Panel. Load the empty layer 2d_bc_FMT_M01_HX_001_P into QGIS from M02_5m_002.gpkg.
  4. Open the 1D_2D_Points_P.shp GIS layer from Module_Data\Module_01\gis folder. Select all objects from within this layer, copy and paste into the 2d_bc_FMT_M01_HX_001_P layer.
  5. Interrogate one of the digitised points and inspect the attributes. The ‘type’ attribute is ‘ZP’ to denote that it is a z-point which will define the elevation on the banks. The ‘f’ attribute is the elevation of the bank link in mAOD.
  6. Now add the layer 2d_bc_FMT_M01_HX_001_L from the FMT_tutorial\FMT_M01\TUFLOW\model\gis folder created in the previous step. Note that all the 'ZP' points created in the layer 2d_bc_FMT_M01_HX_001_P are snapped to vertices of the layer 2d_bc_FMT_M01_HX_001_L. This is because these two layers work together to define the bank locations and crest elevations. The layer 2d_bc_FMT_M01_HX_001_L defines the location and the layer 2d_bc_FMT_HX_001_P defines the elevations.


  7. Save the file.

  8. Please return to the Flood Modeller Tutorial Model.