QTalsim Documentation Version 0.1

QTalsim is a QGIS plugin designed to create hydrological response units (HRUs) suitable for Talsim. The plugin processes three layer, including a sub-basin layer, soil layer and land use layer. It clips the layers in accordance with the sub-basin layer’s boundaries. The plugin then intersects those three layers and creates HRUs. Additionally, the plugin offers functionality to remove duplicate geometries, overlapping features and unwanted gaps.

Input:

• Sub-basin layer
• Soil layer
• Land use layer
• CSV-file containing talsim land use types and parameters

Output:

• Geopackage containing HRU, land use, soil texture and soil type layers
• Layers are also added to the current QGIS project

Getting Started

Install Plugin

If the plugin is not installed yet, you must do this by following these steps:

1. Navigate to the Menu Bar, select ‘Plugins’
2. Choose ‘Manage and Install Plugins’
3. In the search bar, type 'QTalsim'
4. Select the 'QTalsim' plugin from the search results
5. Click the ‘Install Plugin’ button
6. The plugin is now installed and can be used

Once the plugin is installed you can access it by going to the menu bar, selecting ‘Vector’ and then choosing ‘QTalsim’.

Requirements for input layers

All three input layers must be polygon layers and included in the current QGIS project.

1. Sub-basin layer

   This layer should contain the sub-basins as well as a field for Unique Identifiers and another one for slope.

2. Soil Layer

   This layer should contain all soil types within the study area, but it must only consist of one soil layer. It must contain a field specifying the names of the soil types.

3. Land Use Layer

   This layer should contain all land use areas within the study area, and it must contain a field specifying the names of the land use types.

• CSV-File with Talsim land use types + parameters

  In addition to the land use layer, a CSV-File containing the necessary Talsim land use types and their associated parameters is also required. The screenshot below shows one example of what the first lines of the CSV-file could look like:

  

  The following fields should be included in the CSV-file, the bold fields must be included:

  Id, Name, RootDepth, RootDepthMonthlyPatternId, PlantCoverage, PlantCoverageAnnualPatternId, LeafAreaIndex, LeafAreaIndexAnnualPatternId, RoughnessCoefficient, KcCoeffAnnualPatternId, KyYieldAnnualPatternId, BulkDensityChange, pTAW

  However, the plugin does not require every field to contain values.

Step by Step

1. Select Sub-basin Layer

   First, select the layer containing the sub-basins from the drop-down-menu that lists all polygon layers in your current QGIS project. Confirm your selection by clicking on the ‘Confirm Sub-basins’-Button. Upon clicking this button the Sub-basin layer is selected, and overlapping features and duplicates are removed. You can inspect the result in your QGIS project (layer 'Sub-basins').

   After selecting the sub-basin layer's fields containing 1) the unique identifier and 2) the slope values must be selected from the drop-down menu. These fields are utilized in the final EFL-layer and serve as input parameters to Talsim.

   
2. Select & Edit Soil Layer
   • Select Soil Layer

     Choose the soil layer from the drop-down menu and confirm your selection by clicking ‘Confirm Soil’. Upon doing so, all valid geometries of this layer are selected and clipped to match the boundaries of the Sub-basin layer. During this step duplicate geometries are removed from the layer and the soil mapping table is populated with the fields of the soil layer.

   • Soil Mapping

     This table contains Talsim soil parameters in the first column and all the field names of the soil layer in drop-down menus in the second column. In this step, users are required to map each Talsim parameter to its corresponding field in the soil layer. The table below shows the necessary type for these parameters. If the user-mapped field has a different datatype, the plugin, where possible, converts the field’s values to the parameter’s type. If ‘Parameter not available’ is selected, that parameter will be added with null values.

     To finalize the soil mapping, click ‘Confirm Soil Mapping’. This creates a new layer, containing all fields from the soil layer and all parameters from the soil mapping table, assigned with values from their corresponding fields. If there is a datatype mismatch between the soil layer’s field and the parameter, a warning is logged.

     Parameter	Type
     ID_Soil	int
     NameSoil	string
     Description	string
     BulkDensityClass	int
     Category	int
     WiltingPoint	float
     FieldCapacity	float
     TotalPoreVolume	float
     KfValue	float
     MaxInfiltration	float
     MaxCapillarySuction	float
     LayerThickness1	float

     
   • Optional Soil Editing Steps

     Before finalizing the soil layer, users have the option to perform some editing steps. Please refer to section Optional Editing Steps below for a detailed explanation of ‘Check for Overlapping Features’, ‘Delete Overlapping Features’, ‘Check for Gaps’ and ‘Fill Gaps’.

     In addition to the option of deleting all overlapping parts (using button 'Delete Overlapping Features'), you can also selectively remove specific overlapping soil features. This can be done via the table that populates when you click 'Check for Overlapping Features'. This table displays all overlapping soil features across two columns. For each pair of overlapping features, you can decide, which feature's geometry should stay unchanged, and which should have its overlapping part removed from its geometry. In the third column, you can select features to highlight them in the soil layer, allowing for easy viewing. After you have identified all the unwanted overlapping parts, simply press 'Delete overlapping part of selected Features' to remove the overlapping parts from the selected features.

     
   • Create Soil Layer

     This step dissolves the layer according to the Talsim parameters, removes the fields that are not required for Talsim and creates the soil layer used for the intersection.

3. Select and Edit Land use layer
   • Select Land use Layer

     First, select the land use layer from the drop-down menu and confirm your selection by clicking ‘Confirm Layer’. Upon doing so, all valid geometries of this layer are selected and clipped to align with the boundaries of the sub-basin layer. During this process, any duplicate geometries within the layer are also removed. After confirming the layer, you must then select the field containing the land use types and confirm this selection by clicking ‘Confirm Field’. The unique land use types identified here will be used in a subsequent step.

     
   • Upload Talsim Land use Names and Parameters

     The user must upload a CSV-file that includes the Talsim land use types and their associated parameter values. This can be done by by clicking ‘Select CSV-File’, which allows the user to choose the CSV-file. It is important to select the correct delimiter for the file. After uploading, users can check the parameters by reviewing the QTalsim-Log.

     
   • Land use Mapping

     When you click on ‘Start Landuse Mapping’, the land use mapping table will be populated with all unique land use types from the layer in the first column. In the second column, a dropdown-menu with all Talsim fields of the CSV-file will appear. Here, you must match each land use type from your data (in the first column) with the corresponding Talsim land use type (in the second column). For convenience, the second column is automatically prefilled with Talsim land use types that have the same name in the layer and the CSV-file. After completing the mapping, click ‘Confirm Landuse Mapping’ to create a new layer containing the input fields from your layer and the Talsim parameter values, as specified in the CSV-file.

     
   • Optional Editing Steps for Land use Layer

     After confirming the land use mapping you have the option to perform additional editing steps, such as deleting overlapping features and filling gaps. For more detailed information on these steps, please refer to section Optional Editing Steps.

     In addition to the option of deleting all overlapping parts (using button 'Delete Overlapping Features'), you can also selectively remove specific overlapping landuse features. This can be done via the table that populates when you click 'Check for Overlapping Features'. This table displays all overlapping landuse features across two columns. For each pair of overlapping features, you can decide, which feature's geometry should stay unchanged, and which should have its overlapping part removed from its geometry. In the third column, you can select features to highlight them in the landuse layer, allowing for easy viewing. After you have identified all the unwanted overlapping parts, simply press 'Delete overlapping part of selected Features' to remove the overlapping parts from the selected features.

     
   • Create Land use Layer

     Clicking ‘Create Land Use Layer’ dissolves the layer according to the Talsim parameters, removes any fields that are not required for Talsim and generates the land use layer that will be used for intersection.

     
4. Intersection of Layers

   This step results in the creation of the files: BOD, BOA, LNZ and EFL, which can be used as input files for Talsim. To generate the HRUs, the three layers (sub-basins, soil and land use) are intersected in a first step. The user can set a minimum size of the HRUs [m²] and a minimum percentage of HRUs relative to the sub-basin's area. HRUs that fall below the specified size or percentage share are deleted and filled using the ‘Eliminate’-tool. You can select the elimination-mode from the drop-down menu (find further information here).

   Gaps within the sub-basin layer are left unfilled, while all other gaps are appropriately filled. Any overlapping features within the resulted intersected layer are removed.

   

   The resulting layers are then automatically added to the current QGIS project.

5. Save Layers to Geopackage

In the final step, these layers can be saved to a geopackage. First, you have to click ‘Select Output-Folder’ and choose a suitable folder. Once the folder is selected, you can enter a desired name for the geopackage. By Clicking ‘Ok’ the layers are saved to the selected folder in a geopackage, named as specified by the user.

Optional Editing Steps

For both the soil layer and the land use layer, the user has the option to perform additional editing steps.

• Check for Overlapping Features

  This function checks for overlapping features within the layer. It identifies features that are either partially or completely overlapping. The feature-IDs of the overlapping features are logged to the QTalsim-Log. Additionally, a layer named ‘Layer with overlapping features’ is added to the QGIS project. You can then inspect the overlapping features by reviewing this layer’s attribute table by searching for the overlapping feature IDs.

  
• Delete Overlapping Features

  This function removes all overlapping parts of a layer. If two polygons overlap, the overlapping part is assigned to the smaller of the two polygons.

• Check for Gaps

  This function checks for gaps in the soil/land use layer. It identifies not only gaps within the layer itself but also gaps that occur along the boundary of the sub-basin layer. A separate layer, which includes all detected gaps from the soil or land use layer, is then added to the QGIS project. This allows the user to inspect and analyze these gaps more closely.

• Fill Gaps

  This function fills all detected gaps in the layer using the Eliminate-tool. You can specify the elimination-mode from a drop-down menu (find further information here). The result of this step is a layer free of gaps and matching the extent of the sub-basin layer.