GRASS-HRU

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thumb|rechts|GRASS-HRU The complete process chain for the HRU derivation was implemented according to a service-oriented application in GRASS-GIS. The execution enironment is strictly separated from the operating environment by using a preconfigured, virtual machine which is in charge of data preparation and the calculation of HRUs in GRASS-GIS. A plug-in developed for QGIS creates an intuitive, wizard-driven and transparent environment for the execution of the process chain.

Contents

Download and Installation of GRASS-HRU

Downloading the hard disk image (Virtual Appliance) and QGIS-Plugin

The following files should be downloaded from http://www.geoinf.uni-jena.de:

  • grass-hru.mf
  • grass-hru.ovf
  • grass-hrus.vmdk

Together they create a so-called Virtual Appliance which will be required in the following section. In addition, the QGIS plug-in for HRU derivation should be downloaded from the same website:

  • hruwps.zip

Installing the VirtualBox

thumb|links|Installation von VirtualBox The derivation of HRUS with GRASS-GIS, which will be explained below, requires a virtualization software which hosts a linux system and all software and scripts needed. VirtualBox should be used - the current version 3.2.10 can be downloaded at http://www.virtualbox.org/wiki/Downloads. The wizard leads you through the steps of the installation process. It should be noted that:

  • a temporary deactivation of the network connection is necessary and therefore not unusual
  • all necessary drivers should be installed

After a successful installation VirtualBox can be launched and the import of a preconfigured hard disk image can start:

  1. Datei -> Appliance importieren
  2. Load the Appliance under Auswählen (see above) (file grass-hru.ovf)
    Bild:Import_app.jpg

  3. Apply the imported configuration of the Appliance and end the import process with Abschließen
    Bild:Import_app_2.jpg

  4. The appliance is being imported...
    Bild:Import_app_3.jpg

  5. ...and will be available through an entry in the VirtualBox main window (GRASS-HRU 1.0)
    Bild:Import_app_4.jpg

Installing QuantumGIS

thumb|links|Installation von QunatumGISThe current version of QuantumGIS is available at http://www.qgis.org/wiki/Download. The Standalone Installer is recommended - the download address for version 1.6 is http://qgis.org/downloads/QGIS-OSGeo4W-1.6.0-14615-Setup.exe. Please note: For the HRU derivation the GRASS plug-in for QuantumGIS is not required but it is included in the installer version 1.6. As an alternative, the installer version 1.4 of QuantumGIS can be used, which does not install a GRASS plug-in and therefore reduces the filesize. (http://qgis.org/downloads/QGIS-1.4.0-1-No-GrassSetup.exe)

Installing the Plug-in

To install the actual plug-in for HRU derivation in QuantumGIS the following steps have to be followed:

  1. Unzip the zip archive hruwps.zip, which has been dowloaded (see above), into the plug-in file of QuantumGIS. According to the QuantumGIS version the folder is called
    • ../QuantumGIS/python/plugins or
    • ../QuantumGIS/apps/qgis/python/plugins
  2. start QuantumGIS
  3. Plugins -> Plugins verwalten
    Bild:Qgis_plugin_2.jpg

  4. Search for HRU WPS-Client in the QGIS Plugin Manager, activate it and confirm with Ok
    Bild:Qgis_plugin.jpg

  5. The tool for HRU derivation can be started by using a separate button in the menu bar
    Bild:Qgis_plugin_3.jpg

Preparation

Before starting the HRU derivation, the following steps have to be completed:

  1. Run the newly created Virtual Appliance with the name "GRASS-HRU 1.0" by double-clicking on the corresponding entry on the VirtualBox window (or the button "Starten"). The following boot process in a separate window has to be carried out completely and can be minimized when the login prompt appears (donot close!). The virtual machine is working in the background during the whole HRU derivation process.
    Bild:Start_app_1.jpg
    Please note: By entering http://localhost in the address bar of the internet browser you can check if the virtual machine has been successfully started and if a connection with the machine is possible. A website containing the words "It works!" should appear.
  2. Click on Extras -> Netzlaufwerk verbinden in the Windows explorer and enter it as file http://localhost/in. Additionally, you can choose a free hard disk letter, e.g. Z:
    Bild:Start_app_2.jpg

    All input data should now be stored in this folder. The existing subfolder /gehlberg contains example data for input and result layers. New subfolders for the required input data can be created in the new network folder.
  3. Now the plug-in can be started from QuantumGIS. In order to do so, start QuantumGIS and click on the GRASS-HRU-Icon (see above) - the plug-in for HRU derivation opens. By clicking on the magnifying glass to the right of the address bar a message on successful connection should appear.
    Bild:Grass_hru_1.jpg

Details on the HRU derivation Using the Wizard

Step 0: Setup

  • Selection of the digital terrain model (DGM) in GeoTiff format and a shapefile format, each by using the button Datei next to the input field.
  • Selection of additional data layers (land use, soil, geology) by clicking on the button Hinzufügen to the right hand side of the Data Layer chart.
  • Opening a bounding box (first left mouse click: top left-hand corner, second left mouse click: bottom right-hand corner, right mouse click: delete bounding box). The resulting bounding box should comprise the complete catchment area to be analysed.

Bild:Grass_hru_2.jpg

Step 1: Preparation

  • It is possible to delete local sinks from the DGM. In case the current DGM has not been filled yet, default filling should be selected from the methodology list.
  • For the calculation of slope and slope oreintation no further input is neccessary.

Bild:Grass_hru_3.jpg

Step 2: Reclass

  • According to the different indices (DEM, Slope und Aspect) the corresponding map is classified.
  • The standard areas and values can be applied or modified. In case of a modification values cannot be below or above the corresponding minima and maxima.
  • If a data set should not be used for HRU derivation, it can be deselected (Checkbox not required).

Bild:Grass_hru_4.jpg

Step 3: Waterflow

  • For the derivation of the water supply network, flow accumulation and flow direction and for partial catchment areas a threshold value Minimum Size Of Basins is required.
  • This parameter determines, for example, the degree of detail of the water network or the number of partial catchment areas. The threshold value determines the smalles, derivable partial catchment area and is indicated in cells (number of pixels).
  • Example: A value of 1500 (and an assumed solution of 25m) results in a designation of partial catchment areas bigger than (1500*25*25)/1000000 = 0.9375km² ~ 1km².

Bild:Grass_hru_5.jpg

Step 4: Outlet Watersheds

  • The following steps are neccessary for the calculation of a map showing partial watersheds derived from their water levels:
    1. Pan the water level and supply map up in the key, so both data sets are visible.
    2. Check with the zoom tool wether the singular water levels lie exactly on the derived water supply network. If not, modify the level layer until all levels in the watershed lie on the water sections. To do so, please proceed as follows:
      1. Select the level layer on the key and activate the vector editing mode of QuantumGIS 30px
      2. Take the tool for panning vector points 30px and relocate the corresponging watersheds
      3. Finally, cancel the edit mode by clicking on 30px again and agree to save changes
    3. If all water levels in the catchment area have the correct position in the water network, those levels relevant to the calculation have to be selected - use the marker tool 30px.
  • Choose the shapefile attribute on the selection list Name of corresponding attribute (ID) which represents a unique parameter for the level (integer and > 0, e.g. level ID).

Bild:Grass_hru_6.jpg

Schritt 5: Overlay

  • Bei der Verschneidung aller Datenlayer (bestimmte Layer können durch Abwählen auch unberücksichtigt bleiben) entstehen Kleinstflächen, welche als HRUs ungeeignet sind und deswegen eliminiert werden sollten.
  • Zu diesem Zweck wird ein Schwellenwert definiert (Size of smallest area to remove), welcher die Minimumgröße einer HRU (in Zellen) festlegt.
  • Beispiel: Ein Wert von 8 (und eine angenommene Auflösung von 25m) führt zur Ausweisung von HRUs, welche größer als (8*25*25) = 5000m² =0.5ha sind.

Bild:Grass_hru_7.jpg

Schritt 6: Topology

  • Für die Bestimmung der topologischen Verknüpfung von HRUs (und Gewässersegmenten) ist keine gesonderte Parametereingabe erforderlich.
  • Das Modul berechnet
    • die N:1 Topologie (HRUs können in nur eine benachbarte HRU/einen Gewässerabschnitt entwässern)
    • die N:M Topologie (HRUs können in mehrere benachbarte HRUs/Gewässerabschnitte entwässern)
    • die Gewässertopologie (topologische Verknüpfung aller Gewässersegmente)
  • Die Option Enable discrete reaches ist eine Erweiterung des Verfahrens zur Topologie-Ableitung und momentan in der Entwicklung noch nicht abgeschlossen.

Bild:Grass_hru_8.jpg

Schritt 7: Statistics

  • Die bis hierher im Rasterformat vorliegende HRU-Karte (GeoTiff) wird in diesem Schritt in ein Shapefile konvertiert, wobei ausgewählt werden kann, welche zusätzlichen Eigenschaften einer einzelnen HRU in die Attributtabelle übernommen bzw. berechnet werden sollen.

Bild:Grass_hru_9.jpg

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