Assignment 1: QGIS

Assignment 1: QGIS#

In this assignment you will perform a simplified flood-risk analysis for a study area in Slovenia. You will use the QGIS Model Builder to implement the analysis in an automatised way and use git to track your work progress.

This assignment should be done and submitted in pairs of 2 students. You may choose with whom to work with until October 18th. Afterwards groups will be assigned. Add yourself to groups in groups for assignment 1 by clicking the “edit” symbol on the top right.

The data for this analysis is located in the folder ./data in your repository:

  • Copernicus_DSM_10_N46_00_E014_00_DEM.tif: Digital elevation model (DEM)

  • study_area_prevalje.geojson: Area of interest (AOI)

  • observed_event.geojson: Flooded areas in the flood of 2023

Submission:#

Submission deadline: Friday, Nov 1st 2023 on GitLab

Deliverables: The final folder/file structure of your repository should look like this. The map and workflow can also be png oder pdf files.

|__ fossgis_assignment_01
  	|___ documentation
		|__ 01_methodology.md
		|__ 02_fossgis_tools.md
		|__ 03_model_builder_resources.md
		|__ 04_discussion.md
  	|___ models  
		|__ twi.model3
		|__ batch_twi_thresholds.json
  	|___ figures
		|__ map_flood.jpg
		|__ map_twi.jpg
		|__ workflow.jpg

1. Learn how to use the command line#

Watch the following tutorial videos on how to use the command line and try to perform the same tasks on your computer.

Windows#

Mac / Linux#

2. Download the course material using git#

  1. Go to https://courses.gistools.geog.uni-heidelberg.de/fossgis/fossgis_assignment_01 and login using your University ID.

  2. Fork the repository containing the material for the assignment by clicking the fork button on the top right.

  3. Open the command line on your computer. Move to the folder where you want to store the repository. Clone your forked repository to your computer using the following command. Important: Replace the user name test123 in the URL with your Uni ID. Watch this video on how to clone a repository

    $ git clone https://courses.gistools.geog.uni-heidelberg.de/test123/fossgis_assignment_01

3. Flood Risk Analysis in QGIS#

3.1 Preparation#

For the flood risk analysis we are using a simplified version of the methodology proposed by Pourali et al (2016). Before implementing the model in QGIS, answer the questions in the files ./documentation/01_methodology.md and ./documentation/02_fossgis_tools.md. It is sufficient to read only the parts of the paper that are relevant for answering the questions.

Track your changes using git. First, watch the video on how to create a commit. Below you find the commands to create a commit for the file ./documentation/01_methodology.md. Do the same for the file ./documentation/02_fossgis_tools.md.

  1. Change into the directory of the repository: cd ./fossgis_assignment_01

  2. Select a file to be included in the next commit: git add documentation/01_methodology.md

  3. Create the commit with a short description: git commit -m "added answer for question 1"

  4. Push your commits to GitLab: git push origin main

3.2 Implement the QGIS Model#

Implement the model using the QGIS Model Builder according to the requirements described below. If you need help, find useful resources online to learn about the QGIS Model Builder and add them to the file documentation/03_model_builder_resources.md. Name at least 3.

Input parameters of the model

  • Digital Elevation Model (DEM) as raster file

  • Area of Interest (AOI) as vector file

  • Coordinate Reference system

Processing steps

The model should perform the following processing steps. Note that some steps might involve using several processing algorithms.

  1. Clip the DEM to the area of interest.

  2. Reproject the DEM to a coordinate reference system suitable to calculate the TWI.

  3. Calculate the TWI.

  4. Create a raster layer marking flooded areas (TWI >= 5) with value 1 and non-flooded areas (TWI < 5) with value 0. This layer will be called a flood mask from now on.

Track your changes using git: Export your QGIS model and copy it to your repository folder as ./models/twi.model3. Create a commit containing the new file and push it to GitLab.

  1. Since we are not sure if TWI=5 is the best threshold to map flooded areas, we want to run the model several times with different values. To do this, add a number input parameter to the model called twi_threshold. Adjust the model so that this parameter value is used in the creation of the flood mask.

Track your changes using git: Export your QGIS model and copy it to your repository folder as ./models/twi.model3. Create a commit containing the new file and push it to GitLab.

  1. Run the model three times in batch mode with the different twi_threshold values: 5, 10 and 15.

Track your changes using git: Save the batch processing configuration to file and copy it to your repository folder as ./models/batch_twi_thresholds.json. Create a commit containing the new file and push it to GitLab.

3.3 Creating figures#

3.3.1 Create a map in QGIS showing the calculated TWI and the study area. Do not forget to style your map properly e.g. adding a scale bar, legend, title, north arrow, etc. Export the map as an image and store it in your repository as ./figures/map_twi.png.

Track your changes: Create a commit containing the new file and push it to GitLab.

3.3.2 Create a map in QGIS showing the flooded area mapped using the TWI threshold you find most suitable. You can use the file observed_event.geojson, which shows the areas that were flooded during the flood in August 2023, as reference. Do not forget to style your map properly e.g. adding a scale bar, legend, title, north arrow, etc. Export the map as an image and store it in your repository as ./figures/map_flood.png.

Track your changes: Create a commit containing the new file and push it to GitLab.

3.3.3 Document your model in QGIS by giving the processing steps meaningful names and adding group boxes, so that the workflow is easy to understand. Export the workflow as an image and store it in your repository as ./figures/workflow.png.

Track your changes: Create a commit containing the new file and push it to GitLab.

4. Evaluate the results and methodology#

Finally, answer the question in the file ./documentation/04_discussion.md.

References#

Pourali, S. H., Arrowsmith, C., Chrisman, N., Matkan, A. A., & Mitchell, D. (2016). Topography wetness index application in flood-risk-based land use planning. Applied Spatial Analysis and Policy, 9(1), 39-54.

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