Tutorial: Create a groundwater level map from borehole data and a DEM
| Site: | OpenCourseWare for GIS |
| Course: | GIS training for Hydrogeological Applications |
| Book: | Tutorial: Create a groundwater level map from borehole data and a DEM |
| Printed by: | Guest user |
| Date: | Monday, 13 January 2025, 11:07 AM |
Description
Table of contents
- 1. Introduction
- 2. Load a boreholes dataset from a GeoNode SDI
- 3. Export WFS data to GeoPackage
- 4. Select boreholes in a specific area
- 5. Calculate the borehole density
- 6. Download the SRTM 1-Arc Second DEM
- 7. Clip and reproject the DEM
- 8. Style the DEM
- 9. Sample DEM elevation at boreholes
- 10. Compare reported elevation with DEM values
- 11. Replace nodata values with DEM elevation
- 12. Calculate the groundwater level in the boreholes
- 13. Interpolate groundwater levels in boreholes to a raster
- 14. Derive groundwater contours
1. Introduction
After this tutorial you'll be able to:
- Load a borehole/wells dataset from an SDI into QGIS
- Calculate the density of the boreholes in a polygon
- Download the SRTM 1-Arc Second DEM
- Clip and reproject a DEM
- Style a DEM
- Sample elevation at the borehole location and compare it with the elevation attribute
- Make corrections and calculations in the attribute table
- Interpolate groundwater levels of the boreholes to a raster
- Create and visualise contour lines
2. Load a boreholes dataset from a GeoNode SDI
We'll start with loading a boreholes dataset from a GeoNode SDI to QGIS.
In this tutorial we'll use the Borehole Database in the Stampriet Transboundary Aquifer from the Orange-Senqu River Basin GIS Server, which is a GeoNode SDI.
1. Check the metadata of the Borehole Database in the Stampriet Transboundary Aquifer. Read the info tab and check the attributes that are in the layer.
2. Start QGIS with an empty project.
3. Click the Open Data Source Manager button 
in the toolbar.
4. Choose the GeoNode tab.
5. Click the New button to create a new service connection.
6. In the Create a New GeoNode Connection dialogue type ORASECOM for the Name and copy the URL http://gis.orasecom.org.
7. Click Test Connection.
If the test is successful you'll see this popup:
If the connection fails, check your internet connection and the URL.
8. Click OK to close the popup.
9. Click OK in the dialogue to close it and the new connection is added.
10. Click the Connect button.
If you'll get an error in a popup that you can ignore. Click OK to remove the error message.
Then you'll see the layers on the GeoNode listed.
We're going to use data from the Stampriet aquifer.
11. Type stampriet at filter.
12. Click stasboreholes WFS layer (indicated in the figure above).
We use a WFS Web service, because we want to access the data and not just a picture like with WMS data.
13. Click Add to add the layer to the map canvas.
14. Click Close to close the dialogue.
It will take a while to load from the internet.
Just wait until loading has completed. Then you'll see this:
In the next section we're going save this WFS layer to a GeoPackage to further use locally.
3. Export WFS data to GeoPackage
Our borehole dataset is still in the WFS format and in a Geographic Coordinate System (GCS) with coordinates in degrees latitude/longitude. For our purpose of interpolating elevation, we need to store the file locally and reproject it to UTM Zone 34S/WGS-84.
1. In the Layers panel click right on the geonode:stasboreholes layer.
2. Choose Export | Save features as...
3. In the Save Vector Layer as... dialogue choose GeoPackage as the Format. Click the 
button to browse to a folder on your harddisk where you want to store the GeoPackage (e.g. Z:\Stampriet). Name it Stampriet_Data.gpkg. Type for Layer name Boreholes.
4. Click the 
button to change the projection of the output layer.
5. In the Coordinate Reference System Selector dialogue type 32734 (that's the EPSG code) at Filter to search for the WGS 84 / UTM Zone 34S projection. Click on the projection name and click OK to return to the dialogue window.
6. Click OK to perform the export.
7. After the Stampriet_Data Boreholes layer has been added to the map canvas, remove the geonode:stasboreholes layer by clicking right on it and choose Remove layer.... Confirm with OK.
Now we have a local copy of the boreholes layer.
8. Change the OTF projection of the project: in the Layers panel click right on Stampriet_Data Boreholes and choose Set CRS | Set Project CRS from Layer
9. Save the project in the GeoPackage. Call it Strampriet.
In the next section we're going select the boreholes in a specific area.
4. Select boreholes in a specific area
For this tutorial we're only interested in the boreholes in the area around Stampriet.
An imaginary boundary polygon is provided in the tutorial data.
1. Add the Stampriet_boundary shapefile to the project.
2. In the Layers panel click right on Stampriet_boundary and choose Zoom to layer.
3. Style the boundary with a red outline.
Now we're going to clip the boreholes that fall within the boundary and save it to our GeoPackage.
4. From the main menu choose Vector | Clip...
5. In the Clip dialogue choose Stampriet_Data Boreholes as Input layer and Stampriet_boundary as Overlay layer. Save the Clipped result to the Stampriet_Data GeoPackage with the layer name boreholes_clipped.