There is a pond which I am trying to create a 3D model of to view the depth. We have measured the depth every few meters along straight line transects all across the pond, and have GPS coordinates for each of these depths. I have all of the data in excel, and have tried using qgis to map the points, but using the .csv data I was only able to create a 2D map of the pond without the depths being entered. How do I add a z-value and create a 3D model of this pond? Coordinates are in degrees, depth is in meters.
If you are able to view your points in the QGIS canvas with the CSV file added, and if you right-click to view the Attribute Table you can see the depth values are stored in their own field/column, then you can Interpolate the points to create a surface, which is a rasterized elevation model. The one intermediate step is you'll need to right click your CSV layer in the Layers Panel and Save As an Esri Shapefile (or other spatial vector format).
If that's where you are, click Raster - Analysis - Grid(Interpolation). Input your saved shapefile (or other vector layer), set an output file and format, and select your options. It defaults to IDW (inverse distance weighting) for interpolation method, but you can experiment with others as need be. Just ensure that you check the "Z Field" box, and that you assign the appropriate field from the drop-down menu.
Your output DEM will still look like a 2D map when it is complete, but you can then import this (default GeoTIFF format file) into 3D spatial modeler applications, or run processes such as Hillshade to view the relief in your water body.