How to use elevation of raster file as top of model grid or to set up unstructured grid model

[AH-CSM]

Hello all,

I am trying to set up my model so that the elevation data within the raster file I am importing can be used as the top of the model grid. I am doing this because I am trying to set my bottom thicknesses from the top down in layering. The current model will not let me do it because the layer bottoms I want for my model are consistently above SOME of my raster data elevation. In the real world, this would be a pinched-off layer but I am not sure how to set this up in a structured or unstructured grid way to implement raster data for my model top. Any advice is greatly appreciated. Thanks!

[jlarsen-usgs]

Hi @AH-CSM;

If you have vertex information stored in your UnstructuredGrid object (modelgrid) you can use the flopy.utils.Raster class to resample the DEM raster to grid and effectively create an array of model top elevations. Ex.

from flopy.utils import Raster

rstr = Raster.load("my_dem_raster.tif")
top_elevs = rstr.resample_to_grid(
    modelgrid,
    band=rstr.bands[0],
    method="min"  # methods supported are "min", "max", "median", "mean", "nearest", "linear", "cubic"
)
botm_elev = np.zeros((modelgrid.nnodes))
botm_elev = top_elevs - layer_thickness 

# then update the top and botm elevations in your flopy DISU object using the new values
# Note: if you're working with MF-USG and are using the layered option, you may need to reshape your botm_elevations to be consistent 
# with the number of cells per layer

There's a notebook showing the Raster resampling process, here: raster_intersection.

Some good tutorials can also be found in the python for hydrology repository here: python-for-hydrology, flopy

[AH-CSM]

I have been trying to use the notebook you provided above as an example for a while now (there is very little literature on how to use a lot of flopy in unique scenarios) to build my own but some of the lines of code do not run properly and I have to find ways around them. For example, my Python IDE says

"Exception: Cannot find triangle binary executable"

when I try to run the unstructured grid with a triangle module call like your above example shows. I have tried looking in my platform to update flopy or other modules in anaconda but nothing for triangles or utils comes up in the library directory.

[jlarsen-usgs]

@AH-CSM

Triangle is a external modflow related executable program. A full stack of modflow executables can be downloaded from here: https://github.com/MODFLOW-USGS/executables.

Alternatively, once flopy is installed you can run get-modflow :flopy in an anaconda prompt and it will download all of the necessary modflow executables and place them within the anaconda/python path.