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Example

Create the project folder if necessary (i.e. D:\Projects\sagehen) and create an hru_params sub-folder (i.e. D:\Projects\sagehen\hru_params).

Clone the repository

If you already have a local repository of the gsflow-arcpy-tools, pull the latest version from GitHub. If you don't already have a local repository, either clone the repository locally or download a zip file of the scripts from Github. For this example, the local copy will be cloned directly in the project folder (i.e. D:\Projects\sagehen\scripts and D:\Projects\sagehen\remaps)

Study Area

Create a "shapefiles" sub-folder (i.e. D:\Projects\sagehen\shapefiles). Place the study area shapefile in the shapefiles sub-folder (ie.e. D:\Projects\sagehen\shapefiles\watershed.shp). The study area is typically a single watershed (like a HUC8) or a collection of watersheds that will be modeled together. Check the projection of the study area shapefile and make sure it is in a projected coordinate system (like NAD83 UTM Zone 10N).

Input File

Copy the template input file (scripts\template_parameters.ini) to the hru_params folder and rename (i.e. D:\Projects\sagehen\hru_params\example_params.ini) Within the input file, all of the file and folder paths need to be set to the project folder. A simple find and replace of "D:\Projects\gsflow-arcpy-example" to your project folder (i.e. "D:\Projects\sagehen") should work, but doublecheck all of the paths. Eventually, all of the paths will be set as relative paths to the main project folder, but for now they must be absolute paths.

Fishnet / Model Grid

The following parameters must be explicitly set whether you are building a new fishnet/grid shapefile or reading in an existing one. If reading an existing grid, the paramters must match the grid properties exactly.

  • hru_cellsize - cellsize (units will depend on projection)
  • hru_ref_x: snap x coordinate (units will depend on projection, 0 is a good choice for a new grid)
  • hru_ref_x: snap y corodinate (units will depend on projection, 0 is a good choice for a new grid)
  • hru_projection: EPSG code (see spatialreference.org)
  • study_area_path: The full filepath of your study area shapefile
Running the Scripts

Currently, the scripts must be run from the windows command prompt so that the input file can be passed as an argument directly to the script. Eventually, the scipts will be modified so they can be executed by double clicking on the script in Explorer and the input file will be set through a dialog box.
First open the windows command prompt by pressing the "windows" key and "r" or clicking the "Start" button, "Accessories", and then "Command Prompt".

Within the command prompt, change to the target drive if necessary:

> D:

Navigate to the project folder:

> cd D:\Projects\sagehen

Run the fisnet_generator.py script if building a new fishnet. Note, this will overwrite an existing fishnet shapefile if one already exists at the path specified in the input file.

> python scripts\fishnet_generator.py -i hru_params\example_params.ini
Digitial Elevation Model (DEM)

If you don't already have a DEM raster of the study area, download the DEM tiles using the download_ned.py script. You must set the study area shapefile path using the "--extent" argument and the output folder using the "--output" argument. The script will project the shapefile to a geographic coordinate system and download all NED 1x1 degree tiles that intersect the study area.

> python tools\download_ned.py --extent shapefiles\watershed.shp --output dem\tiles

After downloading the tiles, they need to be merged together into a single image and then projected to the fishnet (or watershed) spatial reference. This could be done in ArcGIS or using the GDAL utilities (http://www.gdal.org/gdal_utilities.html) at the command line.

First, the gdal_merge tool can be used to merge the tiles into a single raster.

> gdal_merge.py -of HFA -co COMPRESSED=YES -o dem\ned_30m_merge.img  dem\tiles\imgn39w107_1.img  dem\tiles\imgn39w108_1.img  dem\tiles\imgn40w107_1.img  dem\tiles\imgn40w108_1.img

It is important that the elevation units match the linear unit of the coordinate system. If the fishnet is in a coordinate system with feet as the linear unit, scale the NED rasters by 0.3048 to convert meters to feet. This can be done using the gdal_calc utility

gdal_calc.py -A dem\ned_30m_merge.img --outfile=dem\ned_nad83_feet.img --calc="0.3048*A" --format HFA --co COMPRESSED=YES

Project the raster to the fishnet (or study area) spatial reference using the "gdalwarp" utility.

gdalwarp -r "bilinear" -tr 30 30 -s_srs "EPSG:4269" -t_srs "EPSG:26910" -overwrite -ot Float32 -srcnodata None -dstnodata -3.4028234663852886e+38 -of HFA -co COMPRESSED=YES dem\ned_30m_merge.img dem\ned_30m.img

The output cellsize may need to be adjusted using "-tr" argument for coordinate systems that are not in meters, otherwise 30 should work well for most applications. The output EPGS code (set with "-t_srs") needs to match the fishnet EPSG set in the input file. To subset the raster at this step, use the "-te xmin ymin xmax ymax" argument with coordinates in the projected coordinate system of the fishnet.