Generate estimated flood level polygons

This process generates polygons representing a particular elevation above sea level (AHD) to estimate the impacts of floods reaching that level. This is a simplistic model of water levels and doesn't take into account any detailed hydrologic behaviour.

(This is a rough first-pass at the process - it can definitely be streamlined!)

1. Download digital elevation model(s) for the area of interest

Head to https://portal.spatial.nsw.gov.au/portal/apps/webappviewer/index.html?id=437c0697e6524d8ebf10ad0d915bc219 and download the DEM(s) covering the area of interest.

You may need to use the Define Projection tool in ArcGIS Pro.

2. Merge DEMs

If you downloaded multiple DEMs, use the script processDems.py to merge them into a single raster.

starting_dir_name = r'C:\Users\slead\Downloads\working' # directory containing the zip file
out_gdb_name = "working.gdb"  # output geodatabase to hold the new mosaicked raster
raster_name = "Forbes"         # the name of the new mosaicked raster

Place the zip files in starting_dir_name, set the raster_name to the desired output name and run the script.

(Delete the zip files once processing is complete).

3. Clip the raster to the area of interest

To speed up processing, reduce the size of the raster to cover only the required area, using Geoprocessing Tools or -> Data -> Export Raster with a clipping extent.

4. Estimate the min and max flood levels

Add the raster to ArcGIS Pro and use the Live River Level Height layer (https://geohub.transport.nsw.gov.au/portal/home/item.html?id=b21e407c9bf745319b99fec37ff20fcd) to estimate the min and max levels required for the flood model.

5. Update the config file

Set the appropriate values in the config.yml file:

output_dir: C:\Users\slead\Flood\Flood_20220919.gdb # output geodatabase
dem: ForbesEugowra # input DEM
prefix: ForbesEugowra    # prefix to apply to the output polygons
min_elevation: 246 # starting elevation
max_elevation: 252 # end elevation
step: 0.2  # interval between contours, in metres

5. Generate the flood polygons

Run the script createFloodPolygons.py which will generate one featureclass for each elevation contour.

6. Create layers in ArcGIS Pro

Run the script createLayers.py to add the layers to ArcGIS Pro. Manually create a group layer from these individual layers, and publish to GeoHub. Share with the appropriate groups.

slead / Process_DEMs