Question about routing generated by WRF-Hydro GIS Pre-processing tool

[Ebony]

Hello, I am a new WRF-Hydro user.
This is actually my first time working with any hydrologic model, so I still lack a general understanding of the system.

I successfully compiled Coupled WRF/WRF-Hydro and ran the testcase.
Now I would like to run the model for my own domain, and I realized that preprocessing is required.
Since I have no experience using GIS, I used the WRF-Hydro GIS Pre-processing tool(https://github.com/NCAR/wrf_hydro_gis_preprocessor).
However, unlike the testcase results, the channel data in my generated Fulldom_hires.nc file is not clean, and because my domain includes the ocean, channels are also created over the sea.

I would like to ask two questions:

1. Some channels appear as adjacent, parallel like “small branches.” Is there a way to generate cleaner channel networks?

2. Is there a way to prevent channels from being generated over the ocean?

Thank you for your help!

[Kevin Sampson]

Ebony,

Thank you for your questions. 

Channels will appear adjacent/parallel to each other when the slope of the DEM is very low between cells. There are several reasons this may occur. It is important to start with a clean, hydrologically pre-processed DEM that is close in resolution to your hydrologic routing resolution in WRF-Hydro. This is because channels will be better defined in the elevation values of the DEM. Reprojection and resampling to coarser resolution can cause some of the hydrologic pre-processing to be interrupted. Also, the fill depth setting ('z_limit' variable in the python script) can also contribute to the presence of flat areas in the resulting DEM. Pits will be filled in the input DEM up to the fill depth, and those filled areas will be very flat. Again, starting with a DEM that has been hydrologically pre-processed will minimize the need to fill the elevation layer in the hydrologic routing parameter file (fulldom_hires.nc). You can lower the fill depth from the default value (1000m) to avoid erroneously filling in endorheic basins. Be sure to read the documentation (here, and here), which applies to the ArcGIS version of the WRF-Hydro GIS Pre-processing tools, but will have valuable information that is applicable to the open-source GIS pre-processing tools as well.

To avoid channels being generated over the ocean areas, you can set the elevation data over oceans to NoData in your input high-resolution DEM.

Thanks,

Kevin