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PAWC calculation, from texture data


I am trying to create a raster containing the PAWC fraction (0 to 1) input for the Annual Water Yield model, using the texture triangle of the SPAW model to calculate soil water characteristics, because the InVEST manual mentions it can be used in this case (' has software to help you estimate your PAWC when you have soil texture data').

However, this tool uses texture class, but also uses the organic matter content (%Wt), salinity (dS/m), gravel content (%Wt) and compaction as inputs (see screenshot attached).

I have a shapefile with the soil serie name for each polygon, referring to a manual with the soil physical characteristics (organic matter content, texture etc) for that soil serie, but for each soil horizon, so I don't have information of one texture class or one average number of organic matter content for the whole soil profile. 
In theory, I could take the average values over the depths of the soil profile and use these as inputs for the texture triangle to obtain PAWC, and then create a new shapefile with the PAWC values, but this would be a lot of work, given the amount of soil series in the study area.

Therefore, I'm wondering if this is the suggested method when you refer to this texture triangle tool in the manual, or, if there is a way to use it better/easily. 

Would it be possible to explain this, and give some possible solutions to handle my problem efficiently?

And a second question, since I am working on a Mac I was not able to use the Harmonized Soil Base data, which could have been an alternative. Is there a Mac version for it?

Are there more existing databases/tools to calculate the SPAW in a more efficient and maybe spatially explicit way than this texture triangle?

It would mean a lot if you can help me with these questions.

Thank you in advance.

Looking forward to the answers.

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