Urban Flood Risk Mitigation model - converting dual soil-groups (e.g., A/D) to 1-4

Hi there!

This post is related to Soil Hydrological Group data requirement for the Urban Flood Risk Mitigation Model. Does anyone have any suggested methods for how to convert dual hydrologic soil group (HSG) values (i.e., A/D, B/D, C/D and D/D) to A-D (1-4) values?


Hi @traceymangin -

I use this advice when creating an HSG layer for the Seasonal Water Yield model, which is a combination of information from FutureWater documentation (whose HSG data I often use), and a NatCap hydrologist:

FutureWater: “If these soils can be drained, a less restrictive group should be used” (i.e. A and B for A/D and B/D, respectively). Hydrologist: “Therefore, unless there’s artificial drainage that we are aware of, I’d default to D.”

I’m not sure if/how that advice would be different in an urban context, but it sounds applicable.

~ Stacie

Awesome, thank you so much! That is what I was thinking too.

I have another question about the Urban Flood Risk Mitigation model – the instructions say to include a watershed layer to delineate the area of study. I’m interested in producing the outputs for two development scenarios (for comparison), which are really small relative to the its watershed. Is there an issue with using the site boundary as the “area of study” delineation, instead of the whole watershed? I’m not planning on running any of the optional components of the model.


Hi mam. I am also facing the same issue. But I don’t know how to change the pixel value from 3 to 14 to 1 to 4. Please explain it

Thanks and regards.

Hi @DGowtham -

There are several ways that you can change pixel values in a GIS, depending on whether you need to change all instances of a value to some other value (like change all pixels with value 14 to value 1), or change particular pixels from one value to another. In this case I’m guessing that you need to do the first thing, so the Reclassify tool is probably the easiest.

~ Stacie

Thank you so much mam. It worked. Thanks a lot