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Dual Hydrologic Soil Groups

Dual Hydrologic Soil Groups

Dual Hydrologic Soil Groups

How should I run a dual hydrologic soil group (A/D) in TR-55? It appears the soil group is defined A/D due to the shallow water depth, however, still has drainage characteristics of an A soil. Should I run it as all A soil or 50% A / 50% D?

RE: Dual Hydrologic Soil Groups

You may want to check with the reviewing regulator as they may have locally specific guidance.

Dual classification on HSG is typically Drained vs. Undrained.
  • If one has the time/money and/or it is a critical determination, one could perform site specific soil investigation to determine depth to groundwater to get actual mapping of the soil's drained/undrained condition.
I work in a coastal plain area. Ditching was installed on most farmland to drain the soils. Today, most areas that are still wooded were usually too wet or poor soils to bother farming.
  • So, one assumption that is accepted is: fields in A/D would be considered A and woods would be considered D.
  • In the past, I have mapped buffers from the ditches as being drained (A) and the rest undrained (D).

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