Dual Hydrologic Soil Groups

Question

Dual Hydrologic Soil Groups

RedBauer (Civil/Environmental)

(OP)

26 Aug 16 11:57

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?

TerryScan (Civil/Environmental) · Answer 1 · 2016-08-26 12:43:50

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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