Rawls rate question 1

[daddymem]

See Table D 13.1

http://www.mde.state.md.us/assets/document/sedimentstormwater/Appnd_D13.pdf

(sorry if it takes a while to load, didn't find a clean table elsewhere on the web) It is the Rawls, Brakensiek and Saxton, 1982 "Rawls Rates" table.

What confuses me is the inclusion of soil texture class AND hydrologic soil grouping. My dilemma is this, I have a location that is mapped as HSG D and it is a Loamy Sand confirmed by deep observation holes. For infiltration design would the texture class rule or the HSG? If is is the texture then why are HSGs included in the table?

TIA!

 

[sammyk]

Im going to assume that your HSG info is from a State Soils Survey. HSG is a generic source for types of soils in your area, sort of like the USGS 10' contours.

In Illinois the State Soils Maps seem to be pretty accurate but there are always discrepancies.If you have a geotech report, borings or test pits, use them as they are much more detailed than a general county/state soils map (especially for infiltration calcs).

 

[RWF7437]

http://www.forester.net/sw_0607_voodoo.html

 

[HorazII]

I agree with Sammy, use your test hole data to determine the Soil Group. In MA there is a specific documentation procedure to follow when actual soil conditions very from the Maps that allows you to use your field data.