Pond Boss Forums POND CONSTRUCTION Soil questions A word about using NRCS Soil Surveys

Hi All,
I see several posts regarding looking at NRCS soil surveys to help determine a site's suitability for a pond.

A few tips:

There is no substitute for digging holes. The scale at which the soil survey maps are presented are generally so large that only map units of 4-6 acres at the smallest are shown. That leaves room for LOTS of other soils, better or worse for ponds, to be included in the map unit delineation. It's a good general guide but don't bank on it either way.

Map units with LOTS of wet spot symbols are a good thing. This indicates that the unit is wetter or more clayey than it is supposed to be but the soil surveyors didn't have time or enough acreage to introduce an established series into the legend or set up a new series.

Often, a soil surveyor might map many hundreds of acres in a day with only a few soil borings. Many units are mapped based on what is "expected to be or what should be there".

Sand or gravel spot symbols (unless they use a lot of them) generally indicate a surface deposit and may not be indicative of subsurface conditions.

Poorly drained sandy soils can provide just as good or better EXCAVATED pond sites than clayey soils. You are just digging into the water table....there is no need to "seal" anything.

The lower portions of a ravine or waterway (the part we really are concerned about) are often way different than what the map indicates. Soils are mapped according to slopes and what the majority of the unit is expected to contain. Often the pond footprint is a very small part of the mapped unit. Look at the mapped soils at lower elevations to get an idea of what you might expect in the lower part of a ravine.

The engineering properties are generally based on lab data for less than 5 samples per county (sometimes none).

The maps are good for getting a feel for the size and quality of the watershed. Lots of hydrologic group class C & D soils in the watershed mean more runoff per acre than A & B soils. Steep slopes don't hurt either as they deliver more runoff than infiltration.

One last thing, there is no substitute for doing borings to actually see what is there... did I say that already?

Good post Dirtguy.
I found in building my pond that the lower part of the ravine contained more clay than expected due to the clay moving from the top of the hills to the bottom over the years.