As I have written in previous SoRI cache descriptions, soils are
important natural features on our landscape. One of the most
obvious influences soils have on humans is that we build our homes
and businesses on and in soil. However, not all soils are wel
suited to development. One of the most significant limitations to
development is the depth to the seasonal high water table (SHWT).
The SHWT is the minimum depth to free water in a soil. This depth
changes throughout the year. The water table is at its deepest
during late summer, as plants have actively drawn water up through
their roots all summer. Water tables rise during the fall and
winter and reach a maximum during the spring.
In RI, most homes have basements, and many have septic systems.
Rising water tables can flood basements (as many, including myself,
witnessed during the March 2010 floods) and impair septic systems.
Floods like those in 2010 are uncommon, but what about soils that
regularly have a water table that comes to within 20" of the soil
surface? This land would be unsuitable to build upon. Is there any
way a landowner or developer could determine know how high the
water table gets within a soil?
The answer is yes. Rising water tables typically leave signs
called redoximorphic (redox) features. These features come
in two forms - concentrations (rust colored), and depletions (gray
soil particles). See the included picture for an example. To keep
this simple, these features are basically areas where iron has
moved within the soil profile. Soil evaluators can examine a soil
profile and find the depth at which redox features first appear.
This gives an excellent estimate to the SHWT.
This Earthcache is placed within an area of Rainbow soil.
Rainbow soils are not suitable for development because the parent
material is dense till, an unsorted mixture of soil materials that
was compressed under the massive weight of glaciers 14,000 - 18,000
years ago. This material is extremely difficult to dig through. It
also "perches" infiltrating water, causing a high water table. This
Earthcache will give you some experience in describing a soil
profile and identifying the features that make Rainbow unsuitable
for development.
Your Assignment:
You will need: A measuring device (a roll tape will work best)
and a small trowel, knife, or shovel to help you clear the profile
and obtain samples.
The posted coordinates will bring you to the northwest corner of
an old field. You should see some orange snowfencing around an
excavated area approximately 4 feet deep. Use caution going down
the slope. There is a wooden pallet at the bottom of the pit to
stand on, and there is plenty of room for several people to stand.
The bottom foot or so of this pit may fill with water during the
winter and spring. I do not advise anyone to attempt this cache if
there is water in the pit!
Clear off the soil face, and measure the distance from where the
grass meets the soil to where you see a very obvious color change
from very dark brown to a more yellowish brown. This layer is the A
horizon. It is dark because decaying plant material is a major
component of this soil layer. Record the depth of this soil
layer.
Next, begin digging small clods of soil from the orange soil
materials (B horizon) below the A horizon with your knife or
trowel. Break open the clods and look carefully for rust colored
redox features. Once you find these features, carefully continue
higher in the soil profile to make sure they do not appear higher.
Record the depth that the redox features first appear in the
soil profile. This is the estimated depth of the SHWT!
You will notice a strange "seat" of gray soil material further
down. This is the dense till parent material (C horizon). Record
the depth at which the dense till appears in the soil profile.
You'll notice just how dense this material is if you try to dig
into it!
Congratulations! You just performed some real-life soil
evaluating! To log your find, you must answer all three bold
questions and email them to me. Do not post any answers in your
log.
Congrats to BBWolf+3Pigs for the FTF!