Environmental Engineering Reference
In-Depth Information
wetland with a static water table that is inundated continuously for several months
yet has a soil meeting the Field Indicator F3 Depleted Matrix. Wetland hydrology
during the monitoring period does not match the long term hydrology as the site is
now wetter. Now consider a wetland with a dynamic water table displaying
seasonal saturation and multiple fluctuations in water table depth but the soil
meets the indicator A3 Black Histic. That site is now drier. In this process local
precipitation data should be considered to distinguish between permanent changes
in hydroperiod and unusual short term precipitation patterns.
4.13.2.2 Soil Structure and Horizonation
A number of soil morphological features are associated with dynamic water tables.
Redoximorphic features were discussed previously. Subangular and angular blocky
structure is believed to be caused by forces created by alternating periods of wetting
and drying. We do not expect to see these structural types in soil that consistently
stays wet. Similarly, argillic horizons, a B horizon enriched with illuviated clay, do
not form in soils with a static water table near the surface as a fluctuating water table
is required to transport clay vertically. Therefore, if hydrologic monitoring
indicates a static water table near the surface, but the soil has an argillic horizon
or strong blocky structure, the site is now wetter.
4.14 Additional Resources
4.14.1 National Technical Committee for Hydric
Soils (NTCHS)
The NTCHS is chaired by NRCS and has representation from all federal agencies
involved in wetlands work as well as university experts in hydric soils related
issues. The NTCHS makes all decisions on issues related to hydric soils.
4.14.2 Documents
National Technical Committee for Hydric Soils
2007
. The Hydric Soil Technical
Standard. Hydric Soils Tech Note 11. (
http://soils.usda.gov/use/hydric/ntchs/
tech_Notes/index.html
)
- The standard required to collect long term data to
