Device to Gauge Erodibility of Soil Can Aid
Watershed Planners By
Watershed managers and structural engineers may benefit greatly
from a soil-erodibility testing device developed by the
Agricultural Research Service.
The Jet Test Apparatus, developed by hydraulic engineer Gregory
J. Hanson of the ARS Plant Science
and Water Conservation Research Laboratory in Stillwater, Okla., applies
stresses to soil beds by means of a water jet that can be pumped at various
It may become vital equipment during testing of aging, earthen
flood-control structures such as dams and dikes, as well as in ARS efforts to
understand, predict and control soil erosion and sedimentation within the
nation's streams and lakes.
The device already has been used in cooperative research of
stream bank stability with the ARS
Laboratory in Oxford, Miss.
The apparatus allows users to measure resistance to erosion in
cohesive soils by analyzing the portion of the soil bed scoured by the jet
stream in relation to the hydraulic stress placed upon the surface.
The water-jet test is simple, quick and relatively inexpensive,
and can be used under field and laboratory conditions, according to Hanson. In
addition, it produces coefficients that can be used in common equations fed
into computer models to forecast future erosion.
Hanson works in the Stillwater laboratory's Hydraulic
Engineering Research Unit. ARS is the U.S.
Department of Agriculture's chief scientific research agency.
Originally, the jet-test device, patented in 1993, only
differentiated soil materials in earthen auxiliary spillways on dams. But
recent modifications also allow it to characterize streambed and stream bank
materials. The new version is also smaller and faster than the original.
The device can be set up at different angles, including vertical
ones, and move soil ranging in consistency from fine sand to hard clays. It has
worked in streambeds at depths up to three feet. It can also be used on soils
away from waterways, if a water source is provided.