1. t M an a g e m
Terraces
es
P
osphorus B
en t
Practic
Author: Dennis Carman, USDA-NRCS, Little Rock, Arkansas
Ph
e
s
Protecting
Water Quality
Definition:
An earth embankment,
or a combination ridge and
Author’s email channel, constructed across
dennis.carman@ar.
the field slope that inter-
usda.gov
cepts, detains and safely
Editing and Design: conveys runoff to an outlet.
Forbes Walker
Wanda Russell Purpose:
Gary Dagnan
Terraces are used to re-
Anne Dalton
duce sheet-and-rill erosion
University of and prevent gully develop-
Tennessee Extension ment. Terracing reduces
sediment pollution to lakes
and streams, and traps phos- Where This Practice Effectiveness:
phorus attached to sediment Applies and The erosion reduction
particles. Terraces may also Its Limitations: potential of terraces ranges
retain runoff for moisture Terraces can be used on from 10 to 50 percent.
Developed by SERA-17, conservation. fields where sheet-and-rill Terraces are most effective
Minimizing Phosphorus erosion or ephemeral gul- when used in a planned
Losses from Agriculture How Does lies are a problem. They can conservation system that
http://sera17.ext.vt.edu/ includes a combination of
This Practice Work? also be used where runoff or
sediment could impair wa- practices such as conserva-
Terraces intercept run-
ter quality or cause damage tion tillage, crop rotations,
off on moderate to steep
downstream. contour farming and field
slopes. They transform long
borders. Primary factors
slopes into a series of short-
er slopes. Terraces reduce Terraces may be affecting erosion include
used where: climatic conditions, land
the rate of runoff and allow
• Soil erosion by water is a slope, cropping intensity,
soil particles to settle out.
problem tillage practices and soil
The resulting cleaner water
• There is a need to con- erodability.
is then carried off the field
in a non-erosive manner. serve water
Terraces reduce phosphorus • The soils and topography Types of Terraces:
NRCS transport by reducing soil
erosion and runoff. Water
are such that terraces
can be constructed and
There are two types of
terraces:
This project was funded in erosion moves soil particles farmed with reasonable
part under an agreement that have phosphorus at- effort • Storage terraces collect
with the USDA-NRCS. tached. Sediment that • A suitable outlet can be water and store it until
reaches water bodies may provided it can infiltrate into the
release the phosphorus into • Excess runoff is a problem ground or be released
the water. through a stable outlet.

2. Underground outlets with pipe Potential losses in production be- Remove sediment build-up in
intakes are the most common cause of construction and some the terrace channel to maintain
type of outlet. reduction in crop acres may result the required water-holding
from terrace and waterway place- capacity.
• Gradient terraces are designed ment. Terrace construction costs Repair sections of the terrace
as channels to slow runoff water vary widely and range from $1 to that have eroded or have excessive
and carry it to a stable outlet $6 per linear foot of terrace, with settlement.
such as a grassed waterway. additional costs associated with
construction of waterways and un- References:
There are three typical terrace derground outlets for conveyance USDA AG Handbook 703,
cross-section types. of water to the outlet. NRCS National Conservation
Practices Standards (600), NRCS
• Grassed backslope terraces have Operation and Maintenance: Engineering Field Manual, and
a farmable frontslope with a 2:1 Where terraces are parallel, NRCS local field office technical
back slope (2 feet horizontal to there are few problems with plant- guides. Specific information for
every 1 foot of vertical drop). ing. If terraces are not parallel, this factsheet was taken directly
Downhill slope is seeded to pe- consider how short rows (point from the NRCS Iowa Job Sheet on
rennial grass. rows) are best managed for farm- Terraces.
• ability.
• Avoid farming too close to For Further Information:
intakes. Farming operations can Contact your local conserva-
cause ridges that block drainage tion district, USDA-NRCS or
of the terrace channel. Cooperative Extension Service of-
fice. Cost share may be available.
Contact your local USDA offices.
Grassed backslope
• Narrow base terraces have 2:1
slopes on both the frontslope
and backslope. Both front and
back slopes are seeded to peren-
nial grasses.
• Broadbase terraces are flatter
looking and are farmed on both
Narrow base
slopes. This configuration will
require a flatter land slope, nor-
mally less than 8 percent.
Cost of Establishing and
Putting the Practice in Place:
The cost of terrace installation
includes earth work costs associ-
ated with the terrace construction,
the establishment of an adequate
outlet such as a grassed waterway
or underground outlet and vegeta-
tion establishment of the respec-
tive terrace slopes on grassed
backslope or narrow base terraces. Broadbase
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