General Requirements
The general requirements are:
- Size Area
- Required Erosion, Deposition, and Sediment Yield Estimates
- Major Factors
- Applicability
- Other General Requirements
Size Area
The erosion prediction procedure from this project is to
apply to
"field-sized"
areas
or conservation treatment units.
Although the size of a particular field to which the
procedure applies will vary with degree of complexity within
a field,
the maximum size "field" is about a section (640 acres).
However,
the procedure will not apply to agricultural fields
or
watersheds
having incised,
permanent channels
such as classical gullies and stream channels.
The channels that the procedure is to include are those
farmed over and
known as
concentrated flow or
"cropland ephemeral gullies."
Also, the procedure is to apply to constructed waterways
like terrace channels and grassed waterways.
In rangeland and forest applications,
"fields"
can include gullies up to the size of typical
concentrated flow gullies in
640 acre cropland fields.
These channels are on the order of about
3 to 6 ft in width by about 3 ft deep.
The procedure is not expected to apply to
headcut erosion, sloughing of gully sidewalls, or the effects of seepage
on erosion in concentrated flow channels.
Required Erosion, Deposition, and Sediment Yield Estimates
The procedure is to compute: (a) sheet-rill erosion
and deposition by overland flow
along selected landscape profiles or over an entire field,
(b) concentrated flow
(ephemeral gully)
erosion along selected channels or over the entire channel network
within a field,
and (c) sediment yield and its
sediment
characteristics from selected watersheds within
the field or
at all outlet points from the field.
To meet these requirements,
the procedure is expected to include three basic versions:
(a)
a representative landscape profile
version, (b) a watershed version, and
(c)
a grid version that covers the entire field.
In these User Requirements,
"fineness"
refers to sediment characteristics.
In general,
fineness can be an enrichment ratio
based on specific surface area.
However,
at the request of the user,
the procedure is to compute erosion, deposition, and transport for
a minimum of five sediment particle classes
that can vary by diameter,
density,
and composition
by
primary particles and
organic matter.
Estimates from the water erosion prediction procedure should be in
a form with respect to space and time
that will allow their combination with estimates from wind erosion
prediction procedures to support evaluations of the combined effects of
wind and water erosion.
This requirement can be met by computing average annual erosion rates at any point in the field.
Major Factors
The procedure is to describe the influence on erosion,
deposition,
and sediment yield of the major factors:
(a) climate,
(b) soil,
(c) topography,
(d)
cropping-management,
and
(e) supporting practices.
The last two factors describe land use.
Applicability
Ultimately the procedure is to apply to all U.S. locations
including Alaska, Hawaii,
and Puerto Rico.
Furthermore,
the procedure should be developed with
the goal that it will apply worldwide.
The procedure is to be process based
to meet this broad range
of applicability.
In particular,
the effects of cropping and management will be described by a component
structure based on canopy,
ground cover,
roughness,
soil consolidation,
and similar components.
This project will provide the basic relationships
to meet this requirement, but field application
of the procedure
will depend on the availability of parameter values.
This project will determine
parameter values for a set
of "key"
soils,
crops, management, tillage,
and supporting practices specified in
a later section.
Other General Requirements
The prediction technology
must be easy to use with easily understood guidelines.
Also,
it must use minimal
and easily obtained
inputs,
which are specified in a later section.
When applied to conservation planning,
the procedure must be portable for use in the office,
truck,
field,
or client's house.
The procedure when implemented
on a computer should be accessible by
telephone if the user desires
special features or data not available in a
"standard" field version.
Any Comments Would Be Appreciated
Disclaimer and Copyright Information