AdditionalInfo

	Engineered Information Systems for Natural Resources USDA-ARS Southwest Watershed Research Center Tucson, Arizona

Glossary of Erosion Terms

Canopy cover
The percentage of ground covered by a vertical projection of the outermost perimeter of the natural spread of foliage of plants.

Coefficient
A value required to complete the numeric solution of a mathematical model. A number which is required to relate variables. Synonyms include constant and factor. As an example, the equation relating the diameter of a circle and its area can be written in terms of a coefficient c as Area = cD² where D is the diameter of the circle and c is a coefficient equal to Pi/4 or 3.14159/4.

Concentration
The amount of material in a given amount of water by weight, as used herein, sediment concentration is Kg of sediment per cubic meter of water. Expressed as a percentage, this is Kg of sediment per Kg of water times 100.

Deposition
The process of flowing water redepositing transported material such as sediment particles.

Detachment
The process of removing particles of soil literally by ripping or tearing them from the soil fabric or soil matrix.

Erodibility
An intrinsic property of the soil expressing its propensity to be eroded by detachment of soil particles and soil aggregates which then become sediment particles in the flowing water. The actual physical processes of detachment are not well understood by scientists so it is usually determined experimentally or empirically. Relative erodibility as used herein is a dimensionless value expressing soil erodibility. A soil with a relative erodibility of 2.0 is twice as erodible as a soil with a value of 1.0.

Erosion
The detachment and movement (including transport and deposition by flowing water) of soil and rock material by an agent such as water.

Ground cover
The percentage of material, other than bare ground, covering the land surface. It may include litter, rock, gravel, stone, and plant basal material.

Hillslope
The part of the landscape included between the crest of hills and their drainage lines or channel networks.

Hillslope profile
The two-dimensional form of a hillslope when measured from the top or ridge crest down the steepest gradient to the bottom or toe of the hillslope.

Interrill
The area between rills that carries sheet flow during runoff events. The term evolved from considering erosion processes in cultivated fields with furrows which rilled and the areas between rills as interrill areas. However, a broader meaning used here is areas between concentrated flow paths and which are subject to erosion by raindrop impact and sheet flow of water.

Rill
Small channels that carry concentrated flow during runoff events and are dry most of the time.

Runoff
The total discharge of water. As used herein it is the surface water yield per unit area of the hillslope. Runoff is commonly expressed as an equivalent depth of water, mm or inches, per unit area represented by the entire hillslope profile.

Sediment yield
The total amount of eroded material that passes a downstream point. Sediment yield can be expressed as a total mass of sediment moving past a certain point (Kg) or as a mass per unit area (Kg/m², Kg/ha, etc.).

Simulation model
A mathematical model specifically formulated in representations, algorithms, and routines to be solved on a digital computer.

Slope
The change in elevation between two points on a hillslope (e.g. the top and bottom of a hillslope) divided by the horizontal distance between the points. Slope, or slope steepness, is dimensionless and can be expressed as a percent.

Transport capacity
The amount of sediment material that a given flow can move as suspended load (particles in suspension) and as bed load (sediment particles rolling, jumping, slipping, and sliding along the ground surface or along the bottom of a concentrated flow path) with the flowing water.

State of Technology Development

The Hillslope Erosion Model has been developed by United States Department of Agriculture - Agricultural Research Service (USDA-ARS) research scientists. The software was designed and developed by scientists at the USDA-ARS Southwest Watershed Research Center in Tucson, Arizona, USA. The Hillslope Erosion Model software may not be used to gain income, sold, or passed on to others, without the written permission of the USDA. The software is an evaluation version and should be treated accordingly.

Detachment and deposition estimates may be in error in the case of rapidly decreasing slope coupled with abrupt, sharp increases in canopy or ground cover. However, this situation is rare on rangelands.

For applications that require more comprehensive and powerful erosion prediction technology please consider the WEPP technology available at http://topsoil.nserl.purdue.edu

Disclaimer

The Hillslope Erosion Model Web Site has been written to assist in evaluating erosion and deposition along hillslopes. Where significance is to be placed upon the results of the analysis, the user should have independent methods for checking the accuracy of the outcomes. Proper use of the Hillslope Erosion Model and input data, and interpretation of model output are the responsibility of the user. The Hillslope Erosion Model has been developed in good faith, however, USDA-ARS and model developers and programmers accept no responsibility for any errors or omissions it may contain or any liability or damage that may result from its use.

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