Factors Affecting Erosion

 Erosion is influenced by a variety of elements including rainfall characteristics, soil factors, topography, climate, and land use.

Rainfall Characteristics

For erosion to occur, runoff must first be present. Runoff is defined as that portion of rainfall that does not infiltrate nor accumulate on the soil surface but moves downslope. Rainfall rate and duration both influence runoff and erosion. Runoff occurs only when rainfall intensity exceeds soil infiltration rate. Infiltration will decrease with time during the initial stages of a storm. Thus, no runoff may occur from a storm of short duration, while a storm of the same intensity but of longer duration may result in substantial runoff. Rainfall intensity influences both the rate and volume of runoff. During a high-intensity storm, infiltration capacity is exceeded by a greater margin than during a less intense rainfall event. Thus, even though the precipitation amount may be similar for two events, a high-intensity storm will produce a greater volume of runoff.

Soil Factors

The susceptibility of soil particles and aggregates to detachment is influenced by soil characteristics. Soil texture, organic matter content, structure, and permeability have been shown to influence soil erodibility. Soils containing large stable aggregates are difficult to detach and transport and usually have greater infiltration rates. As soil organic matter content increases, individual aggregates become more stable, soil structure improves, and infiltration rate becomes greater. Cultivated soils recently removed from native vegetation, pasture, or meadow usually have excellent structure and stable aggregates. The incorporation of organic materials into the soil profile helps to increase aggregate stability. Cultivation without the addition of organic materials causes a reduction in aggregate stability and organic matter content and an increase in soil erodibility. More runoff usually occurs from fine-textured than from sandy soils because of differences in infiltration. Maintaining high infiltration rates is one of the most effective means of reducing erosion. Soil surface sealing caused by aggregate destruction and plugging of pores with soil particles may substantially reduce infiltration. High infiltration rates can be maintained when vegetative material protects the soil surface from sealing when soil structure is preserved, and soil compaction is minimized.

Topography

Erosion is influenced by slope gradient, length of the slope, and size and shape of the watershed. The velocity of flowing water becomes greater as the slope gradient increases. A larger runoff velocity allows flowing water to detach and transport additional soil material. An increased accumulation of overland flow on longer slopes results in greater rill erosion. Crops growing in productive areas at the bottom of a hillslope may be covered with water and sediment during extreme precipitation events.

Land Use

Land use is the only factor affecting erosion that can be modified to reduce soil loss potential. Erosion results from different land-use conditions on cropland areas, rangelands and pastures, and forest areas. Cropland areas Soil erosion potential can substantially increase as natural forest or rangeland is converted to cropland. Cropland areas least susceptible to erosion have a complete ground cover throughout the year. The amount of surface cover maintained on a particular site is influenced by cropping and management conditions. The greatest erosion potential on croplands exists after planting when residue cover is usually at a minimum and high-intensity rains frequently occur. Cultivated land left fallow with no vegetative cover is particularly vulnerable to runoff and erosion. Areas with steep slopes on which row crops such as corn and cotton are grown continuously may also be of concern. The dense surface covers resulting when row crops are planted in rotation with grasses and legumes may substantially reduce erosion potential.