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Factors Influencing Erosion
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The climatic factors that influence erosion are rainfall amount, intensity, and frequency. During periods of frequent rainfall, a greater percentage of the rainfall will become runoff. This is due to high soil moisture or saturated conditions.
Temperature is another climatic factor influencing erosion. While frozen soil is highly resistant to erosion, rapid thawing of the soil surface brought on by warm rains can lead to serious erosion. Temperature also influences the type of precipitation. Falling snow does not erode, however, heavy snow melts in the spring can cause considerable runoff damage.
Temperature also influences the amount of organic matter that collects on the ground surface and incorporates with the topsoil layer. Areas with warmer climates have thinner organic cover on the soil. Organic matter protects the soil by shielding it from the impact of falling rain and soaking up rainfall that would otherwise become runoff.
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Vegetation is probably the most important physical factor influencing soil erosion. A good cover of vegetation shields the soil from the impact of raindrops. It also binds the soil together, making it more resistant to runoff. A vegetative cover provides organic matter, slows runoff, and filters sediment.
On a graded slope, the condition of vegetative cover will determine whether erosion will be stopped or only slightly halted. A dense, robust cover of vegetation is one of the best protections against soil erosion.
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Physical characteristics of soil have a bearing on erodibility. Soil properties influencing erodibility include texture, structure and cohesion. Texture refers to the size or combination of sizes of the individual soil particles.
Three broad size classifications, ranging from small to large, are clay, silt, and sand. Soil having a large amount of silt-sized particles are most susceptible to erosion from both wind and water. Soil with clay or sand-sized particles are less prone to erosion.
Structure refers to the degree to which soil particles are clumped together, forming larger clumps and pore spaces. Structure influences both the ability of the soil to absorb water and its physical resistance to erosion.
The last property to consider is cohesion. Cohesion refers to the binding force between soil particles and influences the structure. When moist, the individual soil particles in a cohesive soil cling together to form a doughy consistency. Clay soils are very cohesive, while sand soils are not.
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Slope length, steepness and roughness affect erodibility. Generally, the longer the slope, the greater the potential for erosion. The greatest erosion potential is at the base of the slope, where runoff velocity is greatest and runoff concentrates.
Slope steepness, along with surface roughness, and the amount and intensity of rainfall control the speed at which runoff flows down a slope. The steeper the slope, the faster the water will flow. The faster it flows, the more likely it will cause erosion and increase sedimentation.
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