PERMFILE56635 - Laserfiche WebLink

Home Browse Search

"K Factor: This value indicates the relative susceptibility of a surface soil to water erosion. Values may range from .00 to .70. Higher K values indicate higher erosbn susceptibility. Soils with K factor over about 0.40 are generally considered to be highly susceptible to water erosion. It should be noted that the K factor is primarity derived from physical characteristics of the soil, and does not reflect other soil erosion {actors such as management practices, precipitation, or length and steepness of slope. ErodibilitV Potential 'K" Value Low ErodibilRy .20 or less Moderate Erodibiliry .21 - .40 High Erodibility >.40 '=Hydrologic Group Classification of Soils: Hydrologic soil groups are used in watershed planning to estimate runnoff from rainfall. Soil properties are considered that influence the minimum rate of infitration obtained for a bare soil after prolonged wetting. These properties are: depth of seasonally high water table, intake rate and permeability after prolonged wetting, and depth to a very slowly permeable layer. The influence of ground cover is treated independently -not in hydrologic soil groupings. The soils have been classified into four groups, A through D. The individual classifications are taken from the most current official soil series "Form 5" sheets. Statements in parentheses following the definitions may be helpful to soil scientists wishing to place soils into hydrologic groups using the soil classification system. A.(Low runoff potential). Soils have high (rapid) infiltration rates even when thoroughly wetted and consist chiefly of deep, well to excessively drained sands or gravels. These soils have a high rate of water transmission. (Includes Psamments except those in L'dhic, Aquic, and Aquodic subgroups; soils in Grossarenic subgroups of UduRs and UdaHs, and soils in Arenic subgroups of Udults and UdaHs except those in clayey or fine families). B.(Moderately low runoff potential). Soils have moderate infiltration rates when thoroughly wetted and consisted chiefly of deep, well to excessively drained sands or gravels. ~ These soils have a high rate of water transmission. (Soils other than those in groups A, C, or D). A C.(Moderately high runoff potential). Soils have slow infiltration rates when thoroughly wetted and consist chiefly of soils with a layer that impedes downward movement of water, soils with moderately tine to fine texture, soils with slow iniihration due to salts or alkali, or soils with moderate water tables. These soils may be somewhat goody drained. This category also includes well and moderately well drained soils whh slowly and very slowly permeable layers (fragipans, hardpans, hard bedrock, and the like) at moderate depth (20-40 inches), (Includes soils in Albic or Aquic subgroups; soils in Aeric subgroups of Aquepts, Aquepts, Aquolls, Aquahs, and Aquuhs in loamy tamilRies; soils other than those in group D that are in fine, or clayey families except those with kaolintic, oxidic, or halloysCx: mineralogy; Humods and Orthods; soils with fragipans or petrocalcic horizons; soils in shallow families that have permeable substrata; soils in Lithic subgroups that have rock that is pervious or cracked enough to allow water to penetrate). D.(High runoff potential). Soils have very slow iniihration rates when thoroughly wetted and consist chiefly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a claypan or clay layer at or near the sudace, soils with very slow iniihration due to sahs or alkali, and shallow soils over nearly impervious material. These include Aquods; soils in Aquepts, Aquepts, Aquolls, AquaHs, and AquuRs except for aeric subgroups in loamy families; soils with natric horizons; soils in Lithic subgroups that have impermeable substrata; and soils in shallow families that have impermeable substrata). • •