Wind erosion Wind erosion is the process of detachment transportation and deposition of soil material by wind action Occurs when Soil is loose finely divided and dry Soil surface is smooth and bare Wind is strong Question Which loses more soil A bare smooth surface or a rough surface How do you reduce wind erosion Keep soil moist Soil surface is roughened or covered by vegetation or residue Reduce wind speed near ground Movement of soil by wind Suspension silt or smaller 0 05 mm move great distances Saltation 0 05 mm to 0 5 mm very fine sand fine sand medium sand short flight Surface creep 0 5 mm to 1 or 2 mm coarse sand rolling along can be bumped along by saltating gains and wind force 1 2 Wind erosion can change Air pollution Dust can carry pathogens and cause skin disorders Deposition Sedimentation Dunes Visibility Friction velocity Friction velocity Surface texture Nutrient loss Productivity losses u ro 1 2 p ro surface shear stress dynes cm2 p air density g cm3 erosive force and detaching capacity of a wind Carrying capacity proportional to cube of friction velocity amount of material eroded proportional to 5th power Saltation Wind turbulence roughness and temperature differences Terminal Velocity maximum speed of a raindrop Wind gustiness gust fluctuates widely Prevailing Wind Direction changes can affect movement Threshold Velocity 1945 starts soil movement measured 30 cm above soil 3 Saltation Path of a sand grain in saltation First particle moves by turbulent currents Other stationary particles knocked into air by impact of descending particle Particle caroms off soil surface and back into flight Saltation Particle spin Spin makes first particle move Avalanching Increasing rate of erosion as wind blows across field Erosion often results from high winds coming from some prevailing direction particles farther down field were eroded before Farther leeward the wind moves the more abrasive material it will carry new particles being detached 4 Avalanching Wind smoothes the surface by cutting and filling the humps and hollows smooth surface easier to erode wind speed increases Detaching capacity of wind D f ux1 2 D detaching capacity g cm2 sec ux1 2 friction velocity over an eroding surface cm sec Other factors Factors other than wind that affect wind erosion and influence amount of soil movement Soil cloddiness Amount and nature of field ridging Amount of rainfall Knolly or hummocky topography increase on crests Other factors con t Factors other than wind that affect wind erosion and influence amount of soil movement con t Width of erodible area in the direction of the wind Distribution of vegetative cover 5 Three principle ways of reducing wind erosion Reduce the velocity of the wind close to the soil Remove abrasive material saltating grains from the wind stream Increase the soils resistance to wind erosion 6 7
View Full Document
Unlocking...