Prevention Of Wind Erosion Research Articles

Three dimensional numerical simulation of the flow over complex terrain with windbreak hedge

In order to clarify the effects of windbreaks on flow and to determine where to set windbreaks for the optimum prevention of wind erosion in a complex terrain, a three-dimensional numerical model for simulating wind distribution over a real complex terrain with a variation of relative height less than 100 m is used. The three-dimensional, time-dependent Navier–Stokes equation written with generalized coordinates and the Smagorinsky-type scheme for turbulent parameterization are use in the model. Numerical simulations of windbreak effect on wind speed distribution over a sand dune are carried out by erecting windbreak hedges at different places. The influence of topography and windbreaks on wind distribution, for example the location of the maximum wind speed reduction, are well simulated. Thus, the best setting place of windbreaks for the prevention of wind erosion may be decided by simulating the wind distribution over real terrain using the model. An example, using a 2 m high windbreak hedge for preventing sand shifting around a barchan sand dune, which is 5 m high, 64 m wide and 96 m long, is given and the effect of the windbreak hedge is discussed. The simulation results show that the best place should be at 18–22 m in front of the top of the sand dune.

中国トルファンの乾燥地における防風ネットによる微気象改良と飛砂防止

Investigations of meteorological improvement, prevention of wind erosion or drifting sand, and sand accumulation were done at a dry land of Turpan, China for 3 years.(1) On the meteorological improvement caused by single line net windbreaks, the relative wind speed Ur decreases with the increase of net density from 30 to 50% and becomes 40 to 60%. The minimum Ur increases under the condition of strong wind, however, the wind area decreasing does not change. With the increase of incident angle to net, effective region by windbreak decreases and appearance point of minimum Ur moves close to the net, however, minimum does not change. The recovery of wind speed is gentle and decreased wind region becomes wide by the reason that the net divides from larger wind eddy to many smaller eddy particles with the scale of net mesh. Surface soil temperature (Ts) and air temperature (Ta) increase in windward and leeward sides near the net at daytime, but being apt to decrease by radiation cooling at nighttime. Variation of relative humidity (RH) is the reverse of Ta in dry lands.(2) On the meteorological improvement caused by double line net windbreaks, the first net windbreak affected on the second in the interval of 25H (multiple distance of net height) and the decreasing effect of wind speed accumulates, however, the recovery of wind speed after passing through the second net is faster than that of the first.(3) Heights of sand accumulation for A and B net densities of 30 and 40% are 30 to 40cm, respectively in half year, and that for B net is 45 to 60cm in a year. The affected region is from -5H to 15H. If the bottom space of net is about 5cm in the case lacked of sand supply, there are not sand accumulation but wind erosion.

The effect o Windbreaks on Meteorological Improvement and the Prevention of Wind Erosion

The effect o Windbreaks on Meteorological Improvement and the Prevention of Wind Erosion

中国トルファンの乾燥地におけるタマリスク防風林による微気象改良

At the arid land of Turfan in northwestern China, the effect of tamarisk (Tamarix L.) wind-break forest was investigated in summer and spring.(1) The effects on the decrease of wind speed and prevention of wind erosion were large based on tamarisk canopy of high density stems with small leaves. In the leeward of the windbreak, the wind turbulence and the wind region of eddy were small and the function of sand filtration was effective. The resistances or tolerances against drought, heat, cold and salt were great. Therefore, tamarisk tree is excellent as a windbreak forest at the arid land of northwestern China.(2) It was obtained the measuring result that air temperature increased unnecessarily at the windward and leeward close to the windbreak at the daytime in summer, considering as an unfavorable climatic condition for a crop cultivation, however, the value of temperature increasing is alleviated to a certain degree owing to the shade by windbreak and latent heat by transpiration from the tree leaves.(3) As a favorable meteorological condition for a crop growing, the phenomena of temperature decreasing by the radiation cooling was observed in the region of wind decreasing at the nighttime in summer.(4) The observation effect on the increase of humidity or water vapor by transpiration from the windbreak leaves was recognized for meteorological improvement of dry farming, particularly during weak wind.(5) In spring, the positive effects of decreasing wind, increasing temperature, increasing humidity, decreasing wind erosion, and sand filtration were large, but the negative effects for crop cultivation were small.

Soil Crust Formed by Sprinkler Irrigation for the Prevention of Wind Erosion

Soil Crust Formed by Sprinkler Irrigation for the Prevention of Wind Erosion