Majid Mahmoudabadi; Samira Zamani
Abstract
Wind erosion is one of the aspects of land degradation resulting in some problems especially for arid and semi-arid regions. Recognition of Sediment size Distribution (PSD) as well as transport mechanisms is important in modelling of wind erosion. In the present study, this topic was investigated on ...
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Wind erosion is one of the aspects of land degradation resulting in some problems especially for arid and semi-arid regions. Recognition of Sediment size Distribution (PSD) as well as transport mechanisms is important in modelling of wind erosion. In the present study, this topic was investigated on two soils taken from cropland and sand dune with different PSD, using wind tunnel. Results showed that compared to the original soil, the collected sediment had finer sizes, indicating a selective mechanism in transporting detachable particles. It was found that for cropland soil, increasing wind speed from 2 to 18 m/s at the height of 20 cm, the PSD of sediment approached to the original soil. This trend was reverse for sandy soil so that, for higher wind velocities, the frequency of fine particles was more than the original soil. The result of transport mechanisms indicated that compared to saltation as well as suspension, creeping was the least important mechanism. The contributing percentage of creeping for cropland and sandy soils was determined less than 10 and 1 %, respectively. For the cropland soil at wind speed of 2 m/s, suspension was the most important mechanism of transport and depends on soil's PSD, 61.1- 68.5 % of particles were transported. Increasing wind speed up to 18 m/s, saltation with 50.4- 53.8 % was found as the main transport mechanism. Reversely, in the sandy soil at low wind speed, most of sediment (59.3 %) was transported through saltation, whereas increasing the speed, suspension with 55.3 % became the dominant mechanism. The finding of this study brings up the important of soil PSD on the PSD of sediment as well as transport mechanisms.
Majid Mahmoodabadi; Elham Sirjani
Abstract
Soil erosion is a dynamic process with high variability in sediment size distribution. Dynamic recognition of sediment size distribution is as a base for modeling of soil erodibility and movement of nutrients, pollutants and fine particles in consequence of erosion. This study focused on sediment transport ...
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Soil erosion is a dynamic process with high variability in sediment size distribution. Dynamic recognition of sediment size distribution is as a base for modeling of soil erodibility and movement of nutrients, pollutants and fine particles in consequence of erosion. This study focused on sediment transport mechanisms due to sheet erosion on two different soils (cropland and sandy) using flume experiment. The experiment was performed applying different flume slopes (1.5 and 2 %) and flow rates (75, 100, 125, 150, 175 and 200 ml/s). The result showed that hydraulic condition as well as soil type, played an important role in selective transport of sediment particles so that, in the sediment size distribution of cropland soil two peaks were observed. For the first (fine particles with size of 0.042 mm), the dominant transport mechanism was attributed to suspension- saltation, while for the second peak (large particles with diameter of 1.5 mm), bed load was known as the main transport mechanism. Moreover, increasing stream power, the selectivity of fine particles declined therefore, both fine and large particles were transported by the flow. For sandy soil, only one peak for the range of 0.109 to 0.175 mm was observed. In this soil, saltation was the main mechanism in transporting sediment. Increasing flow rate, the frequency of particles smaller than 0.015 diminished, whereas particles larger than 0.218 mm increased. For both soils at higher stream powers, the relative importance of transport as suspension and bed load decreased and increased, respectively. The findings of this research reveal that sediment size distribution and also transport mechanisms depend on hydraulic condition such as slope and flow rate.
