ارزیابی کارایی نمونه‌گیر BSNE و ظرفیت انتقال‌پذیری ذرات رسوب حاصل از فرسایش بادی با استفاده از آزمایش تونل باد

نوع مقاله: کاربردی

نویسندگان

1 گروه علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه شهید باهنر کرمان، کرمان، ایران

2 دانشگاه شهید باهنر کرمان

3 عضو هیئت علمی مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی کرمان

چکیده

پژوهش حاضر با هدف بررسی کارایی نمونه‌گیر BSNE در تله‌اندازی ذرات رسوب حاصل از اعمال سرعت‌های مختلف باد بر روی خاک‌های با توزیع اندازه ذرات متفاوت و همچنین معرفی پارامتری جدید با عنوان انتقال‌پذیری ذرات رسوب در ارتفاع‌های مختلف با استفاده از آزمایش تونل باد انجام شد. سه سرعت باد شامل 6، 10 و 14 متر بر ثانیه در ارتفاع 40 سانتی‌متری بر روی سطحی به طول 7 متر از سه نمونه خاک (با حداکثر اندازه ذرات 2، 75/4 و 8 میلی‌متر (D2mm، D4.75mm و D8mm) ایجاد و رسوب تولیدی با استفاده از نمونه‌گیر BSNEدر ارتفاع‌های 10، 30، 50، 70 سانتی‌متر جمع‌آوری شد. نتایج نشان داد با افزایش ارتفاع، مقدار رسوب انتقال یافته به صورت نمایی کاهش می‌یابد. با افزایش سرعت باد، مقدار رسوب تولیدی افزایش و با بزرگ‌تر شدن اندازه ذرات خاکدانه، مقدار آن کاهش یافت. شدت انتقال ذرات در نزدیک بستر برای خاک‌های D2mm، D4.75mm و D8mm به‌ترتیب بین 28/0 تا 11/2، 19/0 تا 06/1 و 23/0 تا 65/0 گرم بر سانتی‌مترمربع در دقیقه متغیر بود. کارایی نمونه‌گیر رسوب بسته به سرعت‌های مختلف باد و اندازه ذرات متفاوت خاک، بین 53 تا 82 درصد نوسان داشت. همچنین مشخص گردید که با افزایش ارتفاع از سطح، میزان انتقال‌پذیری ذرات رسوب در واحد سرعت باد، بطور نمایی کاهش می‌یابد. یافته‌ها بیانگر این مطلب نیز بود که در بین کلاس‌های مختلف اندازه ذرات رسوب، برای نمونه‌گیرهای منتخب در دو ارتفاع 10 و 30 سانتی‌متر، ذرات در دامنه اندازه 125 تا 500 میکرون، بیشترین انتخاب‌پذیری را دارند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Assessment of the BSNE sampler efficiency and the capacity of sediment particles transportability in wind erosion using wind tunnel experiment

نویسندگان [English]

  • Hossein Kheirabadi 1
  • Vahidreza Jalali 2
  • Hormozd Naghavi 3
1 Department of Soil Science, Agriculture Faculty, Shahid Bahonar University of Kerman. Kerman, Iran
3 Kerman Agricultural and Natural Resources Research and Education Center
چکیده [English]

Introduction: The trap efficiency of sediment catcher plays an important role in the study of wind erosion and its measurements. The sediment trap efficiency generally varies with particle size distribution and wind velocity. Worldwide, wind tunnel facility has been used by many researchers to determine the efficiency of sediment samplers designed for the measurement of the deposition of Aeolian dust. Therefore, this study was conducted to investigate the efficiency of BSNE sampler, the transportability of sediment particles per wind velocity, using wind tunnel facility under laboratory conditions. In addition, a new parameter by which sediment transportability can be quantified was introduced.
Materials and Methods: The wind tunnel experiments were carried out in an open circulation wind tunnel at the Soil Erosion and Conservation Laboratory, Shahid Bahonar University of Kerman, Iran. The wind tunnel consists of three sections including 1) wind generator section for producing different wind velocities, 2) test area section in which soil sample is placed and 3) sediment collector section. The wind tunnel has a uniform cross section with width and height of 80 cm by 80 cm and a total length of 12 m, with a working section of 7 m in length. The wind velocity can be varied continuously from 1 to 30 m s-1 at 40 cm height equal to 175 km/h at 10 m height. The soil used for the experiments is taken from the surface layer (0-20 cm depth) of a cultivated land from Kerman province (30 14 N and 57 06 E). The soil sample at first was air-dried, thoroughly mixed and then crushed to pass separately through 2, 4.75 and 8 mm sieve sizes in order to prepare three subsamples with different max size of 2 (D2mm), 4.75 (D4.75mm), 8 (D8mm) mm. Experiments were done as factorial based on completely random design with three replications. The factors were the height of sampler, wind velocity and soil aggregate size. Three wind velocities of 6, 10, 14 m s-1 at 40 cm height were introduced over the leveled soil surface with 7 m length and the sediment was collected using BSNE sampler at different heights of 10, 30, 50 and 70 cm at the outlet of the wind tunnel. Also, the total mass of soil loss was measured by differential weighing method for each erosion event.
Results and Discussion: Results showed that the sediment flux decreased with increasing height at different wind velocities and was quantified using an exponential function, satisfactorily. The sediment transport rate near soil surface for soils D2mm, D4.75mm and D8mm ranged from 0.28 to 2.11, 0.19 to 1.06 and 0.23 to 0.65 g cm-2 min-1, respectively. This implies the soil having coarser aggregates exhibits less erodibility. Moreover, sediment flux at all heights was increased with increasing wind velocity, whereas it was reduced as soil surface roughness increased. In general, the efficiencies of the BSNE samplers varied from 53.2% to 82.1%, depending on soil aggregate size and wind velocity. The efficiency of BSNE obtained for D2mm, D4.75mm and D8mm, at wind velocity of 6 m s-1 was 61.4, 53.2 and 77.5%, at wind velocity of 10 m s-1 was 56.5, 78.7, 69.5% and at wind velocity of 14 m s-1 was 62.4, 79.1, 82.1%, respectively. Also, the results indicated that the transportability of sediment particles per wind velocity decreased with height, which was described through an exponential function. Overall, the particles in the size range of 125 to 500 micron exhibited the maximum selectivity and frequency in the sediments collected at 10 and 30 cm heights. The finding of this study revealed the high importance of vertical distribution of sediment size particles and their selectivity in wind erosion studies.
Conclusion: The finding of this study indicated that most sediment particles were transported near the soil surface, this means that by appropriate conservation practices such as making sufficient roughness through this height, wind erosion can be reduced, significantly. Also, it was found the soils containing coarser aggregates due to higher random roughness show less erodibility and wind erosion rates. Finally, the efficiency of sediment sampler was found to be affected by some other factors, therefore, more attention is needed in the application of these types of samplers while the calibration is of importance, as well.

کلیدواژه‌ها [English]

  • Wind tunnel
  • BSNE sampler
  • Sediment transportability
  • Particle size distribution
  • Surface Roughness
  • Wind erosion