- Email: [email protected]
Dynamic wind differences in the formation of sand hazards at high- and low-altitude railway sections
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Contents lists available at ScienceDirect
Journal of Wind Engineering & Industrial Aerodynamics journal homepage: www.elsevier.com/locate/jweia
Dynamic wind differences in the formation of sand hazards at highand low-altitude railway sections Shengbo Xie a, *, Jianjun Qu a, Yingjun Pang b, ** a
Key Laboratory of Desert and Desertification/Dunhuang Gobi and Desert Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, 100091, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords: Railway sand hazard Sand–moving wind Sand drift potential Maximum possible sand transport quantity
Compared with the railway sand hazards at low-altitude regions, whether the railway sand hazards at highaltitude regions have been aggravated or mitigated, which is not conducive to targeted control of sand hazards, is currently unclear. Honglianghe River section of Qinghai–Tibet Railway and Danghe River section of Dunhuang–Golmud Railway were selected as the typical representatives of high- and low-altitude sand hazard sections, respectively, to understand the sand hazard law of different-altitude railway sections. Results show the sand hazards at Honglianghe River section mainly occurred in winter and spring and Danghe River section mainly occurred in summer and autumn. The mean grain size of the sandy materials at Honglianghe River section is larger than that at Danghe River section, causing the speed of the sand-moving wind to increase and the frequency of the sand-moving wind to decrease. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased. Therefore, the dynamic wind of sand hazards at Honglianghe River section weakened and the overall hazards alleviated compared with that at Danghe River section. The results can provide the bases for controlling sand hazards at different-altitude railway sections.
1. Introduction Blown sand has been an important factor confounding road construction and safe operation in sandy regions (Mujabar and Chandrasekar, 2013). As more railways are constructed and being operated in sandy regions, railway sand hazards and its control have been the focus of considerable attention (Chen et al., 2002; Zhang et al., 2010a). Given the fragile ecology in sandy regions, matter and energy balance of the system would be altered by any small disturbance. The construction processes of railways inevitably destroyed the original sparse vegetation and fragile ecological environment in sandy regions and further exacerbated the surface blown sand activities (Shen et al., 2004; Wang et al., 2004). The original relatively stable dynamic balance of blown sand movement in sandy regions was disturbed as a result of the appearance of roadbed (Zhang et al., 2014), particularly after the railway construction was completed. Moreover, the path and intensity of wind–sand flow near the surface were altered, which resulted in sandy materials deposited near the railway. Thus, blown sand hazards became prominent. Current research concerning railway sand hazards mainly focus on blown sand movement law, formation processes, disaster-causing * Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Xie), [email protected] (Y. Pang). http://dx.doi.org/10.1016/j.jweia.2017.07.003 Received 16 December 2016; Received in revised form 7 June 2017; Accepted 9 July 2017 0167-6105/© 2017 Elsevier Ltd. All rights reserved.
mechanisms, and control of roadbed sand hazards at low-altitude sections (Jiang et al., 2014; Zhang et al., 2016). In recent years, with the railway construction and operation at high-altitude sandy regions such as Qinghai–Tibet plateau, particularly the Qinghai–Tibet Railway and Lhasa–Shigatse Railway built and opened to traffic, railway sand hazards have expanded to high-altitude regions (Liu et al., 2007), and the distribution altitudes of sand hazards have become high. The sand hazard sections of Tanggula–Za'gyazangbo of Qinghai–Tibet Railway are distributed above 5000 m altitude (the highest section reached 5067 m) and are currently the highest railway sand hazards of the world. Despite the increase in the number of sand hazard sections at high-altitude regions, studies on railway sand hazards at high-altitude sections are scarce, leading to lack the knowledge of the dynamic processes of blown sand (Han et al., 2014, 2015; Huang and Wang, 2016). Moreover, comparative studies on railway sand hazards between high- and low-altitude sections are few. The laws of railway sand hazards at high-altitude sections have not been intensively investigated and are limited to the construction of railways at high-altitude sandy regions only occurring in recent years. Compared with the sand hazards at lowaltitude regions, whether the sand hazards at high-altitude regions
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
line distance between the two sites is approximately 550 km, with an altitude difference of 3178 m. The experimental fields were established in the two sites to conduct continuous positioning observations (Xie et al., 2015b). Local sand samples were collected, and the granularity composition of the sand samples were analyzed by sieving method in the laboratory using the observational data to calculate sand drift potential (DP) and maximum possible sand transport quantity. Meteorological sensors (HOBO-U30 Automatic Meteorological Station, the model numbers of wind speed and wind direction sensors are S-WSAM003 and S-WDA-M003, respectively) present a surface height of 2 m, with wind speed and wind direction recorded every 5 min. Sand collected from eight directions was used to determine the sand transport quantity. A vertical sand collector was used, with eight intakes that corresponded to the eight directions. Sand DP was calculated using the following transport equation (Lettau and Lettau, 1977; Bagnold, 2005):
have been aggravated or mitigated is still unclear. What are the differences in the dynamic aspects of railway sand hazard formation between high- and low-altitude sections? The answers to these problems are currently unclear, which is not conducive to targeted control of sand hazards. The Honglianghe River section of Qinghai–Tibet Railway and Danghe River section of Dunhuang–Golmud Railway were selected as the typical representatives of high- and low-altitude sand hazard sections, respectively, to answer the aforementioned questions. The source of sandy materials and the dynamic environment of wind at high- and low-altitude sand hazard sections were comparatively investigated through different methods, such as field observation, laboratory analysis, and calculation. This study aimed to reveal the differences of blown sand movement law and provide the bases for controlling sand hazards at different-altitude railway sections. 2. Material and methods
DP ¼ V2(V Vt)t,
The Honglianghe River of Qinghai–Tibet Railway (the experimental observation site is located at 35 030 1300 N, 93 010 1100 E, with an altitude of 4658 m) and Danghe River of Dunhuang–Golmud Railway (the experimental observation site is located at 39 530 2000 N, 94 280 2400 E, with an altitude of 1480 m) were selected as the typical representatives of high- and low-altitude sections (Fig. 1), respectively, to analyze the differences of sand hazards at high- and low-altitude railway sections. The climates of the two sites are characterized by semiarid climate with high elevation and cold temperature and arid climate, respectively, the underlying surface types are characterized by gravel gobi. The straight-
(1)
where DP is the sand DP expressed in vector units (VU), V is the wind speed greater than the sand–moving wind, and Vt is the sand–moving wind speed. When measured by locale (Han et al., 2014, 2015), a wind tunnel was transported to the two sites and installed on the sandy surface, the wind speed was increased slowly, and sand particle movement was monitored by a system of particle image velocimetry, the critical starting speed of the sand particles is the sand–moving wind speed, and the speeds of the sand–moving wind at the Honglianghe River of Qinghai–Tibet Railway and Danghe River of Dunhuang–Golmud Railway
Fig. 1. Location map of the experimental observation fields. 40
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
were 5.7 and 5.0 m s1, respectively. The units of wind speed must be converted to nmile⋅h1. Meanwhile, t is the time affected by sand–moving wind and expressed in frequency, which is commonly the percentage of sand–moving wind time to total observation time during the observation period. Given that wind is a vector, the resultant drift potential (RDP) and resultant drift direction (RDD) were obtained by synthesizing the sand DP in 16 directions on the basis of the vector synthesis rule. Such rule can reflect the size of the net sand transport capacity in a region. An index of directional wind variability is the ratio of RDP to DP, known as RDP/DP, which is used to reflect the combined situation of the wind direction in a region. Wind energy environments were classified as high energy (400 VU), intermediate energy (200 VU to 400 VU), and low energy (200 VU). The index of directional variability was classified as high ratio (0.8), intermediate ratio (0.3–0.8), and low ratio (0.3) on the basis of the magnitude of sand DP (Mckee, 1979; Fryberger et al., 1984). Many methods were used to calculate the sand transport quantity (Leatherman, 1978; Rasmussen and Mikkelsen, 1991; Owens, 1964; Sorensen, 1991; Anderson and Hallet, 1986). From the local conditions and relative results (Ling, 1994, 1997), the maximum possible sand transport quantity was calculated using the following formula: Q ¼ 8.95 101(V Vt) T,
Fig. 2. The particle size composition of sandy materials at the experimental observation fields.
(2)
the sandy materials mainly come from the alluvial and diluvial materials of Danghe River and the mobile sand dunes of Mingsha Mountain, which are located at both sides of the railway and characterized by in situ sand accumulation. The grain size composition of sand with particle size in the range of 0.10 mm–0.25 mm are dominant, followed by sand with particle size in the range of 0.25 mm–0.50 mm (Table 1). The mean grain size is 2.69 (Fig. 2). Therefore, the sandy materials of Honglianghe River and Danghe River mainly come from the alluvial and diluvial materials of local rivers and the mobile sand dunes of nearby sandy mountains and are characterized by in situ sand accumulation. However, the sandy materials at Honglianghe River section are coarser, and the mean grain size is larger than that at Danghe River section.
where Q is the maximum possible sand transport quantity, V is the wind speed greater than the sand–moving wind, Vt is the sand–moving wind speed, and T is the cumulative duration of wind speed with different grades. In the calculation, first, the statistics of the frequency or time of different wind speed grades at each direction were obtained on the basis of 16 directions. Second, the maximum possible sand transport quantities in the 16 directions were calculated under the condition of different wind speed grades to obtain the maximum possible sand transport quantity of each direction. The sum of the maximum possible sand transport quantity in 16 directions is the total quantity of the maximum possible sand transport (Q). Finally, the resultant quantity (RQ) and resultant angle (RA) of the maximum possible sand transport were obtained by synthesizing the maximum possible sand transport quantity in 16 directions on the basis of the vector synthesis rule.
3.2. Dynamic environment of wind 3.2.1. Average wind speed and wind direction In 2013, the average wind speed at Honglianghe River was 3.51 m s1. The average wind speed was high in winter and spring and reached its maximum in February at 4.89 m s1. The average wind speed was low in summer and autumn and reached its lowest in October at 2.57 m s1. By contrast, in 2013, the average wind speed at Danghe River was 4.37 m s1. The average wind speed was high in summer and autumn and low in winter and spring. The average wind speed of Honglianghe River was lower than that of Danghe River (Fig. 3). From the wind rose data in 2013 (Fig. 4), at Honglianghe River, the N wind direction was prioritized, which accounted for 44.92% of the yearly total, followed by the NNW wind direction, which accounted for 31.99% of the yearly total. The frequencies of other wind directions were low, and the frequency of static wind was 1.58%. By contrast, at Danghe River, each direction of the wind accounted for a certain proportion, i.e., the ENE wind direction accounted for the highest proportion, which accounted for 15.18% of the yearly total. Moreover, the frequency of static wind was 18.50%. Therefore, the wind direction of Honglianghe River was single, whereas the wind direction of Danghe River was dispersed and varied.
3. Results 3.1. Source of sandy material As the most sand–damaged section of Qinghai–Tibet Railway (Xie et al., 2013, 2015a), the sand hazard sections at Honglianghe River have an extent of 9.76 km (K1100 þ 400 to K1110 þ 160). The main landforms are the valley of Honglianghe River and the Gongmaorima Hill, and the sandy materials mainly come from the alluvial and diluvial materials of Honglianghe River and the mobile sand dunes of Gongmaorima Hill, which are located at the west side of the railway and characterized by in situ sand accumulation. The grain size composition of sand with particle size in the range of 0.10 mm–0.25 mm are dominant, with content reaching 59.03% and other grains accounting for less than half of the particle size of sand (Table 1). The mean grain size (Mz) is 2.28 (Mz ¼ log2 d) (Fig. 2). As the most sand–damaged section of Dunhuang–Golmud Railway (Yao, 2015), the sand hazard sections at Danghe River have an extent of 11.1 km (K74 þ 900 to K86 þ 000). The main landforms are the valley of Danghe River and the Mingsha Mountain, and
Table 1 Granularity composition of sandy materials at Honglianghe River and Danghe River (%). Sampling place
Honglianghe River Danghe River
Granularity (%) 0.005 mm to 0.05 mm
0.05 mm to 0.10 mm
0.10 mm to 0.25 mm
0.25 mm to 0.50 mm
0.50 mm to 1.00 mm
1.00 mm to 2.00 mm
>2 mm
0 0.27
1.24 23.47
59.03 44.87
36.33 24.90
3.30 5.77
0.10 0.72
0 0
41
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 3. Monthly variations of the average wind speed and sand–moving wind frequency at Honglianghe River and Danghe River in 2013.
3.2.2. Conditions of sand–moving wind The frequency of sand–moving wind in 2013 was 17.04%. The frequency of sand–moving wind was high in winter and spring and reached its maximum in February at 35.02%. The frequency of sand–moving wind was low in summer and autumn and reached its lowest in October at 4.46%. The monthly variations of sand–moving wind frequency and average wind speed of Honglianghe River were consistent throughout 2013 (Fig. 3). By contrast, the frequency of sand–moving wind in 2013 was 37.72%. The frequency of sand-moving wind was high in summer and autumn and reached its highest in June at 49.51%. The frequency of sand–moving wind was low in winter and spring and reached its lowest in November at 24.29%. The monthly variations of sand–moving wind frequency and average wind speed of Danghe River were also consistent throughout 2013 (Fig. 3). Therefore, although the speed of sand–moving wind of Honglianghe River was higher than that of Danghe River; however, the yearly frequency of sand–moving wind of Honglianghe River was lower than that of Danghe River. From the dynamic rose diagram of yearly sand–moving wind in 2013 (Fig. 5), the N wind direction of yearly sand–moving wind at Honglianghe River was prioritized, which accounted for 52.91% of the yearly total. The frequencies of other wind directions of sand–moving wind were low, and the synthetic direction of yearly sand–moving wind
Fig. 5. Dynamic rose diagram of yearly sand–moving wind at Honglianghe River and Danghe River in 2013.
is 340.88 . Although the N wind direction of yearly sand–moving wind at Danghe River was dominant, the proportion was not relatively high and only accounted for 13.90% of the yearly total. The sand–moving wind of other directions accounted for a certain proportion, and the synthetic direction of yearly sand–moving wind is 0.47 . Therefore, the wind direction of yearly sand–moving wind at Honglianghe River was single, whereas the wind direction of yearly sand–moving wind at Danghe River was dispersed and varied. 3.2.3. Sand drift potential Sand DP is an important method used to calculate the intensity of regional wind–sand activities (Wasson and Hyde, 1983a, 1983b) and is an important index employed to measure the evolution of wind–sand landforms in a region (Tan et al., 2016; Liu et al., 2011; Lancaster, 1985, 1989; Thomas, 1988). Therefore, sand DP is usually used in the design of sand prevention measures (Livingstone and Warren, 1996; Bullard, 1997). From the monthly variations of sand DP in 2013 (Fig. 6), the sand DP and RDP of Honglianghe River were high in winter and spring and low in summer and autumn. By contrast, the sand DP and RDP of Danghe River were high in summer and autumn and low in winter and spring. The RDP/DP of Honglianghe River was high and classified as high ratio, which indicated that the wind direction was single during the year. The RDP/DP of Danghe River was low and classified as intermediate and low ratio, which indicated that the wind direction was dispersed and varied during the year. The monthly variation of the RDD of Honglianghe River was stable, whereas the monthly variation of the RDD of Danghe River was significant. From the yearly sand DP in 2013 (Fig. 7), the yearly sand DP, RDP, RDP/DP, and RDD of Honglianghe River were 202.30 VU, 184.80 VU, 0.91, and 166.50 , respectively, indicating an intermediate wind energy environment, a high ratio, and a SSE direction. The yearly sand DP, RDP, RDP/DP, and RDD of Danghe River were 1500.79 VU, 572.67 VU, 0.38, and 174.96 , respectively, indicating a high wind energy environment, an intermediate ratio, and a S direction. Therefore, the yearly sand DP and RDP of Honglianghe River were lower than those of Danghe River, the yearly RDP/DP was higher than that of Danghe River, and the yearly RDD was close to that of Danghe River. 3.2.4. Maximum possible sand transport quantity Sand DP can only reflect the potential sand transport capacity in a certain direction during a period of time and cannot directly show the
Fig. 4. Wind direction rose diagram of Honglianghe River and Danghe River in 2013. 42
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 6. Monthly variations of sand DP at Honglianghe River and Danghe River in 2013.
From the yearly maximum possible sand transport quantity in 2013 (Fig. 9), the yearly Q of Honglianghe River was 656.54 kg m1⋅a1, the wind speed grade with the maximum contribution was distributed at 8 m s1 to 9 m s1 (Fig. 10), the yearly RQ was 598.75 kg m1⋅a1, and the yearly RA was 165.73 (SSE). By contrast, the yearly Q of Danghe River was 3431.48 kg m1⋅a1, the wind speed grade with the maximum contribution was distributed at 10 m s1 to 11 m s1 (Fig. 10), the yearly RQ was 1352.06 kg m1⋅a1, and the yearly RA was 175.81 (S). Therefore, the yearly Q and RQ of Honglianghe River were lower than those of Danghe River, the wind speed grade of Honglianghe River with the maximum contribution to the yearly Q was lower than that of Danghe River, and the yearly RA of Honglianghe River was close to that of Danghe River.
spatial distribution conditions of sand quantity. Therefore, the maximum possible sand transport quantity was adopted when calculating the spatial distribution of sand quantity, which refers to the maximum possible transport capacity of air flow for sandy materials when the sand source is sufficient, the sand surface is flat, bare, loose, and dry, and the air flow functioning on the surface of drift sand is fully saturated (Sarre, 1988). The maximum possible sand transport quantity is the theoretical limit value of sand transport quantity. The maximum possible sand transport quantity can not only directly reflect the spatial distribution of sand quantity but can also be used as reference values for such aspects as quantifying the intensity of regional wind–sand activities, designing the sand prevention engineering, and selecting and configuring the protective measures. From the monthly variations of maximum possible sand transport quantity in 2013 (Fig. 8), the Q and RQ of Honglianghe River were high in winter and spring and low in summer and autumn. By contrast, the Q and RQ of Danghe River were high in summer and autumn and low in winter and spring. The monthly variation of RA of Honglianghe River was stable, whereas the monthly variation of RA of Danghe River was significant.
3.2.5. Measured sand transport quantity Sand transport quantity was measured by using sand collected from eight directions at Honglianghe River and Danghe River in 2013. The results are shown in Fig. 11. The yearly total sand transport quantity of the eight directions of Honglianghe River was 641.41 kg m1 a1, and the sand transport quantity of the SW direction reached its maximum of 162.91 kg m1 a1. By contrast, the yearly total sand transport quantity of the eight directions of Danghe River was 2678.00 kg m1 a1, and the
Fig. 8. Monthly variations of the maximum possible sand transport quantity at Honglianghe River and Danghe River in 2013.
Fig. 7. Yearly sand DP at Honglianghe River and Danghe River in 2013. 43
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 9. Yearly maximum possible sand transport quantity at Honglianghe River and Danghe River in 2013.
Fig. 11. Measured sand transport quantity at Honglianghe River and Danghe River in 2013.
sand transport quantity of the W direction reached its maximum of 421.30 kg m1 a1. These measured results are consistent with the calculated results of sand DP and Q of both sections. Therefore, the measured yearly total sand transport quantity and the sand transport quantity in a single direction of Honglianghe River were lower than those of Danghe River (Fig. 11).
pressure is 297.49 kPa. During summer and autumn (May to October), the precipitation accounted for more than 90% of the yearly total, the air is humid (Fig. 12), and the water content of the surface sand layer is high (Xie et al., 2015a); thus, the sand hazards are further weakened. During winter and spring (November to April), the precipitation is low, the air is dry, and the water content of the surface sand layer is low; therefore, sand hazards are further aggravated because strong winds and dryness synchronously overlap. The average wind speed, sand–moving wind frequency, sand DP, RDP, Q, and RQ of Danghe River were high in summer and autumn and low in winter and spring; therefore, the sand hazards at Danghe River section are serious in summer and autumn. Given that Danghe River section is characterized by an arid climate (Tian et al., 2012), the annual average relative humidity is about 30%, the annual precipitation is 35.7 mm and the effects of precipitation on sand hazards are not obvious because the entire year is dry (Qu et al., 2014). During summer and autumn, temperature and evaporation increase, causing the air to become dry and the water content of the surface sand layer to decrease; therefore, sand hazards are further aggravated. Compared with the low–altitude sections, the sandy materials at Honglianghe River section are coarser, causing the speed of the
4. Discussions From the monthly variations of average wind speed, sand–moving wind, sand DP, and maximum possible sand transport quantity at both sections were determined. The average wind speed, sand–moving wind frequency, sand DP, RDP, Q, and RQ of Honglianghe River were high in winter and spring and low in summer and autumn. Therefore, the sand hazards at Honglianghe River section mainly occurred in winter and spring. The Honglianghe River section is characterized by semiarid climate with high elevation and cold temperature, and the annual precipitation is 250 mm–300 mm (Xie et al., 2015c). The annual average relative humidity is 52.33%, the annual average saturation vapor
Fig. 10. Maximum possible sand transport quantity of wind speed from each grade at Honglianghe River and Danghe River in 2013.
Fig. 12. Monthly variations of the relative humidity and saturation vapor pressure at Honglianghe River in 2013. 44
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Given that the sandy materials at Honglianghe River section are coarser, the speed of the sand–moving wind increased and the frequency of the sand–moving wind decreased. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased. Therefore, the dynamic wind of sand hazards is weakened and the overall hazards are alleviated. The wind direction at Honglianghe River section was single, whereas the wind direction at Danghe River section was dispersed and varied. Therefore, under the condition of approximately the same trend of the railways, the sand hazards at Honglianghe River sections concentrated in one direction, whereas the sand hazards at Danghe River sections dispersed in multiple directions.
sand–moving wind to increase and the frequency of sand–moving wind to decrease. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased; therefore, the dynamic wind weakened. Meanwhile, from the observations, the N wind direction and the sand–moving wind direction at Honglianghe River were prioritized, which accounted for 44.92% and 52.91% of the yearly total, respectively. The frequencies of other wind directions and static wind were low, indicating that the dominant wind direction of Honglianghe River section was obvious. Therefore, the RDP/DP was high and classified as high ratio, the variations of RDD and RA were stable, and the dynamic wind concentrated in the NNW direction, which was confirmed by RQ/Q ¼ 0.91 in this section. The wind direction and sand–moving wind direction at Danghe River section were mainly concentrated in the ENE and N directions, accounting for 15.18% and 13.90%, respectively. The other wind directions and static wind accounted for a certain percentage, indicating that the dominant wind direction of Danghe River section was not obvious. Therefore, the RDP/DP was low and classified as intermediate and low ratio, the variations of RDD and RA were dramatic, and the dynamic wind was dispersed in multiple directions besides the N direction, which was confirmed by RQ/Q ¼ 0.39 in this section. The railways at both sections approximately present a north–south trend (Fig. 1). The sand transport direction of Honglianghe River section is SSE, which substantially parallels with the railway. Related research shows that, when the dominant wind direction parallel with the railway trend or when the angle between dominant wind direction and railway trend is less than 30 , the wind will transport and guide sand (Xie et al., 2015a). The effect of blown sand on the railway is low; therefore, the sand hazards are weakened. The dominant wind direction was not obvious and the dynamic wind was dispersed in multiple directions besides the N direction at Danghe River section. The angles between the E and W wind directions and the railway trend are large. Under the condition of rich sand sources near the two sides, sand deposition would occur when the wind–sand flow is encountered and blocked by the railway subgrade, causing serious sand hazards. Therefore, under the condition of both railways exhibiting an approximately north–south trend, the single wind direction of Honglianghe River section did not exacerbate the sand hazards of this direction, but alleviated the overall sand hazards of the section. The dispersed and varied wind directions of Danghe River section caused serious sand hazards at the E and W directions of this section. Besides wind speed and wind direction, measured sand transport quantity is also affected by environmental conditions, especially those closely related to the local conditions of sand sources, therefore, the distributions of maximum possible sand transport quantity and measured sand transport quantity (Figs. 9 and 11) are not completely consistent at each direction, this result was similar to the findings on Tengger Desert (Zhang et al., 2010b), and Crescent Moon Spring (Pang et al., 2014).
Acknowledgements This research project was funded by the National Natural Science Foundation of China (grant no. 41401611), the China Postdoctoral Science Foundation (grant nos. 2015T81069 and 2014M560817), and one of Special Fund for Forest Scientific Research in the Public Welfare (201504401). References Anderson, R.S., Hallet, B., 1986. Sediment transport by wind: toward a general model. Bull. Geol. Soc. Am. 97, 523–535. Bagnold, R.A., 2005. The Physics of Blown Sand and Desert Dunes. Dover Publications, Inc., Mineola, New York, pp. 57–76. Bullard, J.E., 1997. A note on the use of the “fryberger method” for evaluating potential sand transport by wind. J. Sediment. Res. 67, 499–501. Chen, Y.N., Li, W.H., Yang, S.Q., Xu, H.Y., 2002. Environmental hazards in Xinjiang line of new Eurasian continental bridge. Sci. China (Ser. D.) 45 (Suppl.), 35–40. Fryberger, S.G., Al-Ssri, A.M., Clisham, T.J., Rizvi, A.R., Al-Hinai, K.G., 1984. Wind sedimentation in the Jafurah sand sea, Saudi Arabia. Sedimentology 37, 23–43. Han, Q.J., Qu, J.J., Dong, Z.B., Zhang, K.C., Zu, R.P., 2015. Air density effects on aeolian sand movement: implications for sediment transport and sand control in regions with extreme altitudes or temperatures. Sedimentology 62 (4), 1024–1038. Han, Q.J., Qu, J.J., Dong, Z.B., Zu, R.P., Zhang, K.C., Wang, H.T., Xie, S.B., 2014. The effect of air density on sand transport structures and the adobe abrasion profile: a field wind-tunnel experiment over a wide range of altitude. Bound.-Layer Meteor 150 (2), 299–317. Huang, N., Wang, Z.S., 2016. The formation of snow streamer in the turbulent atmosphere boundary layer. Aeolian Res. 23, 1–10. Jiang, H., Huang, N., Zhu, Y.J., 2014. Analysis of wind-blown sand movement over transverse dunes. Sci. Rep. 4, 7114. Lancaster, N., 1985. Wind and sand movement in the Namib sand sea. Earth Surf. Process. Landforms 10, 607–619. Lancaster, N., 1989. The dynamics of star dunes: an example from the Gran Desierto, Mexico. Sedimentology 36, 273–289. Leatherman, S.P., 1978. Short communication: new aeolian sand trap design. Sedimentology 25, 303–306. Lettau, K., Lettau, H., 1977. Experimental and micrometeorological field studies of dune migration. In: Lettau, K., Lettau, H. (Eds.), Exploring the World's Driest Climate. University of Wisconsin-Madison, pp. 110–147. Ling, Y.Q., 1994. The distributive heterogencity of sand-transporting quantity (rate) along horizontal direction. J. Exp. Mech. 9 (4), 352–356 (in Chinese with English Abstract). Ling, Y.Q., 1997. Engineering calculation of maximum possible sand transporting quantity. J. Desert Res. 17 (4), 362–368 (in Chinese with English Abstract). Liu, B.L., Qu, J.J., Zhang, W.M., Qian, G.Q., 2011. Numerical simulation of wind flow over transverse and pyramid dunes. J. Wind Eng. Ind. Aerodyn. 99 (8), 879–888. Liu, L., Liu, S.H., Xu, Z.Y., 2007. Efficiency of wind erosion control measures at the Dk1562 section of the Qinghai-Tibet railway. Princ. Pract. Desertification control 1, 223–229. Livingstone, I., Warren, A., 1996. Aeolian Geomorphology: an Introduction. Addison Wesley Longman Limited, London, pp. 22–23. Mckee, E.D., 1979. A Study of Global Sand Seas. University Press of the Pacific, Honolulu, Hawaii, pp. 137–169. Mujabar, P.S., Chandrasekar, N., 2013. Coastal erosion hazard and vulnerability assessment for southern coastal Tamil Nadu of India by using remote sensing and GIS. Nat. Hazards 69 (3), 1295–1314. Owens, P.R., 1964. The saltation of uniform sand in air. J. Fluid Mech. 20, 225–242. Pang, Y.J., Qu, J.J., Zhang, K.C., An, Z.S., Niu, Q.H., 2014. Quantitative analysis on the dynamic characteristics of megadunes around the Crescent Moon Spring, China. J. Arid. Land 6 (3), 255–263. Qu, J.J., Cao, S.X., Li, G.S., Niu, Q.H., Feng, Q., 2014. Conservation of natural and cultural heritage in Dunhuang, China. Gondwana Res. 26, 1216–1221. Rasmussen, K.R., Mikkelsen, H.E., 1991. Wind tunnel observations of aeolian transport rates. Acta Mech. Suppl. 1, 135–144. Sarre, R.D., 1988. Evaluation of aeolian sand transport equations using intertidal zone measurements, Saunton Sands, England. Sedimentology 35, 671–679.
5. Conclusions The following conclusions can be drawn under these experimental conditions: The sandy materials of both sections mainly come from the alluvial and diluvial materials of local rivers and the mobile sand dunes of nearby sandy mountains and are characterized by in situ sand accumulation. The sandy materials at Honglianghe River section are coarser, and the mean grain size is larger than that at Danghe River section. Compared with that of the Danghe River section, the yearly average wind speed of the Honglianghe River decreased, the speed of the sand–moving wind increased, the yearly frequency of sand–moving wind decreased, and the yearly sand DP, RDP, Q, and RQ, and the measured yearly total sand transport quantity of the eight directions decreased. The sand hazards at Honglianghe River section mainly occurred in winter and spring, whereas Danghe River section mainly occurred in summer and autumn. 45
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46 Xie, S.B., Qu, J.J., Lai, Y.M., Xu, X.T., Pang, Y.J., 2015b. Key evidence of the role of desertification in protecting the underlying permafrost in the Qinghai–Tibet Plateau. Sci. Rep. 5, 15152. Xie, S.B., Qu, J.J., Lai, Y.M., Zhou, Z.W., Xu, X.T., 2015c. Effects of freeze–thaw cycles on soil mechanical and physical properties in the Qinghai–Tibet Plateau. J. Mt. Sci. 12 (4), 999–1009. Xie, S.B., Qu, J.J., Zu, R.P., Zhang, K.C., Han, Q.J., Niu, Q.H., 2013. Effect of sandy sediments produced by the mechanical control of sand deposition on the thermal regime of underlying permafrost along the Qinghai-Tibet Railway. Land Degrad. Dev. 24 (5), 453–462. Yao, H.L., 2015. The blown sand characteristics and sand hazards comprehensive protective system at the sand dune areas along the Dun-Ge railway. J. Desert Res. 35 (3), 555–564 (in Chinese with English Abstract). Zhang, J., Teng, Z.J., Huang, N., Guo, L., Shao, Y.P., 2016. Surface renewal as a significant mechanism for dust emission. Atmos. Chem. Phys. 16 (24), 15517–15528. Zhang, K.C., Kai, K.J., Qu, J.J., Ling, Y.Q., Niu, Q.H., 2010b. Dynamic changes of a typical linear dune in the Tengger Desert. J. Arid. Land 2 (4), 272–278. Zhang, K.C., Qu, J.J., Han, Q.J., Xie, S.B., Kai, K., Niu, Q.H., An, Z.S., 2014. Wind tunnel simulation of windblown sand along China's Qinghai-Tibet railway. Land Degrad. Dev. 25 (3), 244–250. Zhang, K.C., Qu, J.J., Liao, K.T., Niu, Q.H., Han, Q.J., 2010a. Damage by wind-blown sand and its control along Qinghai-Tibet Railway in China. Aeolian Res. 1, 143–146.
Shen, W.S., Zhang, H., Zou, C.X., Cao, X.Z., Tang, X.Y., 2004. Approaches to prediction of impact of Qinghai-Tibet Railway construction on alpine ecosystems alongside and its recovery. Chin. Sci. Bull. 49 (8), 834–841. Sorensen, M., 1991. A analytic model of wind-blown sand transport. Acta Mech. Suppl. 1, 67–82. Tan, L.H., Zhang, W.M., Bian, K., An, Z.S., Zu, R.P., Qu, J.J., 2016. Numerical simulation of threedimensional wind flow patterns over a star dune. J. Wind Eng. Ind. Aerodyn. 159, 1–8. Thomas, D.S.G., 1988. The nature and deposition setting of arid and semi-arid Kalahari sediments, Southern Africa. J. Arid. Environ. 14, 17–26. Tian, H., Qu, J.J., Yang, G.S., Zhang, W.M., Niu, Q.H., 2012. Study on the feasibility of Dunhuang-Golmud Railway crossing the megadunes area at the east edge of Kumtagh Desert. J. Desert Res. 32 (1), 1–8 (in Chinese with English Abstract). Wang, G.X., Yao, J.Z., Guo, Z.G., Wu, Q.B., Wang, Y.B., 2004. Changes in permafrost ecosystem under the influences of human engineering activities and its enlightenment to railway construction. Chin. Sci. Bull. 49 (16), 1741–1750. Wasson, R.J., Hyde, R., 1983a. A test of granulometric control of desert dune geometry. Earth Surf. Process. Landf. 8, 301–312. Wasson, R.J., Hyde, R., 1983b. Factors determining desert dune type. Nature 304, 337–339. Xie, S.B., Qu, J.J., Lai, Y.M., Pang, Y.J., 2015a. Formation mechanism and suitable controlling pattern of sand hazards at Honglianghe River section of Qinghai–Tibet railway. Nat. Hazards 76 (2), 855–871.
46
Contents lists available at ScienceDirect
Journal of Wind Engineering & Industrial Aerodynamics journal homepage: www.elsevier.com/locate/jweia
Dynamic wind differences in the formation of sand hazards at highand low-altitude railway sections Shengbo Xie a, *, Jianjun Qu a, Yingjun Pang b, ** a
Key Laboratory of Desert and Desertification/Dunhuang Gobi and Desert Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China Institute of Desertification Studies, Chinese Academy of Forestry, Beijing, 100091, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords: Railway sand hazard Sand–moving wind Sand drift potential Maximum possible sand transport quantity
Compared with the railway sand hazards at low-altitude regions, whether the railway sand hazards at highaltitude regions have been aggravated or mitigated, which is not conducive to targeted control of sand hazards, is currently unclear. Honglianghe River section of Qinghai–Tibet Railway and Danghe River section of Dunhuang–Golmud Railway were selected as the typical representatives of high- and low-altitude sand hazard sections, respectively, to understand the sand hazard law of different-altitude railway sections. Results show the sand hazards at Honglianghe River section mainly occurred in winter and spring and Danghe River section mainly occurred in summer and autumn. The mean grain size of the sandy materials at Honglianghe River section is larger than that at Danghe River section, causing the speed of the sand-moving wind to increase and the frequency of the sand-moving wind to decrease. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased. Therefore, the dynamic wind of sand hazards at Honglianghe River section weakened and the overall hazards alleviated compared with that at Danghe River section. The results can provide the bases for controlling sand hazards at different-altitude railway sections.
1. Introduction Blown sand has been an important factor confounding road construction and safe operation in sandy regions (Mujabar and Chandrasekar, 2013). As more railways are constructed and being operated in sandy regions, railway sand hazards and its control have been the focus of considerable attention (Chen et al., 2002; Zhang et al., 2010a). Given the fragile ecology in sandy regions, matter and energy balance of the system would be altered by any small disturbance. The construction processes of railways inevitably destroyed the original sparse vegetation and fragile ecological environment in sandy regions and further exacerbated the surface blown sand activities (Shen et al., 2004; Wang et al., 2004). The original relatively stable dynamic balance of blown sand movement in sandy regions was disturbed as a result of the appearance of roadbed (Zhang et al., 2014), particularly after the railway construction was completed. Moreover, the path and intensity of wind–sand flow near the surface were altered, which resulted in sandy materials deposited near the railway. Thus, blown sand hazards became prominent. Current research concerning railway sand hazards mainly focus on blown sand movement law, formation processes, disaster-causing * Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Xie), [email protected] (Y. Pang). http://dx.doi.org/10.1016/j.jweia.2017.07.003 Received 16 December 2016; Received in revised form 7 June 2017; Accepted 9 July 2017 0167-6105/© 2017 Elsevier Ltd. All rights reserved.
mechanisms, and control of roadbed sand hazards at low-altitude sections (Jiang et al., 2014; Zhang et al., 2016). In recent years, with the railway construction and operation at high-altitude sandy regions such as Qinghai–Tibet plateau, particularly the Qinghai–Tibet Railway and Lhasa–Shigatse Railway built and opened to traffic, railway sand hazards have expanded to high-altitude regions (Liu et al., 2007), and the distribution altitudes of sand hazards have become high. The sand hazard sections of Tanggula–Za'gyazangbo of Qinghai–Tibet Railway are distributed above 5000 m altitude (the highest section reached 5067 m) and are currently the highest railway sand hazards of the world. Despite the increase in the number of sand hazard sections at high-altitude regions, studies on railway sand hazards at high-altitude sections are scarce, leading to lack the knowledge of the dynamic processes of blown sand (Han et al., 2014, 2015; Huang and Wang, 2016). Moreover, comparative studies on railway sand hazards between high- and low-altitude sections are few. The laws of railway sand hazards at high-altitude sections have not been intensively investigated and are limited to the construction of railways at high-altitude sandy regions only occurring in recent years. Compared with the sand hazards at lowaltitude regions, whether the sand hazards at high-altitude regions
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
line distance between the two sites is approximately 550 km, with an altitude difference of 3178 m. The experimental fields were established in the two sites to conduct continuous positioning observations (Xie et al., 2015b). Local sand samples were collected, and the granularity composition of the sand samples were analyzed by sieving method in the laboratory using the observational data to calculate sand drift potential (DP) and maximum possible sand transport quantity. Meteorological sensors (HOBO-U30 Automatic Meteorological Station, the model numbers of wind speed and wind direction sensors are S-WSAM003 and S-WDA-M003, respectively) present a surface height of 2 m, with wind speed and wind direction recorded every 5 min. Sand collected from eight directions was used to determine the sand transport quantity. A vertical sand collector was used, with eight intakes that corresponded to the eight directions. Sand DP was calculated using the following transport equation (Lettau and Lettau, 1977; Bagnold, 2005):
have been aggravated or mitigated is still unclear. What are the differences in the dynamic aspects of railway sand hazard formation between high- and low-altitude sections? The answers to these problems are currently unclear, which is not conducive to targeted control of sand hazards. The Honglianghe River section of Qinghai–Tibet Railway and Danghe River section of Dunhuang–Golmud Railway were selected as the typical representatives of high- and low-altitude sand hazard sections, respectively, to answer the aforementioned questions. The source of sandy materials and the dynamic environment of wind at high- and low-altitude sand hazard sections were comparatively investigated through different methods, such as field observation, laboratory analysis, and calculation. This study aimed to reveal the differences of blown sand movement law and provide the bases for controlling sand hazards at different-altitude railway sections. 2. Material and methods
DP ¼ V2(V Vt)t,
The Honglianghe River of Qinghai–Tibet Railway (the experimental observation site is located at 35 030 1300 N, 93 010 1100 E, with an altitude of 4658 m) and Danghe River of Dunhuang–Golmud Railway (the experimental observation site is located at 39 530 2000 N, 94 280 2400 E, with an altitude of 1480 m) were selected as the typical representatives of high- and low-altitude sections (Fig. 1), respectively, to analyze the differences of sand hazards at high- and low-altitude railway sections. The climates of the two sites are characterized by semiarid climate with high elevation and cold temperature and arid climate, respectively, the underlying surface types are characterized by gravel gobi. The straight-
(1)
where DP is the sand DP expressed in vector units (VU), V is the wind speed greater than the sand–moving wind, and Vt is the sand–moving wind speed. When measured by locale (Han et al., 2014, 2015), a wind tunnel was transported to the two sites and installed on the sandy surface, the wind speed was increased slowly, and sand particle movement was monitored by a system of particle image velocimetry, the critical starting speed of the sand particles is the sand–moving wind speed, and the speeds of the sand–moving wind at the Honglianghe River of Qinghai–Tibet Railway and Danghe River of Dunhuang–Golmud Railway
Fig. 1. Location map of the experimental observation fields. 40
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
were 5.7 and 5.0 m s1, respectively. The units of wind speed must be converted to nmile⋅h1. Meanwhile, t is the time affected by sand–moving wind and expressed in frequency, which is commonly the percentage of sand–moving wind time to total observation time during the observation period. Given that wind is a vector, the resultant drift potential (RDP) and resultant drift direction (RDD) were obtained by synthesizing the sand DP in 16 directions on the basis of the vector synthesis rule. Such rule can reflect the size of the net sand transport capacity in a region. An index of directional wind variability is the ratio of RDP to DP, known as RDP/DP, which is used to reflect the combined situation of the wind direction in a region. Wind energy environments were classified as high energy (400 VU), intermediate energy (200 VU to 400 VU), and low energy (200 VU). The index of directional variability was classified as high ratio (0.8), intermediate ratio (0.3–0.8), and low ratio (0.3) on the basis of the magnitude of sand DP (Mckee, 1979; Fryberger et al., 1984). Many methods were used to calculate the sand transport quantity (Leatherman, 1978; Rasmussen and Mikkelsen, 1991; Owens, 1964; Sorensen, 1991; Anderson and Hallet, 1986). From the local conditions and relative results (Ling, 1994, 1997), the maximum possible sand transport quantity was calculated using the following formula: Q ¼ 8.95 101(V Vt) T,
Fig. 2. The particle size composition of sandy materials at the experimental observation fields.
(2)
the sandy materials mainly come from the alluvial and diluvial materials of Danghe River and the mobile sand dunes of Mingsha Mountain, which are located at both sides of the railway and characterized by in situ sand accumulation. The grain size composition of sand with particle size in the range of 0.10 mm–0.25 mm are dominant, followed by sand with particle size in the range of 0.25 mm–0.50 mm (Table 1). The mean grain size is 2.69 (Fig. 2). Therefore, the sandy materials of Honglianghe River and Danghe River mainly come from the alluvial and diluvial materials of local rivers and the mobile sand dunes of nearby sandy mountains and are characterized by in situ sand accumulation. However, the sandy materials at Honglianghe River section are coarser, and the mean grain size is larger than that at Danghe River section.
where Q is the maximum possible sand transport quantity, V is the wind speed greater than the sand–moving wind, Vt is the sand–moving wind speed, and T is the cumulative duration of wind speed with different grades. In the calculation, first, the statistics of the frequency or time of different wind speed grades at each direction were obtained on the basis of 16 directions. Second, the maximum possible sand transport quantities in the 16 directions were calculated under the condition of different wind speed grades to obtain the maximum possible sand transport quantity of each direction. The sum of the maximum possible sand transport quantity in 16 directions is the total quantity of the maximum possible sand transport (Q). Finally, the resultant quantity (RQ) and resultant angle (RA) of the maximum possible sand transport were obtained by synthesizing the maximum possible sand transport quantity in 16 directions on the basis of the vector synthesis rule.
3.2. Dynamic environment of wind 3.2.1. Average wind speed and wind direction In 2013, the average wind speed at Honglianghe River was 3.51 m s1. The average wind speed was high in winter and spring and reached its maximum in February at 4.89 m s1. The average wind speed was low in summer and autumn and reached its lowest in October at 2.57 m s1. By contrast, in 2013, the average wind speed at Danghe River was 4.37 m s1. The average wind speed was high in summer and autumn and low in winter and spring. The average wind speed of Honglianghe River was lower than that of Danghe River (Fig. 3). From the wind rose data in 2013 (Fig. 4), at Honglianghe River, the N wind direction was prioritized, which accounted for 44.92% of the yearly total, followed by the NNW wind direction, which accounted for 31.99% of the yearly total. The frequencies of other wind directions were low, and the frequency of static wind was 1.58%. By contrast, at Danghe River, each direction of the wind accounted for a certain proportion, i.e., the ENE wind direction accounted for the highest proportion, which accounted for 15.18% of the yearly total. Moreover, the frequency of static wind was 18.50%. Therefore, the wind direction of Honglianghe River was single, whereas the wind direction of Danghe River was dispersed and varied.
3. Results 3.1. Source of sandy material As the most sand–damaged section of Qinghai–Tibet Railway (Xie et al., 2013, 2015a), the sand hazard sections at Honglianghe River have an extent of 9.76 km (K1100 þ 400 to K1110 þ 160). The main landforms are the valley of Honglianghe River and the Gongmaorima Hill, and the sandy materials mainly come from the alluvial and diluvial materials of Honglianghe River and the mobile sand dunes of Gongmaorima Hill, which are located at the west side of the railway and characterized by in situ sand accumulation. The grain size composition of sand with particle size in the range of 0.10 mm–0.25 mm are dominant, with content reaching 59.03% and other grains accounting for less than half of the particle size of sand (Table 1). The mean grain size (Mz) is 2.28 (Mz ¼ log2 d) (Fig. 2). As the most sand–damaged section of Dunhuang–Golmud Railway (Yao, 2015), the sand hazard sections at Danghe River have an extent of 11.1 km (K74 þ 900 to K86 þ 000). The main landforms are the valley of Danghe River and the Mingsha Mountain, and
Table 1 Granularity composition of sandy materials at Honglianghe River and Danghe River (%). Sampling place
Honglianghe River Danghe River
Granularity (%) 0.005 mm to 0.05 mm
0.05 mm to 0.10 mm
0.10 mm to 0.25 mm
0.25 mm to 0.50 mm
0.50 mm to 1.00 mm
1.00 mm to 2.00 mm
>2 mm
0 0.27
1.24 23.47
59.03 44.87
36.33 24.90
3.30 5.77
0.10 0.72
0 0
41
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 3. Monthly variations of the average wind speed and sand–moving wind frequency at Honglianghe River and Danghe River in 2013.
3.2.2. Conditions of sand–moving wind The frequency of sand–moving wind in 2013 was 17.04%. The frequency of sand–moving wind was high in winter and spring and reached its maximum in February at 35.02%. The frequency of sand–moving wind was low in summer and autumn and reached its lowest in October at 4.46%. The monthly variations of sand–moving wind frequency and average wind speed of Honglianghe River were consistent throughout 2013 (Fig. 3). By contrast, the frequency of sand–moving wind in 2013 was 37.72%. The frequency of sand-moving wind was high in summer and autumn and reached its highest in June at 49.51%. The frequency of sand–moving wind was low in winter and spring and reached its lowest in November at 24.29%. The monthly variations of sand–moving wind frequency and average wind speed of Danghe River were also consistent throughout 2013 (Fig. 3). Therefore, although the speed of sand–moving wind of Honglianghe River was higher than that of Danghe River; however, the yearly frequency of sand–moving wind of Honglianghe River was lower than that of Danghe River. From the dynamic rose diagram of yearly sand–moving wind in 2013 (Fig. 5), the N wind direction of yearly sand–moving wind at Honglianghe River was prioritized, which accounted for 52.91% of the yearly total. The frequencies of other wind directions of sand–moving wind were low, and the synthetic direction of yearly sand–moving wind
Fig. 5. Dynamic rose diagram of yearly sand–moving wind at Honglianghe River and Danghe River in 2013.
is 340.88 . Although the N wind direction of yearly sand–moving wind at Danghe River was dominant, the proportion was not relatively high and only accounted for 13.90% of the yearly total. The sand–moving wind of other directions accounted for a certain proportion, and the synthetic direction of yearly sand–moving wind is 0.47 . Therefore, the wind direction of yearly sand–moving wind at Honglianghe River was single, whereas the wind direction of yearly sand–moving wind at Danghe River was dispersed and varied. 3.2.3. Sand drift potential Sand DP is an important method used to calculate the intensity of regional wind–sand activities (Wasson and Hyde, 1983a, 1983b) and is an important index employed to measure the evolution of wind–sand landforms in a region (Tan et al., 2016; Liu et al., 2011; Lancaster, 1985, 1989; Thomas, 1988). Therefore, sand DP is usually used in the design of sand prevention measures (Livingstone and Warren, 1996; Bullard, 1997). From the monthly variations of sand DP in 2013 (Fig. 6), the sand DP and RDP of Honglianghe River were high in winter and spring and low in summer and autumn. By contrast, the sand DP and RDP of Danghe River were high in summer and autumn and low in winter and spring. The RDP/DP of Honglianghe River was high and classified as high ratio, which indicated that the wind direction was single during the year. The RDP/DP of Danghe River was low and classified as intermediate and low ratio, which indicated that the wind direction was dispersed and varied during the year. The monthly variation of the RDD of Honglianghe River was stable, whereas the monthly variation of the RDD of Danghe River was significant. From the yearly sand DP in 2013 (Fig. 7), the yearly sand DP, RDP, RDP/DP, and RDD of Honglianghe River were 202.30 VU, 184.80 VU, 0.91, and 166.50 , respectively, indicating an intermediate wind energy environment, a high ratio, and a SSE direction. The yearly sand DP, RDP, RDP/DP, and RDD of Danghe River were 1500.79 VU, 572.67 VU, 0.38, and 174.96 , respectively, indicating a high wind energy environment, an intermediate ratio, and a S direction. Therefore, the yearly sand DP and RDP of Honglianghe River were lower than those of Danghe River, the yearly RDP/DP was higher than that of Danghe River, and the yearly RDD was close to that of Danghe River. 3.2.4. Maximum possible sand transport quantity Sand DP can only reflect the potential sand transport capacity in a certain direction during a period of time and cannot directly show the
Fig. 4. Wind direction rose diagram of Honglianghe River and Danghe River in 2013. 42
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 6. Monthly variations of sand DP at Honglianghe River and Danghe River in 2013.
From the yearly maximum possible sand transport quantity in 2013 (Fig. 9), the yearly Q of Honglianghe River was 656.54 kg m1⋅a1, the wind speed grade with the maximum contribution was distributed at 8 m s1 to 9 m s1 (Fig. 10), the yearly RQ was 598.75 kg m1⋅a1, and the yearly RA was 165.73 (SSE). By contrast, the yearly Q of Danghe River was 3431.48 kg m1⋅a1, the wind speed grade with the maximum contribution was distributed at 10 m s1 to 11 m s1 (Fig. 10), the yearly RQ was 1352.06 kg m1⋅a1, and the yearly RA was 175.81 (S). Therefore, the yearly Q and RQ of Honglianghe River were lower than those of Danghe River, the wind speed grade of Honglianghe River with the maximum contribution to the yearly Q was lower than that of Danghe River, and the yearly RA of Honglianghe River was close to that of Danghe River.
spatial distribution conditions of sand quantity. Therefore, the maximum possible sand transport quantity was adopted when calculating the spatial distribution of sand quantity, which refers to the maximum possible transport capacity of air flow for sandy materials when the sand source is sufficient, the sand surface is flat, bare, loose, and dry, and the air flow functioning on the surface of drift sand is fully saturated (Sarre, 1988). The maximum possible sand transport quantity is the theoretical limit value of sand transport quantity. The maximum possible sand transport quantity can not only directly reflect the spatial distribution of sand quantity but can also be used as reference values for such aspects as quantifying the intensity of regional wind–sand activities, designing the sand prevention engineering, and selecting and configuring the protective measures. From the monthly variations of maximum possible sand transport quantity in 2013 (Fig. 8), the Q and RQ of Honglianghe River were high in winter and spring and low in summer and autumn. By contrast, the Q and RQ of Danghe River were high in summer and autumn and low in winter and spring. The monthly variation of RA of Honglianghe River was stable, whereas the monthly variation of RA of Danghe River was significant.
3.2.5. Measured sand transport quantity Sand transport quantity was measured by using sand collected from eight directions at Honglianghe River and Danghe River in 2013. The results are shown in Fig. 11. The yearly total sand transport quantity of the eight directions of Honglianghe River was 641.41 kg m1 a1, and the sand transport quantity of the SW direction reached its maximum of 162.91 kg m1 a1. By contrast, the yearly total sand transport quantity of the eight directions of Danghe River was 2678.00 kg m1 a1, and the
Fig. 8. Monthly variations of the maximum possible sand transport quantity at Honglianghe River and Danghe River in 2013.
Fig. 7. Yearly sand DP at Honglianghe River and Danghe River in 2013. 43
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Fig. 9. Yearly maximum possible sand transport quantity at Honglianghe River and Danghe River in 2013.
Fig. 11. Measured sand transport quantity at Honglianghe River and Danghe River in 2013.
sand transport quantity of the W direction reached its maximum of 421.30 kg m1 a1. These measured results are consistent with the calculated results of sand DP and Q of both sections. Therefore, the measured yearly total sand transport quantity and the sand transport quantity in a single direction of Honglianghe River were lower than those of Danghe River (Fig. 11).
pressure is 297.49 kPa. During summer and autumn (May to October), the precipitation accounted for more than 90% of the yearly total, the air is humid (Fig. 12), and the water content of the surface sand layer is high (Xie et al., 2015a); thus, the sand hazards are further weakened. During winter and spring (November to April), the precipitation is low, the air is dry, and the water content of the surface sand layer is low; therefore, sand hazards are further aggravated because strong winds and dryness synchronously overlap. The average wind speed, sand–moving wind frequency, sand DP, RDP, Q, and RQ of Danghe River were high in summer and autumn and low in winter and spring; therefore, the sand hazards at Danghe River section are serious in summer and autumn. Given that Danghe River section is characterized by an arid climate (Tian et al., 2012), the annual average relative humidity is about 30%, the annual precipitation is 35.7 mm and the effects of precipitation on sand hazards are not obvious because the entire year is dry (Qu et al., 2014). During summer and autumn, temperature and evaporation increase, causing the air to become dry and the water content of the surface sand layer to decrease; therefore, sand hazards are further aggravated. Compared with the low–altitude sections, the sandy materials at Honglianghe River section are coarser, causing the speed of the
4. Discussions From the monthly variations of average wind speed, sand–moving wind, sand DP, and maximum possible sand transport quantity at both sections were determined. The average wind speed, sand–moving wind frequency, sand DP, RDP, Q, and RQ of Honglianghe River were high in winter and spring and low in summer and autumn. Therefore, the sand hazards at Honglianghe River section mainly occurred in winter and spring. The Honglianghe River section is characterized by semiarid climate with high elevation and cold temperature, and the annual precipitation is 250 mm–300 mm (Xie et al., 2015c). The annual average relative humidity is 52.33%, the annual average saturation vapor
Fig. 10. Maximum possible sand transport quantity of wind speed from each grade at Honglianghe River and Danghe River in 2013.
Fig. 12. Monthly variations of the relative humidity and saturation vapor pressure at Honglianghe River in 2013. 44
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46
Given that the sandy materials at Honglianghe River section are coarser, the speed of the sand–moving wind increased and the frequency of the sand–moving wind decreased. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased. Therefore, the dynamic wind of sand hazards is weakened and the overall hazards are alleviated. The wind direction at Honglianghe River section was single, whereas the wind direction at Danghe River section was dispersed and varied. Therefore, under the condition of approximately the same trend of the railways, the sand hazards at Honglianghe River sections concentrated in one direction, whereas the sand hazards at Danghe River sections dispersed in multiple directions.
sand–moving wind to increase and the frequency of sand–moving wind to decrease. Under the condition of the decrease in the average wind speed, the sand DP, RDP, Q, and RQ and the measured sand transport quantity decreased; therefore, the dynamic wind weakened. Meanwhile, from the observations, the N wind direction and the sand–moving wind direction at Honglianghe River were prioritized, which accounted for 44.92% and 52.91% of the yearly total, respectively. The frequencies of other wind directions and static wind were low, indicating that the dominant wind direction of Honglianghe River section was obvious. Therefore, the RDP/DP was high and classified as high ratio, the variations of RDD and RA were stable, and the dynamic wind concentrated in the NNW direction, which was confirmed by RQ/Q ¼ 0.91 in this section. The wind direction and sand–moving wind direction at Danghe River section were mainly concentrated in the ENE and N directions, accounting for 15.18% and 13.90%, respectively. The other wind directions and static wind accounted for a certain percentage, indicating that the dominant wind direction of Danghe River section was not obvious. Therefore, the RDP/DP was low and classified as intermediate and low ratio, the variations of RDD and RA were dramatic, and the dynamic wind was dispersed in multiple directions besides the N direction, which was confirmed by RQ/Q ¼ 0.39 in this section. The railways at both sections approximately present a north–south trend (Fig. 1). The sand transport direction of Honglianghe River section is SSE, which substantially parallels with the railway. Related research shows that, when the dominant wind direction parallel with the railway trend or when the angle between dominant wind direction and railway trend is less than 30 , the wind will transport and guide sand (Xie et al., 2015a). The effect of blown sand on the railway is low; therefore, the sand hazards are weakened. The dominant wind direction was not obvious and the dynamic wind was dispersed in multiple directions besides the N direction at Danghe River section. The angles between the E and W wind directions and the railway trend are large. Under the condition of rich sand sources near the two sides, sand deposition would occur when the wind–sand flow is encountered and blocked by the railway subgrade, causing serious sand hazards. Therefore, under the condition of both railways exhibiting an approximately north–south trend, the single wind direction of Honglianghe River section did not exacerbate the sand hazards of this direction, but alleviated the overall sand hazards of the section. The dispersed and varied wind directions of Danghe River section caused serious sand hazards at the E and W directions of this section. Besides wind speed and wind direction, measured sand transport quantity is also affected by environmental conditions, especially those closely related to the local conditions of sand sources, therefore, the distributions of maximum possible sand transport quantity and measured sand transport quantity (Figs. 9 and 11) are not completely consistent at each direction, this result was similar to the findings on Tengger Desert (Zhang et al., 2010b), and Crescent Moon Spring (Pang et al., 2014).
Acknowledgements This research project was funded by the National Natural Science Foundation of China (grant no. 41401611), the China Postdoctoral Science Foundation (grant nos. 2015T81069 and 2014M560817), and one of Special Fund for Forest Scientific Research in the Public Welfare (201504401). References Anderson, R.S., Hallet, B., 1986. Sediment transport by wind: toward a general model. Bull. Geol. Soc. Am. 97, 523–535. Bagnold, R.A., 2005. The Physics of Blown Sand and Desert Dunes. Dover Publications, Inc., Mineola, New York, pp. 57–76. Bullard, J.E., 1997. A note on the use of the “fryberger method” for evaluating potential sand transport by wind. J. Sediment. Res. 67, 499–501. Chen, Y.N., Li, W.H., Yang, S.Q., Xu, H.Y., 2002. Environmental hazards in Xinjiang line of new Eurasian continental bridge. Sci. China (Ser. D.) 45 (Suppl.), 35–40. Fryberger, S.G., Al-Ssri, A.M., Clisham, T.J., Rizvi, A.R., Al-Hinai, K.G., 1984. Wind sedimentation in the Jafurah sand sea, Saudi Arabia. Sedimentology 37, 23–43. Han, Q.J., Qu, J.J., Dong, Z.B., Zhang, K.C., Zu, R.P., 2015. Air density effects on aeolian sand movement: implications for sediment transport and sand control in regions with extreme altitudes or temperatures. Sedimentology 62 (4), 1024–1038. Han, Q.J., Qu, J.J., Dong, Z.B., Zu, R.P., Zhang, K.C., Wang, H.T., Xie, S.B., 2014. The effect of air density on sand transport structures and the adobe abrasion profile: a field wind-tunnel experiment over a wide range of altitude. Bound.-Layer Meteor 150 (2), 299–317. Huang, N., Wang, Z.S., 2016. The formation of snow streamer in the turbulent atmosphere boundary layer. Aeolian Res. 23, 1–10. Jiang, H., Huang, N., Zhu, Y.J., 2014. Analysis of wind-blown sand movement over transverse dunes. Sci. Rep. 4, 7114. Lancaster, N., 1985. Wind and sand movement in the Namib sand sea. Earth Surf. Process. Landforms 10, 607–619. Lancaster, N., 1989. The dynamics of star dunes: an example from the Gran Desierto, Mexico. Sedimentology 36, 273–289. Leatherman, S.P., 1978. Short communication: new aeolian sand trap design. Sedimentology 25, 303–306. Lettau, K., Lettau, H., 1977. Experimental and micrometeorological field studies of dune migration. In: Lettau, K., Lettau, H. (Eds.), Exploring the World's Driest Climate. University of Wisconsin-Madison, pp. 110–147. Ling, Y.Q., 1994. The distributive heterogencity of sand-transporting quantity (rate) along horizontal direction. J. Exp. Mech. 9 (4), 352–356 (in Chinese with English Abstract). Ling, Y.Q., 1997. Engineering calculation of maximum possible sand transporting quantity. J. Desert Res. 17 (4), 362–368 (in Chinese with English Abstract). Liu, B.L., Qu, J.J., Zhang, W.M., Qian, G.Q., 2011. Numerical simulation of wind flow over transverse and pyramid dunes. J. Wind Eng. Ind. Aerodyn. 99 (8), 879–888. Liu, L., Liu, S.H., Xu, Z.Y., 2007. Efficiency of wind erosion control measures at the Dk1562 section of the Qinghai-Tibet railway. Princ. Pract. Desertification control 1, 223–229. Livingstone, I., Warren, A., 1996. Aeolian Geomorphology: an Introduction. Addison Wesley Longman Limited, London, pp. 22–23. Mckee, E.D., 1979. A Study of Global Sand Seas. University Press of the Pacific, Honolulu, Hawaii, pp. 137–169. Mujabar, P.S., Chandrasekar, N., 2013. Coastal erosion hazard and vulnerability assessment for southern coastal Tamil Nadu of India by using remote sensing and GIS. Nat. Hazards 69 (3), 1295–1314. Owens, P.R., 1964. The saltation of uniform sand in air. J. Fluid Mech. 20, 225–242. Pang, Y.J., Qu, J.J., Zhang, K.C., An, Z.S., Niu, Q.H., 2014. Quantitative analysis on the dynamic characteristics of megadunes around the Crescent Moon Spring, China. J. Arid. Land 6 (3), 255–263. Qu, J.J., Cao, S.X., Li, G.S., Niu, Q.H., Feng, Q., 2014. Conservation of natural and cultural heritage in Dunhuang, China. Gondwana Res. 26, 1216–1221. Rasmussen, K.R., Mikkelsen, H.E., 1991. Wind tunnel observations of aeolian transport rates. Acta Mech. Suppl. 1, 135–144. Sarre, R.D., 1988. Evaluation of aeolian sand transport equations using intertidal zone measurements, Saunton Sands, England. Sedimentology 35, 671–679.
5. Conclusions The following conclusions can be drawn under these experimental conditions: The sandy materials of both sections mainly come from the alluvial and diluvial materials of local rivers and the mobile sand dunes of nearby sandy mountains and are characterized by in situ sand accumulation. The sandy materials at Honglianghe River section are coarser, and the mean grain size is larger than that at Danghe River section. Compared with that of the Danghe River section, the yearly average wind speed of the Honglianghe River decreased, the speed of the sand–moving wind increased, the yearly frequency of sand–moving wind decreased, and the yearly sand DP, RDP, Q, and RQ, and the measured yearly total sand transport quantity of the eight directions decreased. The sand hazards at Honglianghe River section mainly occurred in winter and spring, whereas Danghe River section mainly occurred in summer and autumn. 45
S. Xie et al.
Journal of Wind Engineering & Industrial Aerodynamics 169 (2017) 39–46 Xie, S.B., Qu, J.J., Lai, Y.M., Xu, X.T., Pang, Y.J., 2015b. Key evidence of the role of desertification in protecting the underlying permafrost in the Qinghai–Tibet Plateau. Sci. Rep. 5, 15152. Xie, S.B., Qu, J.J., Lai, Y.M., Zhou, Z.W., Xu, X.T., 2015c. Effects of freeze–thaw cycles on soil mechanical and physical properties in the Qinghai–Tibet Plateau. J. Mt. Sci. 12 (4), 999–1009. Xie, S.B., Qu, J.J., Zu, R.P., Zhang, K.C., Han, Q.J., Niu, Q.H., 2013. Effect of sandy sediments produced by the mechanical control of sand deposition on the thermal regime of underlying permafrost along the Qinghai-Tibet Railway. Land Degrad. Dev. 24 (5), 453–462. Yao, H.L., 2015. The blown sand characteristics and sand hazards comprehensive protective system at the sand dune areas along the Dun-Ge railway. J. Desert Res. 35 (3), 555–564 (in Chinese with English Abstract). Zhang, J., Teng, Z.J., Huang, N., Guo, L., Shao, Y.P., 2016. Surface renewal as a significant mechanism for dust emission. Atmos. Chem. Phys. 16 (24), 15517–15528. Zhang, K.C., Kai, K.J., Qu, J.J., Ling, Y.Q., Niu, Q.H., 2010b. Dynamic changes of a typical linear dune in the Tengger Desert. J. Arid. Land 2 (4), 272–278. Zhang, K.C., Qu, J.J., Han, Q.J., Xie, S.B., Kai, K., Niu, Q.H., An, Z.S., 2014. Wind tunnel simulation of windblown sand along China's Qinghai-Tibet railway. Land Degrad. Dev. 25 (3), 244–250. Zhang, K.C., Qu, J.J., Liao, K.T., Niu, Q.H., Han, Q.J., 2010a. Damage by wind-blown sand and its control along Qinghai-Tibet Railway in China. Aeolian Res. 1, 143–146.
Shen, W.S., Zhang, H., Zou, C.X., Cao, X.Z., Tang, X.Y., 2004. Approaches to prediction of impact of Qinghai-Tibet Railway construction on alpine ecosystems alongside and its recovery. Chin. Sci. Bull. 49 (8), 834–841. Sorensen, M., 1991. A analytic model of wind-blown sand transport. Acta Mech. Suppl. 1, 67–82. Tan, L.H., Zhang, W.M., Bian, K., An, Z.S., Zu, R.P., Qu, J.J., 2016. Numerical simulation of threedimensional wind flow patterns over a star dune. J. Wind Eng. Ind. Aerodyn. 159, 1–8. Thomas, D.S.G., 1988. The nature and deposition setting of arid and semi-arid Kalahari sediments, Southern Africa. J. Arid. Environ. 14, 17–26. Tian, H., Qu, J.J., Yang, G.S., Zhang, W.M., Niu, Q.H., 2012. Study on the feasibility of Dunhuang-Golmud Railway crossing the megadunes area at the east edge of Kumtagh Desert. J. Desert Res. 32 (1), 1–8 (in Chinese with English Abstract). Wang, G.X., Yao, J.Z., Guo, Z.G., Wu, Q.B., Wang, Y.B., 2004. Changes in permafrost ecosystem under the influences of human engineering activities and its enlightenment to railway construction. Chin. Sci. Bull. 49 (16), 1741–1750. Wasson, R.J., Hyde, R., 1983a. A test of granulometric control of desert dune geometry. Earth Surf. Process. Landf. 8, 301–312. Wasson, R.J., Hyde, R., 1983b. Factors determining desert dune type. Nature 304, 337–339. Xie, S.B., Qu, J.J., Lai, Y.M., Pang, Y.J., 2015a. Formation mechanism and suitable controlling pattern of sand hazards at Honglianghe River section of Qinghai–Tibet railway. Nat. Hazards 76 (2), 855–871.
46