Geomorphologic significance of airflow and sand transport around an Artemisia ordosica nebkha in the Ordos Plateau， China

doi:10.7522/j.issn.1000-694X.2021.00208

Journal of Desert Research ›› 2022, Vol. 42 ›› Issue (1): 184-195.DOI: 10.7522/j.issn.1000-694X.2021.00208

Geomorphologic significance of airflow and sand transport around an Artemisia ordosica nebkha in the Ordos Plateau， China

Jie Yin¹(), Hasi Eerdun¹(), Jing An², Yanguang Zhou¹, Rina Hu¹, Zifeng Wu¹

^1.School of Natural Resources，Faculty of Geographical Science，Beijing Normal University，Beijing 100875，China
^2.Miyun Affiliated Middle School of Capital Normal University，Beijing 101500，China

Received:2021-10-26 Revised:2021-12-13 Online:2022-01-20 Published:2022-01-28
Contact: Hasi Eerdun

Abstract

Abstract:

Artemisia ordosica shrubs are distributed widely in the Ordos Plateau of China and they interact with air flow to form nebkhas， whose morphological development is mainly controlled by the condition of surrounding aeolian sediment transport. In this study， EC9-1 wind direction and speed sensor and stepped sand traps were used to observe the airflow and sediment transport around the Artemisia ordosica nebkha on flat sandy land， and then the distribution and variation of the horizontal airflow field at 0.3 m， wind speed profile and sand transport rate were systematically analyzed. The results show that the air flow structure and sediment transport rate change with different positions of the nebkha. To be specific， from the windward side through both sides to the leeward， the airflow separates with deceleration， grows on both sides and converges with reduction； The wind speed decreases to the minimum at the foot of the leeward side， increases exponentially with the horizontal distance， and returns to the reference at 4.85H（H stands for total height of the nebkha）； Around the nebkha， the wind speed profiles do not follow logarithmic distribution， and the speed decreases with the increase of height within 0.3-1.0 m at the toe of the leeward side， which indicates the presence of reverse vertical axis vortex； The difference in frequency of sand driving wind makes the change of section sediment transport rate on both sides， which leads to different erosion and deposition pattern and makes the shape of the nebkha evolve from oval to asymmetric spindle； There is no sand tail on the leeward side of the studied nebkhas， that is， the inadequate sand source and the incident wind direction change inhibit the development of shadow dunes in a multi-direction wind environment on the denuded plateau with thin sand layer.

Key words: Artemisia ordosica nebkhas, horizontal airflow distribution, wind speed profile, sediment transport rate

CLC Number:

P931.3

Jie Yin, Hasi Eerdun, Jing An, Yanguang Zhou, Rina Hu, Zifeng Wu. Geomorphologic significance of airflow and sand transport around an Artemisia ordosica nebkha in the Ordos Plateau， China[J]. Journal of Desert Research, 2022, 42(1): 184-195.

Figures/Tables 16

Fig.1 Location of the study area

Fig.2 Monthly variation of meteorological elements （A） and sand transportation rose （B） in the study area

Table 1 Morphological parameters of each nebkha

灌丛沙堆序号	长度 /m	宽度 /m	总高度 /m	灌丛植株高度/m
1	3.70	2.73	1.10	0.55
2	5.88	2.64	1.20	0.51
3	1.20	1.05	0.80	0.50
4	3.20	3.13	1.20	0.50
5	3.46	2.88	1.20	0.70
6	4.00	3.30	1.35	0.65
7	2.10	1.50	0.80	0.35
8	2.80	2.50	1.05	0.60

Fig.3 Layout of observation points of horizontal flow field and sediment transport （A） and wind speed profile （B）

Fig.4 Pictures of horizontal flow， sediment transport （A） and wind speed profile observation （B）

Fig.5 Wind direction and speed at 4 m height of reference point during observation

Fig.6 Horizontal flow field at 0.3 m height on both sides of the nebkha

Table 2 Variation range of average wind speed at observation points on both sides of the nebkha

入射风	指标	参考点	南侧观测点			北侧观测点
入射风	指标	L1	L3	L4	L6	L13	L12	L11
同侧风	平均风速/（m·s^-1)	4.5	4.7	3.0	1.5	3.6	4.6	4.6
同侧风	平均风速变幅/%	—	5.9	-33.7	-66.3	-19.0	2.3	4.1
异侧风	平均风速/（m·s^-1)	4.1	4.6	2.1	1.6	4.0	4.8	3.6
异侧风	平均风速变幅/%	—	11.3	-49.6	-61.9	-4.2	16.7	-12.1

Fig.7 Change of wind direction on the lee of each observation point （L7—L10） and reference point （L7-1—L10-1） in the same time

Fig.8 Observation of reverse vortex flow by smoke tracer method

Table 3 The relationship（y=a·ebx） between the average wind speed at 0.3 m and distance on the leeward side of the nebkha

风向	a	b	R²	P	D/m
292°	0.0979	0.6698	0.9951	0.0009	5.6540
303°	0.0938	0.6531	0.9933	0.0013	5.8641
315°	0.0629	0.7118	0.9880	0.0023	5.9419
326°	0.0126	0.9787	0.9698	0.0058	5.9644
337°	0.0004	1.5710	0.9438	0.0108	5.9117
348°	0.0005	1.6218	0.9181	0.0157	5.5889

Fig.9 Wind speed profile of each observation point around the nebkha

Fig.10 Variation of sediment transport rate at observation points （A-C） and the frequency diagram of sand driving wind direction （D）

Fig.11 Variation of sediment transport rate with height at each observation point

Table 4 The fitting coefficient of the relationship between sediment transport rate and height at each observation point

观测点位	a	b	R²
L1	3.4838	0.2607	0.9990
L2	0.6261	0.2336	0.9709
L4	1.0607	0.2141	0.9865
L5	1.0153	0.2277	0.9961
L6	2.4160	0.2306	0.9975
L11	0.3736	0.1962	0.9726
L12	0.2711	0.1678	0.9725
L14	0.0784	0.1329	0.9760

Fig.12 The relationship between relative wind speed at the toe of leeward slope and morphological parameters of nebkhas

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Geomorphologic significance of airflow and sand transport around an Artemisia ordosica nebkha in the Ordos Plateau， China

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