1. 1.中国科学院西北生态环境资源研究院沙漠与沙漠化重点实验室，甘肃 兰州 730000
2.中国科学院大学，北京 100049
3.北京师范大学地理科学学部，北京 100875
• 收稿日期:2020-10-29 修回日期:2020-12-09 出版日期:2021-03-19
• 通讯作者: 罗万银 E-mail:chexuehua19@mails.ucas.ac.cn;wyluo@lzb.ac.cn
• 基金资助:
国家自然科学基金面上项目“共和盆地巨型风蚀坑的发育对环境变化的响应”(41771015)

### Form-flow Feedback within Blowouts at Different Developing Stages in the Gonghe Basin， Qinghai Province

Xuehua CHE 1 , 2( ), Wanyin LUO 1( ), Mei SHAO 1 , 2, Zhongyuan WANG 3

1. 1.Key Laboratory of Desert and Desertification，Northwest Institute of Eco-Environment and Resources，Chinese Academy of Sciences，Lanzhou 730000，China
2.University of Chinese Academy of Sciences，Beijing 100049，China
3.Beijing Faculty of Geographical Science，Beijing Normal University，Beijing 100875，China
• Received:2020-10-29 Revised:2020-12-09 Online:2021-03-19 Published:2021-03-19
• Contact: Wanyin LUO E-mail:chexuehua19@mails.ucas.ac.cn;wyluo@lzb.ac.cn
• About author:CHE Xuehua (1997-), female, Lüliang City, Shanxi Province, Master student. Research areas include aeolian geomorphology and physics of blown sand. E-mail: chexuehua19@mails.ucas.ac.cn
• Supported by:
the National Natural Science Foundation of China "Mega-blowouts formation and its response to the environmental change"(41771015)

Blowouts are the primary geomorphologic manifestation and driving force of sandy grassland desertification in the Gonghe Basin. However， their feedback mechanism between the flow dynamics and geomorphology is unclear. Two-dimensional ultrasonic anemometers and gradient sand traps were used in this study to measure the characteristics of wind flows and sediment transport at different blowouts of different developing stages in the Gonghe Basin. The feedback between the morphology-dynamic processes of the blowouts was discussed. Results show as follows. $①$ After entering the sand patch and small bowl blowout along the prevailing wind direction， air flow expanded and decelerated， and then accelerated until going outside the blowout； when entering a trough blowout of a small or medium size， it expanded and decelerated at the headwall， accelerated at the bottom of blowout， decelerated at the windward slope of the depositional lobe， and then recovered somewhat at the leeside slope of the depositional lobe. Besides， the wind speed was negatively correlated with steadiness of flow and directional steadiness in the early stage of blowout， but was positively correlated with the steadiness of flow and negatively correlated with the directional steadiness in the middle stage of blowout. $②$ Due to the rotating vortices in the blowout， the wind speed profiles in the trough blowout displayed a nonlogarithmic behavior. $③$ The measured sand flux density at different stations decreased exponentially with height. However， due to the feedback effect between flow dynamics and morphology， the sediment transport fluxes at different positions were obviously different， with the lowest at the bottom of the blowout and the largest in front of the windward slope of the deposition lobe. In conclusion， there is a form-flow feedback in the blowout， and the bigger the blowout is， the more obvious the feedback effect is.

(a）共和盆地区域概况图，研究区位于龙羊峡北岸三塔拉阶地；(b）研究区域风蚀坑分布，影像来自2019年4月无人机三航向飞行拍摄结果(飞行高度为74 m，重叠度为85%/70%，相机倾角为-90°与-60°)；(c)~(f)分别为4个不同发育阶段风蚀坑无人机正摄影像
Fig.1 Location of the study area and the form and distribution of the blowouts in the study site
(a） Regional overview of the Gonghe Basin, the study site is located at the third level terrace of the Tarlatan sandy land; (b） The distribution of the blowouts in the study site, images were taken by a drone’s three course flight in April 2019 (flight height was 74 m, the overlap degree was 85%/70%, the camera tilt angle was -90° and -60°); (c)~(f) The orthoimage of the four targeted blowouts in different develop stages in this study

(a）共和盆地区域概况图，研究区位于龙羊峡北岸三塔拉阶地；(b）研究区域风蚀坑分布，影像来自2019年4月无人机三航向飞行拍摄结果(飞行高度为74 m，重叠度为85%/70%，相机倾角为-90°与-60°)；(c)~(f)分别为4个不同发育阶段风蚀坑无人机正摄影像
Fig.1 Location of the study area and the form and distribution of the blowouts in the study site
(a） Regional overview of the Gonghe Basin, the study site is located at the third level terrace of the Tarlatan sandy land; (b） The distribution of the blowouts in the study site, images were taken by a drone’s three course flight in April 2019 (flight height was 74 m, the overlap degree was 85%/70%, the camera tilt angle was -90° and -60°); (c)~(f) The orthoimage of the four targeted blowouts in different develop stages in this study

Table 1 Summary of morphological parameters of four observed blowouts

Table 1 Summary of morphological parameters of four observed blowouts

(a)风蚀坑B1进行了1次观测，布置测点共20处；(b)风蚀坑B2进行了3次观测，共布置测点34处；(c)风蚀坑B3进行了2次观测，共布置测点28处；(d)风蚀坑B4进行了4次测量，其中测量三与测量四部分点测量位置相同，实际测量部位63处；剔除传感出错仪器并进行数据筛选后，部分测点(图中未标明编号的测点)被排除，最终用于本研究的测点有：风蚀坑B1 18个；风蚀坑B2 27个，测量三未参与分析；风蚀坑B3 26个；风蚀坑B4 48个，测量四未参与分析
Fig.2 Array of the measurement of the near surface air flow
(a) One measurement was made at B1 with 20 locations, (b) Three measurements were made at B2 with 34 locations, (c) Two measurements were made at B3 with 28 locations, (d) Four measurements were made at B4 with 63 locations, among which some measurement positions of the third measurement and the fourth measurement were the same. After removing the instrument data with sensor error and performing data screening, some stations that were not labeled in the picture being excluded from analysis. A total of 18 stations in blowout B1, 27 stations in blowout B2, 26 stations in blowout B3, 48 stations in blowout B4 passed the quality control and were used in this study, the third measurement data in blowout B2 and the fourth measurement data in blowout B4 were not involved in this paper

(a)风蚀坑B1进行了1次观测，布置测点共20处；(b)风蚀坑B2进行了3次观测，共布置测点34处；(c)风蚀坑B3进行了2次观测，共布置测点28处；(d)风蚀坑B4进行了4次测量，其中测量三与测量四部分点测量位置相同，实际测量部位63处；剔除传感出错仪器并进行数据筛选后，部分测点(图中未标明编号的测点)被排除，最终用于本研究的测点有：风蚀坑B1 18个；风蚀坑B2 27个，测量三未参与分析；风蚀坑B3 26个；风蚀坑B4 48个，测量四未参与分析
Fig.2 Array of the measurement of the near surface air flow
(a) One measurement was made at B1 with 20 locations, (b) Three measurements were made at B2 with 34 locations, (c) Two measurements were made at B3 with 28 locations, (d) Four measurements were made at B4 with 63 locations, among which some measurement positions of the third measurement and the fourth measurement were the same. After removing the instrument data with sensor error and performing data screening, some stations that were not labeled in the picture being excluded from analysis. A total of 18 stations in blowout B1, 27 stations in blowout B2, 26 stations in blowout B3, 48 stations in blowout B4 passed the quality control and were used in this study, the third measurement data in blowout B2 and the fourth measurement data in blowout B4 were not involved in this paper

Table 2 Reference wind regime recorded at the 3 m high reference wind tower during the observation periods

Table 2 Reference wind regime recorded at the 3 m high reference wind tower during the observation periods

(a）集沙仪的测量位置分布，共布置7处测点：坑头处(J-4)、坑体中部(J-2、J-6、J-7)、积沙体迎风坡(J-1)、顶部(J-3)及背风坡处(J-5)，且均为同步观测；风速廓线的测量共进行了5次，每次测量部位为3处，部分位置进行了2次测量，故实际测量点位共11处，经数据筛选后本文选用第一次(1-1、1-2、1-4)、第三次(3-1、3-2、3-4)和第四次(4-1、4-2、4-4)测量位置进行研究，第二次观测点位(2-1、2-2、2-4)与第五次观测点位(5-1、5-2、5-4)未参与本文数据分析；(b） 风速廓线的测量风塔布置图，每个风塔配一个数采盒与各层风速仪连接进行数据存储；(c）本研究所用二维超声风速仪DS-2
Fig.3 Array of the measurement of the sediment transport and the vertical wind speed profiles
(a） Arrangement of the gradient sand traps, a total of seven traps were arranged at the blowout, with one trap (J-4) at the headwall, three traps (J-2, J-6, J-7) at the bottom of the blowout, one trap (J-1) at the windward of the deposition lobe, one trap (J-3) at the top of the deposition lobe and one trap (J-5) at the lee side of the deposition lobe, all the instruments were observed simultaneously. Five observations were made for the measurement of the vertical wind speed profiles, a total of 11 sites were measured with three sites of each measurement, and some sites were measured twice. After data screening, the first measurement (1-1, 1-2, 1-4), the third measurement (3-1, 3-2, 3-4) and the fourth measurement (4-1, 4-2, 4-4) data passed the quality control and were used in this paper, the second measurement (2-1, 2-2, 2-4) and the fifth measurement (5-1, 5-2, 5-4) data were excluded in this paper. (b） Site layout of the wind tower, each tower was equipped with a data acquisition box which is connected with wind anemometers of each layer for data storage. (c） Two-dimensional ultrasonic anemometer (DS-2) used in this study

(a）集沙仪的测量位置分布，共布置7处测点：坑头处(J-4)、坑体中部(J-2、J-6、J-7)、积沙体迎风坡(J-1)、顶部(J-3)及背风坡处(J-5)，且均为同步观测；风速廓线的测量共进行了5次，每次测量部位为3处，部分位置进行了2次测量，故实际测量点位共11处，经数据筛选后本文选用第一次(1-1、1-2、1-4)、第三次(3-1、3-2、3-4)和第四次(4-1、4-2、4-4)测量位置进行研究，第二次观测点位(2-1、2-2、2-4)与第五次观测点位(5-1、5-2、5-4)未参与本文数据分析；(b） 风速廓线的测量风塔布置图，每个风塔配一个数采盒与各层风速仪连接进行数据存储；(c）本研究所用二维超声风速仪DS-2
Fig.3 Array of the measurement of the sediment transport and the vertical wind speed profiles
(a） Arrangement of the gradient sand traps, a total of seven traps were arranged at the blowout, with one trap (J-4) at the headwall, three traps (J-2, J-6, J-7) at the bottom of the blowout, one trap (J-1) at the windward of the deposition lobe, one trap (J-3) at the top of the deposition lobe and one trap (J-5) at the lee side of the deposition lobe, all the instruments were observed simultaneously. Five observations were made for the measurement of the vertical wind speed profiles, a total of 11 sites were measured with three sites of each measurement, and some sites were measured twice. After data screening, the first measurement (1-1, 1-2, 1-4), the third measurement (3-1, 3-2, 3-4) and the fourth measurement (4-1, 4-2, 4-4) data passed the quality control and were used in this paper, the second measurement (2-1, 2-2, 2-4) and the fifth measurement (5-1, 5-2, 5-4) data were excluded in this paper. (b） Site layout of the wind tower, each tower was equipped with a data acquisition box which is connected with wind anemometers of each layer for data storage. (c） Two-dimensional ultrasonic anemometer (DS-2) used in this study

Fig.4 Distribution pattern of flow field after oblique air entered different forms of blowouts
The wind roses shows the wind conditions during the near surface airflow observation at the corresponding blowout

Fig.4 Distribution pattern of flow field after oblique air entered different forms of blowouts
The wind roses shows the wind conditions during the near surface airflow observation at the corresponding blowout

Fig.5 Variation of wind speed variation factor (Fs), wind direction stability factor (SD) and relative wind speed (U) at different observation sections of each blowout
The pictures on the left are the schematic diagram of all the observation sections from section L1 to L2 in blowout B1, section L3 to L5 in blowout B2, section L6 to L7 in blowout B3 (due to the lack of measuring positions on the western erosion slope, a measuring line is missing), section L8 to L10 in blowout B4 and their measuring positions used in this study in the blowouts. The gray area represents the topographic relief of the corresponding survey line (taking 3 094 m as the base elevation)

Fig.5 Variation of wind speed variation factor (Fs), wind direction stability factor (SD) and relative wind speed (U) at different observation sections of each blowout
The pictures on the left are the schematic diagram of all the observation sections from section L1 to L2 in blowout B1, section L3 to L5 in blowout B2, section L6 to L7 in blowout B3 (due to the lack of measuring positions on the western erosion slope, a measuring line is missing), section L8 to L10 in blowout B4 and their measuring positions used in this study in the blowouts. The gray area represents the topographic relief of the corresponding survey line (taking 3 094 m as the base elevation)

Table 3 Observation results of reference wind speed and direction at the height of 3 m reference meteorological station during the observation of vertical wind profiles near blowout B4

Table 3 Observation results of reference wind speed and direction at the height of 3 m reference meteorological station during the observation of vertical wind profiles near blowout B4

Fig.6 The wind speed profiles at different positions of the trough blowout B4
The reference wind direction in the figure was measured by the meteorological station during the observation, indicated the initial direction of the airflow before entering the wind blowout. The arrow in the blowout indicates the wind direction at 0.1 m height from the surface of each observation point. The wind speed profile shows the wind speed at different heights of each observation point. Because of the anemometer sensor error, wind speed and the direction at 0.1 m height of station 3-4 and 1.0 m height of station 3-2 were eliminated. Based on the observation results of the near surface airflow above, we believe that wind speed at 0.1 m height of station 3-4 should be lower than the windward side of the deposition, U 0.1 m (3-4)≈0.8 (the solid circle), wind direction should be along with the deposition (the dotted arrow)

Fig.6 The wind speed profiles at different positions of the trough blowout B4
The reference wind direction in the figure was measured by the meteorological station during the observation, indicated the initial direction of the airflow before entering the wind blowout. The arrow in the blowout indicates the wind direction at 0.1 m height from the surface of each observation point. The wind speed profile shows the wind speed at different heights of each observation point. Because of the anemometer sensor error, wind speed and the direction at 0.1 m height of station 3-4 and 1.0 m height of station 3-2 were eliminated. Based on the observation results of the near surface airflow above, we believe that wind speed at 0.1 m height of station 3-4 should be lower than the windward side of the deposition, U 0.1 m (3-4)≈0.8 (the solid circle), wind direction should be along with the deposition (the dotted arrow)

Fig.7 Schematic diagram of uniform wind speed at different heights (a) and the iso-velocity patterns within the blowout (b) at the center axis of the blowout B4

Fig.7 Schematic diagram of uniform wind speed at different heights (a) and the iso-velocity patterns within the blowout (b) at the center axis of the blowout B4

Fig.8 Structure function of wind-sand flow and its fitting equation using the modified three parameter exponential function

Fig.8 Structure function of wind-sand flow and its fitting equation using the modified three parameter exponential function

Table 4 Characteristics of the sand flux density in the blowout B4

Table 4 Characteristics of the sand flux density in the blowout B4

Table 5 Comparisons of the goodness of fit of the five models

Table 5 Comparisons of the goodness of fit of the five models

Fig.9 The sediment transport rate and wind speed of different parts of the blowout
As the anemometer at the sand trap J-2 was deleted due to data error, the wind speed data at that location was missing

Fig.9 The sediment transport rate and wind speed of different parts of the blowout
As the anemometer at the sand trap J-2 was deleted due to data error, the wind speed data at that location was missing