|其他摘要||Sand blocking fence is an important form of physical sand control measures and has apparent effects on the aeolian geomorphology evolution of its periphery region while blocking drift-sand. It disturbs near-surface airflow field and the surface sand material migration process, which results in the change of dunes' morphology and the re-sorting of sand sediment. In this paper, we study the influence of high windbreak on the wind-accumulated relief evolution process, the dynamic response of near-surface airflow field to the high windbreak and the relationship between high windbreak accumulated sand and its protective efficiency by using indoor wind tunnel simulation tests and field observation. The primary conclusion is as follows:
(1) The deposited sand height and width of the windbreaks were gradually increasing, and their sections were all single peak patterns, among which, the early and middle periods of peaks were narrow, but the later period of peak was a little wider; the scales of the deposited sand ranged from -7H to 12H during the stationary periods, and the top point was 2H high. The amount of deposited sand increased with increasing time, and the sand was concentrated on leeward side, the deposited sand mass ratio of windward side to leeward side was close to 1:4.
(2)The windbreaks greatly changed the aeolian sandy movement progress near surface, resulting in enormous spatial changes of the aeolian sandy saturation extent and the alterations of surface erosion and sediment accumulation. The trend of the sediment discharge rate in the early stage of setting up the windbreaks was different from that in the stationary stage, the sediment discharge rate in the early stage was gradually decreasing on the windward side of the windbreaks, but it reached the maximum at the H point of the leeward side and the point of 3H during the stationary periods.
(3)Adaptive changes of near-surface sand flow field were observed. Wind profile and speed-up ratio of average wind speed and change of sand flow field were different at different periods. Average wind speed and its speed-up ratio decreased gradually at initial period and the middle and later periods of experiment, but the minimum values of average wind speed and its speed-up ratio were found at 5H, and they increased gradually after the point of 5H point. However, at stable period, the maximum values of average wind speed and its speed-up ratio were found at H point and the minimum values of average wind speed was found at 3H point. According to the points of the experiment, the sequence of speed-up ratio was initial period, middle period, the mid-late period and stable period at the point of -5H; At the point of -2H, the sequence of speed-up ratio was middle period, the mid-late period, stable period and initial period; At the point of H, the sequence of speed-up ratio was stable period, the mid-late period, middle period and initial period; At the point of 3H, the sequence of peed-up ratio was middle period, the mid-late period, initial period and stable period; At the points of 5H and 10H, the sequence of speed-up ratio was stable period, middle period, the mid-late period and initial period. Windproof efficiency decreased gradually with the increase of wind speed and time and it increased at the middle and later periods but at stable period weakened.
(4)The windproof efficiency decreased gradually with the increasing accumulation of sand in the sand-blocking mesh. Windproof efficiency at different stages was initial period>middle period>the mid-late period>stable period. The windproof efficiency decreased gradually in the process of accumulating sand in the sand-blocking mesh. There was a linear correlation between the exposed height of sand-blocking mesh and windproof efficiency, that is, windproof efficiency decreased gradually with the decreasing exposed height of sand-blocking mesh. However, a negative linear correlation between the windward accumulating sand quantity, the leeward accumulating sand quantity, the total accumulating sand quantity and windproof efficiency was found.|