Wind flow data_Sites1-11.xlsx and Sand Transport data Leba barrier Experiment, Poland

An investigation of wind flow and sand transport over a low to high density <em>Ammophila</em> dominated foredune on the Łeba barrier, Poland, utilising multiple anemometers and sand traps is presented. The study provides the first high resolution data on modified saltation and suspended sand transport over a foredune under conditions of both canopy and skimming flow. Topographic acceleration of flow and topographic steering over the foredune were observed during oblique incident above threshold flow conditions. The concentration of sand in aeolian transport decreases with height to a minimum that is reached at different elevations above the ground, depending on <em>Ammophila</em> grass density. Of the three <em>Ammophila</em> (marram) grass densities investigated, nearly half (46%) of the total sand-transport rate occurred above the lower density <em>Ammophila</em> grass, whereas up to 70% of the total transport occurred above the higher density marram grass. This likely results from both elastic collisions of sand grains with grass leaves over the <em>Ammophila</em> canopy, and the different positions of the canopy rebounding surface, which is sensitive to even slight changes in wind speed. In addition, as plant density increases, there is less flow penetration into the canopy, vegetative forcing (similar to topographic forcing) of vertical flow is greater, and sand in both modified saltation and suspension is forced higher above the canopy in skimming flow. The maximum sand transport above the vegetation canopy increased in elevation from 32cm to 48cm to 53cm as the vegetation density increased from low to moderate to high respectively. The study also demonstrates that in skimming flow relatively more sand is transported at higher elevations above a canopy surface than above a bare sand surface.

本研究针对波兰勒巴障壁沙坝上以滨草属（<em>Ammophila</em>）为优势种的低密度至高密度海岸前丘开展风场与输沙过程调查，采用多台风速仪与集沙器完成观测。本研究首次获取了冠层流与掠流两种工况下，经植被调控的跃移与悬移输沙的高分辨率观测数据。在斜向入射且超过起沙阈值的气流条件下，观测到海岸前丘地形引发的气流加速与转向效应。风沙流中的沙粒浓度随高度升高而降低，且浓度最小值出现的地面高度因滨草属植物种群密度而异。在所设置的三种滨草密度梯度中，低密度滨草冠层上方的输沙量占总输沙量的近一半（46%）；而高密度滨草冠层上方的输沙量占比可达总输沙量的70%。该现象可能源于两方面：一是沙粒与滨草冠层叶片发生弹性碰撞，二是冠层反弹面的位置存在差异，且该反弹面对风速的细微变化极为敏感。此外，随着植物密度升高，气流穿透冠层的能力减弱，气流所受的植被强迫效应（与地形强迫效应类似）会增强，掠流工况下经植被调控的跃移与悬移沙粒会被抬升至冠层上方更高的位置。随着植被密度从低到中再到高依次提升，植被冠层上方输沙量峰值对应的高度分别从32cm升高至48cm、再升至53cm。本研究同时证实，在掠流工况下，冠层表面上方较高高度处的输沙量相对高于裸沙表面的对应高度输沙量。