Grasslands vary with diverse forms and functions ranging from monocultures of perennial rye grass to more biodiverse unimproved grasslands which cover around 5% of Europe. Despite the broad diversity of grassland types, within environmental and flood risk models grasslands are frequently represented by a singular set of hydrological and structural parameters which belies their diversity and complexity. This study aimed to determine empirically the extent to which improved versus unimproved grasslands exhibit different hydrological connectivity. Working in SW England at neighbouring field sites with comparable slopes and rainfall regimes, we used unpiloted aerial vehicles to survey a tussocky Molinia caerulea dominated unimproved grassland field (MCUG) field and a Lolium perenne dominated improved grassland (LPIG) field. Using digital photogrammetry workflows applied to the overlapping aerial images, we produced a digital surface model (DSM) at 0.03-m resolution from which flow pathways were modelled using GIS and compared with 1-m LiDAR and DSM produced by a global navigation satellite system (GNSS). MCUG had longer, tortuous pathways through the dense tussock network with a drainage density of 2.54 m m⁻². This was significantly greater than drainage density in the LPIG (1.82 m m⁻²). As a result of this study, we rescaled the Manning's n value for MCUG according to photogrammetrically-derived roughness values. We suggest it should lie between 0.075 and 0.09. Our data shows that MCUG can play an important role in reducing overland flow impacts when compared to LPIG through lower connectivity which can delay run-off to rivers.

中文翻译：

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比较未改良和改良草地的精细结构和水文连通性

草原的形式和功能各不相同，从多年生黑麦草的单一栽培到覆盖欧洲约 5% 的生物多样性更加丰富的未改良草原。尽管草地类型多种多样，但在环境和洪水风险模型中，草地经常由一组单一的水文和结构参数表示，这掩盖了它们的多样性和复杂性。本研究旨在凭经验确定改善与未改善草地表现出不同水文连通性的程度。我们在英格兰西南部附近具有可比坡度和降雨情况的野外地点工作，我们使用无人驾驶飞行器调查了以草丛状的Molinia caerulea为主的未改良草地 (MCUG) 田地和多年生黑麦草主导的改良草地 (LPIG) 领域。使用应用于重叠航拍图像的数字摄影测量工作流程，我们生成了一个分辨率为 0.03 米的数字表面模型 (DSM)，使用 GIS 从中模拟了流动路径，并与全球导航卫星系统生成的 1 米 LiDAR 和 DSM 进行了比较（全球导航卫星系统）。MCUG 有更长、曲折的路径穿过密集的草丛网络，排水密度为 2.54 m m ^-2。这明显大于 LPIG 中的排水密度 (1.82 m m ^-2）。作为这项研究的结果，我们根据摄影测量得出的粗糙度值重新调整了 MCUG 的曼宁 n 值。我们建议它应该介于 0.075 和 0.09 之间。我们的数据表明，与 LPIG 相比，MCUG 可以在减少地表流量影响方面发挥重要作用，因为连通性较低，可以延迟河流径流。