Seasonal vegetation and management influence overland flow velocity and roughness in upland grasslands
Seasonal vegetation and management influence overland flow velocity and roughness in upland grasslands
复制标题
DOI：
10.1002/hyp.13842
复制
发表时间：
2020-07-06
影响因子：
3.2
通讯作者：
Holden, Joseph
中科院分区：
文献类型：
--
作者：
Bond, Stephanie;Kirkby, Mike J.;Holden, Joseph
有相当大的兴趣，如何源头管理可能会影响下游洪峰在温带潮湿地区。然而，缺乏有关源头山坡流速的数据，并且对地表流速是否受到植被周期或管理中粗糙度季节性变化的影响的了解有限。采用便携式山坡水槽研究了英格兰北方4种常见水源草地生境（低密度放牧、干草草甸、Rank Grassland和灯心草（Juncus effususRush））的地表水流速度。在每个栖息地的重复地块，在响应三个应用的流速，在五个不同时期的草地年周期的实验重复测量地表水流速度。年平均地表径流速度显着较低的排名草原栖息地（0.026米/秒），其次是低密度放牧和灯心草（0.032和0.029米/秒），然后干草草甸（0.041米/秒），其中有最大的年平均流速（从12升/分钟的流量的例子）。将我们的平均坡面流速度应用于理论上100 m的山坡表明，在18 mm的风暴中，与干草草甸相比，Rank草地上的坡面流延迟>1 h。因此，草地管理对于减缓地表径流和推迟高地源头的洪峰流量非常重要。地表粗糙度也受到植被生长、腐烂、放牧和砍伐的年周期的强烈控制。冬季地表水流速度显着高于夏季，在0.004米/秒（灯心草，11月）和0.034米/秒（灯心草，6月）之间变化;和速度显着增加切割后变化在0.006米/秒（干草草甸，7月）和0.054米/秒（干草草甸，9月）。这些结果表明，季节性植被变化应纳入洪水建模，草原表面粗糙度的周期强烈修改地表径流，可能会对下游洪峰和时间产生很大的影响。我们的数据还表明，达西-韦斯巴赫粗糙度近似大大高估了测量的流速。
There is considerable interest in how headwater management may influence downstream flood peaks in temperate humid regions. However, there is a dearth of data on flow velocities across headwater hillslopes and limited understanding of whether surface flow velocity is influenced by seasonal changes in roughness through vegetation cycles or management. A portable hillslope flume was used to investigate overland flow velocities for four common headwater grassland habitats in northern England: Low-density Grazing, Hay Meadow, Rank Grassland andJuncus effususRush pasture. Overland flow velocity was measured in replicate plots for each habitat, in response to three applied flow rates, with the experiments repeated during five different periods of the annual grassland cycle. Mean annual overland flow velocity was significantly lower for the Rank Grassland habitat (0.026 m/s) followed by Low-density Grazing and Rushes (0.032 and 0.029 m/s), then Hay Meadows (0.041 m/s), which had the greatest mean annual velocity (examples from 12 L/min flow rate). Applying our mean overland flow velocities to a theoretical 100 m hillslope suggests overland flow is delayed by >1 hr on Rank Grassland when compared to Hay Meadows in an 18 mm storm. Thus grassland management is important for slowing overland flow and delaying peak flows across upland headwaters. Surface roughness was also strongly controlled by annual cycles of vegetation growth, decay, grazing and cutting. Winter overland flow velocities were significantly higher than in summer, varying between 0.004 m/s (Rushes, November) and 0.034 m/s (Rushes, June); and velocities significantly increased after cutting varying between 0.006 m/s (Hay meadows, July) and 0.054 m/s (Hay meadows, September). These results show that seasonal vegetation change should be incorporated into flood modelling, as cycles of surface roughness in grasslands strongly modify overland flow, potentially having a large impact on downstream flood peak and timing. Our data also showed that Darcy-Weisbach roughness approximations greatly over-estimated measured flow velocities.