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Suspended sediment monitoring in alluvial gullies: a laboratory and field evaluation of available measurement techniques
Hydrological Processes ( IF 3.2 ) Pub Date : 2020-06-19 , DOI: 10.1002/hyp.13824
Nicholas J. C. Doriean 1 , Andrew P. Brooks 2 , Peter R. Teasdale 3, 4 , David T. Welsh 1 , William W. Bennett 1
Affiliation  

Gully erosion is a significant source of fine suspended sediment (<63 μm) and associated nutrient pollution to freshwater and marine waterways. Researchers, government agencies, and monitoring groups are currently using monitoring methods designed for streams and rivers (e.g., autosamplers, rising stage samplers, and turbidity loggers) to evaluate suspended sediment in gullies. This is potentially problematic because gullies have several hydrological features and monitoring operational challenges that differ to those of continually flowing streams and rivers (e.g., short and intense flows, high suspended sediment concentrations, and rapid scouring and aggradation). Here we present a laboratory and field‐based assessment of the performance of common suspended sediment monitoring techniques applied to gullies. We also evaluate a recently‐described method; the pumped active suspended sediment (PASS) sampler, which has been modified for monitoring suspended sediment in gully systems. Discrete autosampling provided data at high temporal resolution, however, it had poor collection efficiency (25 ± 10%) of coarser sediment particles (i.e., sand). Rising stage sampling, while robust and cost‐effective, suffered from large amounts of condensation under field conditions (25–35% of sampler volume), due to harsh climatic conditions creating large diurnal temperature differences at the field site, thereby diluting sample concentrations and introducing additional measurement uncertainty. The turbidity logger exhibited a highly variable response when calibrated at each site with physically collected suspended sediment samples (R 2 = 0.17–0.83), highlighting that this approach should be used with caution. The modified PASS sampler proved to be a reliable and representative measurement method for gully sediment water quality, however, the time‐integrated nature of the method limits its temporal resolution compared to the other monitoring methods. We recommend monitoring suspended sediment in alluvial gully systems using a combination of complementary techniques (e.g., PASS and RS samplers) to account for the limitations associated with individual methods.

中文翻译:

冲积沟中悬浮泥沙监测:可用测量技术的实验室和现场评估

沟壑侵蚀是细悬浮沉积物 (<63 μm) 和相关营养物污染淡水和海水的重要来源。研究人员、政府机构和监测小组目前正在使用专为溪流和河流设计的监测方法(例如,自动采样器、上升阶段采样器和浊度记录器)来评估沟渠中的悬浮沉积物。这可能是有问题的,因为沟壑具有与持续流动的溪流和河流不同的几个水文特征和监测操作挑战(例如,短而强的流动、高悬浮泥沙浓度以及快速冲刷和聚集)。在这里,我们对应用于沟渠的常见悬浮沉积物监测技术的性能进行了实验室和实地评估。我们还评估了最近描述的方法;泵送活性悬浮泥沙 (PASS) 采样器,经过改进,用于监测沟渠系统中的悬浮泥沙。离散自动采样提供了高时间分辨率的数据,但是,它对较粗的沉积物颗粒(即沙子)的收集效率很差(25±10%)。上升阶段采样虽然稳健且具有成本效益,但在现场条件下(采样器体积的 25-35%)遭受了大量冷凝,这是由于恶​​劣的气候条件在现场产生了较大的昼夜温差,从而稀释了样品浓度和引入额外的测量不确定度。当在每个站点使用物理收集的悬浮沉积物样本(R 2 = 0.17–0.83)进行校准时,浊度记录仪表现出高度可变的响应,强调应谨慎使用这种方法。改进的 PASS 采样器被证明是一种可靠且具有代表性的沟渠沉积物水质测量方法,但是,与其他监测方法相比,该方法的时间积分性质限制了其时间分辨率。我们建议使用互补技术(例如,PASS 和 RS 采样器)的组合监测冲积沟系统中的悬浮沉积物,以解决与个别方法相关的局限性。
更新日期:2020-06-19
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