Maltauro R, Stone M, Collins A L, Krishnappan B G, Silins U
Department of Geography & Environmental Management, University of Waterloo, Waterloo, ON Canada.
Net Zero and Resilient Farming, Rothamsted Research, Okehampton, Devon UK.
J Soils Sediments. 2023;23(10):3589-3601. doi: 10.1007/s11368-023-03455-5. Epub 2023 Mar 17.
Multimodal effective particle size distributions (EPSDs) develop as flocculation and particle breakage occur dynamically in a fluid shear and such distributions have been previously reported in coastal and estuarine waters to understand flocculation processes. Here, we use time varying multimodal EPSDs and hydraulic parameters (discharge and bed shear stress) to assess freshwater flocculation in a gravel-bed river in southern Alberta, Canada.
Instantaneous discharge, volume concentration (VC), and EPSD of suspended solids were measured during three high discharge events at four study sites in a 10 km reach of the Crowsnest River. The EPSD and VC of suspended solids (< 500 µm) were measured in the centroid of flow with a LISST-200x. Bed shear stress for measured discharge was obtained using a flow model, MOBED.
Multimodal EPSDs consisted of primary particles, flocculi, microflocs, and macroflocs. Shear dependent flocculation was consistently observed for all sites and events, due to low and high shear stress flocculation, particle breakage, and mobilization of tributary sub-catchment derived particles. Higher shear stress limited flocculation to smaller floc sizes, while lower bed shear stress conditions created higher volumes of macroflocs.
Flocculation and particle breakage processes based on relationships between particle size and hydraulic properties presented herein have implications for advancing fine sediment transport models by a variable cohesion factor as a function of floc size class.
多模态有效粒径分布（EPSD）是在流体剪切作用下絮凝和颗粒破碎动态发生时形成的，此前已在沿海和河口水体中报道过此类分布，用于理解絮凝过程。在此，我们使用随时间变化的多模态EPSD和水力参数（流量和床面剪应力）来评估加拿大艾伯塔省南部一条砾石床河流中的淡水絮凝情况。
在克罗斯内斯特河10公里河段的四个研究地点，于三次高流量事件期间测量了瞬时流量、体积浓度（VC）和悬浮固体的EPSD。使用LISST - 200x在水流质心处测量了悬浮固体（< 500 µm）的EPSD和VC。通过水流模型MOBED获得实测流量的床面剪应力。
多模态EPSD由原生颗粒、絮凝体、微絮凝体和大絮凝体组成。由于低剪应力絮凝、高剪应力絮凝、颗粒破碎以及支流子流域来源颗粒的运移，在所有地点和事件中均持续观察到剪切依赖型絮凝。较高的剪应力将絮凝限制在较小的絮凝尺寸，而较低的床面剪应力条件下会形成更大体积的大絮凝体。
基于本文所呈现的粒径与水力特性之间关系的絮凝和颗粒破碎过程，对于通过将可变凝聚系数作为絮凝尺寸类别的函数来推进细颗粒泥沙输运模型具有重要意义。
