Combining Field and Laboratory Measurements to Determine the Erosion Risk of Cohesive Sediments Best

Abstract

Abstract:In contrast to non-cohesive sediments, the incipient motion of cohesive sediments is characterized by much more complex interactions between several sedimentary, biological, and chemical parameters. Thus, site-specific investigations are required to obtain information about the erosion stability of cohesive materials. This becomes even more relevant for contaminated sediments, stored in riverine sediments as a "burden of the past", because of their remobilization potential during flood events. This article represents a twofold measuring strategy for the detection of erosion thresholds: an in situ device for determination of critical shear stresses in the field, and a laboratory approach where sediment cores are withdrawn and subsequently analyzed over depth. The combined measuring strategy was applied in the River Elbe and at selected sites of the catchment of the River Saale. The results show a great variety of erosion thresholds over depth, demonstrating the need to conduct vertical analyses, especially when addressing buried layers with contaminations. The latter is only possible in the laboratory but the in situ device revealed clear benefits in capturing the loose flocculent layer on top of the sediment that might be easily lost during sediment retrieval and transport. Consequently, it is ideal to combine both approaches for a comprehensive insight into sediment stability. OPEN ACCESSWater 2015, 7 5062

The effect of seasonality upon the development of lotic biofilms and microbial biostabilisation

“…In lotic waters, the dynamics of fine sediments are significantly influenced by a strong feedback between the benthos and the water column, the ETDC-cycle (Erosion, Transport, Deposition and Consolidation) [e.g. Paterson & Black, 2000;Noack et al, 2015]. As the majority of nutrients binds to the grains of fine sediments (Mortimer, 1941;Sfriso, Pavoni & Marcomini, 1995), this interaction not only affects essential features of sediment particles floating in the free water (Droppo, 2001(Droppo, , 2004 but also the primary production of benthic microalgae (Schreiber & Pennock, 1995).…”

Numerical Modelling of Cohesive Bank Migration

“…In the literature, a great variability of the values for the critical erosion bed shear stress τ e is observed, with values covering more than two orders of magnitude [26,29,41,42]. In the present paper, a mean value of 1 Pa for τ e has been adopted, which is within the range of both the Thorn and Parson and Mitchener formulae [43] and also in line with the values experimentally obtained by Amos et al [44] for saltmarshes in the nearby Venice lagoon.…”

“…Many studies show that the incipient motion of cohesive sediments is much more complex to describe compared to the behaviour of granular sediments and it cannot be treated in the same way [41,42]. For example, the results of experiments show great uncertainty in the estimate of erosion thresholds [42][43][44], which is a key parameter in the evaluation of sediment entrainment when an excess shear stress formula is used [43,45].…”

PHOTOSED—PHOTOgrammetric Sediment Erosion Detection

“…Aberle et al [17] have provided an extended overview of different measuring techniques to obtain erosional characteristics of cohesive sediments in the laboratory and field. This review includes recirculating flumes (e.g., [18,19]), straight flow-through flumes (e.g., [20][21][22]), and miscellaneous devices, such as jet tests (e.g., CSM, cohesive strength meter, Paterson, 1989), hole erosion tests [23], microcosm experiments [24], and erosion bells [25].Despite the considerable variety of devices, information about the spatial and temporal variability of erosion rates and the capability of the devices to resolve the spatial and temporal variability is rare in literature. Most often, the erosion rates are determined for larger areas, such as the entire surfaces of sediment cores, or the dimensions of open-bottom measuring sections (e.g., [20,21,26]).…”