Erosion characteristics and floc strength of Athabasca River cohesive sediments: towards managing sediment-related issues

Abstract

Purpose This research aims to investigate: (1) the evolutional sequence of erosion of cohesive sediments entering the Athabasca River, (2) the influence of consolidation/ biostabilization time on bed sediment stability, and (3) the implication of these results on contaminant transport within the Athabasca River. Materials and methods A 5-m annular flume was used to generate bed shear to assess cohesive sediment dynamics for eroded beds with consolidation/biostabilization periods (CBs) of 1, 3, and 7 days. Additional laser particle sizing, image analysis, densitometry, and microbial analysis were employed to further the analysis with respect to bed erosion and eroded floc characteristics. Results and discussion The critical bed shear stress for erosion increased from 0.16 (1-day CB) to 0.26 Pa (7-day CB) with an inverse relationship observed for both suspended sediment concentration and erosion rate with respect to CBs. The 7-day CB yielded the largest eroded flocs that initially have high organic content but were quickly broken up with increasing shear. The strongest eroded floc population occurred for the 3-day CB. Eroded flocs were found to be of an open matrix with high water content and low density. Flocs contained a mixture of clay and silt particles, microbes, algae, diatoms, and secreted extracellular polymeric substances (EPS). Counts of bacteria were observed to decrease with CBs while an increase in the algal community is suggested with time.Conclusions Consolidation was believed to have limited effect on erosion while biostabilization was the main controlling factor. Increasing biostabilization with time resulted in a more stable surficial layer with a reduced erosion rate relative to less biostabilized beds. The highly biostabilized bed (7-day CB), however, yielded the largest flocs which broke up easily compared to those eroded from 1-and 3-day CBs. It is believed that the EPS produced by the sediment biological community is the main component of the bed and flocs that is responsible for the observed stability results.

A model for the settling velocity of flocs; application to an aquaculture recirculation tank

“…With the relationship between fractal dimension and diameter, the values of permeability can be obtained for different fl oc diameters, using eqn (6). A mean value of 20 μm was obtained from SEM (Fig.…”

“…These sediments form fl ocs or aggregates, made of water, inorganic particles and organic particles [3][4][5]. To obtain adequate settling models for these particles is an open fi eld of research [6].…”

Recent advances and future directions in soils and sediments research

“…For example, studies (e.g. Garcia-Aragon et al 2011) have demonstrated the role of periphyton, biofilms and extracellular polymeric substances (EPS) in stabilizing channel bed sediment from erosion and resuspension, thereby limiting the remobilization of contaminated sediment. Indeed Gerbersdorf et al (2011) argue that such process understanding should be part of sediment quality assessment.…”

“…Much of this work on the hydrodynamic and biogeochemical processes operating at the sediment-water interface has involved the use of experimental facilities, such as flumes and within laboratories (e.g. Rex and Petticrew 2008;Garcia-Aragon et al 2011). A challenge facing researchers is to undertake such work in the field in order to confirm the laboratory-based results in more realistic settings.…”

Optical Methods Applied to Hydrodynamics of Cohesive Sediments

“…These sediments form flocs or aggregates, made of water, inorganic particles, and organic particles [6][7][8]. To obtain adequate settling models for these particles is an active field of research [9]. Some researchers include variable fractal dimension functions that depend on a characteristic size of flocs that is difficult to obtain over a large population of flocs [10].…”