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The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS. [ABSTRACT FROM AUTHOR]

The Newfoundland and Labrador Shelves Bioregion, located on the glaciated continental shelf and adjacent continental slope of eastern Canada, is classified into units that reflect its great physiographic diversity. There are ten shelf units: bedrock zone, fjord systems, major inlet, shelf-crossing troughs, four types of offshore banks, basin, and disturbed (glaciotectonic) terrain. There are three units on the continental slope: channelized areas, trough-mouth areas, and large sedimentary drifts. A series of vignettes illustrates both the distinguishing characteristics of the principal geomorphic units and the morphologic diversity within them. A sediment mobility analysis reveals that wave- and current-generated disturbances are dominant and largely depth-controlled within the shelf units, while the south-flowing Labrador Current impacts sediment transport and mobility along the continental slope. [ABSTRACT FROM AUTHOR]

Tidal flats are widely distributed on high-latitude coasts, where sea ice processes have been invoked to explain the abundance and distribution of boulders. This study documents the surface morphology and sediment dynamics of a Low-Arctic macrotidal system, the boulder-rich tidal flats of Koojesse Inlet, fronting the Nunavut capital, Iqaluit, on Baffin Island. This is a region of postglacial isostatic uplift and forced regression, with raised littoral, deltaic, and glaciomarine deposits. The spring-tidal range is 11.1 m and sea ice cover lasts roughly 9 months of the year. The extensive intertidal flats are up to 1 km wide, with a veneer of sand and gravel (including large boulders) resting on an erosional unconformity truncating the underlying glaciomarine mud, forming a terrace within the present tidal range. Over a 3-year study, no consistent pattern of erosion or deposition was evident. Over a longer time scale, the concave hypsometry, low sediment supply, slight ebb dominance of weak tidal currents, abrasion by wave-entrained sand, ebb-oriented ripples formed under subaerial drainage, and slumps on the terrace flanks are consistent with seaward hydraulic and gravitational sediment transport. These processes may be of greater importance than shoreward ice transport. This study underlines the importance of relict glaciomarine deposits, postglacial uplift, and falling relative sea level in the erosional development of these high-latitude tidal flats. Relative sea-level projections for Iqaluit are ambiguous, but a switch to rising sea level, if it occurs, combined with more open water and wave energy, could alter the foreshore dynamics of the system. [ABSTRACT FROM AUTHOR]

Impacts from a changing climate, in particular sea-level rise, will be most acutely felt on small oceanic islands. A common configuration of mid-latitude islands is the sandy barrier island. Sable Island, Nova Scotia, Canada is a vegetated sand island near the shelf edge, 160 km from the nearest point of land, that is morphologically similar to a barrier island. This study uses 60 years of airphoto records to analyse changes in coastline position through digitized shore and vegetation (foredune proxy) lines. Rates of coastal movement are analysed to model the future (2039) coastal configuration. The analyses suggest that the majority of the coastline on Sable Island is in retreat, with net retreat on the south side of the island only partially offset by modest net advance on the north side. The different morphologies of the beach–dune systems of South Beach and North Beach, driven by incident wind and waves, yield these different coastline responses. Projected loss of 10 ha by 2039 of the climax heath vegetative community to shoreline retreat suggests a trend toward island instability due to coastline migration. Island-wide data set trends show support for two different but complementary hypotheses about whole-island evolution: (1) the island is mobile via bank migration driving southern coastline changes and experiencing sediment transport toward the east, or (2) the island is generally immobile and losing subaerial sediments (and thus shrinking) likely due to ongoing (and accelerating) sea-level rise. [ABSTRACT FROM AUTHOR]

This study considers the influence of changing sea ice on nearshore sediment transport in the central north shore of Prince Edward Island, Southern Gulf of St. Lawrence. It is widely accepted that changing climate is causing sea ice to decrease in the region. Sea ice attenuates wave energy thereby reducing sediment transport. The Delft3D hydrodynamic model is used to simulate waves, currents, and sediment transport in seven sea ice concentration scenarios that can be differentiated into four classes: open water (<10%), low ice (10% to 35%), moderate ice (36% to 60%), and high ice (>60%). If ice concentration decreases from high to moderate, sediment transport is expected to increase 23%. Similarly, if ice concentration decreases from moderate to low, sediment transport is expected to increase a further 24%. If ice concentration decreases from low to open water conditions, sediment transport is expected to abruptly increase a further 85%. The increase in sediment transport as sea ice decreases from high concentration to open water conditions is 180%. Linear and power-law fits of sediment transport and sea ice concentration intersect at an ice concentration of 30%, indicating this value may be a useful threshold in planning for increased coastal erosion and developing appropriate adaptation strategies, in particular, adapting to increased sediment transport near tidal inlets and navigation channels. [ABSTRACT FROM AUTHOR]

The objective of this study is to verify whether low amounts of fine sand added to a muddy sediment matrix can be detected and quantified with accuracy using a Mastersizer 3000 (Malvern Panalytical) laser diffraction particle-size analyzer equipped with a Hydro LV large volume liquid dispersion module. To achieve this goal, a postglacial sediment sample was sieved to recover naturally co-occurring sand and clay–silt fractions. Sand in the range of 1%–7% by weight was added to the clay–silt at three concentrations (88, 132, and 276 mg dry weight) and each sample was duplicated. A very strong linear relationship was found between the measured % volume of sand added and the actual weight of sand added to the mud. Sand representing as low as 1% by weight could be detected. On average, there was only a 0.7% absolute difference between the measured and actual % sand values (range 0.02%–1.65%). Sample concentration had a negligible impact on the measured % sand. A range of plausible values for the refractive and absorption indexes, essential parameters for the Mie theory calculation of the size distribution from the measured light scattering, also had very small impact on the measured % sand. The demonstrated possibility of detecting a small input of fine sand to muddy sediment provides a basis for studies using grain-size data to reconstruct past and modern detrital inputs and sediment transport variations. [ABSTRACT FROM AUTHOR]

Elevated phosphorus (P) loading from the watersheds draining into Lake Erie, particularly from agricultural (53%) and urban (43%) sources, is identified as one of the main drivers of the severe eutrophication. In this study, we present a comprehensive evaluation of 11 process-based models to characterize the water cycle as well as nutrient fate and transport within a watershed context, and to find a robust and replicable way to optimize the modelling strategy for the Lake Erie watershed. Our primary objective is to review the conceptual/technical strengths and weaknesses of the individual models for reproducing surface runoff, groundwater, sediment transport, nutrient cycling, and channel routing, and to collectively guide the management of the Lake Erie Basin. Our analysis suggested that the available models either opted for simpler approximations of the multifaceted, nonlinear dynamics of nutrient fate and transport, and instead placed more emphasis on the advanced representation of the water cycle or, introduced a greater degree of biogeochemical complexity but simplified their strategies to recreate the roles of critical hydrological processes. Notwithstanding its overparameterization problem, the MIKE SHE model provides the most comprehensive 3D representation of the interplay between surface and subsurface hydrological processes with a fully dynamic description, whereby we can recreate the solute transport that infiltrates from the surface to the unsaturated soil layer and subsequently percolates into the saturated layer. Likewise, the physically based submodels designed to represent the sediment detachment and erosion/removal processes (DWSM, HBV-INCA, HSPF, HYPE, and MIKE SHE), offer a distinct alternative to USLE-type empirical strategies. The ability to explicitly simulate the daily plant growth (SWAT and APEX) coupled with a dynamic representation of soil P processes can be critical when evaluating the long-term watershed responses to various agricultural management strategies. Drawing parallels with the (sub)surface and sediment erosion processes, a more complicated physically based approach, e.g., the dynamic wave model provided by MIKE SHE (coupled with MIKE URBAN or MIKE HYDRO) and SWMM may be more appropriate for realistically simulating the pressurized flow and backwater effects of water routing in both open channels and closed pipes. While our propositions seem to favor the consideration of complex models that may lack the commensurate knowledge to properly characterize the underlying processes, we contend this issue can be counterbalanced by the joint consideration of simpler empirical models under an ensemble framework, which can both constrain the plausible values of individual processes and validate macroscale patterns. Finally, our study discusses critical facets of the watershed modelling work in Lake Erie, such as the role of legacy P, the challenges in reproducing spring-freshet or event-flow conditions, and the dynamic characterization of water/nutrient cycles under the nonstationarity of a changing climate. [ABSTRACT FROM AUTHOR]

Riverbanks undergo changes caused not only by river hydraulics, mainly sediment erosion and deposition processes, but also by the possible landslides that eventually change the channel bank profiles. Those failures are an important form of alluvial channel adjustments but are usually difficult to include during morphodynamic modeling. This paper proposes a novel approach combining a 2D depth-averaged hydrodynamic, sediment transport and mobile-bed model, SRH-2D, a limit equilibrium slope-stability model, BISHOP, and a bank failure sediment redistribution submodel, REDISSED, into a fully automatic and continuous dynamic simulation to predict vertical bed and lateral bank changes for a river reach undergoing exceptional flooding. The in-stream vertical fluvial changes predicted with the SRH-2D model will be automatically used to update the riverbank geometry profile by profile and assess their geotechnical stability to rotational slip failures with a developed slope-stability model based on Bishop's simplified method. A cone-shaped sliding area is defined in case the driving forces exceed the stabilizing forces. All mesh nodes located within the mass wasting zone will be automatically updated, allowing a new bank face form. The failed materials will be redistributed in the transect according to the geometry of the landslides observed at the study site. The Outaouais River at Notre-Dame-Du Nord, Quebec, is used to test the coupling procedure. Up to 100 m of bank retreat was predicted, and more than 20 cross-sections were reshaped. Typical results showing the effectiveness of the developed framework are presented and discussed. [ABSTRACT FROM AUTHOR]

Physically based numerical simulation models have been developed to predict hazard area relating to debris flows. Since fine sediments are expected to behave as a part of the fluid rather than solid phase in stony debris flows, several models have recently included this process of the phase shift from solid to fluid in the context of fine sediment. However, models have not been fully tested regarding the ability to reproduce a variety of debris flow characteristics. We therefore tested (i) applicability of a numerical simulation model for describing debris flow characteristics and (ii) the effect of phase shift of fine sediment on debris flow behaviors. Herein we applied a numerical simulation model to a well-documented dataset from the Illgraben debris flow observation station in Switzerland. Based on the stony debris flow concept, we physically modeled effects of the phase shift of sediment on transport capacity and flow resistance. We successfully reproduced the observed bulk density, erosion and deposition patterns, front velocity, and erosion rate, although we had to tune the ratio of fine sediment that behaves as a fluid. Considering the effects of the phase shift of sediments, we conclude that physically based numerical simulation models can describe a variety of debris flow behaviors. [ABSTRACT FROM AUTHOR]

Recent sonar surveys of Okanagan Lake, in the central interior of British Columbia, revealed the presence of linear, contour-parallel furrows at depths of 50–130 m. Underwater video imagery shows these furrows to be approximately 0.5–1 m wide by 0.5–1 m deep with variable lengths extending 1–100 m. Their cross-sectional topology varies from semi-rectangular features with steep-walled sides that expose weak laminations in the sediments to shallow U-shaped troughs that appear to be infilled by lacustrine mud. The most likely origin of the furrows is extension deformation (i.e., tension fracturing) caused by periodic failure along the steeply inclined marginal slopes of this deep, glaciated lake basin. A positive feedback mechanism leading to arrested downslope movement, based on the recent findings reported in Carey et al. (2019), is suggested to apply. Less likely alternative explanations are considered and dismissed. The furrows highlight the nature of long-term geomorphic processes in lacustrine environments that contribute to sediment transport and deposition on the lake bed but are not directly linked to the action of surface waves and currents. [ABSTRACT FROM AUTHOR]

Local scour and flow field around cylinders with lenticular geometry and different bluntness factors under the clear-water state were investigated numerically. To examine the scouring, large eddy simulation with a WMLES-Omega sub-grid model incorporating the sediment transport and morphodynamic model was applied. Streamlined geometry of the pier significantly affected the scour pattern and flow field in the lenticular model with length to width ratio of 5 and bluntness factor of zero. In the mentioned case, a very small scoured region was estimated at the sides of the pier, so it can be concluded that scour depth and scoured region decreases as the length to width ratio increases. Investigation of the scouring process and the flow field revealed that, the flow separation can affect the scour mechanism more in comparison to down-flow. [ABSTRACT FROM AUTHOR]

The inner shelf off southwest Newfoundland, bordering the Laurentian Channel, was mapped with multi-beam sonar between depths of 200 and ∼20 m, overlapping with coverage by marine/terrestrial LiDAR from maximum depths of 30 m to above sea level. The new data provide the first clear view of linkages between terrestrial and nearshore coastal systems and the inner shelf. Offshore sand reservoirs associated with adjacent sandy coastal barriers and spits are thin (∼2 m), and isolated from one another, so that bedrock is the dominant seafloor terrain on the inner most shelf. The offshore sand reservoirs link with complex nearshore bar systems, from which it is inferred that sediment exchange with terrestrial systems can occur. Several isolated sand bodies are interpreted as residuals from former coastal systems destroyed during the Holocene transgression. The new data reveal the unexpected existence of a submarine canyon that facilitates transport of sediment from the inner shelf into the deep glacial trough of the Laurentian Channel. [ABSTRACT FROM AUTHOR]

The friction angle of sand in the nearshore zone of Cannon Beach, Yakutat, Alaska, was estimated from the deceleration measured by a portable free-fall penetrometer (PFFP) at 72 test locations. A correlation between the relative density and PFFP's maximum deceleration was developed from controlled PFFP deployments into sand of different relative densities. Two approaches were tested: (i) a correlation between relative density and friction angle and (ii) bearing capacity theory. For the former, laboratory vacuum triaxial tests were performed to adjust an existing correlation between relative density and friction angle for the tested nearshore sediments. In situ peak friction angles were then determined using this adjusted correlation and estimates of relative densities. The resulting in situ relative density and friction angle varied between 32%–88% and 44°–56°, respectively. Two bearing capacity–based methods suitable for shallow penetrations were tested. For this approach, equivalents of static cone resistance were determined from the measured decelerations considering the strain rate effect. A range of empirical strain rate coefficients K = 0.1–1.5 were tested. A K value between 0.2 and 0.4 yielded matching results between the two approaches. The estimated friction angles agreed well with expected values and may be applied to problems of sediment transport or early site assessment. [ABSTRACT FROM AUTHOR]

Present work evaluates the double averaged turbulence characteristics of the sand bed channel subjected to the downward seepage through permeable bed. Measures of turbulent statistics are observed to increase with the application of downward seepage. The form induced stress in near bed has a reducing effect with no seepage and an increasing effect with seepage. The seepage increases the turbulent kinetic energy and turbulent intensities causing the bed particles to move rapidly. The quadrant analysis suggests that at near bed, the sweep events in flows with seepage are the main bursting events towards the Reynolds stress production, while ejection and sweep events in no seepage flow have almost equal contribution. The increase in sediment transport with seepage is caused by an increase in flow turbulence production and an associated decrease in turbulent kinetic energy dissipation and turbulent diffusion. [ABSTRACT FROM AUTHOR]

We use annually laminated lake sediments to estimate suspended sediment yield for a 3850 km2 montane catchment in the British Columbia Coast Mountains. Sediment yield over the past 369 years averages 213 ± 38 Mg·km−2·a−1. Sediment yield increases to 285 ± 50 Mg·km−2·a−1 during the first half of the twentieth century and declines thereafter. The frequency of high-yield events during the 369 year period is irregular: 11 of the 34 events occur in the early part of the twentieth century, a time when glaciers in the watershed underwent major retreat. We fitted a generalized extreme value (GEV) model to estimate quantiles of the sediment yield distribution, and we used epoch analysis to examine persistence in sediment yield following 34 of the largest events. Persistence is greatest for the most extreme events; it is more variable for events that recur, on average, every 10-25 years. Our results indicate that sediment yield is linked to long-term changes in sediment supply to the lake. The results of this study extend earlier sediment yield estimates and improve understanding of linkages to watershed geomorphology, recent glacier retreat, and landslides in the Lillooet River watershed. [ABSTRACT FROM AUTHOR]

Cross vane structures aim to reduce near-bank shear and increase center channel flow intensity to retain flood flow and maintain sediment transport capacity in stream channels. These in-stream structures have been widely applied for river management, but how they interact with the local ice regime is poorly understood. This paper presents a numerical model study of the interaction of cross vane structures with sediment and ice using a two-dimensional coupled river ice-sediment dynamic model. The model was used to simulate a variety of ice and flow conditions to show how cross vanes affect sediment and ice processes. The study showed the design of cross vane structures in cold region rivers should consider the ice effects, especially the increasing potential of ice jam formation and related bed change. [ABSTRACT FROM AUTHOR]

For the efficient design of bridge pier footings, computation of time-evolution of scour depth around bridge piers is essential. In this paper, a semi-empirical model is developed to estimate the temporal variation of clear-water scour depth at a couple of identical cylindrical uniform piers in tandem arrangement. The experiments are carried out using different pier size, pier spacing, and flow intensities. The model development is based on sediment continuity approach and volumetric sediment transport rate from the scour hole using a sediment pickup function. The model results are presented as design charts giving the relation between dimensionless scour depth and time for practical use. Results of the proposed model are in relatively good agreement with the experimental results, in the tested range. [ABSTRACT FROM AUTHOR]

Bridges are vital components of the transportation network and if they are damaged or destroyed during a flood, they isolate communities and limit movement of supplies and emergency services. Evaluating their constructional stability and structural response after a flood event is critical for bridge safety. Bridge studies are usually designed with an assumption of an open channel flow condition, but the flow regime can switch to pressure flow if the downstream edge of a bridge deck is partially or totally submerged during a large flood. The main goal of this paper is to study the pressurized flow scour under a bridge deck and downstream deposition that results from eroded sediment material governed by both steady and unsteady clear-water flow conditions. Experimental conditions used in this study involve clear-water scour of a sand bed of given median sediment size d50 = 0.90 mm and sediment uniformity σg = 1.29, an approach flow characterized by a flow depth and velocity, a rectangular-shaped bridge deck, and a stepwise flood hydrograph defined by its time to peak and peak discharge. Different flow conditions were considered in confined flow under the bridge deck. Relationship between pressure-flow scour and flow conditions is presented and discussed under the obtained experimental data. Additionally, effects of single-peaked stepwise flow hydrographs (unsteady flow conditions) on bridge pier scour depth are investigated under clear-water pressure-flow conditions, whereas previous researches mainly focused on the equilibrium pressure scour under steady flow conditions. [ABSTRACT FROM AUTHOR]

The central north shore of Prince Edward Island comprises embayments separated by subtle headlands that may constrain nearshore sediment transport. The study area includes two such embayments informally known as Brackley and Tracadie bights, both of which are sand-rich onshore and sand-starved between 20 and 50 m water depth. Storm winds and waves from the northwest and northeast are common in autumn and winter. The hydrodynamic model Delft3D is used to simulate waves, currents, water levels, and sediment transport in Brackley and Tracadie bights during 23 autumn seasons between 1955 and 2005. When compared with wave and current measurements from a field experiment in the autumn of 1999, the model successfully simulates conditions during storms and fair-weather periods. Results from the simulations show that, in autumn, the weighted mean direction of transport is to the southeast (133°). Bedload transport is directed onshore to the south (170°), and suspended load is directed offshore to the northeast (67°). When aggregated over the 23 seasons, transport magnitudes and directions differ between Brackley and Tracadie bights. Rates of transport are higher in Tracadie Bight and directed more to the east. During individual storms, transport is dependent on the storm wind and wave direction. Most transport occurs in bed load, and deposition occurs at the shoreline, with erosion offshore. The patterns of bed load and suspended load suggest a mechanism for the landward migration of this shoreline during transgression, and may explain the existence of the sand-starved zone offshore. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the Bay of Fundy and for the integrated management of the Bay. Waves, tidal currents, and wind-driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader Bay of Fundy. The wave and current outputs were coupled with observed grain size in a sediment transport model to predict, for the first time, the seabed shear stresses, sediment mobility, and sediment transport patterns for the entire Bay. The root mean square tidal current, highest in the upper Bay (>1.4 m·s−1), is reduced to moderate in the central Bay (0.5-0.8 m·s−1) and decreases further in the outer Bay (0.2-0.5 m·s−1). The maximum tidal current occurs in the Minas Passage and is >5 m·s−1. The mean significant wave height, in contrast, is the greatest in the outer Bay (∼1.3 m) and gradually decreases to the northeast in the central and upper Bay (<0.5 m). Seabed shear in the Bay of Fundy is mostly due to tides, and wave effects are only important in coastal areas. The strongest mean shear velocity of 10 cm·s−1 occurs in the Minas Passage area. Strong shear velocity of 4-5 cm·s−1 also occurs in Minas Basin, in the central Bay, and in the narrows around Grand Manan Island. Sediment mobilization in the Bay of Fundy is predominantly by tidal current. Mobilization frequency is >30% of the time over most of the Bay and reaches 100% of the time in some areas. The maximum total-load sediment transport rate under spring tide can reach ∼5 kg·m−1·s−1 and is to the northeast during flood and to the southwest during ebb. Net sediment transport flux, however, is dominantly to the northeast and reaches 2 kg·m−1·s−1. Eddies of net transport are found to occur around headlands and at the narrows of Grand Manan Island, largely due to the occurrence of eddies of residual tidal flows. The regional distribution of substrate types and bedform fields and patterns of seabed erosion and deposition are well correlated with tidal current strength and sediment transport patterns. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper aims to develop a robust two-dimensional coupled numerical model based on an unstructured mesh, which can simulate rapidly varying flows over an erodible bed involving wet-dry fronts that is a complex yet practically important problem. Using a modified spatial reconstruction based on the finite volume method, the well-balanced property is preserved, which is important for accurate and efficient simulation of morphological problems. In the present study, the central-upwind scheme is extended to simulation of bed erosion and sediment transport for the first time. It is demonstrated that the proposed scheme shows good accuracy and high efficiency. A modified shallow water system is adopted to improve the model. The shallow water equations, sediment transport equation and bed evolution equation are coupled in the governing system. Multiple test cases are employed to demonstrate the robustness, accuracy, and efficiency of the current model. Furthermore, with a field scale dam-break test case, the efficiency and accuracy of the central-upwind method is verified in comparison with other popular Riemann solvers. The effects of the additional source terms in the adopted modified shallow water equations are also investigated by comparing the numerical results with a laboratory study available in the literature. The proposed scheme can efficiently track wetting and drying interfaces while preserving stability in simulating the bed erosion near the wet-dry fronts. The added terms in shallow water equations can improve the accuracy of the simulation when intense sediment-exchange exists; the central-upwind method adopted in the current study shows great accuracy and efficiency compared with other popular solvers; the developed model is robust, efficient and accurate to deal with various challenging cases. [ABSTRACT FROM AUTHOR]

Many reservoirs in the world are aging, and dredging has been the most common method to maintain the function of the reservoirs. The main problem affecting the useful life of the reservoirs is sediment deposition. Knowledge of both the rate and pattern of sediment deposition in a reservoir is required to predict the types of service impairments that would occur, the time frame in which these impairments would occur, and the types of remedial strategies that could be applied. The present analysis detailed the importance of physical properties to the total load sediment fluxes using 22 equations. The study measured gravel particles and suggested properties that have more control on the final result by providing insight into the relative strengths and weaknesses. The authors concentrated on available field and flume datasets gathered from different sources rather than focusing entirely on total load equations. The artificial neural network (ANN) was used to validate this study. The results emphasized the influence of the parameters detected by ANN and showed that the parameters were directly controlling the error in the total load sediment flux using the measured gravel particle datasets. This research had theoretical and practical significance for the future investigations concerning the fundamentals of total load sediment transport in reservoir engineering. [ABSTRACT FROM AUTHOR]

Recent marine sedimentary deposits and river discharge in two subarctic fjords in Nunatsiavut (Northern Labrador, Canada) have been studied to elucidate patterns and mechanisms of fluvial sediment transfer and accumulation in the fjords, to further our understanding of the longer-term sedimentary record. Multibeam and sub-bottom acoustic data and sediment cores were collected in Nachvak and Saglek fjords, within Canada's Torngat Mountains National Park, as part of the most extensive study of the park's marine resources to date. Cores were subsampled for X-radiography, grain size, and 210Pb/137Cs geochronology. Muddy basin sediments within each fjord are bioturbated, indicating circulation of oxygenated bottom water. Depositional fluxes and inventories of 210Pb indicate efficient marine scavenging of 210Pb by fine suspended sediments. In Nachvak Fjord, with small rivers and steep, presently glaciated catchments, postglacial and recent sediment accumulation rates are similar, implying relatively constant sedimentation over time. In Saglek Fjord, fed by larger rivers with more extensive catchments that lack glaciers, recent sediment accumulation is more rapid than that averaged over postglacial time. Present mass accumulation rates for the Nachvak Fjord basin are on average 39 000 t·year-1 for the entire basin, and for Saglek 43 000 t·year-1 for the entire basin, with sediment-gravity flows being one likely mechanism for sediment delivery to deep basins. Results collectively suggest that both marine basins are excellent natural sediment traps. Comparison of accumulation rates from 137Cs and 210Pb suggest that sediment fluxes to Nachvak Fjord may have decreased slightly over the past ∼130 years. [ABSTRACT FROM AUTHOR]

The observed sedimentation data from some Iranian large reservoirs were used to characterize sediment distribution patterns within these reservoirs and a modified approach was developed. This new idea is of an empirical nature and is based on some parameters obtained from the minimum stream power principle. The main advantage of this new characterization is that it eliminates the need for classification of the dam based on any extra data and solely depends on the characteristics of the reservoir geometry. It also rectifies some practical difficulties for application of the existing method. The developed technique achieved by this study is recommended for preliminary design stages to interpret long-term cumulative distribution of sediment and is applicable for reservoirs that have sediment particles that are mainly of fine-grained material. [ABSTRACT FROM AUTHOR]

In semi-arid and arid regions, civil engineers may be required to plan measures, such as sand fences, to control sand movement affecting developed areas or transportation corridors. In this paper, considering the desertification process for the Minqin Oasis in Gansu Province, China, the design of sand fences and overall sand control strategies to lessen the rate of desertification are discussed. A sand transport model called MOSAND was developed to predict the sand transport rate for the Minqin Oasis. The model was based on a bed load transport (creep and saltation) equation and a logarithmic velocity profile for the wind. Using the measured wind data for the Minqin area, a monthly average sand transport rate was calculated that was used to determine an effective life span of a 3 m high sand fence. Sand fences in conjunction with straw checkerboard sand barriers are recommended to control sand drifts into the Minqin Oasis. [ABSTRACT FROM AUTHOR]

We report the first numerical tests of the two-dimensional vertically-averaged and moment (VAM) equations to simulate scour and deposition along alluvial meandering rivers with fixed banks. The VAM hydrodynamic model assumes a linear vertical distribution of the velocity profile and provides estimates of the magnitude and direction of the both near-bed and surface velocity vectors in a quasi three-dimensional (3D) fashion, reproducing at a very basic level some of the 3D effects of the secondary flow in bends. By assuming that the bed shear stress direction along the bed was given by the VAM's near-bed velocity direction, it was possible to successfully reproduce the scour and deposition observed in a curved experimental flume and a meandering river reach. Although the VAM model is more general and does not require a secondary flow correction, as needed by conventional depth-averaged models, the results were not significantly better for the two cases analyzed. [ABSTRACT FROM AUTHOR]

A numerical scheme for simulation of activated sludge sediment flow in a circular secondary clarifier is developed. The flow and settling processes are simulated, using the k-ε turbulence model on a two-dimensional axisymmetric and orthogonal grid. To incorporate the sedimentation of the activated sludge in the field of gravity, a convection-dispersion equation governing the mass transfer in the clarifier is extended. The computational domain includes the sludge blanket where the viscosity is affected by the rheological behavior of the sludge. The double-exponential equation is used to describe the dependence of the settling velocity on the solids concentration. The compression and consolidation process of the activated sludge is simulated by this equation. The experimental data provided by Weiss et al. show that the rheograms follow the Bingham law at low-shear rates. The modified Bingham model was introduced to overcome the blanket height overestimation problem with the results showing that the local sludge distribution in the clarifier has an excellent agreement with the concentration profile measurements by Weiss et al. (2007) and the sludge viscosity dominates the flow and sedimentation of activated sludge within the sludge blanket. Un modèle numérique est développé pour simuler l'écoulement de sédiments de boues activées dans un clairificateur secondaire circulaire. L'écoulement et les processus de sédimentation sont simulés en utilisant un modèle de turbulence k-ε sur une grille bidimensionnelle orthogonale axisymétrique. Pour incorporer la sédimentation des boues activées dans le champ de gravité, une équation de convection-dispersion régissant le transfert de masse dans le clarificateur est élargie. Le domaine de calcul comprend le lit de boues, dans lequel la viscosité est affectée par le comportement rhéologique des boues. L'équation exponentielle double est utilisée pour décrire la dépendance de la vitesse de sédimentation sur la concentration des solides. Cette équation simule le processus de compression et de consolidation des boues activées. Les données expérimentales fournies par Weiss et al. montrent que les rhéogrammes suivent la loi de Bingham à des taux de faible cisaillement. Le modèle modifié de Bingham a été servi à résoudre le problème de surestimation de la hauteur du lit; les résultats montrent que la distribution locale de boues dans le clarificateur montrait une excellente corrélation avec les mesures des profils de concentration par Weiss et al. et que la viscosité des boues domine l'écoulement et la sédicmentation des boues activées à l'intérieur du lit de boues. [ABSTRACT FROM AUTHOR]

Experimental results on scour at circular and square cylinders in uniform gravel under the clear-water scour condition are presented. Nonintrusive, high-resolution topographic measurements of developing and equilibrium scour holes were performed during running experiments with an experimental installation using a laser distance sensor (LDS) and precision step motors. Measurements were taken by the LDS in different azimuthal half-planes with θ = 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 135°, 150°, 165°, and 180° to study the spatio-temporal variation of geometric properties of scour holes. Experiments were conducted over 40 h until equilibrium, with bed shear stress equal to 95% of the critical bed shear stress for the initiation of sediment motion at the undisturbed plane gravel bed having a d50 of 3.25 mm. Results show that scour in gravel progresses more slowly around the square cylinder, where steeper slopes than at the circular cylinder are observed. During experiments the scour slopes do not exceed the observed repose angle of the sediment particles. Maximum scour depth in different azimuthal half-planes and scoured volume are well correlated with the maximum scour depth at azimuthal half-plane with θ = 0°. Cet article présente les résultats expérimentaux sur l’affouillement autour de cylindres circulaires et carrés dans un lit de gravier uniforme sous des conditions d’affouillement en eau claire. Des mesures topographiques non intrusives et à haute résolution des trous d’affouillement, en développement et à l’équilibre, ont été prises lors d’essais utilisant un capteur de distance au laser (LDS) et des moteurs pas-à-pas de précision. Les mesures ont été prises par le LDS sur différents demi-plans azimutaux dont θ = 0°, 15°, 30°, 45°, 60°, 75°, 90°, 105°, 135°, 150°, 165° et 180° afin d’étudier la variation spatiotemporelle des propriétés géométriques des trous d’affouillement. Des essais ont été réalisés pendant 40 heures jusqu’à l’équilibre, avec une contrainte de cisaillement du lit de 95 % de la contrainte de cisaillement du lit critique pour l’initiation du mouvement des sédiments dans le lit de gravier non perturbé ayant un d50 de 3,25 mm. Les résultats montrent que l’affouillement dans le gravier progresse plus lentement autour des cylindres carrés, où des pentes plus raides qu’autour des cylindres circulaires ont été observées. Durant les essais, les pentes d’affouillement n’excédaient pas l’angle de repos observé des particules de sédiment. La profondeur maximale d’affouillement dans différents demi-plans azimutaux et le volume affouillé concordent bien avec la profondeur maximale d’affouillement à un demi-plan azimutal de θ = 0. [ABSTRACT FROM AUTHOR]

Side weirs are free overflow regulation and diversion structures commonly encountered in flood protection engineering. The lateral loss of water reduces the bed-load transport capacity in the main channel, leading to local sediment deposition near the side overflow. As a consequence, the design overflow is increased in an uncontrolled way. Since this flow-sediment interaction in such a channel has not been studied so far, systematic flume experiments have been performed. Based on these experiments, a two-dimensional empirical model to describe the longitudinal evolution of the aggraded channel reach near the weir has been developed. In addition, a simple and straightforward approach for direct estimation of the side overflow in presence of bed-load transport has been established. To be generally applicable in engineering practice, all input variables are expressed in terms of dimensionless parameters. Finally, the application of the models is demonstrated in a case study on the Rhone River in Switzerland. [ABSTRACT FROM AUTHOR]

Recent research on braided river morphology shows that the intensity (number of anabranches) of braiding channels increases with dimensionless discharge and (or) stream power. This variation in intensity reflects the adjustment of total sinuosity of the river to imposed gradient at a given discharge and grain size. Only a subset of channels is active at a given time and this active braiding intensity reflects the limited number of channels that can sustain bed load transport as the flow is divided. This is governed mechanistically by the dynamics of bifurcations and avulsions. Braided channel networks also have a characteristic length scale (or scales) related to the wavelength of the bars from which braiding develops and to the scale of the bars and confluence-bifurcation units within the braided network. The range of scales is limited by the size (and, therefore, number) of the active channels within the network and the width of the entire river. [ABSTRACT FROM AUTHOR]

The enduring legacy of the Yalin equation of bedload transport is evaluated. The derivation of the equation includes three innovative aspects: (i) a rigorous use of dimensional analysis to simplify the formulation; (ii) a consideration of the randomness of grain placement rather than turbulence, resulting in a definable threshold of motion; and (iii) the introduction of a physically based, dynamic model of grain saltation into a bedload transport theory. The original relation remains useful today. In addition, the treatment of saltation has inspired an innovative line of research that continues to evolve today. [ABSTRACT FROM AUTHOR]

Starting from the model proposed by the authors to analyze the time-evolution of bedforms growing on the surface of an initially flat sand bed, the present study explores associated features of the bedform growth processes, including (i) mechanisms of growth, (ii) evolution of the bedform-induced drag, (iii) transition to antidunes, and (iv) non-equilibrium bedload sediment transport. [ABSTRACT FROM AUTHOR]

Inertia effects are seldom considered in morphological modeling, and most of the transport models were developed from laboratory experiments in steady uniform flow conditions. This paper considers first the hysteresis effects in transient flows between discharge, velocity, and bottom shear stress. These effects can be taken into account as far as the complete shallow-water equations are used. Secondly, inertia effects linked to the sediment response to acting forces are considered. Three types of models are investigated: (i) sediment movement instantaneously adapting to hydrodynamic changes, (ii) spatial or temporal lag laws to give space or time to the sediments to progressively reach the transport capacity, and (iii) a two-layer model, able to account for the inertia of the sediment layer. Finally, three examples are presented: a scour hole downstream of an apron, a jump over a mobile bed, and a dam-break wave. Inertia effects appear significant in the modeling, especially the latter case. [ABSTRACT FROM AUTHOR]

Field and laboratory measurements of the transport of the suspended sediment from the Athabasca River near Hinton, Alberta, Canada are described. The objective of these measurements was to examine the influence of pulp mill effluent entering the river from a nearby pulp mill on suspended sediment. The results of the field measurement showed that the effluent had significant impact on the transport of the sediment. Specifically, the effluent increased the deposition rates of the sediment and caused a substantial reduction of sediment concentrations in reaches downstream of the effluent outfall. The reduction in sediment concentrations and the concomitant sediment loads can only be attributed to the pulp mill effluent as there were no abrupt changes in the hydraulic characteristics of the river in the reach of interest. These observations were confirmed by laboratory experiments that were carried out using a rotating circular flume located at the National Water Research Institute in Burlington, Ontario, Canada. The findings of this study have implications for modelling suspended sediment transport in rivers receiving bleached pulp mill effluents. [ABSTRACT FROM AUTHOR]

It has been a traditional practice of fluvial engineers to apply the uniform water-flow hypothesis to real rivers by averaging the geometric and hydraulic quantities over appropriate portions of the river reach. No quantitative criterion, however, was applied to assess the validity and limitations of this procedure. The present paper collects a number of theoretical considerations and relevant observations (developed in the framework of two recent doctoral theses) that are quite useful for selecting the approximated model most suitable for studying morphodynamic problems at watershed scale. Particularly efficient for this analysis has been consideration of the river in quasi-equilibrium conditions. [ABSTRACT FROM AUTHOR]

On the basis of previous work by the late Professor M. Selim Yalin and the author, the process of self-formation of alluvial streams and the final (equilibrium or regime) geometry of the self-formed stream are considered in the light of thermodynamic principles, including the first and second laws, and the Gibb’s equation; the stream is treated as an isolated and irreversible system. The present analysis suggests that stream self-formation is guided by the need of the stream to progressively decrease its average flow velocity to accommodate the increase in the entropy of the system with the passage of time. The reduction in flow velocity is achieved by an appropriate alteration of stream slope, cross-sectional geometry, and effective roughness, the regime development being the process of this appropriate alteration. A method is presented for the computation of regime width, depth, and slope. The method rests on the channel formation criterion derived from thermodynamic principles and the expression of regime flow width determined on the basis of zero net cross sediment transport rate at the regime state. The regime channels computed from this method are compared with field and laboratory data from various sources. [ABSTRACT FROM AUTHOR]

Mathematical modelling of river processes is, nowadays, a key element in river engineering and planning. River modelling tools should rest on conceptual models drawn from mechanics of sediment transport, river mechanics, and river hydrodynamics. The objectives of the present work are (i) to describe conceptual models of sediment transport, deduced from grain-scale mechanics of sediment transport and turbulent flow hydrodynamics, and (ii) to present solutions to specific river morphology problems. The conceptual models described are applicable to the morphologic evolution of rivers subjected to the transport of poorly sorted sediment mixtures at low shear stresses and to geomorphic flows featuring intense sediment transport at high shear stresses. In common, these applications share the fact that sediment transport and flow resistance depend, essentially, on grain-scale phenomena. The idealized flow structures are presented and discussed. Numerical solutions for equilibrium and nonequilibrium sediment transport are presented and compared with laboratory and field data. [ABSTRACT FROM AUTHOR]

The sedimentology of coastal, meromictic Lake A, Ellesmere Island (83°00′N, 75°30′W), was investigated to understand the linkages between the extreme lake environment and its sedimentary features. Four facies were identified within the sedimentary record that represent stages of the lake’s development from a marine embayment to a meromictic lake. Despite low ecosystem productivity, both clastic and biogenic materials contribute substantially, and highly seasonal sedimentation, pervasive ice cover, and anoxia in the saline bottom water (monimolimnion) act to preserve annual sedimentary units (varves) within the upper part of the sedimentary record. Sediment texture is predominantly silt and clay, but the irregular presence of sand indicates past episodes of higher energy stream discharge to the lake. Oxygen incursions into the chemocline likely cause bacteria mortality and provide elemental sulphur for iron sulphides that are deposited in the sediments. Millimetre-scale sedimentary pellets are also a conspicuous feature in the sediments and are interpreted to result from littoral sediment transport by ice-rafting. Many of Lake A’s notable sedimentary features are also evident in other High Arctic meromictic lakes, particularly those on the northern coast of Ellesmere Island. These similarities and the important biogenic component identified in Lake A suggest that processes in these sedimentary environments are more complex than previously thought. [ABSTRACT FROM AUTHOR]

The effective discharge (Qe) of a channel reach may be analytically determined by fitting the flow-duration relationship with a distribution model and representing the bed-material transport with a power function. Analysis of streamflow data from small southern Ontario streams showed that the commonly used lognormal distribution does not provide a good fit to many streamflow records. A mixed exponential distribution model is proposed and a formula for computing the resulting Qe is derived. The results from this new Qe formula were compared with those obtained using other analytical distribution functions and those from empirical sediment transport effectiveness curves. These comparisons indicate that the new analytical solution provides on average the most accurate estimates of Qe when the exponent β of the power function describing sediment transport at the channel reach is not more than 2; when β > 2, a gamma distribution provides the most accurate estimates followed closely by the mixed exponential distribution. Le débit effectif (Qe) d’un canal peut être déterminé par analyse en ajustant la relation débit-durée à un modèle de distribution et en représentant le transport du matériel du lit par une fonction puissance. L’analyse de l’écoulement dans de petits ruisseaux du sud de l’Ontario a montré que la distribution log-normale couramment utilisée ne fournit pas un bon ajustement à plusieurs données de débits. Un modèle de distribution exponentielle mixte est proposé et une formule de calcul du Qe qui en découle est dérivée. Les résultats de cette nouvelle formule du Qe ont été comparés à ceux obtenus en utilisant d’autres fonctions analytiques de la distribution et à ceux provenant de courbes empiriques d’efficacité de transport des sédiments. Ces comparaisons montrent que la nouvelle solution analytique fournit en moyenne les plus précises estimations des Qe lorsque l’exposant (β) de la fonction puissance décrivant le transport des sédiments dans le parcours du canal n’est pas supérieure à 2; lorsque β > 2, une distribution gamma fournit les estimations les plus précises, suivies de près par la distribution exponentielle mixte. [ABSTRACT FROM AUTHOR]

The Paskapoo Formation of southern Alberta supports more groundwater wells than any other aquifer system in the Canadian Prairies. Located in a region of rapid population growth and straddling watersheds where no new surface water licenses are available, this aquifer system is under increasing pressure to provide water supply. The Paskapoo Formation represents a foreland deposit of a siltstone- and mudstone-dominated fluvial system. The system is highly heterogeneous with broad ranges in physical properties that impact groundwater production. High-porosity coarse-grained channel sandstone can provide productive wells, whereas thin and fractured sands and siltstones are low producers. The basal Haynes Member and western portion of the Paskpaoo Formation have higher sandstone volumes than other portions of the system. Fracture density shows a strong inverse relationship to bed thickness, such that fracture flow becomes more important for thinner sandstone beds. There is no regional-scale flow system associated with the Paskapoo Formation; rather it is dominated by local-scale recharge processes. The geochemistry of Paskapoo Formation groundwater is largely controlled by the variable composition of immediately overlying glacial deposits. La Formation de Paskapoo du sud de l’Alberta supporte plus de puits d’eau souterraine que tout autre système aquifère des Prairies canadiennes. Situé dans une région à forte croissance démographique et chevauchant des bassins versants pour lesquels aucun nouveau permis d’eau de surface n’est disponible, ce système aquifère est de plus en plus sollicité pour des approvisionnements en eau. La Formation de Paskapoo représente un dépôt d’avant-pays d’un système fluvial composé surtout de siltstones et de mudstones. Le système est hautement hétérogène et ses propriétés physiques couvrent une vaste plage de propriétés physiques qui ont un impact sur la production d’eau souterraine. Le grès de chenal, à porosité élevée et à grain grossier, peut alimenter des puits productifs alors que les siltstones et les sables fracturés minces produisent peu. Le membre Haynes à la base et la partie ouest de la Formation de Paskapoo ont des volumes de grès supérieurs aux autres parties du système. La densité des fractures présente une relation inverse à l’épaisseur des lits, telle que pour les lits de grès minces, l’écoulement dans les fractures devient plus important. Il n’y a aucun système à l’échelle régionale associé à la Formation de Paskapoo, il est plutôt dominé par des processus de recharge à l’échelle régionale. La géochimie de l’eau souterraine de la Formation de Paskapoo est principalement contrôlée par la composition variable des dépôts glaciaires qui reposent sur la formation. [ABSTRACT FROM AUTHOR]

Using a laser Doppler velocimeter (LDV) system, experiments were carried out to obtain detailed information on the flow over a long train of fixed two-dimensional rough-wall dunes. The experiments provide quantitative data on conventionally averaged velocity and turbulence parameters, as well as insights on the flow structures that play a crucial role in sediment transport. The results indicate that the shape of the dunes has a major influence on the flow features, whereas the effect of near-bed roughness is limited to the wall region extending to a distance of about 80% of the dune height about the crest. However, the length of the separation eddy seems to be influenced by the near-bed roughness. As in flow over a smooth dune, the turbulence data reveal large peaks along a line roughly coinciding with the shear layer emanating from the separation at the crest. However, the location of the peak turbulence is farther extended into the flow away from the bed with increasing bed roughness. Moreover, with increasing roughness the magnitude of the peak is also reduced. A secondary peak in the streamwise turbulence profiles is noticed at some distance from the bed. This feature is not influenced by the near-bed roughness and indicates sustenance of turbulence generated by the previous dune and relates to the convection of the upstream flow history. Based on the results obtained at several stations between two successive dune crests, one can conclude that the quantitative effect of roughness itself is limited to the near-bed region in the measurements at all levels. [ABSTRACT FROM AUTHOR]

Sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings. In this study, aerial photographs, ground-penetrating radar (GPR), and stratigraphic analysis document the morphodynamics of an individual and compound parabolic dune in the Bigstick Sand Hills, southwestern Saskatchewan. Migration rates for the last 60 years are comparable, although the profile morphologies differ, with the individual dune having a more aerodynamic form. Stratigraphic facies are also similar in both dune types, but the overall internal architecture imaged by GPR differs considerably. Configurations of cross-strata parallel to the downwind axis represent dominant foreset development and lee-slope slipface advance of the individual dune, and impeded slipface development of the compound dune. Stratigraphy transverse to the downwind axis represents radial deposition and foreset development at the individual dune, and vertical accumulation at the compound dune. The overall difference in parabolic dune form and stratigraphy is attributed to variations in sand supply, which determine vegetation development and sedimentation processes along the crest and lee slope. Sand supplied from active blowouts upwind of the individual dune inhibits vegetation colonization on the dune, whereas an absence of sand supply upwind of the compound dune leads to high levels of vegetation cover on the dune. Once supply drops below a threshold level, vegetation cover increases, causing sediment deposition and vertical accretion, and ultimately changing dune form. Overall, this study demonstrates that local sand supply and feedback processes are critical to understanding dune development in vegetated, inland settings. [ABSTRACT FROM AUTHOR]

In this paper the offset jet entering a domain with a movable bed is simulated by the computer program FLUENT. To achieve this aim, sediment transport is numerically simulated using multiphase systems and the empirical coefficients are studied theoretically. The numerical results are verified by comparing the simulated total load with that obtained using existing formulae and concentration profiles from available measured data. In the final step, the offset jet scouring pattern is modeled qualitatively. [ABSTRACT FROM AUTHOR]

A three-dimensional numerical model was used to examine the turbulent flow field and associated sediment transport due to a series of barbs (submerged groynes) in a channel bend. Model results were in good agreement with measured laboratory data and adequately simulated the important features of sediment transport. Statistical comparison of the predicted and measured equilibrium bed geometry found average regression coefficients of determination of 0.77 and 0.72 for the 90° and 135° channels, respectively. The predicted velocity data followed expected trends. The capability of a three-dimensional numerical model to simulate sediment transport through bend sections of a channel containing barbs was verified. This included the simulation of the effects of different arrangements of barb groups and an analysis of the data to determine the relation of the flow field to associated scour and deposition in a complex fluvial environment. These novel results are useful for improved analyses of the bank-protection capabilities of these structures and for the development and improvement of design guidelines. [ABSTRACT FROM AUTHOR]

An overview of cohesive sediment transport processes is given in this paper, and a mass-balance equation that is commonly used to treat cohesive sediment transport is reviewed. The equation highlights transport parameters and processes that are important for modelling the transport of cohesive sediment. The flocculation mechanism that distinguishes cohesive sediment from its noncohesive counterpart is elaborated using a laboratory study that was carried out in a rotating circular flume using sediments from Hay River, Northwest Territories, Canada. A mathematical model of flocculation suitable for predicting flocculation of sediment in rotating circular flumes is reviewed. Other cohesive sediment transport processes such as erosion and deposition processes at the sediment-water interface, entrapment of fines in gravel beds, consolidation, fluid mud, and fluidization due to wave action are reviewed. Additional challenges and knowledge gaps that exist in the area of cohesive sediment transport are identified. [ABSTRACT FROM AUTHOR]

Schemes to restore fish habitat in rivers often involve installing instream structures such as current deflectors to create and maintain riffle-pool sequences. However, there is a lack of field studies on the impact of these structures on flow dynamics and bed topography. The objective of this research is to characterize flow dynamics and sediment transport around paired deflectors used to enhance fish habitat in the Nicolet River, Quebec. Bed and bank topography surveys were taken with a total station, and velocity and bed shear stress estimates were obtained from an acoustic doppler velocimeter. Bedload sediment transport was assessed by two methods: tracer rocks (painted "particles" and passive integrated transponder tags) and sediment traps. Results show marked differences in bedload sediment transport patterns between the left bank and the right bank downstream of the deflectors. This is surprising considering that paired deflectors should produce a relatively symmetrical disruption to the flow field on each side. More high-flow dynamics data during overtopping conditions are required to understand the complex interactions between these instream structures and bedload transport. [ABSTRACT FROM AUTHOR]