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Sediment Dynamics (sediment + dynamics)
Selected AbstractsSediment dynamics and pollutant mobility in rivers: An interdisciplinary approachLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2004Ulrich Förstner Abstract Characteristic dynamic features of sediment-related processes in rivers include dramatic effects of stormwater events on particle transport, rapid and far-reaching effects of sulphide oxidation during resuspension, and biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result of the stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine-grained sediments and suspended matter as these materials exhibit large surface areas and high sorption capacities. Organic materials are highly reactive. Degradation of organic matter will induce oxygen depletion and might enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. Major questions relate to the potential reduction of sorption sites on minerals and degradation of organic carrier materials. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modelling the overall effects of pollutants on the water body and aquatic ecosystems. With respect to handling and remediation of contaminated river sediments, either in-place or excavated, a chemical and biological characterization of the material, of the (disposal) site and of the long-term processes is crucial. Passive techniques (e.g. in situ stabilization, subaqueous capping) provide economic advantages as there are no operation costs following their installation. However, the success of these ecological and geochemical engineering approaches is mainly based on an in-depth knowledge of the underlying processes. [source] Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies,EARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2010J. Le Coz Abstract The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cutoff meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava River (Slovakia). Field measurements were performed in the exit of the Port-Galland cutoff meander, Ain River (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cutoff meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel. Copyright © 2010 John Wiley & Sons, Ltd [source] Sediment budget for an eroding peat-moorland catchment in northern EnglandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2005Martin Evans Abstract This paper describes a detailed contemporary sediment budget from a small peat-covered, upland catchment in Upper Teesdale, northern England. The sediment budget was constructed by measuring: (1) sediment transfers on slopes, (2) sediment flux on the floodplain and through the main stream channel and (3) sediment yield at the catchment outlet. Measurements were taken over a four-year monitoring period between July 1997 and October 2001 when interannual variations in runoff were relatively small. Three sites were selected to represent the major erosion subsystems within the catchment: an area of bare peat flats, a pair of peat gullies, and a 300 m channel reach. Collectively the sites allow detailed characterization of the main patterns of sediment flux within the catchment and can be scaled up to provide an estimate of the sediment budget for the catchment as a whole. This constitutes the first attempt to provide a complete description of the functioning of the sediment system in eroding blanket peatlands. Results demonstrate that fluvial suspended sediment flux is controlled to a large degree by channel processes. Gully erosion rates are high but coupling between the slopes and channels is poor and therefore the role of hillslope sediment supply to catchment output is reduced. Consequently contemporary sediment export from the catchment is controlled primarily by in-channel processes. Error analysis of the sediment budgets is used to discuss the limitations of this approach for assessing upland sediment dynamics. A 60 per cent reduction in fluvial suspended sediment yield from Rough Sike over the last 40 years correlates with photographic evidence of significant re-vegetation of gullies over a similar period. This strongly suggests that the reduced sediment yields are a function of increased sediment storage at the slope,channel interface, associated with re-vegetation. Copyright © 2005 John Wiley & Sons, Ltd. [source] An actualistic perspective into Archean worlds , (cyano-)bacterially induced sedimentary structures in the siliciclastic Nhlazatse Section, 2.9 Ga Pongola Supergroup, South AfricaGEOBIOLOGY, Issue 1 2008N. NOFFKE ABSTRACT Extensive microbial mats colonize sandy tidal flats that form along the coasts of today's Earth. The microbenthos (mainly cyanobacteria) respond to the prevailing physical sediment dynamics by biostabilization, baffling and trapping, as well as binding. This biotic,physical interaction gives rise to characteristic microbially induced sedimentary structures (MISS) that differ greatly from both purely physical structures and from stromatolites. Actualistic studies of the MISS on modern tidal flats have been shown to be the key for understanding equivalent fossil structures that occur in tidal and shelf sandstones of all Earth ages. However, until now the fossil record of Archean MISS has been poor, and relatively few specimens have been found. This paper describes a study location that displays a unique assemblage with a multitude of exceptionally preserved MISS in the 2.9-Ga-old Pongola Supergroup, South Africa. The ,Nhlazatse Section' includes structures such as ,erosional remnants and pockets', ,multidirected ripple marks', ,polygonal oscillation cracks', and ,gas domes'. Optical and geochemical analyses support the biogenicity of microscopic textures such as filamentous laminae or ,orientated grains'. Textures resembling filaments are lined by iron oxide and hydroxides, as well as clay minerals. They contain organic matter, whose isotope composition is consistent with carbon of biological origin. The ancient tidal flats of the Nhlazatse Section record four microbial mat facies that occur in modern tidal settings as well. We distinguish endobenthic and epibenthic microbial mats, including planar, tufted, and spongy subtypes. Each microbial mat facies is characterized by a distinct set of MISS, and relates to a typical tidal zone. The microbial mat structures are preserved in situ, and are consistent with similar features constructed today by benthic cyanobacteria. However, other mat-constructing microorganisms also could have formed the structures in the Archean tidal flats. [source] Wave and sediment dynamics along a shallow subtidal sandy beach inhabited by modern stromatolitesGEOBIOLOGY, Issue 1 2008J. E. ECKMAN ABSTRACT To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1,2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas , the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s,1), wave conditions remain comparatively calm until local winds increase above speeds of ,3,4 m s,1 at which point maximum wave speeds rapidly increase to 50,80 cm s,1. Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7,10 g cm,2 day,1 (,4,6 cm day,1). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions. [source] Flow and sediment dynamics of large riversHYDROLOGICAL PROCESSES, Issue 22 2009J. L. Guyot First page of article [source] Dynamics of suspended sediment transport at field-scale drain channels of irrigation-dominated watersheds in the Sonoran Desert, southeastern CaliforniaHYDROLOGICAL PROCESSES, Issue 16 2007Peng Gao Abstract Suspended sediment is a major source of pollution in irrigation-dominated watersheds. However, little is known about the process and mechanisms of suspended sediment transport in drain channels directly connected to agricultural fields. This paper explains sediment dynamics using averaged 5 min flow discharge Q (m3 s,1) and suspended sediment concentration C (mg l,1) collected during one crop season in a small catchment containing a first-order drain channel and its connected six agricultural fields within the Salton Sea watershed. The statistical properties and average trends of Q and C were investigated for both early (i.e. November) and late (i.e. January) stages of a crop season. Further in-depth analysis on sediment dynamics was performed by selecting two typical single-field irrigation events and two multiple-field irrigation events. For each set of irrigation events, the process of suspended sediment transport was revealed by examining hydrograph and sediment graph responses. The mechanisms underlying suspended sediment transport were investigated by analysing the types of corresponding hysteresis loop. Finally, sediment rating curves for both hourly and daily data at early and late stages and for the entire crop season were established to seek possible sediment-transport predictive model(s). The study suggests that the complicated processes of suspended sediment transport in irrigation-dominated watersheds require stochastic rather than deterministic forecasting. Copyright © 2007 John Wiley & Sons, Ltd. [source] Post-wildfire changes in suspended sediment rating curves: Sabino Canyon, ArizonaHYDROLOGICAL PROCESSES, Issue 11 2007Sharon L. E. Desilets Abstract Wildfire has been shown to increase erosion by several orders of magnitude, but knowledge regarding short-term variations in post-fire sediment transport processes has been lacking. We present a detailed analysis of the immediate post-fire sediment dynamics in a semi-arid basin in the southwestern USA based on suspended sediment rating curves. During June and July 2003, the Aspen Fire in the Coronado National Forest of southern Arizona burned an area of 343 km2. Surface water samples were collected in an affected watershed using an event-based sampling strategy. Sediment rating parameters were determined for individual storm events during the first 18 months after the fire. The highest sediment concentrations were observed immediately after the fire. Through the two subsequent monsoon seasons there was a progressive change in rating parameters related to the preferential removal of fine to coarse sediment. During the corresponding winter seasons, there was a lower supply of sediment from the hillslopes, resulting in a time-invariant set of sediment rating parameters. A sediment mass-balance model corroborated the physical interpretations. The temporal variability in the sediment rating parameters demonstrates the importance of storm-based sampling in areas with intense monsoon activity to characterize post-fire sediment transport accurately. In particular, recovery of rating parameters depends on the number of high-intensity rainstorms. These findings can be used to constrain rapid assessment fire-response models for planning mitigation activities. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrogeomorphology: overview of an emerging scienceHYDROLOGICAL PROCESSES, Issue 4 2004Roy C. Sidle Abstract Here, we introduce a series of 14 papers generated from a symposium related to hydrogeomorphology that was part of the Fifth International Conference on Geomorphology. Additionally, recent developments in hydrogeomorphology are highlighted, particularly with respect to research in Japan. Linkages are drawn between natural hazards and the necessity to focus on hydrogeomorphic processes. Future research needs are discussed in the areas of temporal and spatial patterns of water and sediment dynamics, including the effects of distributed land management practices and interactions with natural hazards. Copyright © 2004 John Wiley & Sons, Ltd. [source] Suspended sediment dynamics in a steep, glacier-fed mountain stream, Place Creek, CanadaHYDROLOGICAL PROCESSES, Issue 9 2003G. Richards Abstract This study examined suspended sediment concentration (SSC) during the ablation seasons of 2000 and 2001 in Place Creek, Canada, a steep, glacier-fed mountain stream. Comparison of stream flow in Place Creek with that in an adjacent, almost unglacierized catchment provided a rational basis for separating the ablation seasons into nival, nival,glacial, glacial and autumn recession subseasons. Distinct groupings of points in plots of electrical conductivity against discharge supported the validity of the subseasonal divisions in terms of varying hydrological conditions. Relationships between SSC and discharge (Q) varied between the two study seasons, and between subseasons. Hysteresis in the SSC,Q relationship was evident at both event and weekly time-scales. Some suspended sediment released from pro-glacial Place Lake (the source of Place Creek) appeared to be lost to channel storage at low flows, especially early in the ablation season, with re-entrainment at higher flows. Multiple regression models were derived for the subseasons using predictor variables including Q, Q2, the change in Q over the previous 3 h, cumulative discharge over the ablation season, total precipitation over the previous 24 h and SSC measured at 1500 hours as an index value for each day. The models produced adjusted R2 values ranging from 0·71 to 0·91, and provided tentative insights into the differences in SSC dynamics amongst subseasons. Introduction of the index value of SSC significantly improved the model fit during the nival,glacial and glacial subseasons for both years, as it adjusts the model to the current condition of sediment supply. Copyright © 2003 John Wiley & Sons, Ltd. [source] Exposure modeling on a river basin scale in support of risk assessment for chemicals in european river basinsINTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 1 2009Jos van Gils Abstract Following the 2000 European Water Framework Directive and recent insights into sediment management on a river basin scale, we discuss in this paper an exposure model aiming to support a risk assessment for chemicals on a basin-wide scale. It establishes spatial relations between causes (pollution sources) and effects (ecological risk), taking into account the geometry, hydrology, and fine sediment dynamics of European river basins. The model, called EXPOBASIN, explicitly takes into account the interaction of chemicals with fine sediment particles, which is important for many policy-relevant chemicals, such as trace metals and polycyclic aromatic hydrocarbons, and it addresses the potential release of historically polluted sediments as a result of extreme floods, which is a major concern in different European river basins. Bioavailability and bioaccumulation are included in the assessment. As a result, the exposure can be quantified not only in terms of water concentrations, but also in terms of sediment concentrations and concentrations in biota. The primary question to be answered by EXPOBASIN is how chemicals, pollution sources, or both rank quantitatively and objectively on a basin-wide scale. Near the end of 2009, the tool will become available to all European water managers and their technical advisors, as a result of the European Union 6th Framework Programme project MODELKEY The calibration and validation of EXPOBASIN has only just started and will be completed in 2008/2009. Applications to 3 case study areas are planned in this respect. This paper presents the key building blocks of EXPOBASIN and shows some sample results illustrating the raking of pollution sources and chemicals. At the end of the paper, some perspectives for future developments are outlined. [source] | |||||||||||||