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Fluvial deposits offer Earth's best‐preserved geomorphic record of past climate change over geological timescales. However, quantitatively extracting this information remains challenging in part due to the complexity of erosion, sediment transport and deposition processes and how each of them responds to climate. Furthermore, sedimentary basins have the potential to temporarily store sediments, and rivers subsequently rework those sediments. This may introduce time lags into sedimentary signals and obscure any direct correlation with climate forcing. Here, using a numerical model that combines all three processes—and a new analytical solution—we show that the thickness of fluvial deposits at the outlet of a mountain river can be linked to the amplitude and period of rainfall oscillations but is modulated by the mountain uplift rate. For typical uplift rates of a few mm/yr, climate oscillations at Milankovitch periods lead to alluvial sediment thickness of tens of meters as observed in nature. We also explain the time lag of the order of 20%–25% of the forcing period that is commonly observed between the timing of maximum rainfall and erosion. By comparing to field datasets, our predictions for the thickness and time lag of fluvial deposits are broadly consistent with observations despite the simplicity of our modeling approach. These findings provide a new theoretical framework for quantitatively extracting information on past rainfall variations from fluvial deposits. Plain Language Summary: Climate influences the evolution of terrestrial landscapes through the amount of precipitation, which provides water to erode rocks and transport sediment in rivers. At the outlets of mountain ranges, rivers can deposit part of their sediment load; the shape of the deposits is influenced by the amount of flow in the rivers. If the climate changes such that the precipitation rate increases, rivers can cut into their own previous deposits. The remaining deposits are then abandoned above the riverbed. On the contrary, if precipitation decreases, rivers tend to deposit more sediment, leading to increases in the thickness of sediments at the outlets of mountain rivers. Thus, there is a relationship between the amount of precipitations and the thickness of sediments deposited at river outlets. We study this with a computer model that allows us to relate the variations in precipitation rates to variations in thickness of fluvial terrace deposits. This work can be used to better understand how rivers respond to climatic changes, and also to reconstruct climatic variations of the past from observed river deposits. Key Points: We use a numerical model and a new analytical solution to quantify a physical link between fluvial deposits and climate oscillationsOur method provides a theoretical framework for extracting information on past climate variations from fluvial terrace depositsOur results explain time lag of 20%–25% of forcing period commonly observed between the timing of maximum rainfall and erosion [ABSTRACT FROM AUTHOR]

The depositional history of alluvial fans on Mars provides insight into the climatic conditions during the time of fan formation in the late Hesperian to early Amazonian. However, traditional stratigraphic analysis of the alluvial fan deposits is not possible across most of Mars. This study assesses the use of thermal inertia data as a tool for sedimentologic interpretation of 437 Mars alluvial fans. Based on previous work demonstrating the relationship between depositional style, grain size, and thermophysical properties, this study uses analysis of the thermal inertia of alluvial fan surfaces across the global population of fans on Mars to make an assessment of depositional styles that built the alluvial fans. The thermal inertia values across the global population of fans are indicative of sand- to pebble-sized sediment. The variability of grain sizes across the global population is more homogenous than expected based on comparisons to terrestrial alluvial fans. Nearly all Mars alluvial fans have an average thermal inertia that corresponds to pebble and smaller grain size, and < 1% of Mars alluvial fans have an average thermal inertia that corresponds to cobble-sized grains. Spatial patterns of thermal inertia variability on alluvial fan surfaces show a small number of fans with evidence for either downslope fining or channelization, but the majority of fans show no recognizable geologic patterns in surface thermal inertia. The interpretation of the thermal inertia-derived grain size suggests that either there is widespread mantling of unconsolidated sand across the surface, or that Mars alluvial fans were built by primarily sand-sized sediment, which may be indicative of lower energy sediment transport events. • Thermal inertia of alluvial fan surfaces indicates primarily sand-sized sediment. • Thermal inertia of Mars alluvial fan surfaces is surprisingly homogeneous globally. • Alluvial fans built by sand-sized sediment suggest low energy fluvial processes. • Fluvial depositional processes may correlate to lack of clay in catchments. [ABSTRACT FROM AUTHOR]

The timespan recorded in deposits from fluvial activity is a key gap in our understanding of ancient environments on Earth and Mars. Because riverine sediment transport occurs under time‐variable water discharge, common models that represent sediment transport with a single bankfull discharge require an intermittency factor. For this reason, the ability to predict intermittency factor values based on environmental factors would improve estimates of time from fluvial deposits. To address this knowledge gap, we calculated intermittency factors from 201 modern rivers and six fans and deltas with depositional timespans of months to millions of years. Intermittency factors range from 0.0064–0.73; they are uncorrelated with averaging timescale, bed‐material grainsize, or climate aridity, but are larger in river catchments with greater rates of denudation relative to precipitation. Application to ancient fluvial systems on Mars indicates long‐lived depositional river systems for up to 104–106 years. Plain Language Summary: To estimate the lifespan of ancient river courses, geologists estimate the time it took to transport and deposit all of the sediment within a landform, such as an alluvial fan or delta. This method relies on sediment‐transport calculations, which often assume a single reoccurring flood event that fills the river channel, even though river discharge varies in time from low flows to large floods. While the discharge of the channel‐filling flood event can be constrained from channel geometry or deposit characteristics, flow variability is unknown, and an intermittency factor is needed to adjust the sediment transport calculation. In this work, we calculated intermittency factors for 201 rivers and six river deposits on Earth. We also examined correlations between intermittency factor and environmental variables, and found no correlation with averaging timescale, bed‐material grainsize, or climate aridity. However, intermittency factors are larger in catchments that receive a large supply of sediment. Applying the new intermittency factor values to river deposits on Mars suggests that some of those rivers persisted for millions of years. Key Points: Rivers transport sediment intermittently; intermittency factor relates river duration to deposit volume and bankfull river characteristicsIntermittency factors we calculated have a 5–95 percentile range of 0.0064–0.73, independent of timescale, grainsize, and climateApplication to Mars implies fluvial activity over thousands to millions of years [ABSTRACT FROM AUTHOR]

Vrgada Island is situated in the central part of the eastern Adriatic coast. Upper Cretaceous limestones crop out on the surface and Pleistocene sediments cover them in some parts of the island. This study focused on a coastal cliff trending N - S on the northern part of the island. Aeolian-alluvial deposits, which are 12.5 m thick were analysed and three different facies in this succession described. The lowermost facies A highlights a strong aeolian influence marked by an increased silt percentage and was deposited during colder climate conditions. Sand and gravel in facies B were deposited by streams of dense, cold water formed by melting snow and ice from the nearby Dinaric mountains. The bioturbated sandy facies C was probably formed during a warmer climate. An unusually high percentage of augite in the lowermost part of facies A can be explained by the input of volcanic dust, most likely from the Roman or Campanian volcanoes in Italy. This, combined with the surface textures on quartz grains detected from SEM photographs indicates a short distance transport for the sediment, no matter which mechanism was dominant. The sediments from Vrgada Island represent a transitional zone between the north Adriatic islands, where aeolian sediments dominate and the South - Eastern Adriatic archipelago, where mixed alluvial and aeolian sediments were observed. [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

The Paleozoic arkoses of the Inkisi Group in both the Republic and the Democratic Republic of the Congo has been investigated in order to examine whether they can represent an alluvial fan originating from the Gondwana supermountains in Northern and East Africa. This study focuses on outcrops' description, lithofacies, bounding surfaces, architectural and sequential organization of sedimentary bodies and paleocurrents. The aim is to determine the nature of the Inkisi sandstones, the provenance of its sediments and the depositional setting, in order to test whether the East African orogen was also the sediments source for the formation of sedimentary fan in the western part of Central Africa. The study shows that the Inkisi Group consists of various sandstone lithofacies, amalgamated by conglomerates. The sediments are immature composed of quartz and feldspars associate with lithic fragments and micas. The sediments originated from the erosion of the West-Congolian belt and the Congo Craton, and were transported by braided fluvial system under mainly upper flow regime and secondarily lower flow regime. Sediments were deposited in the Inkisi basin, which was extensional and affected by burial. The Inkisi sediments setting up in a proximal to medial distributary zone of an alluvial megafan. The flows were directed southward, as opposed to paleofans originating from the Gondwana supermountain in Northern and East Africa. Thus, the Inkisi sandstone constitutes a new alluvial megafan distinguished from the Gondwana superfan derived from the Gondwana supermountain. It originated from the Pan-African belt of Mayombe and the Congo Craton. We name this megafan " the Cambro-Ordovician alluvial megafan of Central Africa ". • The Inkisi Group are arkoses and sub-arkoses associated with conglomerates. Conglomerates are gravel bars and gravity flows. • The Inkisi sediments originated from the peneplanation of the Pan-African West-Congolian/Mayombe and the Congo craton. • The Inkisi sediments were transported by a braided fluvial system and deposited in an extensional basin affected by burial. • The Inkisi Group is an alluvial megafan deposits. • The Inkisi Groupe constitutes a Lower Paleozoic alluvial megafan in Central Africa. [ABSTRACT FROM AUTHOR]

Upper Miocene to Pliocene (Pannonian) sediments of the Pannonian Basin System accumulated in the brackish Lake Pannon and the fluvial feeder systems, between 11.6-2.6 Ma. Their stratigraphic subdivision has been problematic for a long time due to the laterally prograding architecture of the basin fill and the historically independently evolving stratigraphic schemes of the neighbouring countries. We correlated the lithostratigraphic units of the Lake Pannon deposits between Hungary and Croatia in the Drava Basin, using lithological, sedimentological and palaeontological data from boreholes and outcrops, and seismic correlation. The Croatica and Medvedski breg formations in Croatia correspond to the Endrőd Fm. in Hungary, comprising shallow to deep water, open lacustrine, calcareous to argillaceous marls. The Andraševec fm. in Croatia corresponds to the Szolnok and Algyő Fms. in Hungary, consisting of sandstones and siltstones of turbidite systems and of clay marls deposited on the shelf-break slope. The Nova Gradiška fm. in Croatia is an equivalent of the Újfalu Fm. in Hungary, built up of a variety of lithologies, including sand, silt, clay and huminitic clay, deposited in deltaic environments. The Pluska fm. in Croatia corresponds to the Zagyva Fm. in Hungary, consisting of variegated clays, silts, sands and lignites, deposited in alluvial and fluvial environments. Coarse-grained (sand, gravel) basal layers are assigned to the Kálla and Békés Fms. and the Sveti Matej member of the Croatica fm. Coarse-grained intercalations within the deep-water marls belong to the Dorozsma Member of the Endrőd Fm. in Hungary, and to the Bačun member of the Medvedski breg fm. in Croatia. Sediment transport and lateral accretion of the shelf edge in the Drava Basin took place from the N, NW, and W, to the S, SE, and E, respectively. According to the biostratigraphic and chronostratigraphic analyses, the oldest shelf-break slopes in the Mura Basin are more than 8 Ma old, whereas the youngest ones in the southeasternmost part of the Drava Basin may be Pliocene in age (younger than 5.3 Ma). Thus, the 180 km long and at least 700 m deep Drava Basin was transformed into a fluvial plain during the last 3.5 million years of the Miocene. [ABSTRACT FROM AUTHOR]

The properties of sediment grain shape provide valuable information about the transport mechanisms in different sedimentary and geomorphological environments. With the emergence of new, high-resolution analytical techniques, it has become possible to quickly examine the grain shape properties of a large number of individual mineral grains. In this study, we used automated image analysis (Malvern Morphologi G3SE-ID) to investigate mineral particles of four sediment types from different depositional environments (sand sheet (1), floodplain (2) and fluvial channel deposits (3), Pleistocene infilling material of sand wedges (4), n = 20) in the Carpathian Basin (Central Europe). Our primary objective was to identify quantitative key variables that can help objectively distinguish certain geomorphological environments located in the Carpathian Basin. In our analysis and data processing (which included techniques such as hierarchical cluster analysis, Wilks' λ, Kruskal–Wallis, multivariate analysis of variance and principal component analysis) we focused on four variables related to grain shape: circularity (form), convexity (surface texture), solidity (roundness) and elongation (form). The form of sedimentary grains depends largely on the physical properties of their source area, while the roundness depends on the energy of the transport medium and the distance of transportation. Surface texture or convexity can change in a relatively short time in a fluvial environment. The study revealed that distinguishing geomorphological environments can be achieved by analyzing the circularity, convexity and solidity parameters of the sediment grains. Based on the established grouping, the analyses carried out with hundred repetitions showed that high sensitivity circularity, convexity and solidity variables were the most effective attributes regarding Kruskal–Wallis test statistics that provided significant (p < 0.001) results between the analyzed sedimentary environments, while the elongation was not able to provide significant results between the grouped samples. Statistical analyses of the MANOVA test with hundredfold repetitions showed significant differences between the derived groups. Wilks' λ test statistics and PCA showed that convexity and high sensitivity circularity discriminate the groups. Separate analyses of aeolian and fluvial sediments have been carried out. The Kruskal–Wallis analysis of variance showed the significant differences considering all four variables, and differences were also significant in the case of the MANOVA test. Wilks' λ test statistics and PCA showed that convexity, high sensitivity circularity and solidity discriminate the groups. According to our results, the circularity parameter can provide information about the transport distance, while the solidity parameter can indicate the transport energy. The convexity parameter can serve as an indicator of both transport distance, as well as post-depositional processes. Some infilling materials underwent multiple transport processes, including high energy aqueous, wind transport mechanisms, and the post-depositional alteration process (frost weathering), while others originated from sand-sheet covered areas (active during Pleistocene glacials). The solidity parameter proved effective in separating sediments with similarly high convexity values (smooth surface), which were, in our case, from recent aeolian and fluvial environments. This result was due to the investigated fluvial sediments that inherited their form and low level of roundness from their source area. Our research supports that aeolian transport is more effective in rounding the grains than the aqueous environment. Using automated static image analysis producing statistically stable results with hundreds of analyzed mineral grains provides useful indicators for paleogeographical reconstruction studies by investigating paleo and recent sediments. • The high HS circularity values can indicate a longer transport distance. • The solidity factors can be used to identify relative transport energy. • The convexity variable may indicate the post-depositional process. • The low level of roundness can be inherited from the source environment. • Automated static image analysis produces statistically robust results on mineral grains. [ABSTRACT FROM AUTHOR]

We have measured the He isotope composition in detrital native gold, copper, silver, Pt 3 Fe and OsIr alloy grains from placer deposits in order to assess the extent to which cosmogenic He can be quantified and used to determine the exposure history of grains in sedimentary systems. 3He/4He ratios (0.1–273 R a) exceed values typical of radiogenic He. 4He is dominantly the result of the decay of U and Th, or 190Pt in the case of Pt-rich alloys. 3He concentrations in grains from alluvial deposits range from 0.05 to 2 × 108 at g−1 and appears to be dominantly cosmogenic in origin. The absence of significant nucleogenic or mantle-derived 3He in metals is tentatively confirmed by the analysis of grains from underground mine workings. The implantation of cosmogenic He is not the main source of 3He in alluvial metals but can be relatively important for small grains. New GEANT4-based calculations predict the production rate of 3He (including in precursor 3H) from Au and Pt to be approximately 25 at g−1 yr. Using this we determine that cosmogenic 3He concentrations in the detrital grains record minimum exposure times of between 0.5 and 7 million years that generally increase with distance from the putative source. Paired fragments from three large grains show that there is considerable heterogeneity in cosmogenic He concentrations that may reflect the complex origin of detrital metal grains. This work suggests that cosmogenic He in detrital metals and minerals may find use for providing the chronology of sedimentary processes. Concentration of 3He plotted versus deposit type (i.e. the relative distance the grain had traveled from source). Using this we determine that cosmogenic 3He concentrations in the detrital grains record minimum exposure times of between 0.5 and 7 million years, that generally increase with distance from the putative source. Unlabelled Image • Helium isotopes are measured in alluvial Au, Pt 3 Fe, Cu and OsIr. • 3He/4He ratios (0.1–273 R a) exceed values typical of radiogenic He • Production rates of 3He in these metals are determined using GEANT4 • Minimum transportation-storage ages of alluvial metals vary from 0.5 to 7 Myr. [ABSTRACT FROM AUTHOR]

Abstract Megaclast-dominated fluvial systems have been largely ignored by researchers. Yet megaclasts exert an important control on channel geomorphology, flow behaviour and sediment transport, and such systems are probably far more common than this neglect would suggest. Despite the explicit identification of megaclasts as the products of cataclysmic flow, observation of modern fluvial systems confirms that megaclasts can be entrained by flows that lie within the normal flow regime. The pattern of fining along the megaclast-dominated Sabeto River of western Viti Levu, Fiji reveals a strong negative exponential relationship between particle size and distance downstream, and a rate of downstream fining comparable with that of other gravel-bed rivers. The downstream fining pattern is straightforward and step-like discontinuities in the fining gradient are absent. This is suggestive of a sedimentary system only minimally disrupted by the supply of sediment from tributaries or the reworking of material from sources such as hillslopes and alluvial terraces. There is evidence, however, of anomalously coarse sub-populations at two sites. These coarser components must pre-date the other deposits at the sites. We speculate that they represent the products of earlier and higher-magnitude events. The bed sediments may thus be composite features, made up of individual components each transported by a specific event of particular magnitude. Our work confirms the relationship between the rate of downstream fining and particle size. This may arise because the distance over which individual particles are transported is likely to be size dependent. It is also possible that abrasion may be more effective in the case of larger particles than smaller ones, with the result that the coarser fraction of the river's bed sediment fines downstream more rapidly than the finer fraction. There is a long-standing debate about the relative roles of abrasion and sorting in downstream fining. Our data reveal little evidence for a downstream increase in the roundness of the river's gravels, implying that abrasion is likely to play a minor role in the fining process in this system. Highlights • Megaclast-dominated rivers occur widely, but have been largely ignored by researchers. • Megaclasts may be entrained by normal flows and not solely by catastrophic events. • Megaclast downstream-fining rates are comparable with those of other gravel-bed rivers. • There is a close relationship between bed-sediment size and rate of downstream fining. • Bed-sediment assemblages consist of discrete components, each transported by individual events. [ABSTRACT FROM AUTHOR]

Abstract Fluvial suspended sediment concentration and discharge is most commonly estimated by applying rating curves developed over a given base period of sediment monitoring to longer, continuous records of water discharge. This practice invokes the tacit assumption of stationary suspended sediment concentration–water discharge relationships (i.e. suspended sediment behavior). Here the ramifications of this assumption are explored through an investigation into the temporal dependence of suspended sediment concentration–discharge relationships for all hydrologic stations on small rivers draining the west coast of the continental US that have been monitored for suspended sediment over a period of 10 years or more. Persistent suspended sediment behavior was found to be the norm, with 19 of 24 stations expressing apparent monotonic trends over their base periods, and 21 stations with finer scale (subannual to interdecadal) persistent patterns. The identified persistent periods of suspended sediment behavior corresponded to distinct rating curves that differed significantly from other periods in terms of offset, slope, or both. Assuming stationary suspended sediment behavior resulted in 1% to 63% biasing of suspended sediment load. Applying rating curves developed for single persistent periods to broader discharge records resulted in up to 10× potential error in estimated sediment load. The risk of falsely characterizing the long-term (interannual-scale) suspended sediment behavior of a river through a single persistent period of elevated or depressed behavior may be much higher than expected. The average duration of identified persistent periods was 8.6 years, which is longer than the base period of suspended sediment monitoring for most river stations in the US. Peak discharge (high discharge events 20 to 1000 times mean discharge) was usually followed by periods of increased sediment concentration across US Pacific Coast. Seven rivers in Oregon and northern California displayed the same pattern of decadal- to interdecadal-scale elevated suspended sediment concentrations following the Great Christmas Floods of 1964. Highlights • Persistent patterns of suspended sediment dynamics appear to be the norm. • 21 of 24 investigated rivers displayed persistent suspended sediment patterns. • Persistent suspended sediment patterns were 4 months to 36 years in duration. • Persistent patterns resulted in up to a 10× difference in sediment load. • Peak discharge events were usually followed by increases in sediment concentration. [ABSTRACT FROM AUTHOR]

Abstract The particle size, shape, surface texture and composition of aeolian and fluvial sedimentary samples were analyzed and compared using optical microscope-based automatized image analysis, in order to suggest indicators that could discriminate these two modes of transport on Mars. The principal goal is to assess if such indicators – established on Earth – could be used on Mars thereby aiding interpretations on the origin of sediments analysed by the ExoMars 2020 rover during its mission. Wind and water transported sand from, respectively, the Sahara Desert and the Maros river bar in Hungary were investigated and treated as mainly aeolian and fluvial end-members. In addition, two Mars-analogue aeolian and fluvial basaltic sediments from Iceland were analysed similarly. Our analyses demonstrated that useful parameters for the distinction of aeolian and fluvial transport included the degree of sorting, the grain diameter/perimeter ratio, the circularity (reflecting the sphericity of the grains) and convexity (showing roughness of the grains) of particles. Mature aeolian sands are always well-sorted with high diameter/perimeter ratios since they are dominated by rounded grains. Differences were observed in both surface textures and the range of mineral compositions, wherein the aeolian samples reflect a more mature state. Separation of the two Icelandic samples with different origins was less straightforward due to both shorter transport distances and the fact that the fluvial sample was made of scoria, although the intermixing of grains with a probable aeolian origin could be also determined. The characteristics of grain size and shape parameters are potential indicators allowing the separation of the two transport modes, and their determination is shown to be feasible based on high resolution Close-UP Imager (CLUPI) observations. Nonetheless, knowledge of the geological context – for instance sedimentary facies, layering, sorting of the sediments and grain shape – is a requirement for proper interpretations. These sedimentary features could be party determined by MaMISS, CLUPI and PanCam observations. Differences between aeolian and fluvial grains are expected to be more pronounced on Mars than on Earth due to the episodic and likely short-term subaqueous transport, as opposed to the long-term activity of wind. However, future interpretations of the ExoMars 2020 rover images of martian sedimentary grains will be hampered by the limited knowledge of fluvial/aeolian transport on Mars. Based on our results, future research should focus on determining the dominant transport mode of any sediment and the degree of grain mixing, which strongly based on the transport mode. Highlights • Mars-analogue particulate sediments, including basaltic in origin were analyzed. • Morphometric differences in the shapes of aeolian and fluvial grains were identified. • The ExoMars CLUPI camera will be able to distinguish the agents of deposition for grains of 100–200 μm size. • Aeolian grains are expected to be more mature, and differ from fluvial grains on Mars. • Local sedimentary features give important context information to assist the identification of grain origin. [ABSTRACT FROM AUTHOR]

This work presents FLUNETS (FLUvial NETwork Sorting tool), a new MATLAB-based tool designed for channel network ordering by Horton and Hack hierarchies. Differently to Strahler and Shreve hierarchies, Hack and Horton orderings allow organizing a drainage network in a hierarchy, identifying the parent segment over the child segment, giving as a result a network where the value of a river remains unchanged from the mouth upstream to the headwater. The novelty of FLUNETS is that it allows the user to choose the hierarchy attribute. Therefore, a fluvial network can be ordered by distance to the mouth or by accumulation upstream. In addition, FLUNETS offers a wide set of optional parameters, which turns it into a friendly tool to attain a highly tailored ordered fluvial network. A continuous fluvial network is the starting point for multiple landscape analysis applications. The source code is available in the authors' GitHub account (https://github.com/geouned/FLUNETS). [ABSTRACT FROM AUTHOR]

Understanding sediment movement over time and space requires quantitative tools. The trapped charge phenomenon or luminescence properties of sand grains are one of the potential techniques in sediment tracing [4]. Luminescence of sand grains builds up during burial in sedimentary deposits and resets at the Earth's surface when exposed to sunlight. This sensitivity to daylight exposure can be utilized to quantify Earth's surface processes such as sediment transport and or soil mixing. Thus, the variations in the magnitude of the luminescence signal, raise the possibility of quantifying rates of Earth surface processes via measurements of the luminescence signal. In this study, we aim to investigate the luminescence signature of hillslope denudation by measuring the percentage of bleached versus non-bleached (saturated) grains in associated modern fluvial deposits for a large variety of source catchments (in Chile and New Zealand) with contrasting morphometric properties. We will utilize feldspar single-grain pIRIR measurement protocols to measure the luminescence signature and perform the data analyses previously described in [5]. Our research will offer innovative constraints on weathering intensity and hillslope denudation and how they are related to the denudation rates of the selected catchments. We will thus use paired in situ 14C and 10Be terrestrial cosmogenic nuclides (TCN) measurements for some selected catchments in the Southern Alps of New Zealand and Chile (both with pronounced climatic gradients), to complement and compare our luminescence data. Numerous studies have already proven the dependency of denudation rates on landscape characteristics such as the mean slope of the catchments or mean hillslope gradients and to external forces such as tectonic uplift and climate [1,2,3]. [ABSTRACT FROM AUTHOR]

Humid tropical and subtropical regions commonly host thick soils that supply sediment to adjacent streams. These soils are depleted in Ca and Na and enriched in Al and Si, yielding high chemical weathering indices, including chemical index of alteration (CIA) values >90, indicative of intense chemical weathering. Here, we investigated chemical weathering in granitoid-sourced fluvial sediments of Puerto Rico--a region with one of the highest documented rates of chemical weathering on Earth. Although thick soils occur throughout the study area, weathering signatures from fluvial muds (CIA values of 58-69) are significantly lower than expected. Indeed, these weathering indices are similar to values expected in climates 10-20 °C cooler. These remarkably low values likely reflect significant input from partially weathered bedrock mobilized during mass wasting. Furthermore, future climate warming may increase torrential precipitation and accompanying mass wasting, producing a counterintuitive decrease in weathering intensity recorded in fluvial sediments. [ABSTRACT FROM AUTHOR]

Two episodes of intense flooding and sediment movement occurred in the Westmorland Stream alluvial system near Caveside, Australia in January 2011 and June 2016. The events were investigated in order to better understand the drivers and functioning of this composite alluvial system on a larger scale, so as to provide awareness of the potential hazard from future flood and debris flow events. A novel combination of methods was employed, including field surveys, catchment morphometry, GIS mapping from LiDAR and aerial imagery, and hydraulic modelling using RiverFlow-2D software. Both events were initiated by extreme rainfall events (< 1% Annual Exceedance Probability for durations exceeding 6 h) and resulted in flooding and sediment deposition across the alluvial fan. The impacts of the 2011 and 2016 events on the farmland appeared similar; however, there were differences in sediment source and transport processes that have implications for understanding recurrence probabilities. A debris flow was a key driver in the 2011 event, by eroding the stream channel in the forested watershed and delivering a large volume of sediment downstream to the alluvial fan. In contrast, modelled flooding velocities suggest the impacts of the 2016 event were the result of an extended period of extreme stream flooding and consequent erosion of alluvium directly above the current fan apex. The morphometry of the catchment is better aligned with values from fluvially dominated fans found elsewhere, which suggests that flooding represents a more frequent future risk than debris flows. These findings have wider implications for the estimation of debris flow and flood hazard on alluvial fans in Tasmania and elsewhere, as well as further demonstrating the capacity of combined hydraulic modelling and geomorphologic investigation as a predictive tool to inform hazard management practices in environments affected by flooding and sediment movement. [ABSTRACT FROM AUTHOR]

Coogoon Valles is an intricate fluvial system, and its main channel was formed during the Noachian period through the erosion of the clay-bearing basement of the Western Arabia Terra. This region is characterized by a thinner crust compared to the rest of the highlands and by the occurrence of massive phyllosilicate-bearing materials. The origin of this region is still under discussion. Its surface has been exposed to a large-scale volcanism, and several episodes of extensive denudation were primarily controlled by fluvial activity. In this regard, the study of the oldest channels in Arabia Terra is crucial for understanding the global geological evolution of early Mars. The reactivation of the hydrological system by sapping followed by aeolian erosion had reshaped the channel, as well as exposed ancient materials and landforms. The examination of the bed deposits suggests an old episode of detrital sedimentation covering the Noachian basement followed by an erosive event that formed the current Coogoon Valles configuration. A complex system of deltas and alluvial fans is situated at the termination of this channel, which has been proposed as a landing site for the upcoming ExoMars and Mars 2020 missions. [ABSTRACT FROM AUTHOR]

Dams are major obstructions to the flow of water and the transport of sediment in rivers. Much work has shown the construction of dams, and storage of sediment in reservoirs, can lead to significant changes in the morphodynamic behavior of alluvial rivers; however, in most cases, the effect of damming has a finite downstream limit as sediment is supplied back to the river through channel bed/bank erosion and/or tributary inputs. Here we present a study of a natural experiment that isolates one source of sediment downstream of a dam – the lower Rio Grande, which has no major tributary inputs of sediment over a ~450 km reach, from Falcon Dam to the coast. Analysis of the morphology and topography of the Rio Grande shows that prior to damming in the 1950s the coastal Rio Grande was a kinematically active channel with large, subaerial point bars. Subsequent to damming, lateral migration of the river shut down and exposed point bars shrunk in size, becoming static and vegetated. Bathymetric survey data show meter-scale incision of the channel bed for hundreds of kilometers downstream of the dam. Entrenchment of the river is also evidenced by the development of steep banks on the inner portions of channel bends. Damming also impacted the interaction between the river and the floodplain, resulting in the formation of persistent gullies incised into the channel banks, suggesting transport of water and sediment is net positive into, not out of, the channel. Based on all of these observations we conclude that the full ~450 km reach of the Rio Grande, from Falcon Dam to the coast, became net degradational following dam closure. We conclude that the presence of such a long degrading reach is caused by the exposure of bedrock in the Rio Grande channel for nearly 100 km downstream of the dam, which, combined with the lack of tributaries, limits downstream sediment supply to the river. Our results provide new insights into the response to damming for rivers with no tributary sediment input and thin alluvial cover, and more broadly to the kinematic and channel geometry responses to a major drop in water discharge and sediment supply for coastal meandering rivers. • We investigate the response of the coastal Rio Grande to 1950s dam construction. • Image, topography and bathymetric data show the river has become net degradational. • Degradation affects the river all the way to the coast, a length of ~450 km. • This reach has no tributary sediment input and the upstream channel exposes bedrock. • These attributes limit sediment supply resulting in large length of degradation. [ABSTRACT FROM AUTHOR]

Small mountainous rivers (SMRs) play a crucial role in the global sediment and carbon cycle by rapid transfer of huge particulate and dissolved loads into the sea. Gaoping river-sea system is a good representative of SMRs in Oceania, having an extreme high denudation rate (15,000 t km − 2 yr − 1 ) and a high burial efficiency of terrestrial particulate organic carbon (POC) in the Gaoping submarine canyon (GPSC). However, it is contentious whether silicate weathering or POC burial plays more important role in long-term carbon cycling in such a high active orogen. Clay minerals of fluvial sediments not only act as an important carrier of POC, but also encode valuable information of weathering regimes on land and dispersal routes in the seas. To uncover these informations, surface and core sediments are systematically collected from the Gaoping river-sea system for clay-mineral analysis. Comparative studies are carried out on the basis of new results and vast published data to better understand weathering processes and products in Oceanian islands and Southeast Asian continent. We find that clay-mineral compositions in the Gaoping River (GPR) and other Taiwan rivers are a legacy from provenance rocks in the alpine reach, characterized by predominant illite and chlorite and limited compositional change throughout the river courses. These sharply contradict the downstream increase in compositional complexity (rich in kaolinite and smectite) and chemical weathering intensity in Southeast Asian large rivers because of strong hydrolysis and active sediment recycling at the lowland reach with extensive floodplains. High consistency of clay-mineral compositions is also observed in the interior and exterior of GPSC. Careful examination shows that a slight offshore decrease in cumulative illite and chlorite content is accompanied by a slight increase in exotic clay-mineral inputs by ocean circulations. The combination of this finding with previously reported data on the offshore change in δ 13 C org and Δ 14 C org values suggests that petrogenic POC predominates in the river-dominated Gaoping continental margin with high preservation efficiency due to its tight bandage with clay minerals. Moreover, a tardy response of chemical weathering fluxes to high elevated physical erosion rates is remarkably examined in the Oceanian and global river gauging data. We therefore postulate that rapid transfer and high burial efficiency of terrestrial POC in the tectonically active high-standing islands and their adjacent continental margins play much more important role in the long-term carbon cycle than silicate weathering. [ABSTRACT FROM AUTHOR]

Recent studies have shown the super saturation of fluvial networks with respect to carbon dioxide, and the concept that the high carbon dioxide is at least partially the result of turnover of sediment organic carbon that ranges in age from years to millennia. Currently, there is a need for more highly resolved studies at stream and river scales that enable estimates of terrestrial carbon turnover within fluvial networks. Our objective was to develop a new isotope-based metric to estimate the quality of sediment organic carbon delivered to temperate streams and to use the new metric to estimate carbon quality across landscape disturbance gradients. Carbon quality is defined to be consistent with in-stream turnover and our metric is used to measure the labile or recalcitrant nature of the terrestrial-derived carbon within streams. Our hypothesis was that intensively-disturbed landscapes would tend to produce low quality carbon because deep, recalcitrant soil carbon would be eroded and transported to the fluvial system while moderately disturbed or undisturbed landscapes would tend to produce higher quality carbon from well-developed surface soils and litter. The hypothesis was tested by applying the new carbon quality metric to 15 temperate streams with a wide range of landscape disturbance levels. We find that our hypothesis premised on an indirect relationship between the extent of landscape disturbance and the quality of sediment carbon in streams holds true for moderate and high disturbances but not for un-disturbed forests. We explain the results based on the connectivity, or dis-connectivity, between terrestrial carbon sources and pathways for sediment transport. While pathways are typically un-limited for disturbed landscapes, the un-disturbed forests have dis-connectivity between labile carbon of the forest floor and the stream corridor. Only in the case when trees fell into the stream corridor due to severe ice storms did the quality of sediment carbon increase in the streams. We argue that as scientists continue to estimate the in-stream turnover of terrestrially-derived carbon in fluvial carbon budgets, the assumption of pathway connectivity between carbon sources to the stream should be justified. [ABSTRACT FROM AUTHOR]

Restrepo, J.C.; Schrottke, K.; Traini, C.; Ortiz, J.C.; Orejarena, A.; Otero, L.; Higgins, A., and Marriaga, L., 2016. Sediment transport and geomorphological change in a high-discharge tropical delta (Magdalena River, Colombia): Insights from a period of intense change and human intervention (1990-2010). There is strong indication that environmental changes and human interventions have affected freshwater discharge and sediment flux in the Magdalena River (northwestern South America) within the period from 1990 to 2010. Thus, stream flow, suspended sediment load (SSL), and riverbed dynamics were analysed in this study for estimating changes in the suspended sediment transport regime as well as of erosional/depositional patterns in different zones of the delta. It can be shown that stream flow increased at a higher rate than suspended sediment transport, promoting changes in the sediment transport regime. Erosion appeared at the mouth/frontal bar and the outlet zones and modified the sedimentary balance within the prodelta in the early 2000s. There is indication that cycles of erosion and accretion were controlled by the magnitude of fluvial discharge and riverbed scouring in the river outlet, whereas effluent diffusion and sediment dispersion were dominant in the delta front. High freshwater discharge, as buoyancy inputs, promoted the transfer of sediments from the river channel to the outer prodelta through the upper layers of the water column. Total sediment accumulation in the delta corresponded to <5% of the annual mean SSL of the Magdalena River. Overall, delta morphology remained relatively stable, experiencing a slow progradational state with highest sedimentation rates (≤1430 mm y−1) in the deepest zones. [ABSTRACT FROM AUTHOR]

The Nýřany Member in the Pilsen Basin records the evolution of a broad paleotropical alluvial plain that preserves amalgamated lenticular to sheet sandstone bodies separated by basin-wide floodplains. Facies and architectural element analysis in conjunction with well-log correlation was employed in order to reconstruct fluvial system stacking patterns and decipher the controls responsible for the preserved fluvial architectures and identify the possible influence of allogenic processes on basin fill architectures. The main architectural components identified include: 1) sheet-like and lenticular pebbly to cobbly conglomerate thalweg fill representing the lowermost portion of channels that are preferentially preserved; 2) inclined gravel-sand and sandy strata of barforms and rarely preserved (3) mudstone units representing floodplains and abandoned channel fills. These architectural elements combine toform a hierarchy of alluvial cycles represented by channel-bar systems (3-10 m thick), channel-belts (4-15 m thick) and stacked channel-belt complexes (10-35 m thick). Autogenic processes of lateral migration and local and regional avulsion of braided channels of intermediate sinuosity (1.5) controlled the formation of the smaller scale cycles. While the geometry of stacked channel belt complexes (sandbodies) appear to be driven by variations in subsidence rates, their cyclic alternation with extensive floodplains is considered to be related to allogenic processes of variable seasonality of precipitation, which affected sedimentation rates and water-table level in the basin. Their maximum periodicity of 140 k.y. indicate that eccentricity paced changes of Earth's orbit may be a driving force controlling climate stability in the Pennsylvanian paleotropics. [ABSTRACT FROM AUTHOR]

Aeolian deposits are frequently used for palaeoenvironmental change studies. Their formation depends on an array of requirements: the supply of material suitable for aeolian transport and favorable conditions of sediment availability and wind strength. In order to infer palaeoenvironmental information from aeolian sand deposits these factors need to be carefully evaluated. We present a study from northern Chinese Hexi Corridor, based on 11 optically stimulated luminescence (OSL) dated sediment sections. These represent interchanging aeolian and alluvial deposits under gravel surfaces and aeolian sand in dune fields interrupted by interdunal flood deposits. Investigations in two subareas reveal contrasting geomorphologic and sedimentary histories: (1) sediment deposition during the Pleistocene–Holocene transition (~ 12 ka) followed by deflation during the Holocene and (2) frequent sediment recycling revealed by a wide spectrum of ages throughout the Holocene. The late glacial sediment pulse recorded in the western Hexi Corridor is attributed to high sediment supply, generated by efficient (peri-)glacial sediment production during glacial times in the adjacent Qilian Shan (< 5700 m asl) and a moisture increase inducing the reworking of those (glacio-)fluvial deposits during the Pleistocene–Holocene transition. The absence of a powerful reworking agent preserved these late glacial deposits in the western Hexi Corridor in contrast to moister eastern parts where Holocene sediment reworking prevailed. Geomorphological and hydrological preconditions of the subareas are discussed and reveal the controlling influence of fluvial processes on sand supply for the aeolian system. While a perennial drainage is missing in the drier western part, the Hei River drainage is fed by higher monsoonal precipitation in the central Hexi Corridor. It maintains a sediment recycling system and has ensured a sufficient sediment supply throughout the Holocene. The study promotes closer consideration of the fluvial influence on aeolian archives in palaeoenvironmental studies from central Asian and other drylands. [ABSTRACT FROM AUTHOR]

Latest Cretaceous deposits are cropping out in various localities of the Hațeg basin (Romania). Among these localities Pui is of peculiar interest, being the southeastern most one where Maastrichtian fluvial deposits are exposed. These terrestrial deposits are represented mainly by red beds, which yielded since the end of the 19th century, rich vertebrate assemblages. From a channel fill block discovered ex situ, a diverse fossil vertebrate assemblage was recovered (turtles, crocodilians, pterosaurs, and various herbivore and carnivore dinosaurs). This study is focused on the fossil taxa collected from this block and their fossilization processes. [ABSTRACT FROM AUTHOR]

Luminescence dating of sediment requires the sand grains to have been exposed to sunlight prior to their most recent burial. Under fluvial transport, the amount of sunlight exposure may not always be sufficient to reset the luminescence signal, a phenomenon known as ‘partial bleaching'. The extent of bleaching is dependent on a combination of geomorphic, sedimentological and fluvial processes. If bleaching can be quantified, and the relationship with these processes understood, it could potentially be used as a new environmental proxy for changes in the dynamics of river systems. Here, we use a recently developed statistical model to evaluate the extent of bleaching, by inferring the proportion of well-bleached grains in the small-aliquot population. We sampled low-flow and flood deposits at a single site on the River Sabie, South Africa. We show that the low-flow sediment is almost perfectly bleached (>80% of grains well bleached), while sediment at flood elevations is partially bleached (20–70 % of grains well bleached). The degree of bleaching may show a relationship with flood magnitude as defined by elevation above normal river level, and we speculate on the causes of variability in bleaching between flood samples. [ABSTRACT FROM AUTHOR]

Alluvial fans are depositional systems that develop because of a disparity between the upstream and downstream sediment transport capacity of a system, usually at the base of mountain fronts as rivers emerge from the constrained mountain area onto the plain. They are dynamic landforms that are prone to abrupt changes on a geomorphological (decades to centuries) time scale, while also being long-term deposition features that preserve sedimentary strata and are sensitive indictors of environmental change. The complexity of interactions between catchment characteristics, climate, tectonics, internal system feedbacks, and environmental processes on field alluvial fans means that it is difficult to isolate individual variables in a field setting; therefore, the controlled conditions afforded by experimental models has provided a novel technique to overcome some of these complexities. The use of experimental models of alluvial fans has a long history and these have been implemented over a range of different research areas utilising various experimental designs. Using this technique, important advances have been made in determining the primary factors influencing fan slope, understanding of avulsion dynamics, identifying autogenic processes driving change on fan systems independent of any change in external conditions, and the mechanics of flow and flood risk on alluvial fans, to name a few. However, experiments cannot be carried out in isolation. Thus, combining the findings from experimental alluvial fans with field research and numerical modelling is important and, likewise, using these techniques to inform experimental design. If this can be achieved, there is potential for future experimental developments to explore key alluvial fan issues such as stratigraphic preservation potential and simulating extra terrestrial fan systems. [ABSTRACT FROM AUTHOR]

The 1-D saltation-abrasion model of channel bedrock incision of Sklar and Dietrich (2004), in which the erosion rate is buffered by the surface area fraction of bedrock covered by alluvium, was a major advance over models that treat river erosion as a function of bed slope and drainage area. Their model is, however, limited because it calculates bed cover in terms of bedload sediment supply rather than local bedload transport. It implicitly assumes that as sediment supply from upstream changes, the transport rate adjusts instantaneously everywhere downstream to match. This assumption is not valid in general, and thus can give rise to unphysical consequences. Here we present a unified morphodynamic formulation of both channel incision and alluviation that specifically tracks the spatiotemporal variation in both bedload transport and alluvial thickness. It does so by relating the bedrock cover fraction to the ratio of alluvium thickness to bedrock macro-roughness, rather than to the ratio of bedload supply rate to capacity bedload transport. The new formulation (MRSAA) predicts waves of alluviation and rarification, in addition to bedrock erosion. Embedded in it are three physical processes: alluvial diffusion, fast downstream advection of alluvial disturbances, and slow upstream migration of incisional disturbances. Solutions of this formulation over a fixed bed are used to demonstrate the stripping of an initial alluvial cover, the emplacement of alluvial cover over an initially bare bed and the advection-diffusion of a sediment pulse over an alluvial bed. A solution for alluvial-incisional interaction in a channel with a basement undergoing net rock uplift shows how an impulsive increase in sediment supply can quickly and completely bury the bedrock under thick alluvium, thus blocking bedrock erosion. As the river responds to rock uplift or base level fall, the transition point separating an alluvial reach upstream from an alluvial-bedrock reach downstream migrates upstream in the form of a "hidden knickpoint". A tectonically more complex case of rock uplift subject to a localized zone of subsidence (graben) yields a steady-state solution that is not attainable with the original saltation-abrasion model. A solution for the case of bedrock-alluvial coevolution upstream of an alluviated river mouth illustrates how the bedrock surface can be progressively buried not far below the alluvium. Because the model tracks the spatiotemporal variation in both bedload transport and alluvial thickness, it is applicable to the study of the incisional response of a river subject to temporally varying sediment supply. It thus has the potential to capture the response of an alluvial-bedrock river to massive impulsive sediment inputs associated with landslides or debris flows. [ABSTRACT FROM AUTHOR]

The Brazos River is second only to the Mississippi River in terms of sediment load discharged to the Gulf of Mexico (GOM). This study focused on the interaction between a salt wedge and suspended sediment in the lower Brazos River, and the implications for sediment export to the coastal ocean. Salinity and turbidity (optical backscatter sensor) data with depth, swath bathymetry, and CHIRP sub-bottom profiling data were collected from 2007 to 2012 over various river discharge stages. Sampling locations included the lower-most 15 km river reach and the coastal ocean proximal to the mouth. Results indicated that during low to moderate river discharges a salt wedge was present in the lower river, but absent during elevated fluvial discharge. Quantitative analysis showed the salt wedge within the river modulated sediment export to the GOM by trapping sediment along the lower most 9 km reach. Within this reach the trapped sediment formed a decimeter-thick mud layer observed in the CHIRP and bathymetric data. At elevated fluvial discharges the salt wedge was no longer observed in the river, and the lower river reach transitioned from depositional to erosional. Based on the observations and analysis from this study, a fluvial discharge threshold where the salt wedge is not present in the river and sediment export to the coastal ocean was maximized was estimated. This threshold has been met or exceeded only ~ 10% of time since the 1960s. These conditions imply that sediment transport to the coastal ocean is highly variable, and occurs during irregular, pulsed events. This study highlights how estuarine conditions at the river mouth can impact terrestrial material flux to the coastal ocean. [ABSTRACT FROM AUTHOR]

Source-to-sink (S2S) systems have represented a major area of research in recent years; however, few modern S2S system analyses have been applied to typical dryland uplifts/mountains. A modern lacustrine sedimentary system is widely developed in the Great Lakes Basin of western Mongolia, and the Jargalant Nuruu in the Mongolian Altai is a suitable natural laboratory for modern dryland S2S system analysis. In this study, the multi-order S2S system of the Jargalant Nuruu was applied based on a digital elevation model (DEM) and Google Earth database analysis. The Jargalant Nuruu system is subdivided into three second-order sub-S2S systems of the eastern, western, and southern parts (S2S-E, S2S-W, and S2S-S, respectively) and 35 third-order sub-S2S systems (E1–E18, W1–W9, and S1–S8) according to the slope gradients, altitude, and hydrographic net of the Jargalant Nuruu recognized by DEM data, integrated with the quantitative recognition of the topographic drainage divide and structural patterns of the uplift margin. The three second-order S2S systems correspond to three various S2S system coupling models. The S2S-E is characterized by a steep slope gradient system (average 15.61°) with small-scale dominantly alluvial fan deposits (average 4.56 km2). S2S-W is represented by a gentle slope gradient system (average 10.24°) with large-scale dominated fan-shaped lobes (average 30.04 km2). S2S-S, in contrast, is a transformation zone system with transitional features between the two former types. Four major potential controlling factors for the difference in sub-S2S systems are summarized here, including tectonic activity, bedrock properties in the source area, morphology from source to sink, and climatic conditions. The landforms, sedimentary characteristics, and their differences in these sub-S2S systems are the result of the comprehensive influence and control of these multiple factors. This case study could serve as a useful reference for characterizing the sedimentary features of a modern or even ancient S2S system in other regions. [ABSTRACT FROM AUTHOR]

Highlights: [•] 1D FVM model for simulating unsteady flow routing and sediment transport. [•] Sediment transport over mobile alluvium in a vegetated channel network is modeled. [•] Grain resistance for sediment transport is a function of vegetation density. [•] Vegetation impacts on flow and sediment transport were accounted for separately. [•] We test the model by an unprecedented flood event occurred in Santa Cruz River. [Copyright &y& Elsevier]

Abstract: Field studies documenting fine-sediment (<2mm) transport in gravel-bed rivers are rare. For the first time in a fluvial environment, a technique that enhances the magnetic susceptibility of sand is used to trace its longitudinal dispersion and storage. This paper describes the methodology behind the artificial magnetic enhancement of iron-stained sand, and presents the results from sand tracing exercises conducted on two gravel-bed channels with pool-riffle morphology; one unregulated and sinuous in nature (site A), the other regulated and straight (site B), both situated on the River Rede Northumberland, UK. Two tonnes of magnetically enhanced tracer sand was introduced to site A and four tonnes to site B, to provide information on fine-sediment storage dynamics, interaction of fines with the stream bed, and rates of movement, expressed as virtual velocity (Vi ). Sand transport pathways appeared to differ between the reaches; for site A, sand storage was found on bars and riffle margins with no storage or signs of transport through pools, and in contrast pool storage of tracer was a key feature shown at site B. Topographic forcing may cause differences in sediment sorting at site A; topographic highs tend to have low sand transport rates with sand grains becoming congested in these areas, whereas topographic lows show higher transport rates resulting in greater dispersion. Supply limitation of sand on the falling limb of the hydrograph may also become an issue in the topographic lows at this site. Hydrograph differences between the regulated and unregulated reaches could also play a role; however this could not be quantified in this study. There was no evidence of sand infiltration into the bed at site A; however marginal evidence for infiltration into the near-surface (0–15cm) substrate voids was found at site B. The general lack of evidence for significant infiltration may reflect limited availability of void space in substrate framework gravels. Tracer sand was transported over the bed surface, with little vertical interaction with the substrate, despite periods of gravel mobilisation at site A. Vi over the study duration for site A was 2.28mday−1, and 0.28mday−1 for site B. These values are greater than those calculated using existing predictive equations developed from gravel tracer data, possibly reflecting differences in the mode of transport between bedload and saltation load. [Copyright &y& Elsevier]

Abstract: The impressive 2000m thick conglomerates of the Bucegi Formation exposed in the southernmost part of the Eastern Carpathians were interpreted initially as large alluvial fans, and later suggested to be deposited as deepwater submarine-slope deposits. However, the routing system of the coarse sediment transfer from the source area to the deepwater slope (source-to-sink analysis) has not been explained and the mechanisms involved in the shelf sediment storage and bypass onto the slope have not been discussed. The present research on the Albian Bucegi Formation has provided the following new insights on their source-to-sink aspect: (1) that the Upper Member of the Bucegi Formation, with its frequent channelized and sheet like fine conglomerates and sandstones, contrasts greatly with the Middle and Lower members of deepwater slope and basin-floor origin. The Upper Member is interpreted as fluvial and shallow-marine deposits that were temporarily stored and reworked on a ‘shelf’, albeit a narrow one, bridging the area between the deforming hinterland and the deepwater slope deposits; (2) the Upper and Middle members are genetically linked and developed through the basinward migration of a large-scale (hundreds of metres in amplitude) clinoform with relative flat-lying topsets and slightly steeper (few degrees), coarser grained slopes that built out to the south and southeast; a configuration that is common along continental margins and also generally along all types of deepwater basin margins; (3) the Middle Member contains a range of submarine, sediment density flows that vary from high-density, mobile debris flows to lower-density sandy turbidites. The sediment textures (sorted grain populations) inherited from the shelf ‘sorting factory’ can to some extent still be recognised in the slope stratigraphy; and (4) the large (10–20m diameter) carbonate and metamorphic olistoliths that are ubiquitous on the shelf and (to a lesser extent) slope, reflect the steep gradients and very active tectonic setting of the fractured and thrusted hinterland, from which these outsized blocks were transported onto the adjacent shelf. The now-proposed, narrow shelf platform of the Albian Bucegi basin margin thus functioned to temporarily store sands and gravels, to distinctly sort some of this sediment, and to eventually bypass both sorted and new flood-generated, unsorted materials onto the slope. Compared with other basin margins, this Albian Bucegi margin was extremely coarse grained because of its proximity to the actively deforming mountain range, to a fractured basement that produced more gravel than sand, to the great sediment flux from steep short rivers, and to the narrowness (10–20km) of the shelf. [Copyright &y& Elsevier]

Abstract: The Arafura and Timor Seas (ATS) are a crucial link between the Indian and Pacific Oceans and play a vital role in global ocean circulation and climate. Some high-standing islands in the ATS are globally significant sources of sediment. Here we derive a synthesis of river catchments and their role as sources of water, sediment, carbon, and nutrients to estimate the pathways, magnitude, and fate of exported riverine materials. The edge of the Australian continental shelf and slope receives riverine sediment from Asia as isotopes suggest a mixing of sediment sources, with some overlap between the Australian and non-Australian material, including evidence of significant input of volcanic material from Indonesia. The catchments bordering both the Arafura and Timor Seas account for ≈12% of sediment and ≈35% of water discharged from tropical Asia. Northern Australia discharges a volume of freshwater comparable to southwest New Guinea, but 50–65% of total sediment (754Mt), DIC (61.1Mt), POC (7.9Mt), DOC (3.5Mt), TN (2.88Mt), and TP (254,264t) delivered annually to the ATS come from New Guinea. The island of Timor discharges much smaller amounts of water (170km3 yr−1) and sediment (133Mtyr−1), but area-specific rates of DIC (1150tkm−2 yr−1), POC (238tkm−2 yr−1), DOC (94tkm−2 yr−1), TN (61tkm−2 yr−1) and TP (4.4tkm−2 yr−1) are higher, reflecting very high rates of deforestation and land degradation. Compared to other tropical rivers, carbon export into the ATS is dominated by DIC. The ATS catchments are being increasingly affected by human activities, and material discharge to the continental margins will likely increase, impacting shelf communities and highly diverse reef, mangrove, and seagrass habitats. [Copyright &y& Elsevier]

Downstream changes in channel-bed and bank particle size that occur in the Pascagoula River system, a humid sub-tropical, sand-bed stream which flows across the Gulf Coastal Plain are summarized in this paper. Grab samples collected at 59 sites along the two main-stem rivers were characterized through laboratory and statistical analyses and standard sedimentary indices Φ5, Φ16, Φ50, Φ84, Φ95, and sorting) were computed. Channel-bed and bank samples show a downstream fining trend. Inclusive graphic standard deviations were calculated to estimate sorting; the entire basin revealed moderate sorting, with no clear indication of an increase downstream. Modal grain shape of all the samples shows bank material slightly more angular than bed material. Low percentages of coatings were observed on most samples suggesting the Pascagoula River basin has an active sediment transport system. The low relief and similar lithology within the Pascagoula River basin make this empirical data unique and the results relevant within the study of dynamic fluvial systems. [ABSTRACT FROM AUTHOR]

Abstract: Two meter-scale pyroclastic levels are interbedded within the early Miocene succession of the Estancia 25 de Mayo (Patagoniense transgression) and Santa Cruz formations in the foreland Austral (or Magallanes) Basin, Argentina. The Lower Pyroclastic Level (LPL) is a tabular body interbedded within offshore marine deposits, laterally continuous for 30km and varying in thickness from few centimeters to around 4m. Grain-size grades from coarse to extremely fine ash with upward-fining along with a northeastern-fining trends. Structureless fine to very fine tuffs dominate and rare parallel laminations are the only tractive sedimentary structures. The Upper Pyroclastic Level (UPL) lies within low energy fluvial deposits and is laterally discontinuous, and it is composed by lenticular bodies reaching a maximum of 15m thick and 100m wide, with a concave-up base and a plane top. Grain-size range is similar to the LPL but it coarsens upward. The lower portion of the UPL shows parallel lamination, current ripple lamination and mud drapes with large pumice lapilli and plant debris, whereas the upper portion shows parallel lamination and trough cross-stratification. Both pyroclastic levels are composed mainly of pumice grains and glass shards with minor proportions of quartz and plagioclase crystals and lithic fragments. The LPL shows no mixing with epiclastic material whereas the UPL shows an upward increase in epiclastic material, and an upward increment in the scale of cross-bedding. The large thickness in relation to the possible emission center and the content of plant debris of the LPL does not suggest a direct, submarine, ash-fallout origin. The LPL is interpreted as a deposit of hyperpycnal-flows generated at the coastal zone when tephra-laden rivers plunged into the ocean. Large amounts of well preserved plant debris support the hypothesis of a terrestrial source of the sediments. The UPL is entirely composed of tractive deposits, so an ash fallout origin is disregarded. This, together with the lenticular shape and the alluvial plain origin of the encasing sediments, suggests accumulation within fluvial channels. Cycles of upper-flow-regime parallel lamination, current-ripple lamination and mud drapes at the lower portion, suggest short-lived turbulent flows that initially filled semi-abandoned channels. They were followed by sheet floods and channel reactivation, expressed by large-scale cross-bedding. The low degree of particle mixing observed in both levels is explained by the inability of streams to erode the substrate as they are suddenly over-saturated with pyroclastic sediments during and after the eruption. The grain-size distribution of the LPL and geochemical data indicate a contemporaneous volcanic source located to the west/southwest in the Andean ranges, where the South Patagonian Batholith is presently located. [Copyright &y& Elsevier]

Abstract: We present a geometric model to study the role of base-level change in the dynamics of the alluvial-bedrock transition and shoreline positions in a fluvially dominated deltaic system. The domain of the problem is a sediment wedge in the long-profile cross-section. On assuming that the fluvial surface has a quadratic form, its evolution is determined by imposing an overall volume balance, and conditions for the elevations and slopes at the domain boundaries. This results in a coupled system, involving one ordinary differential equation and one non-linear equation. These equations are solved through an explicit Euler time stepping algorithm to predict the movement of the shoreline and alluvial-bedrock transition boundaries under a wide range of base-level change conditions. The mathematics of the approach are verified by comparing predictions from the geometric model with a closed form solution of a downslope gravity-driven transport model under the specific case of a square-root of time base-level change. Testing with more general base-level change scenarios reveals that this simple geometric mass balance is able to predict system dynamics that are fully consistent with both physical and numerical experiments. Moreover, model predictions under a base-level cycle (fall-rise) suggest a behavior where river incision occurs during the base-level rise stage, a predicted dynamic that has not been previously reported. [Copyright &y& Elsevier]

Abstract: Analysis of typhoon- and earthquake-triggered landsliding and fluvial response in the Tachia River, central Taiwan, documents highly episodic sediment supply over decade to century timescales. Landslide data from the Chi-Chi earthquake (1999) and subsequent typhoons (2001, 2004, and 2005) quantify the sediment supply from these events. Fluvial response was investigated by decadal-scale and century-scale longitudinal river profile data spanning 1904 to 2008 and by sediment delivery recorded in suspended sediment load and reservoir sedimentation data. Our results show that the different time periods of satellite images and aerial photographs used in previous studies make it difficult to unambiguously identify the causes of landslides previously attributed by some studies to the effects of the Chi-Chi earthquake rather than subsequent high intensity precipitation. In response to significant variability in sediment delivery from hillslopes, century-scale profile variation data indicate substantial bed surface elevation change of 2.6±6.7m, and decade-scale bed surface elevation change of 1.1±3.3m. Since 1993, the downstream reaches incised in response to bedload sediment trapping by reservoirs while headwater reaches aggraded in response to increased sediment delivery from uplands. A tremendous increase in reservoir sedimentation after 2000 likely reflects the effects of the highest decade-average daily rainfall since 1900. Suspended sediment load data indicate a post Chi-Chi earthquake increase in sediment concentration in low-flow events but do not exhibit the clear influence on sediment yields at higher flows as (e.g., typhoons) reported by others for fluvial response in the epicentral region. [Copyright &y& Elsevier]

Abstract: The integration of sandstone petrography, detrital zircon U-Pb ages, and sedimentological data was carried out for lower Paleogene rocks in four sections of the western Maracaibo Block, allowing for the documentation of a shift from regional to localized fluvial drainage systems associated with intraplate uplifts. The lower to middle Paleocene units have similar thicknesses, and show a depositional profile varying northward from fluvial-estuarine environments to shallow marine carbonates. Sandstones show high quartz percentages (up to 80%) and detrital zircon age populations are dominantly older than 0.9 Ga (with peaks in 1.55 and 1.8 Ga), with minor populations in the range of 400–600 Ma. In contrast, the upper Paleocene units were deposited in marginal, coal-rich environments, and have strong variations in thickness among the four studied areas. These sandstones show quartz percentages between 40 and 70%, and have a significant increase in metamorphic fragments (approximately 13% of the total framework) as compared to the lower Paleocene sandstones (5–7% of metamorphic lithic fragments). The lower Eocene sandstones, on the other hand, show an increase in k-feldspars and quartz content. The detrital zircon age populations for the upper Paleocene and lower Eocene sandstones in the western sections show a strong decrease in ages from 1.3 to 2.5 Ga and an increase in ages from 55 to 360 Ma; in contrast, age populations older than 0.9 Ga persist in the southern section. The lower-middle Paleocene rocks suggest a regional, basin-wide drainage system fed by the Cretaceous sedimentary cover exposed in low-amplitude localized uplifts and developed a mixed siliciclastic-carbonatic platform in the shelf areas. On the other hand, the upper Paleocene-lower Eocene synorogenic succession accumulated in several basin compartments separated by more pronounced source areas and recorded the introduction of new ones. These sandstones contain basement rock fragments from marginal uplifts of the Santa Marta Massif and the Central Cordillera, as well as fragments from emerging intraplate ranges, such as the Perijá Range and the Santander massif. Caribbean subduction along the northwestern margin of South America induced tectonic changes inside the Maracaibo Block, modifing sedimentary depocenters from a regional basin (ca. 300 km width) to isolated intermontane basins, which have been separated since the late Paleocene to present. [Copyright &y& Elsevier]

Abstract: The Fangliao submarine canyon cuts across the shelf and slope of southwest Taiwan. Unlike other canyons along this margin, there is no obvious connection to an individual fluvial sediment source on land. Two recent cruises to Fangliao Canyon provide insight into sedimentation associated with a major typhoon. Box and piston cores were retrieved from Fangliao Canyon in early January 2007, after a local earthquake and an extended period of low-to-moderate river flow in streams that are suspected of contributing sediment to the canyon. Similar cores were collected from the canyon in early October 2009, following one of the largest typhoons to hit Taiwan in the past several decades. Typhoon Morakot delivered several meters of rain to Taiwan, with the largest river floods occurring in the south and southwest regions. In addition, the coastal ocean environment was energized by significant wave heights (>12m). Comparisons of textural, radioisotopic, and geochemical data reveal likely sediment transport and depositional processes within and surrounding Fangliao Canyon. Typhoon Morakot caused a layer ~10cm thick (and greater) throughout the canyon. X-radiographs of the 2007 cores show limited physical structure in most cases, and the 2009 radiographs display obvious changes in sediment density relative to the underlying sediment, as well as distinct physical lamination. Examining signals from different geochemical and radiochemical tracers for terrestrial sediment source indicates that the flood layer deposited by Typhoon Morakot came from several small mountainous rivers. By comparing the results of the 2007 cruise with those from 2009, we gain significant insight to the close linkage between a line source of fluvial sediment and deposition in a submarine canyon, as well as the role that tropical-storm events can play in delivering sediment to these environments. [Copyright &y& Elsevier]

Bed material load, which comprises bed load and suspended load, has been extensively studied in the past few decades and many equations have been developed, but they differ from each other in derivation and form. If a process can be related to various flow conditions on a general basis, a proper understanding of bed material load movement can be ascertained. As the process is extremely complex, obtaining a deterministic or analytical form of it is too difficult. Neural network modelling, which is particularly useful in modelling processes about which knowledge of the physics is limited, is presented here as a complimentary tool for modelling bed material load transport. The developed model demonstrated a superior performance compared to other traditional methods based on different statistical criteria, such as the coefficient of determination, Nash-Sutcliffe coefficient and discrepancy ratio. The significance of the different input parameters has been analysed in the present work to understand the influence of these parameters on the transport process. Editor D. Koutsoyiannis Citation Kumar, B., 2012. Neural network prediction of bed material load transport. Hydrological Sciences Journal, 57 (5), 956–966. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the influence of sea level changes on the stratigraphy and basal topography of latest Pleistocene–Holocene incised valley fill of the Arakawa and Menuma Lowlands in central Japan by using sedimentary drill cores and columnar geologic sections. In the study area, four buried fluvial terrace surfaces (I to IV) formed in response to sea-level fall during the last glacial period. Surface III is covered with As-YP tephra (15–16.5ka) and extends at least 65km landward from the present mouth of the Arakawa River. A buried valley named surface V that extends from at least 85km upstream from the present river mouth to about 120m below present sea level on the continental slope was incised in response to the sea-level lowstand of the Last Glacial Maximum. The incised valley fill can be divided into three units: unit A (gravelly river channel sediments including valley-bottom gravels), unit B (fluvial sediments), and unit C (marine sediments), which intertongues within unit B and pinches out up to 60km upstream from the present river mouth. Unit C marks the landward limit of Holocene transgression. The lower part of unit B is a fining-upward succession formed during rising sea level and indicates retrogressive aggradation of floodplain sediments during transgression, whereas the upper part of unit B was formed during a sea-level highstand. The floodplain migrated more than 85km upstream from the modern shoreline in response to sea-level rise until the middle Holocene and extends over several tens of kilometers beyond the landward limit of the Holocene marine transgression. [Copyright &y& Elsevier]

Abstract: Obstacles in fluvial environments cause flow separation and the emergence of three-dimensional flow fields that can lead to scour and deposition, even when no general sediment transport at the bed occurs. Resulting forms are commonly denoted as ‘fluvial obstacle marks’. The morphology and dynamics of these forms is depended on obstacle-, flow- and sediment characteristics. As no generally approved approach for analysis of these forms exists yet, a process-based method is developed that relates certain dependent morphometric variables to an adapted obstacle Reynolds number. The novel approach was applied by conducting experiments in a laboratory flume and validated against other laboratory and field data. The results of this work have shown a significant relationship between the morphometry of fluvial obstacle marks and obstacle Reynolds number, especially when morphometric variables were combined. Further validation, calibration and extension and of this approach will help to adequately asses the influence of obstacles in the fluvial environment on micro- and meso-scale processes of sediment transport. [Copyright &y& Elsevier]

The last several decades have witnessed the development of both capacity and non-capacity models for fluvial sediment transport. While recent investigations of the multiple timescales of fluvial processes have substantiated the understanding of conditional applicability of capacity models, the extent to which a capacity model differs from a non-capacity model remains to be unravelled. This paper presents a comparative investigation of one-dimensional capacity and non-capacity models. As a corollary to the theoretical analyses of the multiple timescales of fluvial processes, this study demonstrates that bed load transport can adapt to local flow sufficiently rapidly and, accordingly, a capacity model is applicable. However, as bed evolution modifies the flow considerably, a non-capacity model is needed if the flow is to be properly resolved in addition to bed load transport. Furthermore, it takes a long time and space for suspended sediment transport to adapt to capacity. Therefore non-capacity modelling is critical for suspended sediment transport, whereas a capacity model may result in considerable errors at best and become ill-posed at worst because of the requirement for extra boundary conditions. The findings of this work should facilitate the physically enhanced development and applications of mathematical river models. [ABSTRACT FROM AUTHOR]

Climate change and human activities in Europe have altered erosion and riverine sediment transport for thousands of years. The Danube River basin, the second largest watershed in Europe, provides a unique study area to examine these impacts on fluvial discharge through available reconstructed climate data during the ‘Little Ice Age’ cold interval, as well as documented timing of deforestation and large dam emplacement. Suspended sediment flux of the Danube watershed and its variability in response to both climatic adjustments and human influences is analyzed at the sub-basin scale using a numerical modeling approach (HydroTrend 3.0). The system is examined over three time periods under conditions corresponding to: (1) modern day, (2) pre-dam and (3) the ‘Little Ice Age’. Modeled results indicate that modern-day suspended sediment flux is approximately 60% and 80% lower than that simulated under pre-dam and ‘Little Ice Age’ conditions, respectively. Disregarding the effects of modern-day dams, sediment flux has decreased 46% since the ‘Little Ice Age’, largely due to declining rates of deforestation since the mid to late twentieth century. High-resolution (decadal) analyses based solely on climate change, i.e. assuming no human impact, suggest that suspended sediment flux should be approximately 5% higher today than during the ‘Little Ice Age’, despite a 10% decrease in water discharge.This supports the view that human influence is the dominant forcing agent in modifying, and even reversing, natural processes on the Earth’s surface. Results also suggest that a 4°C increase in average European annual temperatures, as predicted by the Intergovernmental Panel on Climate Change for the end of this century, could result in increased sediment flux by 16–63% in individual basins. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to assess the global occurrence of large submarine canyons to provide context and guidance for discussions regarding canyon occurrence, distribution, geological and oceanographic significance and conservation. Based on an analysis of the ETOPO1 data set, this study has compiled the first inventory of 5849 separate large submarine canyons in the world ocean. Active continental margins contain 15% more canyons (2586, equal to 44.2% of all canyons) than passive margins (2244, equal to 38.4%) and the canyons are steeper, shorter, more dendritic and more closely spaced on active than on passive continental margins. This study confirms observations of earlier workers that a relationship exists between canyon slope and canyon spacing (increased canyon slope correlates with closer canyon spacing). The greatest canyon spacing occurs in the Arctic and the Antarctic whereas canyons are more closely spaced in the Mediterranean than in other areas. River-associated, shelf-incising canyons are more numerous on active continental margins (n=119) than on passive margins (n=34). They are most common on the western margins of South and North America where they comprise 11.7% and 8.6% of canyons respectively, but are absent from the margins of Australia and Antarctica. Geographic areas having relatively high rates of sediment export to continental margins, from either glacial or fluvial sources operating over geologic timescales, have greater numbers of shelf-incising canyons than geographic areas having relatively low rates of sediment export to continental margins. This observation is consistent with the origins of some canyons being related to erosive turbidity flows derived from fluvial and shelf sediment sources. Other workers have shown that benthic ecosystems in shelf-incising canyons contain greater diversity and biomass than non-incising canyons, and that ecosystems located above 1500m water depth are more vulnerable to destructive fishing practices (bottom trawling) and ocean acidification caused by anthropogenic climate change. The present study provides the means to assess the relative significance of canyons located in different geographic regions. On this basis, the importance of conservation for submarine canyon ecosystems is greater for Australia, islands and northeast Asia than for other regions. [Copyright &y& Elsevier]

Volcanic terrains such as magmatic arcs are thought to display the most complex surface environments on Earth. Ancient volcaniclastics are notoriously difficult to interpret as they describe the interplay between a single or several volcanoes and the environment. The Early Miocene Tepoztlán Formation at the southern edge of the Transmexican Volcanic Belt belongs to the few remnants of this ancestral magmatic arc, and therefore is thought to represent an example of the initial phase of evolution of the Transmexican Volcanic Belt. Based on geological mapping, detailed logging of lithostratigraphic sections, palaeocurrent data of sedimentary features and anisotropy of magnetic susceptibility, mapping of two-dimensional panels from outcrop to field scale, and geochronological data in an area of ca 1000 km, three periods in the evolution of the Tepoztlán Formation were distinguished, which lasted around 4 Myr and are representative of a volcanic cycle (edifice growth phases followed by collapse) in a magmatic arc setting. The volcaniclastic sediments accumulated in proximal to medial distances on partly coalescing aprons, similar to volcanic ring plains, around at least three different stratovolcanoes. These volcanoes resulted from various eruptions separated by repose periods. During the first phase of the evolution of the Tepoztlán Formation (22·8 to 22·2 Ma), deposition was dominated by fluvial sediments in a braided river setting. Pyroclastic material from small, andesitic-dacitic composite volcanoes in the near vicinity was mostly eroded and reworked by fluvial processes, resulting in sediments ranging from cross-bedded sand to an aggradational series of river gravels. The second phase (22·2 to 21·3 Ma) was characterized by periods of strong volcanic activity, resulting in voluminous accumulations of lava and tuff, which temporarily overloaded and buried the original fluvial system with its detritus. Continuous build-up of at least three major volcanic centres further accentuated the topography and, in the third phase (21·3 to 18·8 Ma), mass flow processes, represented by an increase of debris flow deposits, became dominant, marking a period of edifice destruction and flank failures. [ABSTRACT FROM AUTHOR]

Abstract: Sediment transport and bed deformation in alluvial rivers are space and time dependent. The knowledge of the space and time scales can be helpful for the definition of predictive procedures of an alluvial reach response to changing boundary conditions. In this work, attention is paid to scouring process occurring downstream of the rigid basement of a hydraulic structure. The analysis is focused on transient bed profiles which are determined, under steady flow conditions, by a decrease of the upstream sediment transport rate. In particular, the paper is aimed at improving understanding of the space and time scales required by the alluvial system to reach the equilibrium conditions. For this purpose, movable-bed runs are carried out in a straight laboratory channel, for two values of the water discharge. During each run, the longitudinal bed profiles are measured at different times. Based on experimental data, spatial scale factors of the bed scouring and of the bed load transport to reach the equilibrium conditions are defined. Particularly, it is found that the scour length varies especially during the first evolution phase and then it oscillates around of a mean value that is about 40% of the channel reach interested by the phenomenon under consideration; an expression is found for the adaptation coefficient which allows the estimation of the spatial delay of the bed load transport rate. Using both the collected data and literature data an expression defining the time scale of scouring is deducted. According to this expression the non-dimensional time scale is related to Shields parameter through an exponential law. Then, by the help of a 1-D numerical model previously developed by the writer, the implications for choosing the spatial and temporal resolutions, on which numerical results depend significantly, are shortly discussed. The results show that the time and space scales, which represent physical constraints of the spatial and temporal resolutions, need to be properly defined in order to simulate the scouring process evolution. [Copyright &y& Elsevier]

Abstract: Forced riffle-pools occur in gravel-bed rivers where a large nonalluvial element leads to local scour and deposition. To manage rivers where this type of morphology is found and to specify restoration measures that mimic this process, more field data on sediment mobility in forced riffle-pools is needed. The objectives of this study are to describe the spatial variability of sediment mobility and deposition in a developing forced riffle-pool and to use high-resolution flow velocity measurements to explain the observed dynamics. The field site is a forced riffle-pool in Moras Creek, a 6-m-wide gravel-bed stream with a 1.2% bed slope in Quebec, Canada. Topography and the movement of sediment particles equipped with Passive Integrated Transponder (PIT) tags are surveyed through a series of competent floods. Bed shear stress is estimated from near-bed measurements of time-averaged velocity and turbulent kinetic energy. The sediment transport regime of the creek is characterized by partial mobility, exponential distributions of path lengths, and a negative relation between particle size and path length. Full mobility occurs in the center of the pool and over the exit slope where flow is accelerated from the constriction of flow during two events above the bankfull discharge. Partial mobility occurs during the same events over the entrance slope to the pool. Lateral gradients of deposition and mobility suggest that the majority of sediment in motion is routed over the side bar at the entrance to the pool. High levels of turbulence intensity that occur as a result of flow deceleration may explain the removal of finer sediments from the head of the pool. [ABSTRACT FROM AUTHOR]

Rivers crossing coastal plains are often inefficient conveyors of sediment, so that changes in upstream sediment dynamics are not evident at the river mouth. Extensive accommodation space and low stream power often result in extensive alluvial storage upstream of estuaries and correspondingly low sediment loads at the river mouth. However, gaging stations with sediment records are typically well upstream of the coast, and thus tend to overestimate sediment yields by under-representing the lower coastal plain and because there is often a net loss of sediment in lower coastal plain reaches. Studies of alluvial sediment storage have generally focused on accommodation space, but, using examples from Texas, we show that low transport capacity controlled largely by slope is a crucial factor. [Copyright &y& Elsevier]