Transport Sediment Research Articles

Landscape-Scale Modeling to Forecast Fluvial-Aeolian Sediment Connectivity in River Valleys.

Sedimentary landforms on Earth and other planetary bodies are built through scour, transport, and deposition of sediment. Sediment connectivity refers to the hypothesis that pathways of sediment transport do not occur in isolation, but rather are mechanistically linked. In dryland river systems, one such example of sediment connectivity is the transport of fluvially deposited sediment by wind. However, predictive tools that can forecast fluvial-aeolian sediment connectivity at meaningful scales are rare. Here we develop a suite of models for quantifying the availability of river-sourced sediment for aeolian transport as a function of river flow, wind regime, and land cover across 168 km of the Colorado River in Grand Canyon, USA. We compare and validate these models using topographic changes observed over 10 years in a coupled river sandbar-aeolian dunefield setting. The models provide a path forward for directly linking fluvial hydrology with the management and understanding of aeolian landscapes.

Luminescence dating of the MIS 6 glaciation of the Pamir mountains (Central Asia)

The Pamir Mountains are one of the highest mountain systems in the world; they act as sources of fresh water for the main rivers of Central Asia: the Amudaria and Syrdaria. Throughout the Quaternary, the Pamirs played a major role in controlling atmospheric circulation and land-surface processes, and provided great volumes of terrigenous sediments for transport by large rivers to the depressions in the Aral and Caspian regions. These ultimately provided broad aeolian cover in the sandy deserts, and finer dust for the widely distributed loess-palaeosol sequences. The glaciation history of this highly dynamic region provides an important basis for understanding climate change, sediment source and landscape evolution in Central Asia during the Quaternary. The question of the number, distribution, extent and timing of Pleistocene glaciations in the Pamir is debated. One of the main obstacles to research, together with difficulties of access and severity of current climate, is the varying degree of preservation of traces of previous glaciations in the western and eastern Pamir. As a result of a geological survey, we for the first time identified a thick lacustrine deposit at high altitudes in a tributary of the Panj – the valley of the Sary-Shitharv River – this records the damming of the Panj River valley by a large glacier. Luminescence measurements were undertaken to obtain the age of the Sary-Shitharv glacially-dammed lake. As often in mountain catchments the quartz OSL signal was unsuitable for dose estimation, and so the chronology of the Sary-Shitharv section is based entirely on post-IR IRSL signals from K-rich feldspar. We used pIRIR50,290 and pIRIR200,290 protocols and obtained indistinguishable ages from both protocols. Given the high sedimentation rates deduced from the structure of lacustrine deposits, the entire sequence must have been accumulated rather quickly, over a period of no more than a few thousand years. The average age over the whole series of dates is 165 ± 11 ka. This places the existence of the glacially-dammed lake at Sary-Shitharv in late MIS 6, a result that fits well with the general course of the glacial history of the Pamirs.

Provenance of the late Jurassic to Cenomanian sedimentary succession of the Araripe Basin (NE Brazil) and implication for the geodynamic evolution of Western Gondwana

The separation of Gondwana was controlled by preexisting Proterozoic structures and by the development of rift aborted basins, of which the Araripe Basin (NE Brazil) is one of the best examples. Previous studies have focused on the presence and provenance of Aptian–Albian shallow-marine incursions in the Araripe Basin but to date, little attention has been given to its paleodrainage evolution during sedimentation stages. Understanding the paleodrainage evolution is crucial for determining sediment sources and how topographic changes relate to the geodynamic development of the northern part of South America during the fragmentation of Gondwana, and this study investigates the provenance of Mesozoic rift and post-rift sedimentary rocks in the Araripe Basin using a multi-proxy dataset comprising major and trace element concentrations, Sm–Nd isotopic composition, and detrital zircon U–Pb ages. The low Eu/Eu* ratios (0.3–0.9) and high Th/Sc ratios (>0.64) in the most of analyzed samples suggest a felsic and silicic source. The εNd(0) values (−12.3 to −23.7) and TDM ages (1.68 to 2.55 Ga) of analyzed samples suggest overall ancient crustal sources. The presence of oval and elongated zircon grains suggests a major contribution of first-cycle transport sediments. The presence of 2.3–1.8 Ga and 0.63–0.58 Ga U–Pb zircon ages further indicates the dominant contribution of the Borborema Province influenced by the Brasiliano cycle (650–520 Ma). The low contribution of Tonian (∼940 Ma) zircons to the U–Pb zircon age distribution of the rift-beginning stage sample associated with published paleocurrent direction suggests sources located in the northern and northwestern terranes of the Borborema Province. The increase of Tonian (0.9–1.0 Ga) zircon grains during the rift stage suggests a provenance change with a dominant source in the eastern terranes during the rift stage. During the post-rift I stage, the decrease of 1.2–0.72 Ga zircon ages suggests a change in the source areas, with the paleodrainage coming from northern Borborema Province, similar to that of the rift-beginning stage. The samples of the post-rift II stage exhibit dominant contributions of Paleoproterozoic and Neoproterozoic U–Pb ages related to the Albian to Cenomanian uplift of the Borborema plateau during the opening of Equatorial Atlantic Ocean. Together with previous published studies, these findings highlight the significant role played by the post-rift continental uplift to the paleodrainage of the northern part of South America.

The length and spacing of river tributaries

River networks are composed of a mainstem and tributaries. These tributaries dissect landscapes, regulate water and habitat availability, and transport sediment and nutrients. Despite the importance of tributaries, we currently lack theory and data describing whether and how tributary length and spacing varies within watersheds, thereby limiting our ability to accurately describe river network geometry. We address this knowledge gap by analyzing 4,696 tributaries across six landscapes with varying climate, tectonic setting, and lithology. Our results show that both tributary length and spacing systematically increase with downstream distance along the mainstem river, following a power-law scaling. This power-law scaling can be modulated by basin shape, with tributaries becoming shorter and, in some cases, more closely spaced as basin elongate. Furthermore, the power-law scaling may break down in cases where river networks have been disturbed by pervasive faulting, raising the possibility that the scaling we observe is not unique to all branching networks, and instead may be universal across undisturbed fluvial networks. These findings can be used to improve predictions of river network geometry and potentially to distinguish fluvial river networks from other branching networks.

Multivariate analysis of inlet morphodynamics: The mixed sand-gravel ebb-tidal delta of Deben Estuary, Suffolk

The morphodynamics of inlets and ebb-tidal deltas often exhibit cyclic behaviour, controlled by wave-tide interactions and the influence of these on sediment-bypassing processes. Variation in the form and timing of inlet dynamics can occur in response to changes in the key sediment transport processes and sediment supply, and particularly the relative dominance of differential wave direction driving alongshore sediment transport. This paper investigates the morphodynamics of the Deben ebb-tidal delta through multivariate analysis of multi-annual bathymetry and metocean parameters covering the period 1991 to 2023. Results show that sediment bypassing and associated morphological change in this ebb-tidal delta follows variable behaviour mid-cycle, leading to change in the morphology and configuration of the ebb-delta from cycle to cycle. In the most recent cycle (since 2003), delta volume followed a stepwise growth driven by sediment influx periods, evident primarily in the updrift shoal, followed by cross-shore redistribution. Interannual variability in wave climate was clustered into four groups that capture the relative balance between the dominant NE and SW forcing. Sediment influx periods are mostly associated with subdued SW and increased NE forcing, but the summer and winter NE wave climate play different roles on the up- and downdrift, and upper and lower components of the ebb-delta system. Tide level has increased in the last 33 years, which is strongly correlated with ebb-delta volume increase. Wave and tide conditions have discrete and independent effects on the ebb-tidal delta, whereas wave-tide interactions do not significantly change these underlying influences.

Fine particle contents in sediment drive silica transport and deposition to the estuary in the turbid river basin

Changes in riverine sediment transport are an important part of land-sea geochemical cycling and further impact geochemical element fluxes in turbid rivers. However, as a vital nutrient element supporting primary productivity, silica mobilization from drainage in turbid rivers is overlooked. The turbid Yellow River has a strong ability to adsorb reactive silica, thereby exerting a substantial impact on the estuarine deposition of silica. Through an integration of monitoring databases, field sampling and historical hydrological data, we concluded that riverine fine particles control the exchangeable silica in the river and its estuary under soil erosion. Indoor simulation further revealed that the adsorbed content of exchangeable silica (ex-Si) in fine sediment constituted 35 % of total sediment matter. In addition, the transport of phosphorus and ex-Si was jointly regulated by fine sediment in global fluvial sediment transport, thereby exerting additional influence on the trophic structure of estuarine ecosystems. Against the backdrop of sediment budget deficit in the estuary, the heightened content of fine particles is depleting the silica storage from estuarine sediments.

X-ray tomography applied to tsunami deposits: Optimized image processing and quantitative analysis of particle size, particle shape, and sedimentary fabric in 3D

The analysis of particle size, shape, size, and their spatial arrangement (i.e. fabric) in a sedimentary deposit plays a significant role in their interpretation in terms of transport mechanism, flow conditions, and sediment source. The present work focuses on the use of X-ray computed tomography (X-CT) to analyze tsunami deposits (core samples), as examples of complex sedimentary assemblages. A workflow of image processing is proposed to measure 3D parameters of particle size, shape, and orientation using two different software packages (Fiji-ImageJ, and IPSDK) and two different methods of image segmentation. The semi-automated method provides better segmentation quality of the tsunami deposit, as compared with the poor performance of fully-automated image segmentation. We also provide some clues to reduce the computational time. This workflow is applied to two examples of tsunami deposits on the coasts of the Algarve (1755 Lisbon tsunami, southern Portugal). Optimized processing of X-CT images gives access to detailed vertical variations of grain size, grain shape, and componentry (clayey matrix, silicates, and carbonates, including marine bioclasts), as well as information on flow directions inferred from the sedimentary fabric in 3D. High-resolution analysis of the bedforms and vertical grain size grading allows determining the flow conditions during the inundation phase of the tsunami.

The hydromorphological effects of dams in an extreme desert environment - The Fish River Canyon, Namibia

Arid ecohydrology relies on sporadic rainfall and flooding to sustain linear river oases, crucial for supporting flora and fauna during the long dry season and drought years. Growing water demands have led to large reservoir constructions, severely impacting the fragile arid ecosystems. We analyse the hydro-geomorphological impacts of the large Neckartal Dam (completed in 2019) on the Fish River oasis based on existing dams, regional studies, field surveys, hydrological data, and modelling. The Neckartal Dam, along with three smaller dams, impounds 80 % of the desert oasis basin (1235 Mm3, 55,870 km2), exceeding the average annual runoff threefold. A gradient of dam-induced changes was identified, varying with distance from the dam wall. Immediate downstream, hydromorphological impacts include channel narrowing (⁓15 %) and reduce mean annual sediment yield (⁓20 %). Also, water distribution losses create chronic low flows, favour for invasive flora and fauna to spread, significantly disrupting the pristine nature of the desert ecosystem. This phenomenon has been observed over a 70 km stretch below the Hardap Dam. This situation is irreversible, as the invasive flora can withstand even large floods. As the distance increases, the dam suppresses low to moderate annual floods and prolongs droughts from months to years or even decades. Based on our flood routing model, only the largest floods (recurrence interval, RI >25 years) can exceed the dam storage, continue downstream, transport sediment and maintain the pool-bar morphology along 245 km of the oasis. The lack of significant flows between major floods means that sediment from smaller, lower arid basins accumulates in the Fish River valley, filling pools and further reducing water availability during dry periods. The Neckartal Dam's impact assessment demonstrates potential changes in arid river systems globally.

Areas simultaneously susceptible and (dis-)connected to debris flows in the Dolomites (Italy): regional-scale application of a novel data-driven approach

ABSTRACT In mountain regions, the impact of areas on the sediment conveyance can not only be described by their susceptibility to debris flow release, but also by their structural connectivity to the rivers. This generates the need to combine susceptibility and connectivity for accurate analyses of sediment transport. Our study exploits an approach developed by [Steger, er al. 2022; https://doi.org/10.1002/esp.5421] and upscales it to the South Tyrolean Dolomites region. The approach comprised the modeling of debris flow release susceptibility using an interpretable machine learning algorithm, the training of a logistic regression model, and the combination of the resultant classified maps to create a joint susceptibility-connectivity map. The results show the quantitative thresholds for the susceptibility probability and the Index of Connectivity (IC) that allow to discriminate between susceptible and not susceptible, as well as connected and disconnected areas, which are represented via a variety of maps.

Density‐dependent effects of parasitism on the activity of a benthic engineer species: potential impact on ecosystem functioning

While parasitism is a common lifestyle on Earth, its importance for the functioning of marine ecosystems has been overlooked for a long time. In particular, parasites have significant potential to influence central ecological processes through their impacts on hosts that serve as ecosystem engineers. Using an ex situ experimental approach, we explored the effects of trematode parasites on the engineering bioturbation activity of a common and abundant bivalve along European Atlantic soft‐bottom coastlines, the peppery furrow shell Scrobicularia plana, as well as knock‐on effects for nutrient exchanges at the sediment–water interface (SWI). Trematodes negatively impacted the host's ability to transport sediment particles and solutes in a density‐dependent way, with parasite burden explaining 22–31% of the inter‐individual variability. This could be explained by parasitism impairing the bivalve physiological state and ability to burrow, as we observed a decrease in the condition index and the burrowing depth of the bivalves with an increase in the number of parasites they host. In contrast, the influence of S. plana on benthic biogeochemical fluxes did not vary significantly according to parasitic burden over a short time scale. Here, we focused on the effects of trematode parasites on the behaviour of S. plana alone, and thus excluded other macrofaunal organisms. We should next test whether trematodes modulate the structure and functioning of benthic communities dominated by S. plana to better understand and quantify the engineering role of parasites in soft‐bottom coastal environments.

The study of the criterion of the marginal and dynamic equilibrium of the riverbed

The article analyzes the results of theoretical and experimental studies on the stability criterion of Rusle from non-cohesive soils, and notes their advantages and disadvantages. A significant influence of the average slope and transport sediment flow on head losses was revealed. An assessment was made of the shape of the channel of the limiting and dynamic equilibrium of the channel laid in easily eroded soils - justified for considering the parameters of molasses. A number of empirical substitutabilities are given A number of empirical substitutabilities are given w0=f(d) and i=f(H⁄d), constructed based on hydrometrological data of Central Asian water basins, which can be used for practical calculation of watercourses. An improved method has been proposed that allows the design of river structures taking into account the criterion of equilibrium of fine sand sediment grains.

River capacity prediction based on flood discharge probability scenario and sediment transport consideration: Study Case in Sayung River

Pantura road at estuary of Sayung River is often flooded because it has a lower elevation than the river embankment. To avoid this, we must know the flood capacity of the river so that we can plan flood control and maintenance of river channels. Usually in flood prevention planning, it only design structure with unsteady flow model without sediment transport analysis. It is contrary with river nature because bed and river bank will easily erode, then transported as sediment and deposited in the lower reaches of the river. It makes river geometry will vary along with increasing of sedimentation. Therefore, capacity of the river will be analyzed with sediment transport using HEC-RAS 6.2 quasi unsteady flow model. Based on transport sediment simulation, sediment material deposition at Sayung River is 45,000 m3 every year. It makes river capacity decreased. Sayung River capacity is currently 242.15 m3/s, in 2023 is 200 m3/s, in 2024 is 185m3/s, in 2025 is 170 m3/s, year 2026 is 155 m3/s, in 2027 is 140m3/s, in 2028 is 120m3/s, in 2029 is 100m3/s, in 2030 is 77.5m3/s.

Assessment of plot-scale sediment transport on young moraines in the Swiss Alps using a fluorescent sand tracer

Abstract. Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of overland flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investigate how the surface characteristics of young moraines affect OF and sediment transport, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF and peak OF flow rate) and measured sediment transport (turbidity, sediment concentrations, and total sediment yield). To determine and visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow as well as ultraviolet (UV) and light-emitting diode (LED) lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. Thus, this study demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways as well as the fact that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.

The influence of onshore harbour layout on coastal sedimentation and erosion at Pekalongan

Pekalongan City is an area that experience floods. Therefore, the government launched program for flood management in the Pekalongan area. The program requires the PPN Pekalongan to be relocated. The construction of the Pekalongan Onshore Harbour will change the hydrodynamics pattern and transport sediments. To overcome this problem, it is necessary to conduct a study of these changes. High current speeds and high waves will cause high sediment transport, but it can have a different impact. The first impact is high erosion, like in the existing condition T3. The second impact is high sedimentation, such as in T1 layout 1. The third impact is experiencing slight erosion or sedimentation at the end of modelling, but fluctuations during the modelling process are very large, such as in T5 layout 2. The bed level change is -313.5 mm, 20.88 mm, and -13.66 mm, respectively. Slow currents with high waves cause large sedimentation such as T4 layout 2 or high erosion such as T2 in existing conditions with bed level changes of 41.53 mm and -332.07 mm, respectively. Layouts 1 and 2 are in accordance with regulations because it has current speeds below 0.4 m/s and wave heights below 0.5 m.

Characteristics of Flow Hydrophysics Variables and Flood Potential Around Kuala Jengki Estuary Manado City

Flood disasters along the river resulted from damage to flood barrier construction along the river bank. The damage to the flood retaining wall is technically caused by the very large hydrophysical parameters of the river flow. In theory, the flow mass density parameter shows the concentration of sediment transported through one cross-section. As a result of changes in the volume of sediment transport, there will be an increase in flow energy, followed by changes in large water masses, and this is seen as a destructive force component in some equivalent places or riverbanks, which can physically be formulated in the form of a model function. It is important to do a map of the hydrophysical character variable flow and flood potential along Kuala Jengki estuary Manado City, it is important to do because the estuary is often flooded. Measurement of the hydrophysical variable mass flow density was carried out at a depth of 0.6 rivers at high and low tides. The mass density of the flow is the mass of water containing transport sediment divided by its volume. The mass of water (sample) is measured using a scale, while the volume is measured using a measuring cup or another container that has a volume measurement. For the presentation of density data profiles and other analytical purposes, the measured data were reproduced using linear interpolation techniques. The mass density data modeling was carried out using an experimental function iteration technique containing constants. The results of the research at high tide, the position which is approximately 275 meters at measurement points 10 to 13 at a distance of 675 meters to 950 meters becomes a location that is very prone to river lip damage if there is a rise in water level due to high rainfall, or a position where it becomes flood-prone when the flow density increases, along with an increase in the volume of river water, which is followed by changes in river flow velocity carrying various types of sediment. At a distance of 165 meters at low tide, the measurement position is between 10 and 13, there is an increase in large flow discharge accompanied by an increase in flow velocity that carries flow mass (mass density) with various types of sediment transport. In this condition, the location which is 165 meters away according to the model map becomes prone to river lip damage, which means that it is a location that has the potential for flooding. In contrast to measurement positions 5 and 6 at high tide, there is a significant increase in the low mass density, while at low tide this condition does not occur, this is because the flow velocity at low tide does not change significantly, causing the mass flow density to be relatively the same.

Numerical Simulation and Sensitivity Analysis of Sediment Issues in Pumped Storage Power Stations: Sediment Conveyance of Turbine and Sedimentation of Reservoirs

In this paper, a 1D process-based numerical model is established to study the sediment concentration via the turbine (TSC) and sedimentation of the lower reservoir and the upper reservoir of a certain pumped storage power station (PSPS), which is intended to be built on a sandy river. In addition, the sensitivity of TSC to some factors, such as suspended sediment gradation, the water level of the lower reservoir, and the coefficients of the sediment-carrying capacity formula, are analyzed in this paper. It is revealed that (1) the TSC will decrease by 30.8~34.5% when the incoming sediments of particle sizes less than 0.002 mm (which accounts for 3.95% of the totality) are replaced with incoming sediments of particle sizes between 0.002 mm and 0.004 mm. At the same time, the sedimentation thickness of the upper reservoir will decrease by 20.9%, and the siltation rate of the lower reservoir will increase by 2.4%. (2) The TSC will decrease by 12.6~13.1% as the water level of the lower reservoir rises by 17.55 m. This represents an increase of 8.4% in the average water depth and 26.4% in the storage capacity of the lower reservoir. At the same time, the sedimentation thickness of the upper reservoir will decrease by 32.2%, and the siltation rate of the lower reservoir will increase by 2.5%. (3) The TSC will decrease by 1.2~1.4% as the index of the sediment-carrying capacity formula m changes from 1.12 to 0.666, and the coefficient of the sediment-carrying capacity formula K changes from 0.2 to 0.6. At the same time, the sedimentation thickness of the upper reservoir will decrease by 7.2%, and the siltation rate of the lower reservoir will increase by 1.7%. Through the research on the sensitivity of the TSC, the direction and amplitude of the TSC changes with the boundary conditions are found, which provides a basis for the scheme comparison of specific projects and further supplements the prediction method system of the TSC. Meanwhile, the results remind researchers to pay more attention to the determination of boundary conditions and also provide the basis for the error analysis of the TSC. In summary, the results have certain guiding significance for the related research, and the sensitivity analysis results of the case could provide a reference for other specific projects.

The April 2015 Calbuco eruption pyroclastic density currents: deposition, impacts on woody vegetation, and cooling on the northern flank of the cone

The 22-23 April 2015 eruption of the Calbuco volcano (Southern Andes, Chile) led to extensive pyroclastic density currents (PDCs) interactions with vegetation. We seek to describe the PDCs which affected both Tepu and Frío rivers, northern Calbuco, from their timing and deposition to cooling and erosion, as well as their impacts on forests. Our investigation is based on field stratigraphy, forest disturbance assessment, and geothermometry from degassing pipes and charcoal. These PDCs reached at least ~540-603 °C, as estimated from fumaroles, and consisted of both concentrated and dilute PDCs during the first pulse (22 April) at Tepu and mainly during the second pulse (23 April) at Frío. Effects of PDCs on forest vegetation recorded in Tepu consisted of heating, abrasion, burial, and impact force. On the valley floor, trees were buried with up to 4 m of deposits from the concentrated PDCs, and all trees in this deposition zone died with no subsequent sprouting. Conversely, in the margins of the valley, defoliated fallen trees and standing shrubs indicate scorching due to the passage of dilute PDCs, and some of them were later sprouting. Estimated impact forces required to produce toppling range from 1.5 to 3.7 kPa, and PDC velocities reached up to 36 m s-1. Charring of the buried wood involved an emplacement temperature of 400-550 °C within PDC deposits. The rapid watershed formation may have facilitated infiltration, decreasing the temperature in the basal part within the deposits at the Tepu river. Runoff during the subsequent months triggered lahars and caused the rivers to incise the deposits and transport sediment downstream. This set of observations provides valuable insights into how the interaction between volcanic phenomena and margine forest on the valley floors informs eruptive processes, dynamics, and impacts. Our study is also relevant to interpret the thermal history and potential hazards of PDCs.

Controls on upstream-migrating bed forms in sandy submarine channels

Abstract Submarine channels parallel river channels in their ability to transport sediment. However, in contrast to rivers, sediment transport and bed-form development in submarine channels are less well understood. Many steep (>1°), sandy submarine channels are dominated by upstream-migrating bed forms. The flow conditions required to form these upstream-migrating bed forms remain debated because the interactions between turbidity currents and active bed forms are difficult to measure directly. Consequently, we used a depth-resolved numerical model to test the role of flow parameters that are hypothesized to control the formation of upstream-migrating bed forms in submarine channels. While our modeling results confirmed the importance of previously identified flow parameters (e.g., densiometric Froude number), we found that basal sediment concentration in turbidity currents is the strongest predictor of upstream-migrating bed-form formation. Our model shows how locally steep gradients enable high sediment concentrations (average >5 vol%) in the basal parts of flows, which allow the development of cyclic step instabilities and their associated bed forms. This new insight explains the previously puzzling observation that upstream-migrating bed forms are abundant in proximal, steep, sandy reaches of submarine channels, while their occurrence becomes more intermittent downslope.

Determination of the maximum run‐off sediment transport capacity during a rainstorm flood in a small watershed on the Loess Plateau

AbstractThe channel sediment transport capacity is an important parameter in soil erosion models, and it determines the proportion of soil erosion that is sent outside the watershed. However, the calculation and judgment methods for the sediment transport capacity of channel are still incomplete, and further research is needed. Therefore, this paper takes Chabagou, a typical watershed in the hilly and gully region of the Loess Plateau, as an example and, based on the measured hydrological and sediment data collected during rainstorm floods in 1961–1969 at three hydrological stations, Caoping, Shejiagou, and Tuanshangou, studies the sediment transport capacity of channels in a small watershed from the perspective of energy dissipation. Clearly, the sediment transport capacity is better determined by using a single flood and sediment concentration peak process. The discriminant conditions are determined for the sediment concentration to reach sediment transport capacity during the flood rising and falling sections of the sediment process of the small watershed storm flood. When determining sediment transport capacity based on the characteristics of the flood and sediment concentration peak, we find that sediment transport capacity is reached in the flood discharge peak when the flood discharge peak occurs earlier than the sediment concentration peak. When determining sediment transport capacity based on the flow discharge and sediment concentration characteristics of the sediment fall section, we find that when the flood event exhibits a counterclockwise hysteresis curve and a time‐lagged effect occurs, the sediment concentration at that time reaches sediment transport capacity. In this study, the sediment concentration as a function of run‐off amount is logarithmic at different subbasin scales when run‐off reaches its maximum capacity to transport sediment. The R2 is high, ranging from 0.78 to 0.92. The results of this research provide a reference for the study of sediment transport capacity.

Fluvial geomorphic evolution and stream fish community trajectories in the Bayou Pierre, Mississippi, U.S.A.

Abstract Human activities have often altered sediment dynamics in rivers, leading to aquatic habitat degradation. The dominant paradigm in fish–sediment interactions focuses on excessive fine sediments as indicators of habitat and water quality degradation. In contrast, geomorphologists have provided frameworks linking altered sediment dynamics to much broader and more complex changes to channel morphology and stream habitats across spatial scales. In this paper we use an interdisciplinary approach with historical and contemporary channel morphology and fish community datasets to examine how altered sediment dynamics have affected stream fish community evolution in the Bayou Pierre, Mississippi, U.S.A. Erosional process regimes have advanced upstream consistent with models of knickpoint propagation and channel evolution, leaving most of the catchment in a state of increased sediment transport and local sediment deficits. Fish communities in modern samples have less α and β diversity and fewer habitat specialist taxa than in historical samples. Whole‐community analysis via non‐metric multidimensional scaling found a strong gradient of homogenisation towards a fauna comprised of small‐bodied taxa adapted to large rivers. Comparisons of community and geomorphic change on this gradient found that reaches that transitioned between process regimes had more community change, and that local habitat factors relating to advanced channel evolution were strongly positively related to total community change. These results demonstrate that a catchment‐scale geomorphic analysis provided a strong tool for understanding fish community change on a decadal scale. Our findings further demonstrate concordant ecological responses to a complex sequence of disturbances and suggest that a broader view of sediment dynamics offers a rich toolkit for ecological analyses.