Variations In Sediment Flux Research Articles

Sediment flux variation as a record of climate change in the Late Quaternary deep‐water active Corinth Rift, Greece

AbstractThe value of deep‐water sedimentary successions as reliable records of environmental change has been questioned due to their long response times and sediment pathways leading to complex responses to climatic change and tectonic signals over differing timescales. We studied the Gulf of Corinth, Greece, to test the value of deep‐water stratigraphic successions as records of external controls on sediment flux in a setting with short response times and transport distances. The confinement of the rift basin allows for a near‐complete accounting of clastic sediment volumes. The recent acquisition of high‐resolution seismic reflection data, utilisation of International Ocean Discovery Programme Expedition 381 cores and a robust chronological framework, enable evaluation of the stratigraphy at a high temporal resolution. Combining borehole and high‐resolution seismic reflection data, distinct seismic units can be correlated to multiple paleoenvironmental proxies, permitting quantification of sediment flux variation across successive glacial–interglacial cycles at ca. 10 kyr temporal resolution. Trends in average sediment flux since ca. 242 ka show ca. 2–9 times greater sediment flux in cooler glacials compared to warmer interglacial conditions. The Holocene is an exception to low sediment flux for the interglacials, with ca. 5 times higher rates than previous interglacials. The short and steep configuration of the Sythas canyon and its fan at the base of an active submarine normal fault results in deep‐sea deposition at all sea‐level stands. In contrast, adjacent canyon systems shut down during warm intervals. When combined with palynology, results show that periods of distinct vegetation re‐organisation correlate to sediment flux changes. The temporal correlation of sediment flux to palynology in the Gulf of Corinth over the last ca. 242 kyr is evidence that variability of sediment supply is largely governed by climate‐related changes in hinterland catchments, with sea‐level and tectonics being second‐order controls on sediment flux variability.

Does a braided river aggrade or degrade in response to changes in water and sediment fluxes?

Braided rivers undergo continuous morphological evolution in response to variations in water and sediment fluxes associated with a plethora of natural and anthropogenic disturbances, which has to date remained poorly understood. Here, a one-dimensional hydro-sediment-morphodynamic model is proposed for braided rivers. It is built upon an extended synthetic channel geometric model which encodes the essential, three-dimensional morphological information into a one-dimensional synthetic channel. It is first applied to the Rees River (New Zealand) to investigate overall morphological evolution (aggradation/degradation) during a single flood event. It is shown that the channel tends to degrade with increasing peak discharge and decreasing sediment supply, while the effect of baseflow discharge on aggradation/degradation is negligible unless the baseflow discharge exceeds a critical value. Then the proposed model is applied to resolve long-term morphological evolution in the Tuotuo River (China) reach (up to the year 2050), the source region of the Yangtze River, in response to projected water and sediment fluxes. Sustained degradation in the river reach is observed. The present study yields a viable physics-based method to predict overall aggradation or degradation of braided rivers under unsteady water and sediment fluxes over both short and long time scales.

Semi-quantifying vertical sedimentary succession and microfacies characterization from a delta system in a lacustrine basin, Huangqihai Lake, North China

The formation of vertical sedimentary succession of a delta in the arid and semi-arid basin-margin progradation dramatically depends on the variation of sediment flux and accommodation, but the discontiguous record of signals tends to exist enormously variable, which renders the bulk record of microfacies difficult to quantify from the vertical sedimentary succession. We analyzed the 18 vertical sedimentary successions collected from 18 field trenches of a lake delta by the cusp-catastrophe model, allowing detailed mapping of microfacies. The present detailed study indicates the suitability of cusp-catastrophe theory for explaining vertical sedimentary succession in the BWH (Bawanghe) delta. Three equilibrium states of processes responsible for the deposition of the BWH delta's evolution were established: sandy-dominated upper leaves primarily exhibit the delta plain; sandy/muddy-dominated lower leaves present the delta plain and pro-delta; and sandy-dominated middle leaves which commonly developed the delta front. The result of analysis shows that the reliability of the cusp-catastrophe model to identity mutation of vertical sedimentary succession exceeds 50 %, and to identity microfacies transitions with a precipitation periodicity exceeds 70 %. These cognitions support the previous view that changing precipitation results in an abrupt change in margin progradation. Simultaneously, the study gives new insights into the microfacies quantification of lake deltas and reveals the influence of crest value changes of precipitation on vertical sedimentary succession can be understood from the dependence of microfacies distribution on the change of sediment flux and accommodation.

Water discharge and sediment flux intermittency in the fluvial Escanilla Formation, Spain: Implications for changes in stratigraphic architecture

AbstractWater discharge and sediment flux variations are important parameters controlling the morphodynamic behaviour of rivers. Although quantitative estimates for water discharge and sediment flux variability are well‐constrained for modern rivers, far fewer assessments of flow and sediment flux intermittency in ancient fluvial systems from the rock record are available. In this study, a relationship between water discharge, sediment flux variability and patterns of changing fluvial stratigraphic architecture in the Middle Eocene Escanilla Formation, Spain, is explored. Water discharge intermittency factor (IWF), calculated as a ratio of the total water discharge (over the averaging time period) to the instantaneous channel‐forming water discharge if sustained for the same period, ranges from 0.03 to 0.11 in the high amalgamation intervals and from 0.10 to 0.32 in the low amalgamation intervals. Similarly, the sediment flux intermittency factor (ISF) is estimated to be in the range of 0.008 to 0.01 in the high amalgamation intervals and of 0.01 to 0.03 in the low amalgamation intervals. Consequently, high amalgamation intervals were most probably deposited under more intermittent and short‐lived intense precipitation events while low amalgamation intervals were the result of less intermittent flows spread throughout the year. Overall, these estimates are consistent with values from modern ephemeral rivers typically found in arid to semi‐arid climate and is in agreement with available proxy data for the Middle Eocene climatic context of the studied alluvial system. This highlights an important connection between hydroclimate, river morphodynamics and landscape evolution, and has implications to predict river flow and sediment transport across the Earth's surface in the geological past.

Investigating limnological processes and modern sedimentation at Lake Żabińskie, northeast Poland: a decade-long multi-variable dataset, 2012–2021

Abstract. Here, we present a dataset of a decade-long monitoring project of Lake Żabińskie, a hardwater eutrophic lake in northeast Poland. The lake contains annually laminated (varved) sediments that form a unique archive of past environmental variability. Regular measurements of the lake water physical and chemical characteristics were done using a multiparameter sonde and a set of temperature sensors deployed in the water column. Seasonal variability in sediment fluxes was documented by a sediment trap. Field sampling provided information about the hydrochemistry of incoming streams and of the lake outflow. The overall monitoring program was designed to assess relationships among meteorological conditions, limnological processes, and modern sedimentation and to answer the question of whether meteorological and limnological phenomena can be precisely tracked with varves. However, this dataset can also be used for modeling physical and biogeochemical processes in lakes. The dataset is archived at https://doi.org/10.34808/w8w7-9x34 (Tylmann et al., 2023).

Spatial and temporal control of the volcanic activities over the distribution of sediments in the Magadi basin, Kenya Rift

High-velocity layers in basins with significant sub-basalt coverage, such as the Magadi basin, can impede geophysical imaging of potential subsurface hydrocarbon deposits. Using magnetic and gravity methods, this study examines the influence of volcano-tectonic processes and the basement on the evolution of the Magadi basin. Regional-residual separation analyses identified key structures and signatures. Lineaments and depths of the causative sources were determined using Euler deconvolution. Butterworth low-pass filters on aeromagnetic data isolated depth-varying magnetic layer responses. The study demonstrates a westward displacement of volcanic flows in the Magadi basin, originating from nearly all volcanic plugs. Depocenters near the western boundary fault are more affected by westerly movements of the volcano-tectonic flows than depocenters near the eastern boundary fault. The Rift underwent internal compartmentalization, resulting in depocenters with unique and intermittent tectonic and sedimentary occurrences. Rift segmentation led to modifications in catchment areas, which caused sudden variations in sediment flux, ultimately leading to the isolation of the depocenters. This study identifies the initial compartmentalized depocenters of Nguruman, Koora, and Forty-six. The initial Nguruman depocenter is oriented SW-NE and spans approximately 2512 sq. km with a sediment thickness range of 2000–4000 m. The presence of horsts in the southern and northern parts precludes volcaniclastics from the depocenter. Active tectonics and inversion caused the initial Nguruman depocenter to split into two halves: the northern Musenke depocenter and the southern Pakase. Euler depth analysis indicates sedimentary formations are thicker in compartmentalized depocenters in Magadi's western and southern regions than near the eastern boundary fault. The sediment thickness range in the Koora basin is approximately 1000–3000 m, while Pakase on the western flank has a sediment thickness range of 2000–3800 m.

Long-distance recovery of nonuniform suspended load in the Middle Yangtze River owing to upstream damming

The amount of suspended sediment entering the Middle Yangtze River (MYR) was greatly reduced owing to the operation of the Three Gorges Dam (TGD) and other upstream dams, which has caused the process of sediment transport in the MYR at a severe non-equilibrium state. A detailed investigation was conducted into the transport of nonuniform suspended load in the MYR using about 30-year observed data: (i) firstly, the spatiotemporal variations in fractional sediment fluxes were investigated during the pre- and post-TGD periods. The total sediment flux decreased after the TGD operation, and the magnitude for the coarse fraction (d > 0.125 mm) was smaller than those for the fine (d < 0.031 mm) and medium (d = 0.031–0.125 mm) fractions; moreover, the sediment flux for each fraction continuously recovered along the 955-km-long reach, with the recovery distance for the coarse fraction being much shorter than the other two fractions; it was mainly attributed to the fact that the riverbed could supply abundant coarse sediment to the flow, and this fraction experienced a considerably higher recovery degree than the other two fractions; (ii) secondly, the sediment budgets for the fine, medium and coarse fractions were calculated to assess the contributions of different sediment sources to the recovery of graded sediments in the MYR. About 50 %, 29 % and 14 % of the increased fractional sediment amounts for fine, medium and coarse fractions were originated from the tributary confluence, while the remaining sediment was supplied from the riverbed during the process of channel erosion. Therefore, the recovery of suspended load was largely attributed to the supply of sediment from the riverbed, especially for the coarse fraction; (iii) finally, the impacts of the altered flow-sediment regime and the bed-material composition on sediment recovery efficiency were analysed. The sediment recovery efficiency greatly increased after the TGD operation, which was caused by the reduced sediment concentration; and the sediment recovery efficiency for the coarse fraction was much larger than those for the fine and medium sediment fractions. It is attributed to the fact that the channel can provide abundant coarse sediment to the flows in the MYR, while the sediment recovery efficiencies of fine and medium fractions were restricted by the low degree of sediment supply from the riverbed.

Decoupling external forcings during the development of Miocene fluvial stratigraphy of the North Patagonian Foreland

AbstractThe Patagonian Andean foreland system includes several intermountain basins filled with a Miocene non‐marine record deposited under syn‐tectonic conditions related to the Andean uplift and a regional climate change triggered by a rain shadow effect. Many of those basins, such as the Collón Cura basin in Neuquén Province, Argentina, present a well‐preserved fluvial record (i.e. the Limay Chico Member of the Caleufú Formation). Sedimentological and palaeomagnetic studies have allowed the interpretation of coeval transverse distributary fan and axial mixed‐load fluvial systems deposited between 10.6 ± 0.2 and 12.8 Ma. The basin infill arrangement shows that, while the axial mixed‐load fluvial system exhibits an aggradational stacking pattern, the transverse distributary fluvial fan system denotes three different orders of stratigraphic patterns: (i) large‐scale progradation of the transverse fluvial fan system over a time scale of 106 year; (ii) intermediate‐scale progradational–retrogradational transverse intra‐basinal fluvial fan episodes over a time scale of 105 year; and (iii) small‐scale transverse lobe progradation over a time scale of 105–104 year. These patterns were interpreted as transverse sediment flux variations triggered by variable external forcings. To decouple those forcings, we estimated the Collón Cura basin equilibrium time at 3–5 × 105 year and compared it with the time scale over which different external forcings varied in the Patagonian Andean and foreland regions during Miocene times. Large‐scale progradation is linked to an increase in sediment flux triggered by a long‐term tectonically driven exhumation forcing associated with the Miocene Patagonian Andean contractional phase. Intermediate‐scale progradational–retrogradational episodes are linked to variations in sediment flux due to a mid‐term tectonic forcing associated with the western fault system activity. The small‐scale fan lobe progradation is related to increases in sediment flux triggered by indistinguishable short‐term autogenic processes and/or high‐frequency tectonic and climatic forcings. This contribution shows the applicability and limitations of the basin equilibrium time concept to decouple external forcings from the geological record, considering their magnitude, nature and time scale, as well as the basin characteristics.

A century of human interventions on sediment flux variations in the Danube-Black Sea transition zone

Many deltas around the world have recorded a decreasing sediment input, mostly due to retention in dams constructed on the river or in the river basin. The Danube River has recorded a significant decrease of its sediment supply to the Danube Delta and the NW Black Sea. This study uses 210Pb and 137Cs dating, to investigate the effects of the decreasing sediment flux in lakes, lagoons, delta front and prodelta area. Both the effects of the Iron Gate I and II dams and other local factors are discussed. These results define the period of 1960-1990 as the ‘major anthropic interventions period’ in the Danube Delta. Results show a decrease in siliciclastic flux, especially in lakes, the Sahalin lagoon and the prodelta area and a general increase in the Musura lagoon and the delta front area. Sand content is also shown to decrease in most areas and is replaced by silt. The changes in sediment accumulation rates depend mostly on the hydrological connectivity of the area and the local hydrotechnical works. Overall, the local anthropic interventions in the delta affect sediment flux in the subaerial delta and the delta front, while the prodelta is affected by the overall decrease caused by interventions in the river basin. This study can contribute to improving management strategies in the area and to a better understanding of future research needs in the Danube Delta-Black Sea system.

Three-phase data augmentation for the prediction of sediment flux in mountain basins during typhoon events

Abstract Discrepancies between estimated sediment and actual yields are large. The sedimentation often causes severe damage due to a lack of on-site measurement data in the current disaster prevention system. This paper presents a robust early-warning system in which the statistical analysis used to predict sedimentation is conducted within the context of the underlying physical mechanisms. This three-phase early-warning system employs data collection, data generation, and AI (Artificial Intelligence) prediction. Data collection involves the use of HEC-HMS (Hydrologic Engineering Center – Hydrologic Modeling System) to transform measured precipitation data into flow discharge from various sub-catchments. Empirical formulas related to landslide volume and soil erosion are then used to establish suitable boundary conditions for data generation. Finally, a 2D model, SRH-2D (Sediment and River Hydraulic-Two Dimension model), is used to simulate data pertaining to temporal variations in sediment flux under various storm event scenarios. The simulated data are then used as input for the training and testing three artificial neural networks. The primary strength of this study is to improve the prediction ability in large-scale sedimentation issues in mountain rivers. These models returned good prediction results with 1–6 h lead times by interdisciplinary integration with the hydraulic and statistical fields.

Spatial and temporal changes in suspended sediment fluxes in central Chile induced by the mega drought: The case of the Itata River Basin (36°-37°S)

Central Chile has been affected by a sustained deficit in precipitation since 2010, the so-called mega drought, that has led to decreased water discharge in the fluvial basins of this region, affecting sediment fluxes. We investigate changes in sediment fluxes in the Itata River Basin (36-37°S, 11,326 km2) in central Chile over a period of 30 years (1986–2017) to evaluate the role of the mega drought in this region. We use a dataset of water discharge and suspended sediment concentration measured on a daily basis from a network of gauging stations that cover the basin from the mountain area to the river mouth. We estimated temporal variations in sediment fluxes within the basin. When comparing the pre-drought (1986–2009) and drought (2010–2017) periods, we found that annual sediment fluxes during the mega drought decreased between 28% and 67% from pre-drought values with variable intensity among the main tributaries. In addition, the season of maximum sediment transport in the basin has shifted from May–June to August during the mega drought along with a shift in the seasonality of maximum water discharge. We interpret that the precipitation deficit during the mega drought delays the recharge of the soil moisture and the establishment of favorable conditions to mobilize sediment in hillslopes. Because sediment transport in the basin occurs under conditions of lower water discharge compared to the pre-drought period, we also interpret the drought inhibits sediment transport in this system. Considering future climate projections for central Chile, it is likely that sedimentary dynamics in this basin, as well as similar fluvial basins in the region, will continue changing as the dry hydroclimatic conditions continue in the coming decades.

An integrated assessment of land use impact, riparian vegetation and lithologic variation on streambank stability in a peri-urban watershed (Nigeria)

Bank erosion is an important source of sediment and phosphorus to inland fluvial systems and is generally responsible for more than half of the total watershed sediment export. Numerous studies have quantified bank erosion and the spatio-temporal variation of sediment flux in different watersheds. However, there is sparse research to date on the linkages between bank erosion/accretion and sediment export under different land uses, especially in rapidly evolving peri-urban watersheds. This research, therefore, integrated remote sensing techniques and repeated field survey of erosion pin plots to quantify bank erosion and sediment flux in the 80 km2 Nkisi River watershed (NRW), southeast Nigeria, over a three-year period. The impact of land use change on streambank erosion was evaluated by utilising remotely sensed Landsat datasets of 2003, 2010, 2016 and 2019. Geotechnical tests were used to characterise the lithologic properties of the banks, while the Bank Stability and Toe Erosion Model (BSTEM) was used to determine the stability of the banks under various hydrological conditions and mechanical properties of the riparian vegetation. Mean bank recession rates increased from 10.7 cm during the 2017–2018 monitoring period to 17.5 cm for the 2019–2020 monitoring period. The percentage of total watershed export ascribed to bank erosion in the three stream reaches varied from 6.6 to 44.9%. The high rates of bank erosion and accretion within the NRW were attributed to rapid changes in land use, which evolved from grassland and woodland to cropland, built-up and bare land. The BSTEM accurately predicted the high erosion rates of the streambanks and showed that riparian vegetation has a mechanical effect on bank stability. However, the mechanical effect diminishes as the depth to water table rises during high streamflow events.

Quantitatively distinguishing the factors driving sediment flux variations in the Daling River Basin, North China

Understanding the riverine sediment load regime is crucial to sustainably managing fluvial-deltaic ecosystem restoration. However, in studies on global river sediment transport characteristics, small mountainous rivers (SMRs), transporting 45% of the global sediment flux into the sea, have been largely ignored. Furthermore, SMRs have hydrologic characteristics of instantaneous enormous fluxes under extreme climate, but the research on their driving factors affecting sediment transport is insufficient. Partial derivation method and multiple double mass curves were applied to a small mountainous river in North China, the Daling River to study how the three most variable factors—precipitation, vegetation coverage, and reservoirs—have quantitatively controlled sediment flux in the basin and its subregions in the last 50 years. The results of the two methods showed that the 78.55% reduction in sediment flux from 1961–1979 to 1980–2015 was due primarily to restored vegetation coverage (50.42%-61.11%), followed by reservoirs (18.13–44.09%) and precipitation (5.49–22.34%) in the Daling River Basin (DRB) and its subregions. The restored vegetation in the DRB has intercepted a large amount of sediment, reducing the sediment flux transported to the reservoirs. Besides, the Daling River releases enormous amounts of sediment during heavy rainfalls. However, increasing vegetation coverage in recent years has changed the transport characteristics of sediment into temperate changes in runoff and sediment flux under extreme climatic conditions; thus this river provides a useful example of studying the characteristics of sediment transport controlled by nature and human activities against extreme climate conditions. In the DRB, topography, lithology, and vegetation density are the motivators for the differences in sediment flux and its change rates, from upstream to downstream. These findings emphasize the crucial role of vegetation in driving sediment transport from source to sink in temperate SMRs.

Influence of Tea Plantations, Forest and Mixed Farming on Stream Flow and Sediment Loads, Case of Sondu Miriu River Basin, Kenya

The changing patterns of land cover and land use in the tropical river basin over time are critical. The hydrological phenomena at basin and sub basin scale are affected positively or negatively by dynamics of the land cover and land use patterns. Hence identifying causes and driving factors aid in taking appropriate measures to avert the impacts. This study determined the influences of sub basins dominated by tea plantations, forests and agricultural land uses in terms of streamflow and sediment flux variability in Sondu Miriu River Basin in Kenya, East Africa. Field-based investigations were conducted through sampling of flow velocities, turbidity and TSSC obtained from existing River Gauging Stations established within the three sub basins. The sub basin dominated by mixed farming land cover exhibits high turbidity approximately 620 NTU and high levels of total suspended sediment concentration (TSSC) of the order of 630 mg/l in wet seasons. The turbidity levels and TSSC were low in sub basins dominated by forest and tea plantations with approximately mean value of 17 - 29 NTU and 0.019 g/l. The sediment loads in sub basin dominated by mixed farming in the pre planting season in January to February were about 900 tonnes/day higher than that in crop growing season. In sub basins dominated by forest cover and tea plantations, sediment loads were low ranging between 2 - 7 tonnes/day. The relationship between stream flows and area under tea plantations, forests and mixed farming ranged between R2 of 0.025 and 0.16. Tea plantations and forests influence the stream flows and sediment yields in long term duration while in mixed farming variations were observed seasonally. The strong relationships between rainfall and stream flows at the sub basins ranging between R2 of 0.84 and 0.97 revealed the significance of rainfall in hydrologic response of the Sondu Miriu River Basin.

Impact of Late Pleistocene climate variability on paleo-erosion rates in the western Himalaya

It has been proposed that at short timescales of 102–105 yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained. To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya. We compare past and present 10Be-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data. Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene. We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 ± 13°) erode at lower rates of 0.1–0.4 mm/yr compared to steeper (>40°) crestal regions of the Dhauladhar Range that erode at 0.8−1.3 mm/yr. In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed. Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas.

Reconstructing environmental signals across the Permian-Triassic boundary in the SE Germanic Basin: A Quantitative Provenance Analysis (QPA) approach

Global tectonic and climatic models for the Permian-Triassic boundary (PTB) are highly debated. One of the most disputed topics is the temperature increase associated with CO 2 emissions generated by the Siberian Trap volcanism and its potential influence on chemical weathering and associated variations in sediment fluxes. By integrating crustal architecture, plate modelling, structural kinematics, and two climatic models, we reconstruct the drainage evolution of Variscan tectonostratigraphic units from the SE portion of the Germanic Basin, from which we also extract the parameters necessary to calculate sediment flux across a time-scale of 28 Ma (Guadalupian-Lower Triassic). We reconstruct the sedimentary response to climatic and tectonic perturbations using Quantitative Provenance Analysis (QPA) and integrate compositional data into a sedimentological framework, paleodrainage and paleoclimatic models. Raman heavy mineral analysis, as well as geochronology and geochemistry of detrital apatite, zircon, and rutile, document variation in drainage lithologies and sediment flux which are controlled by regional extensional tectonics and increasingly humid conditions at the PTB. The sedimentary successions of the SE Germanic Basin record climatic perturbations on a 10 4 years timescale, while the effects of tectonics are visible on a 10 6 years timescale. The interplay of climate, tectonics and lithology, and their effects on sediment production and drainage evolution resulted in changes in sediment flux from 2.3 Mt./yr during the Guadalupian (Capitanian), to 3.80 Mt./yr in the Lopingian (Changhsingian) to 7.44 Mt./yr at the end of the Lower Triassic (Olenekian). The multifaceted workflow provided in this study represents the first step towards more precise reconstructions of sediment routing systems in deep-time and provides the first ground-truthed quantification of sediment flux across the Permian-Triassic Boundary. • Drainage modifications are efficiently identified via Quantitative Provenance Analysis. • Constraining Environmental Signals in deep-time requires paleoclimatic/tectonic models. • Paleodrainage analysis provides the parameters to calculate sediment flux. • Sediment flux increases in the Lower Triassic in response to climate change.

How do modeling choices and erosion zone locations impact the representation of connectivity and the dynamics of suspended sediments in a multi-source soil erosion model?

Abstract. Soil erosion and suspended sediment transport understanding is an important issue in terms of soil and water resources management in the critical zone. In mesoscale watersheds (&gt;10 km2) the spatial distribution of potential sediment sources within the catchment associated with rainfall dynamics is considered to be the main factor in the observed suspended sediment flux variability within and between runoff events. Given the high spatial heterogeneity that can exist for such scales of interest, distributed physically based models of soil erosion and sediment transport are powerful tools to distinguish the specific effect of structural and functional connectivity on suspended sediment flux dynamics. As the spatial discretization of a model and its parameterization can crucially influence how the structural connectivity of the catchment is represented in the model, this study analyzed the impact of modeling choices in terms of the contributing drainage area (CDA) threshold to define the river network and of Manning's roughness parameter (n) on the sediment flux variability at the outlet of two geomorphologically distinct watersheds. While the modeled liquid and solid discharges were found to be sensitive to these choices, the patterns of the modeled source contributions remained relatively similar when the CDA threshold was restricted to the range of 15 to 50 ha, with n restricted to the range 0.4–0.8 on the hillslopes and to 0.025–0.075 in the river. The comparison of the two catchments showed that the actual location of sediment sources was more important than the choices made during discretization and parameterization of the model. Among the various structural connectivity indicators used to describe the geological sources, the mean distance to the stream was the most relevant proxy for the temporal characteristics of the modeled sedigraphs.

Seasonal changes of sediment fluxes in the Yangtze River: roles of precipitation change, human conservation measures in sub-basins, and large dams

Abstract Seasonal sediment flux change is a key issue in riverbed evolution and flood control. This paper analyzed variations in sediment fluxes of the Yangtze River in dry and flood seasons during 1961–2014 and the impacts of precipitation change and human interference. Sediment fluxes in both dry and flood seasons decreased by 6.8–74.6 and 14.6–38.7%, respectively, based on daily sediment observations at six mainstream stations. However, precipitation increased sediment yields in both dry and flood seasons by 0.72–4.22 t/km2 (3.5–17.8%) and 4.95–73.32 t/km2 (1.9–25.5%), respectively, based on the reconstructed sediment series without anthropogenic interference. Therefore, sediment reduction due to human conservation measures and dam construction was up to 0.07–20.74 t/km2 (0.9–64.6%) in dry seasons and 27.47–85.35 t/km2 (6.5–23.7%) in flood seasons during 1980–2002, and further reduced 3.61–41.31 t/km2 (46.0–102.9%) in dry seasons and 175.63–471.52 t/km2 (59.6–126.2%) in flood seasons after the Three Gorges Reservoir (TGR) became operational in 2003. Contributions of human activities in six subregions to the reduction of the seaward sediment fluxes were calculated. Therein, the TGR only took up 3.2 and 23.9% in dry and flood seasons, respectively, which is below expectation.

Insights on the Impacts of Hydroclimatic Extremes and Anthropogenic Activities on Sediment Yield of a River Basin

Streamflow and sediment flux variations in a mountain river basin directly affect the downstream biodiversity and ecological processes. Precipitation is expected to be one of the main drivers of these variations in the Himalayas. However, such relations have not been explored for the mountain river basin, Nepal. This paper explores the variation in streamflow and sediment flux from 2006 to 2019 in central Nepal’s Kali Gandaki River basin and correlates them to precipitation indices computed from 77 stations across the basin. Nine precipitation indices and four other ratio-based indices are used for comparison. Percentage contributions of maximum 1-day, consecutive 3-day, 5-day and 7-day precipitation to the annual precipitation provide information on the severity of precipitation extremeness. We found that maximum suspended sediment concentration had a significant positive correlation with the maximum consecutive 3-day precipitation. In contrast, average suspended sediment concentration had significant positive correlations with all ratio-based precipitation indices. The existing sediment erosion trend, driven by the amount, intensity, and frequency of extreme precipitation, demands urgency in sediment source management on the Nepal Himalaya’s mountain slopes. The increment in extreme sediment transports partially resulted from anthropogenic interventions, especially landslides triggered by poorly-constructed roads, and the changing nature of extreme precipitation driven by climate variability.

Holocene progradation and retrogradation of the Central Texas Coast regulated by alongshore and cross‐shore sediment flux variability

AbstractFifteen transects of sediment cores located off the central Texas coast between Matagorda Peninsula and North Padre Island were investigated to examine the offshore record of Holocene evolution of the central Texas coast. The transects extend from near the modern shoreline to beyond the toe of the shoreface. Lithology, grain size and fossil content were used to identify upper shoreface, lower shoreface, ebb‐tidal delta and marine mud lithofacies. Interpretations of these core transects show a general stratigraphic pattern across the study area that indicates three major episodes of shoreface displacement. First, there was an episode of shoreface progradation that extended up to 5 km seaward. Second, an episode of landward shoreline displacement is indicated by 3–4 km of marine mud onlap. Third, the marine muds are overlain by shoreface sands, which indicates another episode of shoreface progradation of up to 5 km seaward. Radiocarbon ages constrain the onset of the first episode of progradation to ca 6.5 ka, ending at ca 5.0 ka when the rate of sea‐level rise slowed from an average rate of 1.6–0.5 mm/yr. Results from sediment budget calculations and sediment transport modelling based on reasonable estimates of an ancient shoreline shape and wave climate indicate that the first progradation was a result of sand supplied from erosion of the offshore Colorado and Rio Grande deltas. The transgressive phase occurred between ca 4.9 ka and ca 1.6 ka and coincided with a major expansion of the Texas Mud Blanket, which resulted in burial of offshore sand sources and the shoreface being inundated with mud. The second, more recent episode of shoreface progradation began ca 500 years ago with a maximum rate of ca 6 m/yr. This most recent change signals a healing phase of coastal evolution from the late Holocene transgressive event. Currently, the shoreline along the central Texas coast is retreating landward at an average rate of 0.30 m/yr, indicating that the second progradation event has ended.