Sediment Transport Dynamics Research Articles

Effectiveness of stormwater control measures in protecting stream channel stability

AbstractWhile research on the hydrologic impact of different types of stormwater control measures (SCMs) is extensive, little research exists linking urbanization, widespread implementation of SCMs and channel stability in headwater streams. This study evaluated whether the unified stormwater sizing criteria (USSC) regulations in the state of Maryland, USA, which require the use of both end‐of‐pipe and distributed, small‐scale SCMs, protect channel stability. To achieve this goal, a coupled hierarchical modelling approach utilizing the Storm Water Management Model (SWMM) and the Hydrologic Engineering Center River Analysis System 6.3 (HEC‐RAS) was developed to predict changes in streamflow and sediment transport dynamics in a first‐order gravel‐bed, riffle‐pool channel. Storm event discretization revealed that 88% of observed storm events during the 16 years (2004–2020) had durations less than 18 h and that the greatest peak flows resulted from storm events with durations less than 24 h. HEC‐RAS simulation results also showed that both channel degradation and aggradation, as high as 1.2 m, will likely occur due to regulations which require the use of 24 h duration design storms with a target stormwater detention time rather than bed material sediment transport limits. Overall, this study provides valuable insights into the complex interactions between SCM practises, flow regimes and sediment transport dynamics in heavily urbanized watersheds. It is recommended that SCMs be designed using a continuous simulation model with at least 10 years of continuous rainfall data. Furthermore, to protect channel stability, the SCM design goal should focus on maintaining pre‐development sediment transport regimes across a range of flows.

Random and time-persistent depositional processes in turbidite successions: an example from the marine deep-water Aoshima Formation (Neogene, Kyushu Island, southwest Japan)

ABSTRACT The deposits of flood- and earthquake-derived subaqueous sediment gravity flows represent a significant fraction of lacustrine and deep-sea sedimentary successions, thus providing a valuable record of such natural disasters. The magnitude of these events and the thickness of the associated deposits are considered to follow a lognormal or power-law frequency distribution, whilst that of time intervals between subsequent events appear to be best approximated by a Poisson model, indicative of a random, time-independent phenomenon. However, the debate on whether the sedimentary record of these natural disasters is governed by randomness alone or whether there is some underlying stratigraphic ordering is still unsettled and requires detailed time-series analysis. This study consists of a time-series analysis of mudstone- and sandstone-dominated turbidite successions offshore a fan-delta system in the Neogene Aoshima Formation that belongs to the sedimentary fill of the forearc basin of southwest Japan. The formation consists of a monotonous alternation of very fine- to medium-grained sandstones capped by hemipelagic mudstones and, more rarely, by turbidite mudstones. The results show that the autocorrelation function of the time series suggests quasi-periodic variability in the upper sandstone-dominated part, whereas the lower mudstone-dominated part shows a white-noise-like pattern. Rescaled range analysis shows that the number of events per unit time in the lower part is characterized by a random time series, such as Brownian noise with a Hurst exponent of 0.5. In contrast, the thickness of event beds of the lower part and the thickness and the number of events of the upper part are persistent time series with a Hurst exponent > 0.5. These results suggest that the number of turbidite depositional events in the mudstone-dominated part indicates random timing, whereas its thickness time series and the sandstone-dominant part are not governed by simple stochastic processes but are affected by sea-level changes, sediment transport dynamics, and other factors such as, for example, seafloor topography.

Quantification of sediment fluxes and intermittencies from Oligo–Miocene megafan deposits in the Swiss Molasse basin

AbstractThe conglomerates preserved in alluvial fans in the Swiss Molasse basin provide crucial insights into the sedimentary dynamics of these routing systems. In particular, the architectural trends and grain sizes of such deposits reveal information on the sediment fluxes and record variations in the intermittency — a proxy for the fan's activity — that indicate on the relative importance of tectonic or climatic controls on sediment production and transport. Here, we calculated intermittencies from sediment transport dynamics using the ratio between the long‐term average and the short‐term instantaneous unit sediment fluxes during bankfull discharge conditions. For this, we collected grain size data from three palaeo‐fan systems that were active through Oligo–Miocene times and that reveal preserved proximal–distal relationships. The three fan systems, which we term the western, central and eastern fans, show significant differences in their long‐term sediment budget but equivalent magnitudes of the sediment transport dynamics expressed through the intermittency factor. The eastern fan records a low long‐term sediment flux (5.7 km2 Myr−1), which needed the fan to be active during ca. 8 h yr−1 (intermittency factor of 0.89 × 10−3). The western fan reveals a higher long‐term sediment flux (16.2 km2 Myr−1), which could have accumulated during ca. 16 h yr−1 (intermittency factor of 1.83 × 10−3), thereby reflecting a more active system. The central fan records the largest long‐term sediment flux (40.3 km2 Myr−1), where ca. 57 h yr−1 of sediment transport would be required to deposit the supplied material (intermittency factor of 6.53 × 10−3), thus representing the most active system. By relating these characteristics to the regional exhumation history, we consider that the central fan mainly recorded the transient response of the Alpine surface to the break‐off of the European mantle lithosphere slab. Contrarily, the western and eastern fans were formed during the Alpine evolution when steady‐state conditions between uplift and erosion were reached and when sediment fluxes to the basin were lower. Despite differences in the tecto‐geomorphic and climatic boundary conditions, our data suggest that these Oligo–Miocene megafans could accomplish their mean annual sediment transport work within a few hours or days per year.

Suspended sediment load modeling using Hydro-Climate variables and Machine learning

Machine learning (ML) models have the potential to improve the accuracy of Suspended Sediment Load (SSL) predictions. However, their ability to incorporate climate data to enhance SSL predictions remains underexplored. This study investigates the efficacy of ML models in modeling sediment transport using hydro-climate variables as input data. Boosted decision tree models, including Xgboost, LightGBM, and Catboost, were employed to estimate SSL using hydro-climate variables such as streamflow and precipitation, as well as maximum and minimum temperatures. The models were trained, optimized, and evaluated using either climate/streamflow data or a combination of both, encompassing 47 gauges across the contiguous United States (CONUS) between 1950 and 2022. The results demonstrate that streamflow data alone is insufficient for accurate SSL estimation in all rivers. Consequently, integrating climate data and streamflow data proved effective in predicting SSL at the daily scale across diverse climate zones with commendable accuracy. The models achieved an average Nash-Sutcliffe Efficiency (NSE) of > 0.66, Kling-Gupta Efficiency (KGE) of > 0.67, and Willmott Index (WI) of > 0.83 during the unseen (test) phase. These findings highlight the potential of ML models, particularly when combining climate data with streamflow, to enhance SSL predictions and improve our understanding of sediment transport dynamics.

Sediment provenance changes in the southwestern Okhotsk Sea since MIS 5 and their implications for sediment transport dynamics

The Okhotsk Sea, located between the Asian continent and the western Pacific, is a natural laboratory for investigating sediments source-to-sink influenced by atmosphere–ocean–land–sea ice interactions. However, despite their paleoenvironmental significance, changes in sediment provenance within the Okhotsk Sea are still debated due to the diversity of sediment sources and transport processes. Here, we investigate Sr and Nd isotope compositions in surface sediment samples from regions across the Okhotsk Sea, as well as Sr and Nd isotope compositions and elemental abundances in the sediments of core LV55‐40-1, collected from the southwestern Okhotsk Sea. Our results reveal an increasing trend of εNd values over the past ∼110 kyr, with an abrupt increase during the transition into the last deglacial/early Holocene (MIS 1). We also observed minor variations characterized by less radiogenic εNd during the glacial/stadial (G/S) periods (MIS 5d, MIS 5b, MIS 4, MIS 2), and more radiogenic εNd during the interglacial/interstadial (I/I) periods (MIS 5c, MIS 5a, MIS 3). The major terrigenous sediment sources in the northwestern Okhotsk Sea are via the Amur River and from Sakhalin Island (∼60–80%), with a minor volcanic contribution (∼20–40%) from the Okhotsk-Chukotka volcanic belt and the southern Kuril Islands/Hokkaido. Provenance variations are primarily controlled by the interplay of sea-ice drifting and ocean circulation, reflecting a dominant transport mode shift from sea ice to surface current dominance since the early Holocene. During the G/S periods with severe sea-ice condition, terrigenous materials from the Amur River and Sakhalin Island were transported to the study site, due to the southeastward drift of sea ice driven by the prevailing northwesterly winds and enhanced Okhotsk Sea Intermediate Water circulation. In contrast, during the I/I periods with moderate sea-ice conditions, an increased contribution from the Okhotsk-Chukotka volcanic belt was caused by sea-ice drifting southwestwards under the prevailing northerly and northeasterly winds, supplemented by surface currents. This study provides the first Sr-Nd isotopes record spanning the last glacial cycle in the Okhotsk Sea and it offers new insights into the relationship between sediment provenance and the interplay of sea ice and ocean currents in this region.

Insight into the dynamics of a long-runout mass movement using single-grain feldspar luminescence in the Pokhara Valley, Nepal

Abstract. Mass movements play an important role in landscape evolution of high mountain areas such as the Himalayas. Yet, establishing numerical age control and reconstructing transport dynamics of past events is challenging. To fill this research gap, we bring luminescence dating to the test in an extremely challenging environment: the Pokhara Valley in Nepal. This is challenging for two reasons: (i) the optically stimulated luminescence (OSL) sensitivity of quartz, typically the mineral of choice for dating sediments younger than 100 ka, is poor, and (ii) highly rapid and turbid conditions during mass movement transport hamper sufficient OSL signal resetting prior to deposition, which eventually results in age overestimation. Here, we first assess the applicability of single-grain feldspar dating of medieval mass movement deposits catastrophically emplaced in the Pokhara Valley. Second, we exploit the poor bleaching mechanisms to get insight into the sediment dynamics of this paleo-mass movement through bleaching proxies. The Pokhara Valley is a unique setting for our case study, considering the availability of an extensive independent radiocarbon dataset as a geochronological benchmark. Single-grain infrared stimulated luminescence (IRSL) signals were measured at 50 ∘C (IRSL-50) and post-infrared infrared stimulated luminescence signals at 150 ∘C (pIRIR-150). Our results show that the IRSL-50 signal is better bleached than the pIRIR-150 signal. A bootstrapped minimum age model (bMAM) is applied to retrieve the youngest subpopulation to estimate the paleodose. However, burial ages calculated with this paleodose overestimate the radiocarbon ages by an average factor of ∼23 (IRSL-50) and ∼72 (pIRIR-150), showing that dating of the Pokhara Formation with a single-grain approach was not successful for most samples. Some samples, however, only slightly overestimate the true emplacement age and thus could be used for a rough age estimation. Large inheritances in combination with the scatter in the single-grain dose distributions show that the sediments have been transported under extremely limited light exposure prior to deposition, which is consistent with the highly turbid nature of the sediment-laden flood and debris flows depositing the Pokhara gravels. To investigate the sediment transport dynamics in more detail, we studied three bleaching proxies: the percentage of grains in saturation 2D0 criteria, the percentage of best-bleached grains (2σ range of bMAM-De) and the overdispersion (OD). None of the three bleaching proxies indicate a spatial relationship with runout distance of the mass movement deposits. We interpret this as evidence for the lack of bleaching during transport, which reflects the catastrophic nature of the event. While not providing reliable burial ages of the Pokhara mass movement deposits, single-grain feldspar dating can potentially be used as an age range finder method. Our approach shows the potential of luminescence techniques to provide insights in sediment transport dynamics of extreme and rare mass movement events in mountainous regions.

Experimental Evaluation of Estimating Local Bed Shear Stress Using Log Law in a Straight River Channel

Bed shear stress is a critical parameter in riverine environments, directly influencing sediment transport, erosion, deposition, and flow dynamics. However, direct measurement of bed shear stress in natural rivers is nearly impossible, and estimating bed shear stress by extrapolating the Reynolds stress profile, though known for accuracy, faces practical limitations due to the challenges of measuring turbulence in natural rivers. As alternatives, indirect methods, such as global bed shear stress estimation based on bed slope and hydraulic radius (assuming uniform flow) and local bed shear stress estimation through regression of velocity profiles using the log law, have been employed. The estimation of local bed shear stress using the log law has primarily been derived from laboratory flow conditions due to the limitations in observing detailed turbulence in field conditions. Consequently, the applicability of the log-law method under field conditions has not been sufficiently evaluated. This study aims to assess local bed shear stress using the log law through a dedicated field experiment in a specific river condition, comparing it with methods utilizing the Reynolds stress profile. The experiment was conducted in a straight river channel with a width of approximately 6.5 m, a depth of 0.61 m, and a mean flow velocity of 0.56 m/s. A total of 197 points of regularly distributed velocity and turbulence data for the given cross-section were acquired using micro-acoustic Doppler velocimeter measurements with a duration of 90 s. We found that the log-law method overestimated local bed shear stress by an overall factor of 2.3 compared to the method using Reynolds stress profiles. Thus, the experimental results conclusively indicate that local bed shear stress estimated from the log law in natural river conditions could be overestimated. However, additional research is needed under more diverse flow and geometric conditions to develop a correction formula for applying the log law in estimating local bed shear stress.

Monitoring Suspended Sediment Transport in the Lower Yellow River using Landsat Observations

The spatiotemporal variations in suspended sediment concentration (SSC) in the lower reaches of the Yellow River exhibit significant variability and are influenced by reservoir operations. Understanding the spatiotemporal distribution characteristics of SSC in water holds crucial implications for environmental protection and reservoir operation management. Based on daily-scale SSC monitoring data from four hydrological stations in the lower Yellow River, this study established an SSC remote sensing model applicable to Landsat series satellite data. The independent variable of the model, Rrs(NIR)/(Rrs(G) + Rrs(R) + Rrs(SWIR)), demonstrated sensitivity to water bodies with different SSC values. Distinctive spatiotemporal characteristics in sediment transport were observed across the lower Yellow River. Spatially, the SSC values in the Sanmenxia and Xiaolangdi reservoirs were notably lower than those in other river sections, averaging 1008.42 ± 602.83 mg/L and 1177.89 ± 627.95 mg/L, respectively. Over time, the majority of the river sections (96%) exhibited decreasing trends in SSC during 1984–2022, particularly in the downstream Xiaolangdi reservoir, with average SSC values of 4265.58 ± 1101.77 mg/L in the 1980s and 1840.80 ± 2255.15 mg/L in the 2020s. Seasonal variations in SSC were prominent, with higher summer concentrations, averaging 5536.43 ± 2188.77 mg/L (2020s summer) and 814.11 ± 158.27 mg/L (2020s winter). Reductions in SSC during 1984–2022 primarily occurred in summer, weakening its seasonal variability in the lower Yellow River. Water discharge emerged as a critical factor influencing suspended sediment transport, with SSC increasing in high-water-flow months. Following the construction of the Xiaolangdi reservoir, the relationship between SSC and water discharge at different stations underwent notable alterations. This study enhances our understanding of the spatiotemporal dynamics of suspended sediment transport in the lower Yellow River, providing valuable insights for utilizing long-term Landsat series data in the dynamic monitoring of river sediment transport.

Assessment of sediment transport in Luxiapuqu watershed using RUSLE-TLSD and InSAR techniques: Yarlung Tsangpo River, China.

The Yarlung Tsangpo River Basin is characterized by its intricate topography and a significant presence of erosive materials. These often coincide with heavy localized precipitation, resulting in pronounced hydraulic erosion and geological hazards in mountainous regions. To tackle this challenge, we integrated the RUSLE-TLSD (Revised Universal Soil Loss Equation-Transportation-limited sediment delivery) model with InSAR (Interferometric Synthetic Aperture Radar) data, aiming to explore the sediment transport process and pinpoint hazard-prone sites within mountainous small watershed. The RUSLE-TLSD model aids in evaluating multi-year sediment transport dynamics in mountainous zones. And, the InSAR data precisely delineates changes in sediment scouring and siltation at sites vulnerable to hazards. Our research estimates that the potential average soil erosion within the watershed stands at 52.33 t/(hm2 a), with a net soil erosion of 0.69 t/(hm2 a), the sediment transport pathways manifest within the watershed's gullies and channels. Around 4.32% of the watershed area undergoes sedimentation, predominantly at the base of slopes and within channels. Notably, areas (d) and (e) emerge as the most susceptible to disasters within the watershed. Further analysis of the InSAR data highlighted four regions in the typical area (e) from 2017 that are either sedimentation- or erosion-prone, referred to as "hotspots." Among them, R1 exhibits a strong interplay between water and sediment, rendering it highly sensitive to environmental factors. In contrast, R4, characterized by a sharp bend in siltation, remains relatively impervious to external elements. The NDVI (normalized difference vegetation index) stands out as the pivotal determinant influencing sediment transport within the watershed, exerting a pronounced impact on the outlet section, especially in spring. By employing this approach, we gained a deeper understanding of sediment transport mechanisms and potential hazards in small watershed in uninformative mountainous areas. This study furnishes a robust scientific framework beneficial for erosion mitigation and disaster surveillance in mountainous watersheds.

Quantification of bedrock structural controls of longitudinal sediment connectivity using the probability of connectivity and sediment continuity model

The structural controls of sediment connectivity are poorly understood in low-gradient watersheds and stream networks. We developed a field- and modeling-based framework to understand the timescales and thresholds associated with the structural controls of sediment connectivity and continuity in the Inner Bluegrass region of Kentucky, USA. Field reconnaissance was carried out to assess stream morphology and sediment connectivity, which was leveraged to derive instream sediment connectivity indices for 181 pool-riffle sequences in the low-gradient bedrock stream network. Our model framework coupled a probability-based connectivity formulation with the sediment continuity formula to assess sediment transport and connectivity in the stream network. Results indicated that the bedrock system reflects an end-member in which lithology controls longitudinal stream morphology. Specifically, we found that regional morphology controls pool-riffle length scales via bedrock outcrops, which therein controls the timescales of sediment connectivity over multiple hydrologic regimes. The pool to riffle length ratio was found to be 4.6, an order of magnitude greater than the ratio for alluvial systems. The new formulation of the sediment continuity formula coupled with the probability of connectivity framework adequately captured both short-term and long-term continuous dynamics of sediment transport, as indicated by evaluation metrics with measured sediment flux and field reconnaissance. Based on the analysis of 362 riffles and pools, we found that sediment in pools upstream of bedrock outcrop barriers are disconnected 93 % of the time whereas riffles are connected and allow full continuity 99 % of the time. Longitudinal sediment connectivity within the stream network was found to be controlled by both functional connectivity and structural connectivity, which contrasts recent findings describing the controls of sediment connectivity over lateral pathways on hillslopes.

Review on different shapes of spurs and their effects on channel morphology

Abstract In this paper, the significance of the shape of spurs on flow and bed morphology is understood, accompanied by an appeal to investigate alternative shapes like L-head, T-head spurs, and hockey-shaped spurs, which could offer considerable benefits for river management. The spurs with T-head shape are found to be more efficient in reducing the bed scouring of the channel relatively, although it depends on the orientation of the spur, location of installation, and shape of the channel. Furthermore, development of horseshoe vortex is found insignificant near the base of the T-head spur dike. T-head spurs could more effectively redirect flow and prevent erosion while L-head spurs may enhance riverbank stability. This highlights the need for more investigation into how different spur shapes collectively affect river morphology, flow velocity, and sediment transport patterns. Temporal variations in bed morphology, especially the scour depth and sediment transport dynamics near spur dikes, should also be investigated to understand their changing impact better. Finally, this study provides a complete summary of existing knowledge gaps and future research initiatives relevant to various shapes of spur dikes and their role in riverbank erosion management.

Stratigraphic framework and late Holocene history of a lacustrine beach-ridge complex: Paleoclimate archives within migrating strand promontories

This paper focuses on the physiography, stratigraphy, and age composition of a migrating strandplain promontory on Lake Michigan, discussing implied changes in alongshore sediment-transport dynamics within context of regional climate data. The Zion Beach-ridge Plain, a mainland-attached system believed to have migrated by >10 km over the past 4.5 kyrs, is partitioned into distinct physiographic zones. Its structural compartmentalization into distinct ridge sets, recognized in LiDAR-based topographic datasets and subsurface reflection geophysical records, reflects a punctuated morphodynamic development that has implications for understanding groundwater-flow patterns, wetland ecology, and coastal morphodynamic evolution. The most recent physiographic boundary within the strand dates to a high-amplitude lake-level rise event (>3 m in magnitude) that coincided with a regional shift in dominant storm-wind direction. The abrupt juxtaposition of young, high-relief dune-ridge terrain against old, low-relief wetland meadow attests to increased rates of littoral sand transport under conditions of heightened wave and current energies. Ongoing work to refine the geochronology of this and similar events is underway and stands to enhance our understanding of late Holocene coastal evolution. Strandplains are studied globally as important coastal paleoclimate archives, yet in the Great Lakes region the emphasis has been on embayed systems. While sheltered environments (e.g., bedrock-confined strandplains) foster high preservation potentials, optimal for paleohydrographic reconstructions from progradational sequences, the complex depositional architectures of strandplain promontories may provide information on open-water processes not contained within the former.

The effect of compound channel shape for local scouring and flow dynamics using NaysCUBE-3D RANS at Downstream Tukad Unda River Bali Province

The prediction of sediment transport and flow dynamics are important issues in channel design as the local scouring has an important effect on the shape of the channel, especially on the compound channel. Tukad Unda River in Bali has river section in the form of compound channel. It consists of two sections with different dimension, the main channel and the flood plain. These dimensional differences cause two different flows. Transformation of flow velocity and turbulence cause movement of sediment transport, generates a complex 3D flow structure in the boundary of main channel and floodplain. This study uses morphology data in Tukad Unda River and simulated by using NaysCUBE. NaysCUBE is a three-dimensional numerical modeling which use the Reynold Average Navier Stoke equation (3D RANS model). The result in this study shows the different pattern of flow dynamics and local scouring in the boundary between main channel and floodplain as the concrete block located in that boundary compare to the nature compound channel. In the 40-minute simulation, the nature compound channel represented significant deformation of the river bed in the interface area, with a decrease in elevation of 0.01 meters higher than the compound channel with concrete blocks. while the increase in elevation in the main channel is around 0.09 meters lower than the compound channel with concrete blocks. Application of concrete blocks can be useful to reduce local scour at the interface as the impact of compound channel flow characteristics.

Multi‐Year Tracing of Spatial and Temporal Dynamics of Post‐Fire Aeolian Sediment Transport Using Rare Earth Elements Provide Insights Into Grassland Management

AbstractAeolian sediment transport occurs as a function of, and with feedback to ecosystem changes and disturbances. Many desert grasslands are undergoing rapid changes in vegetation, including the encroachment of woody plants, which alters fire regimes and in turn can change the spatial and temporal patterns of aeolian sediment transport. We investigated aeolian sediment transport and spatial distribution of sediment in the surface soil for 7 years following a prescribed fire using a multiple rare earth element (REE) tracer‐based approach in a shrub‐encroached desert grassland in the northern Chihuahuan desert. Results indicate that even though the aeolian horizontal sediment mass flux increased approximately three‐fold in the first windy season in the burned areas compared to control areas, there were no significant differences after three windy seasons. The soil surface of bare microsites was the major contributor of aeolian sediments in unburned areas (87%), while the shrub microsites contributed the least (<2%) during the observation period. However, after the prescribed fire, the contribution of aeolian sediments from shrub microsites increased considerably (∼40%), indicating post‐fire microsite‐scale sediment redistribution. The findings of this study, which is the first to use multiple REE tracers for multi‐year analysis of the spatial and temporal dynamics of aeolian sediment transport, illustrate how disturbance by prescribed fire can influence aeolian processes and alters dryland soil geomorphology in which distinct soils develop over time at very fine spatial scales of individual plants.

Representing the impact of Rhizophora mangroves on flow in a hydrodynamic model (COAWST_rh v1.0): the importance of three-dimensional root system structures

Abstract. Coastal wetland vegetation modulates water flow by exerting drag, which has important implications for sediment transport and geomorphic dynamics. This vegetation effect on flow is commonly represented in hydrodynamic models by approximating the vegetation as an array of vertical cylinders or increased bed roughness. However, this simple approximation may not be valid in the case of Rhizophora mangroves that have complicated three-dimensional root structures. Here, we present a new model to represent the impact of Rhizophora mangroves on flow in hydrodynamic models. The model explicitly accounts for the effects of the three-dimensional root structures on mean flow and turbulence as well as for the effects of two different length scales of vegetation-generated turbulence characterized by stem diameter and root diameter. The model employs an empirical model for the Rhizophora root structures that can be applied using basic vegetation parameters (mean stem diameter and tree density) without rigorous measurements of the root structures. We tested the model against the flows measured by previous studies in a model mangrove forest in the laboratory and an actual mangrove forest in the field, respectively. We show that, compared with the conventional approximation using an array of cylinders or increased bed roughness, the new model significantly improves the predictability of velocity, turbulent kinetic energy, and bed shear stress in Rhizophora mangrove forests. Overall, the presented new model offers a more realistic but feasible framework for simulating flows in Rhizophora mangrove forests with complex root structures using hydrodynamic models.

Abrupt and persistent shutdown of the thermohaline forcing during MIS5e in the Adriatic Sea: Insights from shallow-water sapropel sediments

During the Quaternary, the Eastern Mediterranean Sea (EMS) experienced cyclical events of stagnation driven by natural climate variability. The resulting deoxygenation left well-preserved evidence in the sedimentary record as organic carbon-rich deposits referred to as sapropels. Although drastic modifications in the degree of dense-water formation over the EMS shelves exerted first-order control on the deoxygenation, most of the focus has been traditionally placed on the deep EMS. To provide a shallow-water perspective, here we investigated the sapropel S5 in the Adriatic shelf (borehole PRAD1-2) deposited during MIS5e (129-116 ka). This archive is strategically located in a region where the Northern Adriatic Dense Water (NAdDW) interacts with the seabed before cascading across the continental slope. We used Zr/Rb and MgO/Al2O3 to assess bottom current energy and north-to-south sediment transport dynamics, both regulated by the changes in NAdDW production intensity. In addition, we used stable isotopes (δ13C and δ18O) of foraminifera, redox sensitive elements (U, Mo and Sb), foraminifera assemblages as well as alkenones to reconstruct the paleo-environmental conditions during the S5 formation.Our study provides an unprecedented reconstruction of the physical forcing controlling the deoxygenation during the S5 formation. Results reveal that the shutdown of the NAdDW occurred in a few centuries (0.67 ± 0.22 kyrs), when freshening of surface waters combined with warming of winter temperatures mutually hampered the dense water formation. A few centuries after the NAdDW shutdown, the Adriatic shelf experienced euxinic waters for about 2 kyrs followed by a progressive reoxygenation that lasted 4 kyrs. We explain this second phase as a general recovery driven by increased surface salinity over the EMS combined with winter cooling. This favoured surface water mixing without, however, producing dense water in the Northern Adriatic and thus collectively the interruption of the dense water production lasted for 6 kyrs since the onset of MIS5e. Overall, our finding highlights that the thermohaline forcing responded to climate change much quicker than inferred by earlier studies that suggested instead a millennial-scale prelude necessary to develop stagnation. In addition, our results provide solid evidence about the large-scale impact of the deoxygenation during S5 that is capable of invading the continental shelf. Comparison with the latest regional models illustrates how none of the future simulations covering different climate change scenarios reproduces an event over the EMS margins comparable with what described in this study.

Textural characteristics and sediment transport dynamics of the sandstones of the Nkporo group, Southern Anambra Basin (Nigeria): evidence for the upper cretaceous sea-level lowstand

The Anambra sedimentary basin is one of the major inland basins in Nigeria. It covers an area of approximately 30,000 square kilometres and is named after the Anambra River, which traverses the basin. The geology of the basin is characterized by a complex sequence of sedimentary rocks that record a long history of deposition and tectonic activity. Detailed and systematic field investigation of its rock sequences exposed at Leru junction and adjoining localities revealed five dominant lithologic units consisting of massive sandstone facies, argillaceous sandstone facies, fissile black shale and mudstone facies, planar and ripple laminated sandstone facies, and massive and pebbly sandstone facies. The area is dominated by transgressive facies characterized by alternating sequences of thinly and parallel laminated fissile black shales, mudstones, and argillaceous sandstones overlain by regressive deposits dominated by massive and partly pebbly sandstones. The transgressive sequences perhaps represented shelf mud sedimentation that was probably interrupted by episodic influxes of sands rich in argillaceous materials transported down the shelf probably by shoreface waves or gravity-driven flows, while the regressive facies may have probably been emplaced by liquefied sand flows of the frontal slope of an advancing mouth bar. The erosion of the shelf deposits by the pebbly sandstones possibly reflected seaward migration of shallow distributary channels during sea-level low stand. Thus, facies transition from argillaceous sandstones to massive and pebbly sandstones within the continental shelf perhaps signified a fall in the relative sea level possibly triggered by the erosion of the shelf or perhaps a high rate of sediment supply.

Modeling bioinfiltration surface dynamics through a hybrid geomorphic-infiltration model

Abstract Bioinfiltration systems are an increasingly prevalent mechanism for urban stormwater mitigation. One major challenge for the sustainability of bioinfiltration systems is erosion and channelization due to high bed shear stresses developed during large storm events. Sedimentation within these systems could also impact their performance as fine sediment may clog pathways necessary for infiltration. Understanding the geomorphology, shear stress, and sediment flux in the system can help predict maintenance needs associated with erosion and deposition. The current study introduces a framework for addressing this problem by combining a sediment transport model, FaSTMECH, with the Green-Ampt infiltration model. A comparison of observed and predicted ponding depths shows very good agreement (median Nash–Sutcliffe efficiency coefficient = 0.93) and demonstrates the ability of this novel framework in predicting the hydraulics and morphology within a bioswale bioinfiltration system. The framework introduced in this study opens the door to understanding sediment transport dynamics within a bioswale, which has the potential to advance planning and design to minimize impacts due to excessive erosion or deposition within bioswale bioinfiltration systems.

Impacts of human activities and climate change on water and sediment evolution in four large subtropical river basins in China

Human activities and climate are two key factors affecting hydrological and soil erosion processes. Understanding their impacts on water discharge and sediment transport is very important for sustainable development of watersheds, particularly in subtropical regions with high precipitation and high sediment loads. We here compared the long-term dynamics of water discharge and sediment transport in four large contiguous watersheds in subtropical China and explored the importance of the main influencing factors including climate, nature endowment such as geology, and human activities. Significant differences have been observed between watersheds in terms of sediment and water discharge (p < 0.001). Pairwise comparison among the four basins demonstrated significant differences in sediment modulus among 5 of the 6 pairs (p < 0.05). The sediment modulus in the Lishui Basin was significantly higher than those in other basins, mainly due to the substantial presence of steep slopes in the mountainous region, which is prone to soil erosion. Temporally, sediment transport in the four basins was well synchronized showing significant decreasing trends with abrupt change points (p < 0.001). In contrast, no trends and abrupt change points were detected in water discharge, mainly influenced by precipitation. Human activities played a predominant role to the reduction of sediment transport (80% to 102%) compared with those of climate (-2% to 19%) across the four basins. Additionally, our study also showed land cover had various basin-independent impacts on the change of sediment transport. Through cross-basin comparisons of the long-term changes in water discharge and sediment transport, our study revealed the similarities and differences in their driving mechanisms, providing valuable information for land use planning and water resource management in large subtropical basins.

Catchment and climatic influences on spatio-temporal variations in suspended sediment transport dynamics in rivers

Abstract Suspended sediment concentration (SSC) is an important attribute for water resources management. However, the interactions between climate and catchment characteristics that control the temporal variability of SSC in rivers are not fully resolved. The study aim is to evaluate how these variables influence spatial and seasonal variations in SSC dynamics at a continental scale. Daily SSC (mg/l) and site attribute data from 120 sites (USA) with minimum 10 years of record (1971–2000) were analysed. New indicators of SSC dynamics (magnitude and frequency) were developed and applied annually and seasonally. Geographically weighted regression (GWR) models were created for each ordinary least squares (OLS) regression model, and GWR coefficients were analysed by ecoregion. Land cover, rainfall and erosivity, baseflow index and soil texture were the most common variables in the OLS models. GWR coefficients displayed significant variation across the continent. Agricultural cover was positively associated with low frequency SSC events, while urban and forest cover predicted higher frequency events, except in the desert areas. PPT30 was generally a negative predictor for SSC magnitude, except the marine west coasts forests. These findings on catchment and climate controls on SSC will support future predictive models of SS transport dynamics.