Channel Sediment Research Articles

Quantitative analysis of crevasse-splay systems from modern fluvial settings

ABSTRACTAlthough crevasse splays are a common constituent of many fluvial and fluvio-deltaic systems, they remain less well understood than the channel deposits in those settings, especially with respect to controls on their occurrence, distribution, and geometry. The current study aims to redress this balance and investigate controls on 1) splay formation and occurrence and 2) splay size and geometry. The study has used Google Earth-based satellite imagery to examine crevasse-splay deposits from eight modern fluvial systems. A total of 1556 crevasse splays were identified using imagery from 1984 to 2020. Most of the splays (c. 70%) occur on the outer sinuous river bank with offtake angles ranging from 10° to 140° (mean 75°) to the channel flow direction. Three different types of splays have been identified: i) single crevasse splays, ii) laterally amalgamated crevasse splays, and iii) crevasse-splay complexes. The areal extent of splay bodies varies widely and ranges from less than 1 km2 up to 221 km2. The single crevasse splays are the primary and smallest form of splay, with an average area of 0.61 km2. Compensational stacking or progradation significantly increase the splay area and form laterally amalgamated splays and splay complexes, respectively. The average areal extent of laterally amalgamated splays is 1.33 km2, and of splay complexes, 39 km2.The climate, discharge, floodplain morphology, vegetation, trunk channel slope, sinuosity, and sediment load primarily control the occurrence, geometry, and dimensions of crevasse splays. Results demonstrate that sparse or no floodplain vegetation favors the formation of elongated tongue-shaped crevasse splays while densely vegetated floodplains produce more lobate splays. The highest splay frequency occurs in systems where the river experiences sudden high magnitude variation in discharge, has a low cross-sectional area, and noncohesive bank materials. Larger splay size is correlated with lower river slope angles and higher sinuosity, discharge, and floodplain relief. Channel size has little influence on the extent of splays. This work suggests that autogenic factors such as trunk-channel slope and sinuosity are more influential in arid–semiarid settings while allogenic factors such as discharge are important in temperate–equatorial settings.

Optimization of river environmental management based on reinforcement learning algorithm: a case study of the Yellow River in China.

Generating scientific management strategy contributes to the sustainable development of river ecological environment. In this study, a multi-objective coupled water and sediment regulation model aiming at minimizing sedimentation and inundation loss as well as maximizing ecological value in the lower Yellow River has been developed. A reinforcement Q-learning algorithm was used to obtain optimized strategies from the multi-objective of sediment reduction, flood control and ecological restoration under different hydrological years. The results showed that the simulated channel sedimentation is very close to the measured value, which proves the applicability of the developed model. Under dry, normal and wet hydrological year, the effects of various regulation strategies on silt reduction, flood control and ecological restoration were obviously different. The regulation scheme of discharge at 3700 m3/s was verified to be suitable for dry and wet year, and that of discharge at 2600 m3/s was more suitable for normal year. Increasing the spacing of the beach area was better in normal year and wet year. Our findings suggested optimized strategies to address environmental challenges of the lower Yellow River in different hydrological years. This paper provides a reliable reference for improving the management of the lower Yellow River.

Textural and geochemical characteristics of the Yikpata river channel sands, Nigeria

The Yikpata river is one of the major rivers that empty into the River Niger, Nigeria. River Niger cuts across the Bida Basin thereby contributing to the alluvium deposits found within the Bida Basin. The properties and compositions Yikpata river channel sediments input in the River Niger where alluvium deposits are found is yet to be documented. Furthermore, the geology of where the studied river is located is sparse. Therefore, the textural, petrological, and geochemical analyses were used to examine the Yikpata river channel sediments for their compositions and characteristics in other to infer their provenance, tectonic settings and chemical weathering intensity as well as give information about sediments that are been transported as recent alluvium along River Niger in the Bida Basin. This study likewise lays some foundations for the comprehensive assessment of watershed environmental quality. This study revealed that the Yikpata river channel sediments are moderately well to poorly sorted sediments and were classified as sub-arkose based on log Na2O/K2O vs SiO2/Al2O3. Low CIA, PIA, ICV, Rb/Sr values, and ternary plot of A-CN-K demonstrate that the river sands were derived from low to moderately weathered source rocks and the major-element-based discrimination diagrams revealed that sediments were from a rift tectonic setting (passive margin). Additionally, the river sediments are derived from weathered sedimentary rocks that are of the felsic source, based on the major element discriminates functions, TiO2 vs Zr, Al2O3/TiO2, La/Sc, La/Co, Th/Sc, Cr/Th and LREE/HREE. The pollution status of the river from the sediments revealed that the river is currently not polluted and the sediment is not toxic.

The Response Mechanisms of Topographic Changes in Small Loess Watershed under Rainstorm

This paper uses a small watershed entity model to simulate the rainfall experiment and combines traditional water and sediment observation and terrain three-dimensional laser scanning technology to reveal the characteristics of erosion and sediment yield in small watersheds and the law of channel sediment transport and quantitatively describe the response mechanism of terrain changes in small watersheds to the layout of silt dams and rainfall intensity. Rainfall intensity with three types (30, 60, and 120 mm/h) under three soil conservation measure types (none dam, single dam, and double dams) was simulated, and a small watershed entity model was adopted. The changes in topography were recorded by a Focus 3D laser scanner (Faro) for each experiment. The main results were as follows: (1) Soil erosion under the effect of rainfall occurs on the slope of the watershed and in the gully, while deposition usually occurs on the gentle slope of the gully or in low-lying areas. (2) When the runoff volume is small, deposition occurs easily in the gully, and vice versa. (3) The increase in the number of silt dams deployed has a small effect on the rate of runoff yield on the small watershed, but the limitation on the rate of sand production is especially obvious. Silt dam measures have a good flood and sand reduction effect on small- and medium-intensity rain, but for high-intensity rain, their runoff and sand reduction effect will be reduced, so rainfall is the dominant factor in the formation of soil erosion. Our results provide the scientific basis for identifying key parts of soil erosion and for the rational arrangement of soil and water conservation measures in loess areas.

Record of a dense succession of drowning phases in the Alpstein mountains, north-eastern Switzerland: part I—the Lower Cretaceous Tierwis Formation (latest Hauterivian to latest Barremian)

In the Alpstein massif of north-eastern Switzerland, a complete succession of uppermost Hauterivian to uppermost Barremian condensed hemipelagic sediments crops out. This succession is known as Tierwis Formation, comprising in ascending order, the Altmann and Drusberg members. The sedimentary succession bears a number of fossiliferous glauconite- or phosphate-rich beds. A large number of newly discovered ammonites from these key beds and from several poorly explored levels of the Tierwis Formation allows for a new age calibration. The new dating as well as revised sequence stratigraphic interpretations and geochemistry contribute to a better understanding of the lithostratigraphic complexity of the Tierwis Formation and its spatio-temporal relationship with the Schrattenkalk Formation. The new lithostratigraphic observations, backed by ammonites, shows that the Altmann type-section and the Tierwis paratype-section do not cover the same stratigraphic interval because of dynamic sedimentation processes as erosion and sedimentation in submarine channels. We suggest that a phosphatic conglomerate in the Dursberg Member of middle late Barremian age corresponds to the Chopf Bed, which we recognised for the first time in the Alsptein massif. The Drusberg Member strongly thickens toward the southeast and progressively covers an upward extended stratigraphic range. Furthermore, the new dating of the key-surfaces and beds highlight a dense succession of drowning phases which occurred through the latest Hauterivian to late Barremian time interval. The latest Hauterivian onset of the glauconite-rich sedimentation of the Altmann Member is associated with a first major drowning phase, followed by the Faraoni oceanic anoxic event. The change of sedimentation to a rhythmic marl-limestone alternation of the Drusberg Member takes place over a polyzonal phosphatic conglomerate. This conglomerate coincides with a second major drowning phase and the onset of the Mid-Barremian Event, which is calibrated on the Tethyan ammonite biozonation.

Field testing a High-Frequency acoustic attenuation system for measuring fine suspended sediments and algal movements

Acoustic measurements of suspended sediment have the potential to allow remote, autonomous monitoring of sediment movements at much higher temporal resolution than traditional manual sampling methods. Although suspended sands present a challenging measurement problem due to their logarithmic distribution with depth, fine clay sediments are distributed evenly throughout a stream cross section, making them amenable to point measurements. In order to improve measurement capabilities for fine sediments in stream channels, The National Center for Physical Acoustics at The University of Mississippi has developed a remote, autonomous acoustic system to monitor fine sediments transported in streams. The system was tested on the Middle Rio Grande near San Acacia, New Mexico, and in Goodwin Creek in Panola County, Mississippi. The acoustic instruments were compared to sediment concentrations from physical samples in both deployments. Diurnal patterns were found in the acoustic signals from the Middle Rio Grande, and a follow up experiment at The University of Mississippi Biological Field Station was used to investigate the potential effects of algal biomass on acoustic attenuation measurements. The results showed diurnal patterns in attenuation were associated with patterns in light, temperature, and dissolved oxygen. These results combined with information from the literature indicate diel movement of algal colonies in the water column of some water bodies may interfere with high-frequency acoustic measurements in natural environments and that acoustic methods have the potential to allow ecological researchers to evaluate mass algal movements in the field. Results from Goodwin Creek demonstrate that the acoustic system is able to provide measurements of sediment concentration with high temporal resolution that track well with expected sediment transport patterns in response to discharge hydrographs.

Spatial and Temporal Variability of Bed Exchange Characteristics of Fine Sediments From the Weser Estuary

Sedimentation of fine-grained sediments in estuaries is a natural physical phenomenon influenced by biogeochemical processes. In the estuarine turbidity maximum (ETM), enhanced net deposition of sediments is observed even in areas with higher hydrodynamic exposure, such as the navigational channel. Maintenance dredging is a common method to maintain the navigational channel, which requires large financial effort and has potential negative impacts on the environment. Research at the Institute for River and Coastal Engineering addresses the challenge of understanding the processes leading to net sedimentation and accumulation in estuarine navigational channels in reach of the ETM. In this contribution, investigations of bed exchange properties of estuarine cohesive sediments conducted in field and laboratory studies are presented. The results provide rarely available and estuary-specific parameters characterizing sediment transport, mainly related to erosion processes. By performing field campaigns within the ETM of the Weser estuary, cores of freshly deposited sediments have been sampled from two sites (Blexer Bogen and Nordenham) along the center of the navigational channel. Sediment characteristics (grain size distribution, water content, loss on ignition, density profiles) have been derived, and the erodibility of the deposits is investigated both quasi in situ and in the laboratory using an erosion microcosm system. Erodibility experiments are run in a closed system so sediment concentration above the lutocline increases during the experiment. This is a unique feature of this study, and it is expected to produce more natural characteristics of net erosion. By proving the reproducibility of the natural structure of the deposited sediments (stratification and density profiles) in the laboratory, systematic studies for analyzing the sensitivity of determined parameters (shear stresses and erosion rates) to varying environmental conditions (settling conditions and density) could be performed. Temporal development of suspended sediment concentration and erosion rates is the main result of the erodibility experiments, from which we derive bandwidths for erosion parameters, like floc erosion rate, critical shear for floc erosion, and critical shear for mass erosion.

Long-term investigation of morphodynamic variations of a tidal inlet by remote sensing: A case study of the Meidani Inlet, Hormozgan, Iran

Barrier-island inlets are among the most common inlets worldwide. The variation of the inlets, different sediment bypassing mechanisms, and lack of data are some issues for using numerical modeling in all cases. Remote sensing techniques are helpful for analytical investigation and making time series of the study area for categorizing the inlets and defining the morphological processes. The current study employs a feasible method for investigating tidal inlets, evaluates the morphodynamic changes, and applies the method to the Meidani Inlet in Iran. In this study, Landsat images from 1972 to 2019 were acquired and corrected to investigate changes in the ebb-tidal delta by employing the shoreline determination method, performing bathymetry in shallow areas, evaluating the extracted profiles in specific locations within the ebb-tidal delta, and comparing the Landsat image series at various times (change detection). In order to illustrate the morphological changes during the study period, a conceptual model was proposed. The conceptual model presents three reiterated actions of the ebb-tidal delta that varied from 15–25 years due to different environmental conditions. Regional waves, tidal, and wind data were analyzed in detail using Landsat image intervals to investigate the effects of factors causing changes and instability in the cyclic morphodynamic behavior of the Meidani Inlet and characterize the region’s environmental behavior pattern. By employing the method mentioned above, preparing a temporal inlet channel profile and sedimentation trend in the ebb-tidal delta, the Meidani Inlet is determined to be a mixed-energy inlet and a possibility of long-term behavior is predicted. Eastward main inlet channel and the whole ebb-tidal delta migration is the strongest possibility based on the remote sensing investigation over the investigated period.

Beach Placer Deposit Modelling using Geospatial Methods: A Case Study from Brahmagiri Mineral Sand Deposit, Puri District, Odisha

Abstract An integrated approach has been attempted for 3D representation of various geo-exploration data pertaining to Brahmagiri Mineral Sand Deposit (BMSD). GIS platforms are utilized to represent the prime depositional environments of sediments under which Total Heavy Minerals (THM) concentrated. In recent times, deeper exploration by sonic drilling has been carried out in the main sand bar of the deposit and retrieved huge lithological data. Different 3D visualization of exploration data using various geological Softwares (ArcGIS, Rockworks and Datamine) carried out.Understanding the morphology of the deposit is carried out using the topographic representation on GIS platform. Discontinuous linear dune ridges are present across the deposit. Sand column explored at an average depth of 40m represents the variety of depositional environment (lagoonal, barrier and beach) within basin. Lithological correlation for the entire (20km) stretch of BMSD carried out and major sand units have been summarized for the area. Heavy mineral (HM) concentrations in each sand column and their correlation using geospatial methods classify the trend and extent of mineralization into two potential zones (Zone 1 and Zone 2) depth wise. This study emphasizes the relationship between surface and subsurface manifestation of exploration data which reveals that BMSD could be part of Barrier bar system having different sub-depositional environments as back-barrier, barrier beach and inlet channel which are controlling the total heavy mineral concentration at various depths. Upper zone of ore body is confined to beach regime whereas lower zone is controlled by combination of beach, back-barrier and inlet channel sediments.

The Late Cretaceous—Miocene supra‐salt structures in Block M, Lower Congo Basin (Congo, West Africa) and the controls on channel development

The Lower Congo Basin is a typical passive continental margin basin of West Africa and is currently the focus and hot spot of deep‐sea oil and gas exploration. Previous studies have focused on the deformation process and mechanism of the salt rock itself, but have ignored the interaction process between the faults and salt diapirs. The direct influence of the interaction process between the faults and salt diapirs on oil and gas exploration is reflected in the control of the reservoir distribution. In recent years, most of the oil and gas discovered in the Lower Congo Basin have been concentrated in the Oligocene–Miocene turbidite reservoirs, and the distribution of channel sand bodies is largely affected by supra‐salt tectonic activity. In this study, Block M in the Lower Congo Basin was selected for study. Based on the 3D seismic, drilling, and logging data, the typical structural styles and stress mechanisms were analysed. The 2D Move software was used to restore the tectonic evolution history and, based on this, established the interaction model of salt diapirs and faults, and summarized the action modes of diverse types of sedimentary channels. The research results are expected to lay the foundation for follow‐up studies on the laws of hydrocarbon accumulation.

Identification of Bacterial Flora and Metabolic Function of Sediments in Different Channels of Duliujian River Basin, Tianjin

Bacterial communities are highly sensitive to environmental changes, but their metabolic functions may be convergent under similar ecological conditions. In order to test this environmental attribute of the bacterial community and verify the feasibility in using the bacterial metabolic data to divide functional units at the river basin scale, the surface sediments in three continuous spatial units of the main stream (MS), left tributary (LT), and right tributary (RT) of the Duliujian River basin were selected as the research objects. Therefore, 16S rDNA high-throughput sequencing and the PICRUSt platform were used to analyze the bacterial diversity and metabolic function of sediments in different units. The results showed that there were no significant differences for the Shannon and Simpson indices between the different river channels (P>0.05); however, the bacterial diversity indices of Chao1, ACE, Observed_species, and PD_whole_tree of LT and RT were significantly higher than those of the MS (P<0.05). Moreover, the dominant bacterial phyla were not significantly different among the different river channels. In the present study, a total of 41 metabolic pathways were predicted based on the KEGG database, among which 34 metabolic pathways such as membrane transport, amino acid metabolism, and carbohydrate metabolism were significantly different. The functional metabolic abundance was higher in MS than that in RT and LT (P<0.05); however, there was no significant difference between those of RT and LT (P>0.05). Except for exchangeable phosphorus and nitrate nitrogen, there were no significant differences in other physicochemical properties among the different river channels (P>0.05). Furthermore, pH and iron/aluminum-phosphorus were found to significantly affect the bacterial structure, and SOM and TN were found to significantly affect the bacterial metabolic function. Overall, the sediments of MS and tributaries (LT and RT) of the river were clearly divided into level-1 and level-2 groups, indicating that the metabolic abundance of the bacterial community can be used as the key indicator in the division of functional units at the river basin scale. This study provided a theoretical basis and technical support for ecological functional division and management in coastal river basins.

Impacts of Human Activities and Environmental Changes on Spatial-Seasonal Variations of Metals in Surface Sediments of Zhanjiang Bay, China

This study investigated the total concentrations and geochemical compositions of metals (Cd, Cr, Cu, Ni, Pb, Zn, Fe and Mn) in surface sediments of Zhanjiang Bay (ZJB) in spring and summer, to assess the contamination status, mobility and influencing factors of spatial-seasonal changes of these metals. The average total concentration for each studied metal in the surface sediments of ZJB was 0.173 μg/g for Cd, 58.25 μg/g for Cr, 17.11 μg/g for Cu, 16.89 μg/g for Ni, 28.70 μg/g for Pb, 67.91 μg/g for Zn, 30.18 mg/g for Fe, and 275.5 μg/g for Mn during the investigation period. Generally higher total concentrations of metals were found in the channel and coastal sediments of ZJB compared with those in the central ZJB, which may be probably resulted by the input of Suixi river, domestic sewage and industrial wastewater. The grain size compositions and TOC contents also had influences on the distributions of metals in ZJB. In the channel, total metals and reducible and bioavailable fractions of metals generally showed decreased concentrations in summer compared with those in spring, suggesting the release of metals from sediments. Organic matter degradation and Fe and Mn (hydr)oxides reduction processes may contribute much to this phenomenon. Relatively high proportions of Cd and Zn (average of 21.7% and 14.6%, respectively) were associated with the acid soluble fraction, indicating their high risk to the environment. The combined assessment results of enrichment factor, contaminated factor and the percentages of acid soluble fraction indicated that Cd and Zn in the surface sediments of ZJB were generally contaminated and they had medium to high risk to the environment. The average values of pollution load index in the channel, coastal and central ZJB were 1.28, 0.93 and 0.81, respectively, indicating the deterioration of surface sediments in the channel of ZJB. More attention should be paid on the metals in surface sediments of the channel of ZJB.

3D Sedimentary Architecture of Sandy Braided River, Based on Outcrop, Unmanned Aerial Vehicle and Ground Penetrating Radar Data

Ground Penetrating Radar (GPR) is a geophysical method that uses antennas to transmit and receive high-frequency electromagnetic waves to detect the properties and distribution of materials in media. In this paper, geological observation, UAV detection and GPR technology are combined to study the recent sediments of the Yungang braided river study area in Datong. The application of the GPR technique to the description of fluvial facies and reservoir architecture and the development of geological models are discussed. The process of GPR detection technology and application includes three parts: GPR data acquisition, data processing and integrated interpretation of GPR data. The geological surface at different depths and scales can be identified by using different combinations of frequencies and antenna configurations during acquisition. Based on outcrop observation and lithofacies analysis, the Yandong Member of the Middle Jurassic Yungang Formation in the Datong Basin has been identified as a typical sandy braided river sedimentary system. The sandy braided river sandbody changes rapidly laterally, and the spatial distribution and internal structure of the reservoir are very complex, which has a very important impact on the migration and distribution of oil and gas as a reservoir. It is very important to make clear the characteristics of each architectural unit of the fluvial sand body and quantitatively characterize them. The architectural elements of the braided river sedimentary reservoir in the Datong-Yungang area can be divided into three types: Channel unit, bar unit and overbank assemblages. The geological radar response characteristics of different types of sedimentary units are summarized and their interfaces are identified. The channel sediments form a lens-shaped wave reflection with a flat at the top and convex-down at the bottom in the radar profile, and the angles of the radar reflection directional axes are different on both sides of the sedimentary interface. In the radar profile, the deposit of the unit bar is an upward convex reflection structure. The overbank siltation shows a weak amplitude parallel reflection structure. The flood plain sediments are distributed continuously and stably in the radar profile, showing weak reflection characteristics. Different sedimentary units are identified by GPR data and combined with Unmanned Aerial Vehicle (UAV) detection data, and the establishment of the field outcrop geological model is completed. The development pattern of the diara is clarified, and the swing and migration of the channel in different stages are identified.

Controls on near-surface and burial diagenesis of a syn-rift siliciclastic rock succession: A study from Permian Barren Measures Formation, Southern India

Distinct processes during the syn-depositional sedimentation and the post-depositional diagenesis determine the fabric of a clastic sedimentary rock. Temporal and spatial variations in any of these processes cause development of specialized characters in the sedimentary rocks. The Permian Barren Measures Formation in the Pranhita-Godavari Valley in southern peninsular India, is characterized by signatures of early to late diagenetic cementations within coarse-grained sandstones and mudstones. An integrated petrographic-geochemical study is carried out to understand the post-depositional near-surface and burial processes. Facies architecture manifests sedimentation in fluvial (channel, bar and overbank) to tide-influenced fluvio-tidal mixed depositional condition. Post-depositional near-surface early diagenesis changes include – (i) partial dissolution of detrital grains, (ii) biotite kaolinization, (iii) localized extensive ferruginous cementation, (iii) calcite cementation, and (iv) development of rhizocretions observed at different stratigraphic levels. These point to the role of meteoric water during the pre-burial stage that changed the pore water chemistry within the fluvial channel and bar sediments, along with onset of pedogenic (calcretization) processes in the vadose zone within the fine-grained overbank deposits. Marine (tidal) water influx in fluvial regime under a semi-arid climate modified the pore water chemistry. Shallow burial diagenetic changes, under elevated temperature and pressure include – (i) extensive calcite cementation in intergranular pore spaces and fractures, and (ii) late phase partial dissolution producing secondary porosity. A predictive model is derived to decipher the role of post-depositional changes in developing potential reservoir heterogeneity in a fluvio-tidal mixed depositional system.

Industrial and Technological Waste Mismanagement and Its Implications for the Present and Future Geology of the Earth: A Field Study of the Ekulu River in Enugu Metropolis, Southeastern Nigeria

Aim: Field study of the Ekulu River in the coal mining and industrialized part of the Enugu Metropolis was done in order to evaluate the impacts of industrial and technological waste mismanagement on the present and future geology of the Earth.&#x0D; Methodology: The study includes field observation, sampling and description of nature and composition of the sediments from the ancient/abandoned and present/active river channels.&#x0D; Result: The findings of the study shows incorporation of non- decomposable particles such as nylon, plastics, leather, chicken feather, pieces of broken bottles, electrical wire, coal chips, aluminum foil, cloth materials, metallic containers, coal tar and chippings scraped off from failed road etc as part of the present river channel sediments in an active areas such as Onyeama Mine and surroundings and Abakpa Bridge.&#x0D; Conclusion: Occurrence of these debris referred to as “Technofossils” in the sediments and sedimentary rocks that is or will be preserved in these fluvial settings now and in the near future will serve as one of the evidences of human impacts on the Earth System through the use of technological inventions and industrial revolution. These anthropogenic materials in the present river channel sediments are markers which support the argument on a clear shift in geologic time from Holocene to Anthropocene, a proposed human influenced geologic epoch.

Morphological adjustments of the lower Orba River (NW Italy) since the mid-nineteenth century

A multi-temporal and multi-scale analysis based on historical data collection and review, maps and aerial photograph interpretation, field observations, topographic surveys, and GIS investigations was performed to (i) examine the morphological evolution of lower Orba River since the mid-nineteenth century, (ii) identify its controlling factors, and (iii) correctly interpret ongoing hydrogeomorphic conditions under a river management perspective. The riverbed experienced overall slight and non-homogeneous morphological adjustments, along with some horizontal displacements, up to the early twentieth century (Phase 0). Subsequently, two phases of channel degradation were identified. The first, from the 1920s to the 1950s (Phase 1), is characterized by slight narrowing (12.3%), the beginning of incision, and rare and little lateral migration. The second, between the 1950s and the years around 2010 (Phase 2), displays significant channel incision (mostly from the 1950s to the 1970s, from 0–1 m to 4–5 m), weak narrowing (21.0%), and only minor horizontal displacements. Over the last decade (Phase 3), widespread slight channel widening (3.4%, up to 25.7% at the reach scale) associated with the absence of a generalized bed-level variation trend was observed. The study reach has exhibited a single-thread or transitional channel since the mid-nineteenth century. Channel incision was mainly caused by extensive in-channel sediment extractions primarily carried out between the 1950s and the early 1980s at the reach and catchment scales. The long-term presence of widespread channelization works was recognized as the main reason why overall little riverbed planform adjustments occurred during the whole period investigated. The most recent dynamics were triggered by floods and were interpreted as the river response to human-induced alterations. The riverbed changes that occurred during the twentieth century match the channel adjustments commonly experienced by Italian single-thread and transitional channels as a response to various types of human disturbances. However, the detected morpho-evolutionary phases of the Orba River are only partially in agreement with those reported in the literature for other Italian rivers affected by similar anthropogenic pressures, as some differences exist in timing and magnitude of prevalent channel adjustments. An overall slight potential for channel recovery, priorities for rehabilitation, and the main objectives for the next-decades management were identified. This research provides insights into the medium- and short-term morphological evolution of Italian rivers, and its outcomes represent an essential piece to drive river management towards sustainable and effective river restoration and risk mitigation measures framed within a larger, multidisciplinary, and objective-based context. A wide spectrum of both consolidated and newly developed GIS-based planform metrics was considered to assess the channel morphological evolution in detail, providing an operative reference framework for future investigations.

STUDY OF CONTAMINATION BY METALLIC ELEMENTS IN COASTAL SEDIMENTS: CASE OF THE COTONOU CHANNEL

Coastal aquatic ecosystems are environments increasingly affected by human activities due to urban discharges and their use as dumps. The objective of this study is to determine the profiles of metallic elements concentration (Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, and Pb) of Cotonou channel sediments and to evaluate their quality. For this, surface sediments (0-5cm) were sampled at 13 sites along the channel. Thus,Geoaccumulation Index (Igeo), Enrichment Factor (EF) and Sediment Pollution Index (SPI) were calculated to assess the chemical quality of these sediments. The metal contents of the sediments follow the following order of abundance: Fe &gt;Al&gt;Mn&gt; Zn &gt;Cr&gt;Cu &gt; Co&gt; Ni &gt;Pb&gt; As&gt; Cd. The Igeo geo-accumulation index and the Enrichment Factor FE reveal moderate polymetallic contamination by several elements. The results show Fe, Co, and Ni being the most concerning. As for the Sediment Pollution Index (SPI), it reports low, moderate and high pollution of sediments.

Loss of geomorphic diversity in shallow tidal embayments promoted by storm-surge barriers.

Coastal flooding prevention measures, such as storm-surge barriers, are being widely adopted globally because of the accelerating rise in sea levels. However, their impacts on the morphodynamics of shallow tidal embayments remain poorly understood. Here, we combine field data and modeling results from the microtidal Venice Lagoon (Italy) to identify short- and long-term consequences of flood regulation on lagoonal landforms. Artificial reduction of water levels enhances wave-induced sediment resuspension from tidal flats, promoting in-channel deposition, at the expense of salt marsh vertical accretion. In Venice, we estimate that the first 15 closures of the recently installed mobile floodgates operated between October 2020 and January 2021 contributed to a 12% reduction in marsh deposition, simultaneously promoting a generalized channel infilling. Therefore, suitable countermeasures need to be taken to offset these processes and prevent significant losses of geomorphic diversity due to repeated floodgate closures, whose frequency will increase as sea levels rise further.

Diagenetic facies classification and characterization of a high-temperature and high-pressure tight gas sandstone reservoir: A case study in the Ledong area, Yinggehai Basin

A high-temperature and high-pressure tight gas sandstone reservoir, located in the Ledong area of the Yinggehai Basin, shows considerable resource potential. However, the diagenetic characteristics of this reservoir remain unclear. In this study, reservoir petrology and diagenetic characteristics were systematically investigated through different experimental methods. Further, the porosity and diagenetic evolution models were constructed. The methods employed included petrophysical analysis, observation of core and thin sections, and grain-size distribution analysis. Furthermore, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, cathodoluminescence, carbon and oxygen isotope analysis, digital image analysis, mercury injection capillary pressure tests, and micro-CT imaging were also employed. In the study area, gravity-flow channel sediments composed of feldspathic litharenite primarily developed in a restricted submarine canyon. And tight sandstones in target formation have an average porosity of 9.34% and permeability of 1.79 mD. Mechanical compaction and cementation (mainly illite and ferrocalcite) were regarded as crucial roles in the densification process. Further, the diagenetic evolution model indicated that the reservoir underwent a high degree of thermal diagenetic evolution. Five diagenetic facies types were classified and characterized at multiple scales. Moreover, a vertical distribution model of different diagenetic facies was also developed considering the overpressure, depth of formation, thickness and frequency of mudstones, and injection concentration of the CO2. This study helps to improve the understanding of the diagenetic characteristics and diagenetic facies types in high-temperature and high-pressure clastic reservoirs.

Assessing Groundwater Dynamics and Hydrological Processes in the Sand River Deposits of the Limpopo River, Mozambique

Drought and water scarcity constrain the socioeconomic development of many (semi-)arid regions of Southern Africa. Moreover, due to the increase of water withdrawals upstream, the Limpopo River is no longer perennial in Mozambique. Fortunately, its river bed can store significant amounts of freshwater, because of the occurrence of thick and often coarse sand deposits formed through pronounced dryland weathering, erosion, and sedimentation in the river channel. Such so-called “sand rivers” exist in many parts of semi-arid Africa and have varying configurations and hydrological conditions. The current research aims to comparatively assess the Limpopo sand river aquifer in terms of recharge and discharge dynamics, storage potential, and interactions with the surface water flow, as a function of its specific hydrological conditions: its large size, location downstream of a dam releasing permanent ecological flow, and its relatively undeveloped state. For this purpose field investigations were carried out at two sites, involving groundwater level measurements, 2D geoelectrical surveying, water chemical and stable isotope analysis, and sediment classification. These investigations reveal the occurrence of medium to coarse sands with thicknesses that can reach 10–15 m, dropping to 2–5 m in the main river channel, underlain by less permeable clays and silts. Analysis of the river level shows that large parts of the sand river are flooded almost every year, providing optimal conditions for recurring and rapid recharge of the system (confirmed by infiltration tests) through two mechanisms: direct infiltration of surface runoff and lateral flow toward non-flooded areas of the river valley, also confirmed by the chemical and isotope study. During the dry season, groundwater provides base flow to the river and the average water level drop in the sand river system is about 1.8 m. The connectivity with the river margins is limited, due to the clayey nature of the river bank sediment, but local paleochannels can result in a continuation of sand layers. Hydrological processes controlling the water quality are evapoconcentration, mixing of discharging groundwater with the perennial surface water flow, and to a minor extent mineral dissolution, with the groundwater being of Ca-HCO3 type. The combination of the large size, high permeability, and frequent flooding of the sand river deposits provides optimal conditions for groundwater abstraction, requiring additional assessment of the impact on riparian vegetation and downstream users.