Scour Features Research Articles

Scour Features due to Inclined and Curved Rock Sills at River Bends

Scour Features due to Inclined and Curved Rock Sills at River Bends

Moats & comets - A methodology to explore for submerged prehistory at sea floor erosional features formed at artificial reefs, Atlantic continental shelf, GeorgiaUSA.

Our primary objective is to demonstrate a method that uses marine processes, principally seafloor scour, to broadly expose prehistoric landforms and associated localities. Too often, the loss of prehistoric strata to scour processes such as ravinement during broad-scale, continental shelf transgressions, are decried without the recognition of the potential for erosion at the local scale can expose those same strata for systematic study. The analysis of sea floor erosional features formed around artificial reefs by turbulent flows in the Georgia Bight have used interferometric side-scan sonar (SSS), Remotely Operated Vehicles (ROVs), ultra-high-definition videography (UHD), and sedimentological, palynological, paleontological, archaeological analytical techniques. These techniques were integrated within a geoarchaeological methodology focused on exploring the Continental Shelf for preserved evidence of prehistoric landforms, flora and fauna once thereon. A stepwise protocol was developed to first gather interferometric side-scan sonar data to be then processed by commercial software packages such as HYPACK Hydrographic and HYSWEEP together with HYSCAN and SONAR Wiz software. The sonar mosaics were imported to ArcGIS/QGIS software to characterize scour features/targets around artificial reefs that had exposed paleo-land surfaces previously obscured by the modern palimpsest sand sheet. Analysis of scours and depressions - “moats and comets” - adjacent to reef structures were evaluated using the profile tool within the HYPACK-HYSWEEP editor package. Symbology for the bathymetric raster layers was edited to provide a clear contrast and measurement at scour features. Measured GIS images were then classified as to scour extent and depth with respect to prevailing current directions responsible for producing turbulence. A ranking of the artificial reefs by factors such as scour depth and extent was used to guide subsequent investigation by ROVs. Sediment cores and grab samples were collected, and those samples underwent particle size analysis (PSA), macro-and micro-botanical analyses. All data – geophysical, GIS, video and geological – were collated and synthesized to produce an assessment of the potential of sea floor scour features to expose previously buried geomorphological/geological, paleontological and/or archaeological features of interest.

Bedforms and sediment dynamics under reduced sediment input and estuarine engineering: the case of the Bou Regreg estuary, Morocco

The Bou Regreg riverine estuary constitutes a microtidal environment located within an urban region and characterized by limited sediment inflow from its catch basin hinterlands. The construction of the Sidi Mohamed Ben Abdellah (SMBA) dam has notably diminished sediment supply, especially coarser fractions. In light of these conditions, this study aimed to classify sediment types according to the Folk and Ward classification, stratify morphometric parameters and temporal fluctuations based on dune types, and ultimately evaluate the sediment dynamics driving observed bedform variations. Using an integrated approach, data collection involved various techniques, including CTD profiling, bottom videography, side-scan sonar imaging, sub-bottom profiling, and Van Veen bottom grab sampling. The bed morphology includes segments of smooth bed, erosional and dredged bottom, localized scour features, and submarine dune fields, displaying notable heterogeneity. Acoustic seabed reflections indicated two bedform clusters with maximum lengths of 42.6 m and heights of 1 m. Flow velocities were linked to the presence of 2D and 3D dune forms. Morphological variations encompassed straight, sinuous, and barchan dune configurations, mainly asymmetric with NNW–SSE seaward orientation. Sediment mean size fluctuations spanned from muddy to medium sand deposition. The findings revealed the intricate interplay of dynamics shaping dune field configurations and the heterogeneous dispersion of bedforms throughout the estuary likely due to a sharp decline of sediment discharge caused by the dam upstream and coastal engineering. The study emphasizes the dynamic nature of dunes, highlighting their sensitivity to shifting hydrodynamic conditions and sediment availability, leading to morphological fluctuations over time.

Hydro-environmental Characteristics for Flows Over Inclined Block Carpet

A significant oxygenation is associated with flows over most of the hydraulic structures due to the entrainment of air into the flow. Block carpets are low-head hydraulic structures, which aim to control the sediment transport, dissipation of flow energy and contribute to considerable oxygenation. Studies have been conducted to investigate the effects of block carpet on the hydraulic jump, scouring phenomenon and variation in the hydro-environmental parameters. The study also investigates the aeration efficiency created by the hydraulic jump inflows over block carpet. Dissolved oxygen as a principal hydro-environmental parameter was measured and analysed upstream of the block carpet, along the BC (heel, mid and toe) and post hydraulic jump in the channel bed. The results show that in the tested range of slopes (20%, 25% and 30%) and block carpet material, the flow has attained a maximum aeration efficiency of 0.181. The characteristics of the hydraulic jump for different inclinations of block carpet and for two-channel bed sediment sizes were observed. Predominantly, for higher discharges and steep slopes, considerable scouring takes place downstream of the block carpet. Based on the physical features of the downstream scour, a qualitative description of three scour forms has been distinguished.

Scour Features at Wood Bundles

Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters.

Experimental Analysis of Scour Features at Chevrons in Straight Channel

Eco-friendly river restoration structures are used to create localized scour pools which serve as fish nurseries and promote biodiversity. In this category, chevrons are relatively new structures designed to maintain navigability in rivers. The scour hole formed in the wake region of chevrons can either act as a disposal site for dredged material or as a resting spot for different fish species. However, only few studies are present in the literature dealing with the scour mechanism due to chevrons. Therefore, this work aims to analyze the scour features at equilibrium, under different hydraulic conditions and transversal locations in a straight channel. Tests were conducted with both isolated and multiple chevrons in series arrangement. Scour morphology types were classified and their fields of existence were established as well. A detailed dimensional analysis was conducted, allowing us to identify the main parameters governing the scour phenomenon and derive a novel equivalent densimetric Froude number. Finally, empirical equations were developed to predict the maximum scour depth and length as well as the maximum dune height.

Geometry of obstacle marks at instream boulders—integration of laboratory investigations and field observations

AbstractObstacle marks are instream bedforms, typically composed of an upstream frontal scour hole and a downstream sediment accumulation in the vicinity of an obstacle. Local scouring at infrastructure (e.g. bridge piers) is a well‐studied phenomenon in hydraulic engineering, while less attention is given to the time‐dependent evolution of frontal scour holes at instream boulders and their geometric relations (depth to width, and length ratio). Furthermore, a comparison between laboratory studies and field observations is rare. Therefore, the morphodynamic importance of such scour features to fluvial sediment transport and morphological change is largely unknown. In this study, obstacle marks at boulder‐like obstructions were physically modelled in 30 unscaled process‐focused flume experiments (runtime per experiment ≥ 5760 min) at a range of flows (subcritical, clear‐water conditions, emergent and submerged water levels) and boundary conditions designed to represent the field setting (i.e. obstacle tilting, and limited thickness of the alluvial layer). Additionally, geometries of scour holes at 90in‐situboulders (diameter ≥ 1 m) located in a 50‐km segment of the Colorado River in Marble Canyon (AZ) were measured from a 1 m‐resolution digital elevation model. Flume experiments reveal similar evolution of local scouring, irrespective of hydraulic conditions, controlled by the scour incision, whereas the thickness of the alluvial layer and obstacle tilting into the evolving frontal scour hole limit incision. Three temporal evolution phases—(1) rapid incision, (2) decreasing incision, and (3) scour widening—are identified based on statistical analysis of spatiotemporal bed elevation time series. A quantitative model is presented that mechanistically predicts enlargement in local scour length and width based on (1) scour depth, (2) the inclination of scour slopes, and (3) the planform area of the frontal scour hole bottom. The comparison of field observations and laboratory results demonstrates scale invariance of geometry, which implies similitude of processes and form rather than equifinality.

Effect of debris accumulation on scour evolution at bridge pier in bank proximity

Abstract Large debris transported by flood affects scour features at bridge piers and increases the risks of structural failure. Geometric characteristics of the debris and the relative position of the pier with respect to the river bank are important parameters for the scour process. The interaction between the water flow and debris accumulation increases the shear stress, turbulence and consequently enhances the scour depth at the pier. This paper aims at analyzing such effects on scour evolution at bridge piers. To this end, two series of tests were carried out under clear water condition with different debris geometries and percentage blockage ratios. Experimental evidences showed that the pier position only influences scour evolution and equilibrium morphology for low water depths. Conversely, its effect becomes negligible for scour at bridge piers with debris accumulation and higher water depths. Useful practical relationships have been derived, with satisfactory prediction capability of the scour evolution for all the tested configurations.

Morphological characteristics of eco-friendly protected basins downstream of block ramps in river bends

Block ramps are hydraulic structures used to control the sediment transport in rivers and to dissipate flow energy. Moreover, they serve as useful structures to maintain and preserve ecological habitat and to facilitate fish migration. In the past, scour features of both protected and unprotected stilling basins of block ramps have been studied for straight river branches. Sometimes, these structures are placed at channel curves where the flow distribution is characterized by a significant asymmetry, resulting in a scour formation in correspondence with the channel bank, that needs to be carefully predicted and controlled to minimize the risk of a structural failure. Apparently, so far there are no studies focusing on the scour mechanism occurring in protected stilling basins downstream of block ramps in river bends. Hence, this paper aims at investigating the effect of stilling basin protection on the scour process under a combination of different hydraulic conditions, block ramp configurations and locations of the protection structure along the stilling basin. To this end, tests were carried out by placing the block ramp in a curved channel and varying both the flow discharge and the downstream tailwater depth. The downstream stilling basin was protected by introducing a rock sill at various distances from the ramp toe. It has been found that the equilibrium scour morphology mainly depends on hydraulic conditions and it is also influenced by the position of the rock sill in the basin. A classification of different morphological configurations is proposed as well. Finally, an empirical equation is provided to estimate the maximum scour depth under the tested configurations.

Mass transport deposit or complex channel system? A case study of the 3D Nimitz seismic survey, Taranaki Basin, New Zealand

The Taranaki Basin is well known for studies examining the seismic stratigraphy, depositional and erosional features, and tectonic frameworks linked to the New Zealand (NZ) continent. We have examined a “funny looking thing” (FLT) that we associate to be consistent with that of a braided channelized system. We observe this feature within the 3D Nimitz survey, located in the northern Taranaki Basin, off the western continental coast of North Island, NZ. The FLT occurs within Quaternary deposits of the Whenuakura Formation, which are interpreted to reflect shelfal topset sediments. It is underlain by the Giant Foresets Formation of Pliocene to Pleistocene age, which are described as large-scale progradational and aggradational continental successions that migrated west to northwest in a basinward direction. It comprises a shelf-to-slope succession of claystone to siltstone with argillaceous sandstone intervals defining an overall coarsening-upward succession. The FLT within the Whenuakura Formation is characterized by chaotic facies in cross section, which shares characteristics with potential mass-wasting events. However, further analysis using seismic attributes improved the spatial and stratigraphic architecture of the FLT, which favored a complex channelized system interpretation over a mass transport deposit complex. Geological feature: Braided channel system Seismic appearance: Splayed structurally controlled feature, with internally abundant, continuously lineated patterns on horizon slice Alternative interpretations: Erosional scour Features with similar appearance: Mass transport deposit Formation: Whenuakura Age: Pleistocene–Recent Location: Offshore Taranaki Basin, North Island, New Zealand Seismic data: Nimitz 3D seismic survey; obtained by Origin Energy Ltd. Analysis tools: Variance and curvature attributes

Hydrodynamic Structure with Scour Hole Downstream of Bed Sills

Experimental turbulence measurements of scour hole downstream of bed sills in alluvial channels with non-cohesive sediments are investigated. Using an Acoustic Doppler Velocimeter (ADV), the flow velocity-field within the equilibrium scour hole was comprehensively measured. In this study, we especially focus on the flow hydrodynamic structure in the scour hole at equilibrium. In addition to the flow velocity distribution in the equilibrium scour hole, the turbulence intensities, the Reynolds shear stresses, the turbulent kinetic energy, and the turbulent length scales are analyzed. Since the prediction of equilibrium scour features is always very uncertain, in this study and based on laboratory turbulence measurements, we apply the phenomenological theory of turbulence to predict the maximum equilibrium scour depth. With this approach, we obtain a new scaling of the maximum scour depth at equilibrium, which is validated using experimental data, satisfying the validity of a spectral exponent equal to −5/3. The proposed scaling shows a quite reasonable accuracy in predicting the equilibrium scour depth in different hydraulic structures.

Bridge pier scour under pressure flow conditions

AbstractThe probability of pressurized flow conditions occurring in existing bridges is forecast to increase due to possible changes in extreme precipitation, storm surges, and flooding predicted under climate change scenarios. The presence of a pressure flow is generally associated with scouring processes in proximity to the bridge. Scouring can also occur around bridge piers, possibly causing infrastructure failure. Although there is a vast literature on bridge pier scour and pressure flow scour, only a few studies have investigated their combined effect. This study will provide a new overview of the main features of bridge pier scour under pressurized flow conditions, based on laboratory experiences. Special focus is placed on the analysis of the flow features under pressure and free surface conditions and to the temporal evolution of the scour. A comparison with existing literature data is also conducted. The results highlight the nonlinear nature of scour processes and the need to consider pressurized flow conditions during structural design, as the interaction between pressure flow and the bridge pier strongly influences scour features and leads to scour depths much greater than the sum of the individual scours created only by pressure flow or pier presence.

Gravitational, erosional, sedimentary and volcanic processes on the submarine environment of Selvagens Islands (Madeira Archipelago, Portugal)

Volcanic oceanic islands are the emerged portions of large volcanoes that rise abruptly from the ocean floor. Although the geological record of these islands provide some insights into the evolution of their entire volcanic edifices, for a complete picture, it is essential to study the islands' submarine pedestals and surrounding settings. In this study we document the submarine morphology of the Selvagens Islands (Madeira Archipelago, Portugal) and relate it with their subaerial evolution, in order to gain a more complete insight on the evolutionary history of these islands. To this purpose, we employed bathymetric surfaces, backscatter mosaics and subbottom profiler data integrated with geological observations of the subaerial part of the islands. Our study reveals the presence of a complex submarine morphology composed mainly of two deeply eroded central volcanoes – the edifices of Selvagem Grande and Selvagem Pequena – and a less eroded saddle-like ridge related to a fissural volcanic system located between them. Other secondary landforms generated by volcanism, erosion, gravitational collapses, and possible faulting activity, are also present. Whilst the building of the two central volcanoes relates to the older volcanic stages of both islands, the fissural system, with a general NE-SW trend, is probably contemporaneous of the younger volcanic stages of Selvagem Grande. The shelf of Selvagem Grande also features the eroded remains of numerous relatively young volcanic cones, seemingly forming several NW-SE and NE-SW lineaments, the same direction observed onshore for the younger volcanic stage of this edifice. The shelves' break of both Selvagens was affected by multiple landslide scars and channel headwalls. The channels constitute a large drainage network that fans out in a radial pattern along the flanks of both central edifices. In the deeper parts of this submarine drainage, large sediment wave fields are observed in some locations with wavelengths of 300–1,900 m and 2–45 m in height; these tend to form cyclic steps that change gradually downslope to antidunes, and their origin is attributed to sediment density flows that suffer hydraulic jumps when their channel confinement ends and the slope gradient decreases from ~7° to ~2.5°. Several scour features are also found at 3,300–4,000 m water depth, being 3–20 km in width, 10–20 km in length, rectangular or U-shaped in cross-section and 40–100 m deep. They occur around the base of the submarine edifices, where seafloor gradients change to 3.0°–0.5°. Their origin is also related to hydraulic jumps of unconfined sediment density flows, which are able to erode the seafloor and create these features. These morphologies are a testimony to how volcanic, erosional and depositional processes conjugate to shape the flanks of a very long-lived volcanic island system, one of the oldest in the North Atlantic Ocean.

FVCOM model simulation of local scouring around bridge pile

Scouring is one of many damages that water can cause. Scouring can occur as a consequence of bridge pile existence. The problem on local scour around single pier will be studied by using FVCOM numerical model. This study objective is to find out how accurate FVCOM model to predict local scour behavior. FVCOM model is based on the finite volume method to solve Navier Stokes, Meyer Peter Muller, and Exner equations. FVCOM computed numerical result then will be verified with computed and measured data in previous numerical (FSUM model) and experimental study. Results from this study show FVCOM model were successfully simulated typical features of local scour around piers such as downflow and wake vortex, but failed to simulate horseshoe vortex. Both computed numerical (FSUM and FVCOM) results are then compared with measured experimental data for its magnitude and time-series of maximum scour depth. FVCOM result shows value 0.99 r-squared correlation and 5.96 percent average error, and FSUM result shows value 0.98 r-squared correlation and 6.82 percent average error. Therefore, it can be deduced that FVCOM successfully predict local scour depth and its time-series and proven that FVCOM is more accurate than FSUM model.

New insights on coral mound development from groundtruthed high-resolution ROV-mounted multibeam imaging

Currents play a vital role in sustaining and developing deep water benthic habitats by mobilising food and nutrients to otherwise relatively barren parts of the seabed. Where sediment supply is significant, it can have a major influence on the development and morphology of these habitats. This study examines a segment of the Belgica Mound Province, NE Atlantic to better constrain the processes affecting a small-sized cold water coral (CWC) mound habitat and conversely, the hydrodynamic influence of CWC mounds on their own morphological development and surroundings. Here, we utilise ROV-mounted multibeam, ROV-video data, and sediment samples to investigate current processes, mound morphology, density and development. Detailed mapping shows that the area may have the highest density of coral mounds recorded so far, with three distinct mound types defined based on size, morphology and the presence and degree of distinct scour features. A residual current of 36–40 cm s−1 is estimated while large scour features suggest low-frequency, high-magnitude events. These 3 mound types are i) smaller mounds with no scour; ii) mounds with scour in one to two distinct directions and; iii) larger mounds with mound encircling scour. The differing mound types likely had a staggered initiation where younger mounds preferentially developed near clusters of pre-existing mounds. Given the high density of these small CWC mounds, we support the hypothesis that over time, this clustering may eventually lead to these mounds coalescing into larger coral mound features.

Regional-scale groundwater investigations for the Crossrail project

The Crossrail project includes a new underground railway through the heart of London. It will connect with 110 km of new or upgraded sections of surface rail to Reading, Shenfield and Abbey Wood. Ground investigations for the central tunnelled sections began during the 1990s and continued until 2011 according to a strategy that was based on a review of other major tunnelling projects and best practice. The level of detail in the investigations and subsequent groundwater monitoring varied according to local geological complexity and design requirements. A total of 1019 boreholes were drilled to a maximum depth of 114 m and contained a total of 1314 piezometers. Of these, 233 piezometers were installed during the 1990s and 1081 piezometers and several other monitoring types were installed in the following phase during the 2000s. The ground and groundwater investigation strategy included the following: (1) groundwater monitoring to accurately determine the multiple aquifer regional groundwater regime with varying underdrainage, in the west; (2) tidal monitoring in the east, where an unconfined single aquifer system predominated; (3) investigation of the impact of local features (e.g. fault zones and scour features); (4) determination of long-term groundwater trends. Crossrail data were supplemented with third-party data to provide more information on the far field and provide more definition on larger scale geological structures (e.g. faulting at Farringdon and Limmo). Installation trials were conducted on several types of installation, and their performance for monitoring multiple aquifers, in particular during permeability tests, is discussed. For large projects such as Crossrail, long-term performance of groundwater monitoring installations is critical for establishing a baseline in addition to obtaining information for design. Annual reviews of data backed up by remediation works allowed many installations to provide reliable groundwater data for up to a decade prior to the construction phase.

Effect of unsteady flow conditions on scour features at low-head hydraulic structures

The study of scour mechanism downstream of low-head control structures is a fundamental topic for hydraulic engineers. Generally, the analysis of the scour process is conducted under steady flow conditions, assuming that the maximum discharge is occurring for sufficient time to reach the equilibrium scour configuration. Nevertheless, in rivers the scour process generally occurs in correspondence with a flood event, which is characterized by discharge varying with time. This last condition is still less studied and analyzed in terms of effects on bed morphology. Researchers mainly focused on the maximum scour depth assuming that it occurs in correspondence with the peak discharge, but they rarely took into account the evolution of the scour process under unsteady flow conditions. The aim of the present paper is to analyze the evolution of scour morphology under unsteady flow conditions, and compare it with that obtained under steady flow conditions. In particular, three structure typologies were tested: a stepped gabion weir with upstream impermeable filtering layer, a straight rock sill, and a curved rock sill. The results showed that the scour phenomenon deeply depended on inflow conditions. Nevertheless, it was also shown that the equilibrium morphology of the downstream stilling basin is essentially the same under both unsteady and steady flow conditions if the duration of the unsteady event is enough long.

Ichnology of an Eocene shallow marine passive margin condensed section, eastern Gulf coastal plain, Alabama, U.S.A.

Exposures of the Eocene Tallahatta Formation in southern Alabama (U.S.A.) provided the opportunity to document the ichnologic character of a highly condensed, passive-margin transgressive systems tract and its two component parasequences. The studied succession is dominated by variably glauconitic, fossiliferous muddy sands deposited in shallow marine shelf settings. Thorough bioturbation and abundance of mud indicate quiet background conditions, whereas admixed sand and localized scour features indicate periodic influence by bottom currents. Parasequences, delineated based on vertical trends in glauconite abundance, are bounded at their bases by flooding surfaces marked by Thalassinoides-dominated firmground ichnofabrics but internally host moderately diverse Cruziana ichnofacies assemblages. Recurring softground ichnofossils include Asterosoma, Chondrites, Diopatrichnus, Ophiomorpha, Planolites, Rosselia, Teichichnus, Thalassinoides, and enigmatic composite structures, the distributions and abundances of which vary within and between parasequences. Increasing prominence of Diopatrichnus and Rosselia towards parasequence tops reflects organismal responses to environmental changes associated with shallowing and/or enhanced preservation potential of shallow-tier structures in response to increased sedimentation rates. Maximum sediment starvation during deposition of the uppermost parasequence is reflected by peaks in burrow density, softground ichnofossil diversity, and concentrations of Entobia-bored shells and Teredolites-bored logs. Enigmatic composite burrows and common Thalassinoides with linings and/or meniscate backfills are ubiquitous and may be diagnostic of sediment starvation and prolonged habitation of slowly accreting substrates.

Facies and depositional architecture according to a jet efflux model of a late Paleozoic tidewater grounding-line system from the Itararé Group (Paraná Basin), southern Brazil

During the Late Paleozoic, the Gondwana supercontinent was affected by multiple glacial and deglacial episodes known as “The Late Paleozoic Ice Age” (LPIA). In Brazil, the evidence of this episode is recorded mainly by widespread glacial deposits preserved in the Paraná Basin that contain the most extensive record of glaciation (Itararé Group) in Gondwana. The Pennsylvanian to early Permian glaciogenic deposits of the Itararé Group (Paraná Basin) are widely known and cover an extensive area in southern Brazil. In the Doutor Pedrinho area (Santa Catarina state, southern Brazil), three glacial cycles of glacier advance and retreat were described. The focus of this article is to detail the base of the second glacial episodes or Sequence II. The entire sequence records a deglacial system tract that is represented by a proximal glacial grounding-line system covered by marine mudstones and shales associated with a rapid flooding of the proglacial area. This study deals with the ice proximal grounding-line systems herein interpreted according to lab model named plane-wall jet with jump. Detailed facies analysis allowed the identification of several facies ranging from boulder-rich conglomerates to fine-grained sandstones. No fine-grained deposits such as siltstone or shale were recorded. According to this model, the deposits are a product of a supercritical plane-wall outflow jet that changes to a subcritical jet downflow from a hydraulic jump. The hydraulic jump forms an important energy boundary that is indicated by an abrupt change in grain size and cut-and-fill structures that occur at the middle-fan. The sedimentary facies and facies associations show a downflow trend that can be subdivided into three distinct stages of flow development: (1) a zone of flow establishment (ZFE), (2) a zone of transition (ZFT), and (3) an established zone (ZEF). The proximal discharge is characterized by hyperconcentrated-to-concentrated flow due to the high energy and sediment-laden nature of the flows. At the transitional zone, a hydraulic jump produces a rapid shift of conglomeratic to sandy facies with associated scour features. Towards the distal zones, the jet detaches to originate a vertical turbulent jet characterized by more diluted flows. Discussion of fan facies and architecture within a framework of jet-efflux dynamics provides an improved understanding of grounding-line fans systems that produce coarse-grained strata commonly enclosed by fine-grained rocks. The results have clear implication in terms of prediction of facies tract and geometry of oil and gas reservoirs deposited under similar conditions. And also can be useful to identifying the position of a glacial terminus through time.

Characterization of Dredged Oyster Shell Deposits at Mobile Bay, Alabama Using Geophysical Methods

The need for disposing materials dredged from ship channels is a common problem in bays and lagoons. This study is aimed at investigating the suitability of scour features produced by dredging oyster shell deposits in Mobile Bay, Alabama, to dispose excavated channel material. A study area approximately 740 by 280 m lying about 5 km east of Gaillard Island was surveyed using underwater electrical resistivity tomography (UWERT) and continuous electrical resistivity profiling (CERP) tools. The geophysical survey was conducted with the intent to map scour features created by oyster shell dredging activities in the bay between 1947 and 1982. The geoelectrical surveys show that oyster beds are characterized by high resistivity values greater than 1.1 ohm.m while infilled dredge cuts show lower resistivity, generally from 0.6 to 1.1 ohm.m. The difference in resistivity mainly reflects the lithology and the consolidation of the shallow sediments: consolidated silty clay and sandy sediments rich in oyster shell deposits (with less clay content) overlying unconsolidated clayey materials infilling the scours. Results show that most of the infilled dredge cuts are mostly distributed in the north-south direction. Considering that the scours are generally up to 6 m deep across the survey location, it is estimated that about 0.8 million cubic meters of oyster shells and overlying strata were dredged from the survey location.