Sediment transport inferred by submarine bedforms

By means of bathymetric and side scan sonar records, the net circulation of sediments caused by tidal currents and waves in the outer Principal Channel of Bahía Blanca Estuary is inferred. On the northern coast of the studied area there are two harbours, Belgrano and Rosales, which are simultaneously affected by internal and external hydrosedimentological processes. Through this study, present and potential negative interactions between human activities and natural processes within the studied area are demonstrated.A través del análisis de registros batimétricos y de sonar de barrido lateral se infiere la circulación neta de sedimentos causada por olas y mareas en el sector externo del Canal Principal del estuario de Bahía Blanca. Sobre la costa norte del área de estudio se encuentran dos puertos, Puerto Belgrano y Puerto Rosales, los cuales son simultáneamente afectados por procesos hidrosedimentológicos internos y externos al estuario. Por medio de este estudio se evidencian las interacciones negativas, presentes y futuras, entre las actividades humanas y los procesos naturales.Fil: Cuadrado, Diana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Gomez, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

An interconnected system of tidal channels in Bahía Blanca estu ary, Argentina: an evaluation of bedload sediment tr ansport through acoustic methods

El estuario de Bahía Blanca, ubicado al sur de la provincia de Buenos Aires (Argentina), constituye una costa baja con extensas llanuras de marea, islas y una compleja red de canales de diferentes magnitu- des. Estos últimos integran un sistema de canales interconectados. El objetivo de este trabajo es establecer la circulación sedimentaria como carga de fondo en un sistema de canales interconectados (Cabeza de Buey, El Alambre, La Lista y Principal) mediante el análisis de los rasgos morfológicos de fondo, utilizando métodos acústicos (ecosonda y sonar lateral). El canal Cabeza de Buey se comunica con el canal La Lista a través del canal El Alambre. Los dos primeros vierten sus aguas en el canal Principal. El canal Cabeza de Buey posee un lecho plano constituido por material pelítico con arena muy fina. En su tramo más interno se presentan dunas medianas compuestas por arena fina, con un perfil asimétrico según el reflujo. Estas formas, continúan su desarrollo ininterrumpidamente hacia el canal El Alambre, donde se originan dunas grandes (altura 1,5 m) formadas por arena muy fina. Sus crestas son sinuosas o barjanoides y poseen su talud hacia la corriente de bajante. En el canal La Lista se determinan dunas asimétricas medianas orientadas según el reflujo y grandes linea- ciones sedimentarias (sand ribbons) sobre un fondo consolidado. El sedimento movilizado por la corriente co- rresponde a la fracción limo-arena fina. La distribución y configuración de las geoformas evidencian que el transporte sedimentario como carga de fondo se concentra principalmente en el canal La Lista. Es así como en el sistema de canales estudiado, sólo un canal de mare a regula la dispersión de arena, transportando un impor- tante volumen hacia el canal de navegación.Bahía Blanca estuary located in the south of Bue nos Aires province, Argent ina, is characterised by a low coastal area with large tidal plains, islands, a nd a complex network of tidal channels of different dimensions. The latter form an interconnected tidal channel system. The aim of this study was to determine the net bedload sediment transport in an interconnected channel system (Cabeza de Buey, El Alambre, La Lista, and Principal channels) through an analysis of the morphological features of the bottom using acoustic data (echosounder and side scan sonar). Cabeza de Buey channel is connected to La Lista channel through El Alambre channel. The first two flow into the Principal channel. Cabeza de Buey channel has a flat bed of mud with very fine sand and medium-sized dunes of fine sand in its inner sector that display an asymmetrical section according to the ebb flow. These dunes continue to develop uninterrupted towards El Alambre channel, where large dunes (1.5 m high) of very fine sand originate. Their crestlines are either sinuous or barchanoid and they have their lee towards the ebb current. In La Lista channel, medium-sized asymmetrical dunes and large sand ribbons form on a rocky bottom according to the ebb flow. The sediment mobilized by the currents is characterized by the fine sand – silt fraction. The di stribution and configuration of bed forms reveal that the bedload sediment transport is mainly concentrated in La Lista channel. Thus, only one tidal channel regulates the dispersal of sandy material, transporting a significant volume of sediment towards the shipping channel.Fil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Lizasoain, Guillermo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

Seafloor Morphosedimentology in the Entrance Sector of Bahía Blanca Estuary, Argentina

En el amplio sistema estuarial de Bahia Blanca (provincia de Buenos Aires) existen sectores carentes de un conocimiento integral de las características morfosedimentológicas submarinas. Dentro de este contexto, en el presente trabajo se estudia el fondo marino a lo largo de la costa norte ubicada en el sector de entrada del Canal Principal del estuario de Bahía Blanca. Se realizaron relevamientos acústicos (ecosonda y sonar lateral) y muestreos de sedimentos de la superficie del fondo. Se determinó la presencia de geoformas depositacionales y erosivas. Entre las de carácter acrecional se han establecido diferentes tipos de dunas y lineaciones arenosas (sand ribbons). Entre los rasgos generados por erosión se encuentran escarpas, relativamente continuas e irregulares y afloramientos rocosos aislados. Asimismo, también se diferencian fondos de sedimentos cohesivos, tanto masivos como estratificados. Como formas antrópicas se distinguen surcos de dragado y la presencia de cañerías de oleoductos y restos metálicos. El análisis de las geoformas y los sedimentos permitió establecer que en el sector este de la franja costera estudiada, prevalece un transporte sedimentario como carga de fondo hacia la Plataforma Continental, mientras que en aguas someras del sector oeste, existe una marcada deriva de sedimentos hacia el interior del estuario. La conjunción de datos morfológicos y sedimentológicos posibilitó ampliar la caracterización de dos paleoniveles costeros, indicativos de períodos de estabilización del nivel del mar durante el último proceso transgresivo.In the large Bahia Blanca estuarine system (province of Buenos Aires) there are sectors without a comprehensive assessment of submarine morpho-sedimentological features. Within this context, in this paper the seabed along the north coast of the entrance to the Principal channel of the estuary is studied. Acoustic surveys (echo sounder and side scan sonar) and sediments sampling were performed. The presence of depositional and erosional geoforms was determined. Among those of accretional nature have been established different types of dunes and sand ribbons. The erosive forms are scarps, relatively continuous and irregular, and rocky isolated outcrops. Also, seabed cohesive sediments, both massive and stratified, were differentiated. As anthropogenic forms furrows dredging and the presence of pipes for oil and metal debris were distinguished. The analysis of geoforms and sediments determined that in the east sector of the coastal strip studied prevails sediment transport as bedload towards the Continental Shelf, while in shallow waters of the western sector, there is a marked litoral drift towards the inside of estuary. The conjunction of morphological and sedimentological data allowed to extend the characterization of two ancient coastal levels, indicative of stabilization periods of sea level during the last transgressive process.Fil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Spagnuolo, Jorge Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Minor Salvatierra, Marta Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin

Sediment Transport

Sediment transport is a book that covers a wide variety of subject matters. It combines the personal and professional experience of the authors on solid particles transport and related problems, whose expertise is focused in aqueous systems and in laboratory flumes. This includes a series of chapters on hydrodynamics and their relationship with sediment transport and morphological development. The different contributions deal with issues such as the sediment transport modeling; sediment dynamics in stream confluence or river diversion, in meandering channels, at interconnected tidal channels system; changes in sediment transport under fine materials, cohesive materials and ice cover; environmental remediation of contaminated fine sediments. This is an invaluable interdisciplinary textbook and an important contribution to the sediment transport field. I strongly recommend this textbook to those in charge of conducting research on engineering issues or wishing to deal with equally important scientific problems

Impact of a rocky outcrop on hydrodynamics and geomorphology in a mesotidal channel

The purpose of the present work is to study the effect of an isolated depression and a related rocky outcrop on the flow field in a mesotidal channel of the Bahía Blanca Estuary, Argentina. To this end, measurements of current velocity (ADCP), swath bathymetry (multibeam), and seismostratigraphic surveys (3.5 kHz) were made in the study area. In general, the channel bed studied (Cabeza de Buey Channel) is flat and mainly composed of clayey silts. In the inner sector, there is a depression 6 m-deep and 50–60 m in diameter, and on either side (in a streamwise sense) there are two isolated rocky outcrops that extend up to 2 m in height relative to the prevailing bed level. The two features differ in that the up-estuary outcrop is longer and extends over the whole width of the hole, while the down-estuary outcrop is shorter and only extends over part of the diameter of the hole. Seismostratigraphic analysis, in correlation with bathymetric and lithological data, indicates that these high points correspond to the outcropping of relict deltaic materials that formed part of a regional Late Pleistocene drainage system. Fine-grained estuarine sediments deposited above the old deltaic materials show evidence of the present-day sedimentological conditions related to the hydrodynamics of the channel. The flow patterns within the depression observed over a complete tidal cycle demonstrate that the flow behaves differently depending on the stage of the tide. The depth-averaged flow shows higher velocities during the ebb tide, generating a net flow directed towards the sea. Results reveal the generation of return flows (turbulent eddies) at the bottom of the hole, which expand immediately towards the water surface. During the ebb tide, intense vertical currents develop inside the hole. The eddy formation is attributed to the unequal size of the outcrops. Hence, the larger upstream channel outcrop plays an important role in eddy generation, just as downwelling-upwelling interaction produces erosion and transport of sediments, which exerts a strong influence on the deepening of the hole.Fil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin

Morphosedimentological features of the sea floor in the outer sector of the Bahia Blanca estuary, Argentina

The purpose of this paper is to analyze the morphology of the Quaternary relict features and bedforms that characterize the outer zone of an extensive mesomareal system, which is part of the Bahía Blanca estuary (Argentina), and to estimate the prevailing hydro-sedimentological conditions on the continental shelf adjacent to the estuary. Surveys with a multibeam bathymetric system, side-scan sonar and a high-resolution seismic system (3.5 kHz) were carried out and bottom sediment samples were collected. In general, the seafloor presents a varied configuration, marked by changes in its physiography. The Quaternary relict features are composed of two terraces (12–14 m and 18–22 m deep), with steeply sloping escarpments, that are oriented approximately parallel to the current coastline. Associated with these terraces, wide abrasion platforms develop with irregular and plateau-like structures up to 4 m high, together with large rocky blocks up to 6 m in diameter. Here, the predominant sediment corresponds to a gravel-sized material composed of quartzite boulders, siltstone fragments of up to 7 cm, and biogenic remains with different degrees of fragmentation. These sedimentological data, together with the bathymetric and seismostratigraphic information, indicate that the terraces and abrasion platforms are ancient shorelines that originated in an environment with high wave energy, corresponding to periods of stabilization of sea level rise during the final stage of the last postglacial transgression (late Pleistocene-Early Holocene). On the other hand, asymmetric dunes of different sizes (0.5 m 300 m) and comet marks originated in equilibrium with the present-day hydro-sedimentological conditions. The availability of sandy material mobilized as bedload is the determining factor for the generation of the varied bedforms. Thus, sand ribbons and comet marks are generated especially in the northern sector of the area, with mobile sediment thicknesses ≤ 0.5 m. With larger thicknesses the formation of dunes occurs. Their size and asymmetry show an intense transport of sand as bedload towards the continental shelf, the southern sector of the area being the main route of the sediment that leaves the estuary. This sediment is the supply source of the sandy shoals that are part of the great ebb delta developed on the continental shelf in the external area of the Bahía Blanca estuary.Fil: Andreoli, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin

Morphodynamics and seismostratigraphy of a deep hole at tidal channel confluence

The sedimentary circulation pattern at a deep hole at a tidal channel junction in an estuary environment is examined using morphosedimentological and seismostratigraphic data. The bottom and sub-bottom acoustic information (side scan sonar and 3.5 kHz pro fi ler) obtained at a tidal channel con fl uence in Bahía Blanca estuary (Argentina) evidences the depositional and erosive features, bed load sediment transport pathways and morphological evolution of the depression. This important depression in the con fl uence zone of the channels is characterised by the presence of steep scour faces (14°) at the mouth of both channels and gentle slopes (1.5°) opposite to them. Bed load sediment transport analysis reveals a differential circulation pattern of sand on both sides of the hole, which is associated with the different sediment availability in each channel. The side scan sonar information therefore indicates that there is no available sand in one of the channels whereas the other channel is characterised by the presence of a large amount of sediment coming from its inner area. Deposition therefore occurs on the side where sediment is mobilised as bed load by the ebb current dominance and on the face developed downstream. In the latter, a part from the sediment is de fl ected inward by the tidal fl ood currents which produce the deposition of sediment on the gentle side. The rest of the sediment is exported from the system by ebb currents. In contrast, erosion occurs on the opposite side of the hole and at the mouth of each channel and it is manifested by the outcrop of old sedimentary strata. The seismostratigraphic information collected in this study indicates that the depression was originally a fully erosive morphological feature. A descriptive model of the morphological evolution at a channel con fl uence is presented in this study.Fil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Lizasoain, Guillermo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

Seismic stratigraphy of late Neogene: Quaternary units and evolutionary model in the inner sector of Bahia Blanca estuary (Argentina)

The Quaternary sedimentary deposit of the inner sector of Bahía Blanca estuary (BBE), Argentina, was studied using high-resolution seismic profiles, core samples and correlation with continental – marine units outcropping in the continent. We interpreted four prominent seismic reflection surfaces and the acoustic basement which together defined five seismic stratigraphic units (S0, S1, S2, S3, S4) and four related systems tracts. Studying those units, we proposed a fourth Stage deposition evolutionary model that took place in a relative sea-level fluctuation context after the Miocene in the BBE area. The first stage contained the deposition of the regressive seismic units S0 and S1. The S0 was determined as an acoustic basement. The top of the S0 erosional surface (SU) was determined and it was formed by subaerial processes during the Late Pleistocene fall in sea-level and the following marine reworking during transgression. The unit was correlated with the oldest continental Miocene loess deposit and was associated with an Early Lowstand Systems Tract (ELST). Unit S1 was associated with a Late Lowstand Systems Tract (LLST). An irregular stratigraphic surface was observed above it. It was inferred as a Maximum Regressive Surface and the Ravinement Surface (RS/MRS) which are related to a maximum regression and subsequent transgression. The S1 unit was correlated with Pliocene-Pleistocene continental deposits. The Miocene - Pleistocene coastline movement in this sector would be associated with both Neogene Andean dynamics and the Last Maximum Glacial. After that, during the second Stage in the Late Pleistocene - middle Holocene the sea-level on the Bahia Blanca coast rose and unit S2 was formed. We interpreted unit S2 as a Transgressive System Tract which developed until the maximum sea-level of the Mid-Holocene. The coastline extension on the continent conformed the Maximum Flooding Surface. After a stabilization period to the mid Holocene, the sea-level started falling, offering conditions for the deposition of the High Stand System Tract (S3 – S4). Following stabilization, the third Stage took place and a progradation unit S3 was deposited overlying the MFS and a minor stratigraphic surface Bedset Boundary (BsB) separated this unit from S4. During the fourth phase, the sea-level continued to fall until the present level and the last HST (S4) was interpreted, which is interpreted as an aggradational – progradational deposit formed in the Middle Holocene to the present day by a change in the rate of sediment supply or energy flux.Fil: Pereyra Fernández, Eliana Adabella. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; ArgentinaFil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Aliotta, Salvador. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin

Tidal and longshore sediment transport associated to a coastal structure

In order to understand the subtidal marine dynamics relative to the coastal engineering works in the Bahía Blanca Estuary (Argentina), the balance of sediment transport caused by tidal currents was estimated in the Puerto Rosales area and compared with the predicted potential littoral transport. The breaking wave height used in the littoral drift calculation was estimated after applying different wave transforming procedures over the deepwater wave which was predicted by the occurrence of predominant wind, blowing long enough in an essentially constant direction over a fetch. The effect of a breakwater on currents and circulation was studied by bathymetric and side-scan sonar records, sedimentology, and tidal current measurements. Different modes of transport occur on either sides of the breakwater. On the east side, longshore transport is the principal mode, and on the west side, tidal transport is predominant.Fil: Cuadrado, Diana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; ArgentinaFil: Gomez, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin