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Mouth Bar (mouth + bar)

Distribution by Scientific Domains

Earth and Environmental Science	50%

Selected Abstracts

Spatial patterns of water surface topography at a river confluence

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2002
Dr Pascale M. Biron
Abstract Understanding flow structures in river confluences has largely been the product of interpretations made from measured flow velocity data. Here, we turn the attention to the investigation of the patterns of both the average and standard deviations of the micro-topography of the water surface at an asymmetrical natural discordant confluence for different flow conditions. Water surface topography is measured using a total station to survey the position of a reflector mounted on a custom-built raft. To limit error problems related to changes in the water level, measurements are taken and analysed by cross-stream transects where five water surface profiles are taken before moving to the next transect. Three-dimensional numerical simulations of the flow dynamics at the field site are used to examine predicted water surface topography for a steady-state situation. The patterns are interpreted with respect to flow structure dynamics, visual observations of boils, and bed topography. Results indicate that coherent patterns emerge at the water surface of a discordant bed confluence for different flow conditions. The zone of stagnation and the mixing layer are characterized by super-elevation, a lateral tilt is present at the edge of the mixing layer, and a zone of super-elevation is present on the tributary side at the downstream junction corner. The latter seems associated with periodical upwelling and is not present in the numerical simulations that do not take into account instantaneous velocity fluctuations. Planform curvature, topographic steering related to the tributary mouth bar, and turbulent structures associated with the mixing layer all play a key role in the pattern of both the average and standard deviation of the water surface topography at confluences. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Tectonic,Hydrocarbon Accumulation of Laoyemiao Region in the Nanpu Sag, Bohai Bay Basin

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009
Cuimei ZHANG
Abstract: This paper aims to gain insight into Laoyemiao (LYM) tectonic features and utilizes the tectonic,hydrocarbon accumulation model by integrated analysis tectonic controls on suitable reservoirs, trap styles, and hydrocarbon migration. On the basis of 3-D seismic data interpretation and the Xi'nanzhuang (XNZ) Fault geometry analysis, it has been assessed that the LYM tectonics is essentially a transverse anticline produced by flexure of the XNZ Fault surface and superimposed by Neocene north-east-trending strike-slip faults. Transverse anticline is found to exert controls both on major sediment transportation pathways and sedimentary facies distribution. Fan-delta plains that accumulated on the anticline crest near the XNZ Fault scrap and fan-delta front on the anticline front and the upper part of both limbs slumps on synclines and the Linque subsag. In combination with the reservoir properties, suitable reservoirs are predicted in the subfacies of subaqueous distributary channel and mouth bar deposited on the anticline crest. The LYM-faulted anticline accounts for the following trap groups: faulted-block and anticline-dominated trap, fault-dominated traps, and combined and stratigraphic traps. Evidence from biomarkers of crude oil and hydrocarbon-filling period simultaneous, or a little later to the strike-slip fault activity, reveal that the strike-slip faults penetrating into the deep source rock, by connecting with shallow reservoirs, provide the major hydrocarbon migration pathways. [source]

Deltas in the Abisko area, northern Sweden: the Abiskojokka delta in lake Torneträsk

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3-4 2002
Hans Andrén
Several small river deltas are found within the Abisko area. This study deals with the Abiskojokka delta in Lake Torneträsk. The aim is to describe the recent delta and its morphological development since the middle 1960s. In the apex of the delta, bars consist of boulders and cobbles while the mouth,bars are built by pebbles, gravel and to some extent sand. Birch vegetation is found on the sandy levées while willows and sedges dominate the interlevée basins. Mouth bars close to the lake generally lack vegetation. A comparison of the map in the present study with a map from 1965 shows comparatively small changes since 1964. Similar results are achieved when comparing aerial photographs from 1959 and 2000. Thus, the growth of the Abiskojokka delta is rather small compared to several other deltas in the Scandinavian mountains. This low growth rate is a result of upstream lakes trapping the major part of the fluvial sediments. Therefore, most of the delta sediment is redistributed old glaciofluvial material from the terraces within the Abiskojokka valley. Some material might also emanate from the Abiskojokka canyon. Formation of the main part of the delta is probably associated with the lowering of the Torneträsk ice,lakes, during and after the deglaciation of the region. Although some extreme rainstorm events have occurred in the area during recent decades, the effects of these on the delta are small. The result of such events is, however, visible as deposition of sand and silt on the levées after flooding. On the other hand, the shoreline and the mouth bars are continuously changing due to rather high wave energy especially during northerly winds. Along several mouth bars, spits are formed and reformed due to wave action. Minor changes of, and within, the two main distributaries have also been noticed, especially as bank erosion and redistribution of bars. The project will continue with a survey of the distal slope (foreset slope) of the delta as well as a study (including X,ray radiography) of the bottom sediments in Lake Torneträsk close to the delta front. The upstream deltas within this drainage basin as well as other deltas within the Torneträsk region will be studied. [source]