1,721,094 research outputs found
River sediment supply, delta formation and adjacent shelf processes: conference report and introduction
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Sediment yield studies of headwater catchments in Sussex, S.E. England
No full textThe transport of sediment from six small (0.2 to 17.6 km2) headwater catchments is described. The catchments under investigation were located in relation to predominant lithological deposits within the Cretaceous rock succession; two of the areas were underlain by (Weald) clay, two by sandstone (Ashdown Sand and Tunbridge Wells Sand) and two by chalk. The climate of the region under investigation is temperate, with an average annual precipitation (850 mm) in excess of potential evapotranspiration (450 mm).The transport of suspended material from within the catchments was examined by collecting samples of the water-sediment mixture draining the areas, using hand held depth-integrating and permanently installed stage sampling systems. The results of the regularly maintained sampling programme, over a two-year period, are described. Attempts were made to both measure and compute bed load transport.Suspended sediment concentrations are compared between catchments and related to hydrological characteristics. The nature of the material in transit is examined.Sediment rating curves are derived for each of the headwater catchments, defining the relationship in the form y = Axb (where y = suspended sediment concentration (mg/1) and x = water discharge (m3/s)). Annual rating curves are used to derive annual suspended sediment loads by combination with water discharge data, using a log-incremental computerized approach. Multiple regression techniques have been used to examine annual loads in terms of hydrological and morphological characteristics of the headwater catchments.Based on the field information available, a generalized model for the relationship between suspended sediment concentration and water discharge is described.Finally, the derived annual loads from the headwater catchments are combined with both limited observations from the larger Sussex rivers and data available for other catchment investigations in the British Isles, to produce a series of prediction equations for catchment yield under temperate climatic conditions
Processes and controls involved in the transfer of fluviatile sediments to the deep ocean
No full textThe 5m long Recirculating Flume at the School of Ocean and Earth Sciences (SOES), University of Southampton, Part I: Descriptive manual
Full text linkSediment resuspension events within the (microtidal) coastal waters of Thermaikos Gulf, northern Greece
No full textHigh-frequency flow, pressure and suspended sediment concentration (SSC) measurements are presented from the Paralia-Katerinis coastal area, in Thermaikos Gulf. The data were collected along a cross-shore transect, between the 6 and 12 m water depth contours. The relative importance of wave- and tidally-induced resuspension is examined. Resuspension events are shown to be dominated by wind-generated waves, especially under storm conditions. Some evidence is provided for tidal resuspension, but the overall impact of this process is minimal, compared to wave resuspension. Such resuspension, under storm conditions, increased the SSC levels in the waters of the nearshore zone to 35 mg/l; this is a >15-fold increase over the ambient levels (1–2 mg/l) of turbidity
Sediment transport under waves and tidal currents: A case study from the northern Bristol Channel, U.K.
No full textBed-load transport under tidal currents and waves, and waves alone, is predicted from near-bed self-recording current-meter data and observations from a wave-rider buoy. Transport rates and paths are derived using seven different unidirectional transport formulae and those of Bagnold (1963), Bijker (1967) and Madsen and Grant (1976) for combined flows. Predicted rates are compared with the results of a fluorescent sand tracer study.The data are available from Swansea Bay, a high tidal- and wave-energy embayment on the British continental shelf. Sediment transport paths in this region had been determined previously using a variety of techniques, including bedform orientation and sea-bed drifter recovery patterns.Transport is enhanced under the superimposed effect of waves and, in some circumstances, the direction of the resultant vector is altered. Such storm-induced catastrophic transport is different to that predicted under tidal currents alone; this could provide a mechanism for long-term sediment supply. In some areas, there is correspondence between bedform orientation and storm-induced transport paths; in others, there is opposition
The 5m long Recirculating Flume at the School of Ocean and Earth Sciences (SOES), University of Southampton, Part II: Unidirectional flow characteristics
Full text linkLinear features on side-scan sonar images: an algorithm for the correction of angular distortion
No full textThe distortion ellipse graphical method is used regularly by scientists for the correction of compressional effects caused in side-scan sonar images by variable ship speeds. An algorithm is derived for this correction for the calculation of the true angle of linear objects (e.g. sandwaves) in relation to the ship's track:where R is the ratio of the ship's speed to the optimal ship speed (i.e. for no distortion) and ? is the false angle between the ship's track and the linear object measured directly from the image (sonograph) (0° < ? < 90°). The algorithm is applicable for any combination of chart paper speed and width. The results obtained using this approach are considered to be more accurate than conventional graphical methods of analysis of analogue output. Interpretation of imagery for sedimentological investigations should be enhanced by the adoption of this procedure.<br/
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