Backwash-and-swash-oriented current crescents: indicators of beach slope, current direction and environment

Abstract: The lower tidal stretch of the river Ganges, known as Hugli (ca. 280 km), flows southward before entering the Bay of Bengal forming a vast mangrove-enriched estuarine delta called Sunderbans. Hugli estuary is a typical example of tide-dominated sink for contaminants from multifarious sources. This major important river is subjected to anthropogenic stress due to the socio-economic importance of these areas based on growth of industry, agriculture, aquaculture, port activities, fishing and tourism. The living resources have been degraded recently due to increases in population pressure, pollution and natural resource consumption to the extent of overexploitation. The present paper critically examines the physicochemical characteristics and level of dissolved heavy metals at three ecologically distinct zones along the course of the river – Babughat located in the eastern part of the metropolitan megacity Calcutta (140 km upstream from seaface), Diamond Harbor (70 km upstream from sea face) and Gangasagar positioned at the mouth of the Ganges estuary. Physicochemical characteristics of this partially mixed estuary are largely influenced by the interaction of seawater and discharge of riverine freshwater, annual precipitation and surface runoff. The levels of salinity, total dissolved solids, hardness and conductivity showed an increasing downward trend. Marked increase in biochemical oxygen demand (BOD) values (2.20–5.95 mg/l) was recorded in Babughat whereas correspondingly low values (0.75–2.82 mg/l) were noticed at Gangasagar. This can be attributed mainly due to huge organic load of untreated sewage from the twin city Howrah and Calcutta situated in the east and west of the river. Spatiotemporal distribution of heavy metals reveals a wide range of variations reflecting input of huge anthropogenic inputs associated with a number of physical and chemical processes. Levels of metals registered a seasonal pattern, with an increase during late monsoon months (September–October), a period characterized by low salinity and relatively low pH of the water. Elevated levels of dissolved Hg and Pb were also recorded in Babughat, with values ranging from 0.16 to 0.95 μg/ml and 0.017 to 0.076 μg/ml, respectively, this high values for Hg can be attributed to the discharge from pulp and paper manufacturing units and to atmospheric input and runoff of automobile emission for Pb. It was revealed that the socio-economic development of Calcutta, the most potential economic zone in India situated on the east bank of Hugli river, has had a significant impact on the water quality of this major river. The deterioration of water quality is directly related to nonfunctioning and malfunctioning of wastewater treatment plants and lack of environmental planning and coordination. To restore the ecological stability and economic vitality of this river, the following measures have been suggested: (i) strong vigilance programme is to be undertaken towards installation and maintenance of the wastewater treatment plants to check the flow of persistent contaminants in the river water and (ii) execution of legislation and mass awareness programmes are to be enacted to restore the sound health of the river. The authors urge that environmental education should be used as an effective tool for water resource management dealing with intricate and complex problems in the interaction between nature, technology and human beings.

Abstract: The paper presents the first comprehensive account of congener profiles of polycyclic aromatic hydrocarbons (PAHs) in intertidal bivalve mollusks [Meretrix meretrix, Macoma birmanica, and Sanguilonaria (Soletellina) acuminata] of Sunderban mangrove wetland (India). The main aim of this work was to use the bivalves as bioindicators of the contamination of the 16 USEPA PAH. The PAH profile in bivalves is largely dominated by a petrogenic fingerprint, with over-imposition of pyrolytic PAH sources, as evidenced by diagnostic molecular ratios. Bioaccumulation factors (BAF) of individual compounds from the sediments were calculated, and it reveals overall higher values in the visceral mass of the bivalves. S acuminata showed significantly higher levels of PAHs, especially the high molecular weight (HMW) PAHs, compared to the other two species as a sensitive indicator of trace organic stress in future monitoring programs.

Abstract: This study examines the spatial distributions of third-order moments of velocity fluctuations, the turbulent kinetic energy (TKE) fluxes, and the conditional statistics of Reynolds shear stress across the equilibrium crescentic scour structures generated upstream of short horizontal static cylinders. Detailed velocity data were collected using three-dimensional (3D) micro-acoustic Doppler velocimeter (ADV) across and within the equilibrium scour marks. The analysis reveals that the positive and negative values of third-order moments associated with the level bed surface and the scour holes are directly related to coherent structures. The components of TKE flux are discussed for the near-bed region of the level bed surface and scour holes in relation to sweep–ejection events. A cumulant-discard method is applied to the Gram-Charlier probability distribution of two variables to describe the statistical properties of the term u′w′. The conditional statistics of the Reynolds shear stress show a good agreement with the experimental data. The distribution of the joint probability density function in the near-bed region changes cyclically along the scour hole depending on the bottom fluid velocity, which implies a change from upward to downward flux of momentum and vice versa. Both the ejection and sweep events at near-bed points on the level surface are more important than within the scour region; and in contrast, both events are stronger for the scour marks than the level bed surface at the outer layer. Sweeps dominate over ejections for the scour hole induced by smaller diameter and ejections dominate for larger diameter. Copyright © 2013 John Wiley & Sons, Ltd.

Abstract: Mud clasts are common in non-marine to marine sedimentary records, however, why lack a widely accepted classification scheme? We propose that it is the relative balance of volumetric abundance, sor...

Abstract: Armoured mudballs have been reported from modern fluvial catchments and preserved in ancient (Quaternary and older) sedimentary sequences. Despite many descriptions of mudballs in the literature there is little systematic analysis of their physical properties, genesis, transport and deposition within alluvial sequences. This study uses two adjacent catchments developed on identical geology in southeast Spain that offer a unique opportunity to examine the key controls on armoured mudball development as one catchment produces armoured mudball whilst the second does not. Field survey using a Total Station together with laboratory tests for material composition and aggregate stability were used to examine the catchment and the armoured mudballs. The results show that the generation of the armoured mudballs is heavily dependent on the correct sediment supply (suitable aggregates to act as mudball ‘seeds’, and suitable fragments to source the armour) and good slope-channel coupling within the catchment. Coupling is facilitated by steep gully sides which deliver the weathered blocks of marl (mudball ‘seeds’) to the gully floor. The ‘seeds’ form the core of the mudballs in the ’mudball factory’ zone. If the ‘seeds’ are subjected to sealing by moisture from rainfall the mudball will hold together through negative pore pressures and can be transported by the ensuing gully flow. As the mudball rolls it picks up a surface armour which becomes embedded into the mudball. With longer transport paths the turbulent nature of the flow creates spherical mudballs which are size sorted downstream by the hydraulics of the flow rather than attrition. Armoured mudball deposition occurs within unit braid bars in areas of waning flow (due to transmission losses), within vegetated, point or mid-channel bars. The armoured mudballs are preferentially deposited within the coarser bar head of these depositional units, with smaller marl fragments forming the finer bar tail. Trenching of the bars reveals that the armoured mudballs are preserved in the subsurface although they may become increasingly flattened upon burial at depth, and may be difficult to recognise due to disaggregation by roots. This study suggests that armoured mudballs recognised in ancient alluvial sequences imply seasonality of climate and good slope-channel coupling within the catchment area, and that they are capable of transporting delicate flora undamaged, making them good targets for pollen recovery in ancient alluvial sequences. Where armoured mudballs were present but go unrecognised in the ancient record the mode and energy of transportation and deposition of the fine sediment may be misinterpreted as the fines are in fact being transported as bedload rather than suspended load. The armoured mudballs have also been noted to transport pristine microfauna such as ostracod shells from the source area material. This may provide challenges to palaeoenvironmental interpretations of the mud-dominated unit as environmentally significant fauna may not be contemporaneous with the unit.

Abstract: 1. Environmental Fluid Dynamics. 2. Entrainment and Transport of Sedimentary Particles. 3. Particle Motions at Low Concentrations: Grading in Pyroclastic-Fall Deposits. 4. Packing of Sedimentary Particles. 5. Orientation of Particles During Sedimentation: Shape-Fabrics. 6. Transition to Turbulence and the Fine Structure of Steady Turbulent Boundary Layers: Parting Lineation and Related Structures. 7. Models of Transverse Bedforms in Unidirectional Flows. 8. Empirical Character of Ripples and Dunes Formed By Unidirectional Flows. 9. Climbing Ripples and Dunes and Their Cross-Stratification Patterns. 10. Bedforms in Supercritical and Related Flows: Transverse Ribs, Rhomboid Features, and Antidunes. 11. Transverse Bedforms in Multidirectional Flows: Wave-Related Ripples Marks, Sand Waves, and Equant Dunes. 12. Ripples and Dunes in Changing Flows.

Abstract: 1. Introduction. In the case of nearly all branches of science a great advance was made when accurate quantitative methods were used instead of merely qualitative. One great advantage of this is that it necessitates more accurate thought, points out what remains to be learned, and sometimes small residual quantities, which otherwise would escape attention, indicate important facts. Since it applies to nearly all branches of geology, it is necessarily a wide subject, but so connected together that it seems undesirable to divide it. My object is to apply experimental physics to the study of rocks. At least six different kinds of physical questions are involved, some of which have been sufficiently studied, but others require experiments which would be very difficult to carry out, and all that I can now do is to endeavour to deduce plausible results from what is known. In doing this, it may be necessary to assume cases sufficiently simple for calculation, which may but imperfectly correspond to natural conditions, so that the results may be only approximately correct. In some cases, facts seem to show that there are important properties connected with subsiding material which cannot be explained in a satisfactory manner. Notwithstanding this, it appears desirable to do the best that I can with the material at my disposal, hoping to lead others to do what I intended to do, and correct such errors as are now unavoidable. In order to clear the way for subsequent detail, I describe a few general facts.

Abstract: Sediments and bed forms from three braided outwash plains and one steep non-braided mountain stream in the Rocky Mountains of Alberta are compared to sediments and structures exposed in a paleo-out...

Abstract: SUMMARY Bed forms arise by interaction between a fluid flow and the sediment transported over or close to the bed. The geometry of bed forms is two-dimensional or three-dimensional. Two-dimensional bed forms generate two-dimensional internal sedimentary structures and are adjusted to two-dimensional flow-vector fields. Three-dimensional bed forms generate three-dimensional internal sedimentary structures and are adjusted to three-dimensional flow-vector fields. Many shallow-water flow systems observable today are each characterised by flow-vector fields of unequal rank, and hence are hierarchically structured. Hierarchies of bed forms and internal structures which parallel the hierarchies of flow-vector fields can also be established in the case of these flow systems. A single type of bed form or internal structure from an hierarchically structured flow system cannot specify that system fully with regard to either its directional or flow-dynamic characteristics. An approach to palaeocurrent analysis that is more flexible and comprehensive than previously attempted may therefore be desirable.