Effect of Meander on Bridge Pier Scour

Lots of work regarding the scour around bridge piers in straight channelhave been done in the past by many researchers. Many factors which affectscour around piers such as shape of piers, size, positioning and orientationetc. have been studied in detail by them. However, similar studies inmeandering channels are scanty. Very few researchers have studied theeffect of angular displacement which has considerable effects of scouraround bridge piers.In this paper an attempt has been made to carry out a detailed study ofangular displacement on scour. A constant diameter bridge pier of circularshape has been tested in a meandering channel bend with bend angle as 800 .The test bed was prepared by using uniform sand having d50 as 0.27 mmand run was taken for a discharge of 2.5 l/s.

Effects of Spur Dyke’s Orientation on Bed Variation in Channel Bend

Spur dykes also known as Groynes are often used to either divert or attract the flow from the main structure to safeguard their life. Those structures may be bridge piers, abutments or any similar hydraulics structures. Spur dykes are also used to save the cutting of banks on concave side of stream. Lots of work have been done in recent past on spur dykes by many investigators in which various hydraulic and geometrical parameters of spur dykes such as discharge, sediment size, flow velocity, shear stress, spur dykes shape, size and submergence etc. are studied in detail. But mostly all the studies were pointed out in straight open channels. Very few studies were done in curved channel and only their similar effects were studied. In present thesis main emphasis is given to study the effect of orientation and location of spur dykes in meandering channel on the bed of downstream side. In the present study experimental work has been carried out in 80° bend and constant discharge (Q = 4.5 l/s) is allowed to pass in channel without spur dyke. It is found that maximum scouring occurs at angular displacement θ = 60° to 80° in the vicinity of outer bank. To minimize this scouring, spur dyke has been installed at angular displacement θ = 20°, 40° & 60° by changing the dyke angle α = 60°, 90° & 120° respectively. It is found that scouring at θ = 60° is reduced by installing spur dyke at angular displacement θ = 40° which is oriented at α = 60° and scouring at θ = 80° is reduced by installing spur dyke at angular displacement θ = 60° which is oriented at α = 60°.

Palaeogeography of a Mid Miocene Turbidite Complex, Moki Formation, Taranaki Basin, New Zealand.

<p>The Moki Formation, Taranaki Basin, New Zealand, is a Mid Miocene (Late Altonian to Early Lillburnian) sand-rich turbidite complex bounded above and below by the massive bathyal mudstone of the Manganui Formation. The Moki Formation is a proven hydrocarbon reservoir with its stacked, thick, tabular sandstone packages totalling more than 300 m in places. Previous regional studies of the formation have been based primarily on well data and resulted in varying palaeogeographic interpretations. This study, restricted to the southern offshore region of the basin, better constrains the spatial and temporal development of the Moki Formation by combining well data with seismic interpretation to identify key stratal geometries within the sediment package. Nearly 30,000 km of 2D seismic reflection profiles and two 3D surveys, along with data from 18 wells and three cores were reviewed and key sections analysed in detail. Seismic facies have been identified which provide significant insights into the structure, distribution and progressive development of the Moki Formation. These include: a clearly defined eastern limit of the fan complex, thinning and fining of the distal turbidite complex onto the basin floor in the north and west, evidence of fan lobe switching, spectacular meandering channel systems incised into the formation at seismic scales, and the coeval palaeoshelf-slope break in the south east of the basin. In addition, a Latest Lillburnian / Waiauan turbidite complex has been mapped with large feeder, fan and bypassing channels traced. This study presents an improved palaeogeographic interpretation of the Moki Formation and the younger, Latest Lillburnian / Waiauan-aged, turbidite complex. This interpretation shows that during the Late Altonian, sandstone deposition was localised to small fan bodies in the vicinity of Maui-4 to Moki-1 wells. A bathymetric deepening during the Clifdenian is identified, which appears to have occurred concurrently as the establishment of the Moki Formation fan system, centred around the southern and central wells. With continued sediment supply to the basin floor, the fan system prograded markedly northward and spilled onto the Western Stable Platform during the early Lillburnian. Sand influx to the bathyal basin floor abruptly ceased and large volumes of mud were deposited. By the Waiauan stage, sands were again deposited at bathyal depths on fan bodies and carried to greater depths through a complex bypassing channel system.</p>

Palaeogeography of a Mid Miocene Turbidite Complex, Moki Formation, Taranaki Basin, New Zealand.

<p>The Moki Formation, Taranaki Basin, New Zealand, is a Mid Miocene (Late Altonian to Early Lillburnian) sand-rich turbidite complex bounded above and below by the massive bathyal mudstone of the Manganui Formation. The Moki Formation is a proven hydrocarbon reservoir with its stacked, thick, tabular sandstone packages totalling more than 300 m in places. Previous regional studies of the formation have been based primarily on well data and resulted in varying palaeogeographic interpretations. This study, restricted to the southern offshore region of the basin, better constrains the spatial and temporal development of the Moki Formation by combining well data with seismic interpretation to identify key stratal geometries within the sediment package. Nearly 30,000 km of 2D seismic reflection profiles and two 3D surveys, along with data from 18 wells and three cores were reviewed and key sections analysed in detail. Seismic facies have been identified which provide significant insights into the structure, distribution and progressive development of the Moki Formation. These include: a clearly defined eastern limit of the fan complex, thinning and fining of the distal turbidite complex onto the basin floor in the north and west, evidence of fan lobe switching, spectacular meandering channel systems incised into the formation at seismic scales, and the coeval palaeoshelf-slope break in the south east of the basin. In addition, a Latest Lillburnian / Waiauan turbidite complex has been mapped with large feeder, fan and bypassing channels traced. This study presents an improved palaeogeographic interpretation of the Moki Formation and the younger, Latest Lillburnian / Waiauan-aged, turbidite complex. This interpretation shows that during the Late Altonian, sandstone deposition was localised to small fan bodies in the vicinity of Maui-4 to Moki-1 wells. A bathymetric deepening during the Clifdenian is identified, which appears to have occurred concurrently as the establishment of the Moki Formation fan system, centred around the southern and central wells. With continued sediment supply to the basin floor, the fan system prograded markedly northward and spilled onto the Western Stable Platform during the early Lillburnian. Sand influx to the bathyal basin floor abruptly ceased and large volumes of mud were deposited. By the Waiauan stage, sands were again deposited at bathyal depths on fan bodies and carried to greater depths through a complex bypassing channel system.</p>

Giant meandering channel evolution, Campos deep-water salt basin, Brazil

Submarine channels are conduits for sediment delivery to continental margins, and channel deposits can be sandy components of the fill in tectonically active salt basins. Examples of salt-withdrawal basin fill commonly show successions of sandy channelized or sheet-like systems alternating with more mud-rich mass-transport complexes and hemipelagites. This alternation of depositional styles is controlled by subsidence and sediment-supply histories. Salt-basin fill comprising successions of largely uninterrupted meandering-channel deposition are less commonly recognized. This begs the questions: can sediment supply be large enough to overwhelm basin subsidence and result in a thick succession of channel deposits, and, if so, how would such a channel system evolve? Here, we use three-dimensional seismic-reflection data from a &gt;1500 km2 region with salt-influenced topography in the Campos Basin, offshore Brazil, to evaluate the influence of salt diapirs on an Upper Cretaceous–Paleogene giant meandering submarine-channel system (channel elements &gt;1 km wide; meander wavelengths several kilometers to &gt;10 km). The large scale of the channels in the Campos Basin suggests that sediment discharge was large enough to sustain the meandering channel system in spite of large variability in subsidence across the region. We interpreted 22 channel centerlines to reconstruct the detailed kinematic evolution of this depositional system; this level of detail is akin to that of recent studies of meandering fluvial channels in time-lapse Landsat satellite images. The oldest channel elements are farther from salt diapirs than many of the younger ones; the centerlines of the older channel elements exhibit a correlation between curvature and migration rate, and a spatial delay between locations of peak curvature and maximum migration distance, similar to that observed in rivers. As many of the younger channel centerlines expanded toward nearby salt diapirs, their migration pattern switched to downstream translation as a result of partial confinement. Channel segments that docked against salt diapirs became less mobile, and, as a result, they do not show a correlation between curvature and migration rate. The channel migration pattern in the Campos Basin is different compared to that of a tectonically quiescent continental rise where meander evolution is unobstructed. This style of channelized basin filling is different from that of many existing examples of salt-withdrawal minibasins that are dominated by overall less-channelized deposits. This difference might be a result of the delivery of voluminous coarse sediment and high discharge of channel-forming turbidity currents to the Campos Basin from rivers draining actively uplifting coastal mountains of southeastern Brazil. Detailed kinematic analysis of such well-preserved channels can be used to reconstruct the impact of structural deformation on basin fill.

Submarine canyon systems focusing sub-surface fluid in the Canterbury Basin, South Island, New Zealand

This work uses a high-quality 3D seismic volume from offshore Canterbury Basin, New Zealand, to investigate how submarine canyon systems can focus sub-surface fluid. The seismic volume was structurally conditioned to improve the contrast in seismic reflections, preserving their lateral continuity. It reveals multiple pockmarks, eroded gullies and intra-slope lobe complexes occurring in association with the Waitaki Submarine Canyon. Pockmarks are densely clustered on the northern bank of the canyon and occur at a water depth of 500–900 m. In parallel, near-seafloor strata contain channel-fill deposits, channel lobes, meandering channel belts and overbank sediments deposited downslope of the submarine canyon. We propose that subsurface fluid migrates from relatively deep Cretaceous strata through shallow channel-fill deposits and lobes to latter seep out through the canyon and associated gullies. The new, reprocessed Fluid Cube meta-attribute confirms that fluids have seeped out through the eroded walls of the Waitaki Canyon, with such a seepage generating seafloor depressions in its northern bank. Our findings stress the importance of shallow reservoirs (channel-fill deposits and lobes) as potential repositories for fluid, hydrocarbons, or geothermal energy on continental margins across the world.

Supplemental Material: Giant meandering channel evolution, Campos deep-water salt basin, Brazil

<div>File S1: Base channel system horizon in comma-separated values (CSV) format. File S2: Intermediate channel system horizon in CSV format. File S3: Top channel system horizon in CSV format. File S4: Time steps between channel centerlines in Encapsulated PostScript (EPS) format. File S5: Graphics Interchange Format (GIF) animation of channel migration.<br></div>