scholarly journals Modeling large scale shoreline sand waves under oblique wave incidence

2012 ◽  
Vol 117 (F3) ◽  
pp. n/a-n/a ◽  
Author(s):  
N. van den Berg ◽  
A. Falqués ◽  
F. Ribas
Keyword(s):  
Large Scale ◽  
Sand Waves ◽  
Oblique Wave ◽  
Wave Incidence

Study of sand wave migration over five years as observed in two windfarm development areas, and the implications for building on moving substrates in the North Sea

2014 ◽  
Vol 105 (4) ◽  
pp. 241-249 ◽  
Author(s):  
Ken P. Games ◽  
David I. Gordon
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
Oil And Gas ◽  
Sand Wave ◽  
Sand Waves ◽  
Migration Rates ◽  
The North ◽  
The North Sea ◽  
Wave Migration ◽  
The Impact

ABSTRACTSand waves are well known indicators of a mobile seabed. What do we expect of these features in terms of migration rates and seabed scour? We discuss these effects on seabed structures, both for the Oil and Gas and the Windfarm Industries, and consider how these impact on turbines and buried cables. Two case studies are presented. The first concerns a windfarm with a five-year gap between the planning survey and a subsequent cable route and environmental assessment survey. This revealed large-scale movements of sand waves, with the displacement of an isolated feature of 155 m in five years. Secondly, another windfarm development involved a re-survey, again over a five-year period, but after the turbines had been installed. This showed movements of sand waves of ∼50 m in five years. Observations of the scour effects on the turbines are discussed. Both sites revealed the presence of barchans. Whilst these have been extensively studied on land, there are few examples of how they behave in the marine environment. The two case studies presented show that mass transport is potentially much greater than expected and that this has implications for choosing turbine locations, the effect of scour, and the impact these sediment movements are likely to have on power cables.

scholarly journals Study on hydraulic resistance of erodible bed at the Chiyoda experimental flume

2014 ◽  
Vol 39 ◽  
pp. 81-87
Author(s):  
T. Kakinuma ◽  
T. Inoue ◽  
R. Akahori ◽  
A. Takeda
Keyword(s):  
Large Scale ◽  
Flow Distribution ◽  
Longitudinal Survey ◽  
Sand Wave ◽  
Vertical Flow ◽  
Sand Waves ◽  
Wave Development ◽  
Logarithmic Distribution ◽  
Steady Flow Condition ◽  
Experimental Flume

Abstract. The authors made erodible bed experiments under steady flow condition at the Chiyoda Experimental Flume, a large-scale facility constructed on the floodplain of the Tokachi River, and observed sand waves on the bed of the flume. In this study, the characteristics of the sand waves are examined along the longitudinal survey lines and confirmed to be dunes. Next, the authors estimated Manning's roughness coefficients from the observed hydraulic values and assumed that the rise of the coefficients attributed to the sand wave development. Finally, vertical flow distribution on the sand waves are examined, and observed velocity distribution on the crest of waves found to be explained by the logarithmic distribution theory.

scholarly journals ANOTHER APPROACH TO LONGSHORE CURRENT EVALUATION

1986 ◽  
Vol 1 (20) ◽  
pp. 100
Author(s):  
M.A. Losada ◽  
A. Sanchez-Archilla ◽  
C. Vidal
Keyword(s):  
Simple Model ◽  
Predictive Model ◽  
General Expression ◽  
Current Velocity ◽  
Laboratory Data ◽  
Reynolds Stresses ◽  
Longshore Current ◽  
Current Generation ◽  
Oblique Wave ◽  
Wave Incidence

A simple model to predict the longshore current velocity at the breaker line on a beach with oblique wave incidence, is presented. The model balances driving and resistance terms (gradients of radiation and turbulent Reynolds stresses and bottom friction) to get a general expression for the velocity. This equation shows explicitely the influence of Iribarren's parameter on longshore current generation. It has been tested with field and laboratory data, obtaining a reasonable fit to measured values. The resulting (predictive) model is expected to be valid for any type of breakers though the calibration has been mainly done for spilling and plunging types, due to the scarcity of results for other breakers.

scholarly journals Evaluation of internal geometries within the Miocene Utsira Formation to establish the geological concept of observed CO2 responses on 4D seismic in the Sleipner area, North Sea

2019 ◽  
Author(s):  
Christopher Kennett ◽  
Christopher Aiden-Lee Jackson
Keyword(s):  
Injection Site ◽  
North Sea ◽  
Large Scale ◽  
High Energy ◽  
Sand Waves ◽  
Reservoir Architecture ◽  
Seismic Surveying ◽  
Stratal Architecture ◽  
Area North ◽  
Well Data

CO2 has been injected into the Miocene Utsira Formation at the Sleipner field in the Norwegian North Sea since October 1996. Repeat seismic surveying over the injection site in 1999, 2001, 2004 and 2006 have revealed the temporal development of the CO2 plume. However, in order to help better understand future plume development and aid in locating a new injection site the geological evolution of the Utsira Formation and its resultant stratal architecture needs further development in the greater Sleipner area. Combined used of seismic and well data show that the base of the Utsira Formation, the Middle Miocene Unconformity (MMU), is heavily deformed by soft sedimentary deformation. The source for this deformation is mass sand mobilization and injection of Skade Formation sandstones in the otherwise dominantly argillaceous sediments of the Upper Hordaland Group. Skade Formation sandstones are observed thickening in up-folded, and mounded regions of MMU, where seismic data reveal V-shaped amplitude anomalies or ‘chaotic’, noisy areas. Outside the deformed areas the Upper Hordaland Group is an otherwise flat sequence of continuous acoustic reflectors that are offset by a pervasive network of polygonal faults. Onlapping reflection terminations of lower Utsira Formation reflectors onto the deformed surface of the MMU indicate that soft sedimentary deformation occurred at a shallow depth before deposition of the Utsira Formation. Stratal elements within the sand rich (0.98 N:G) Utsira Formation include: i) south westerly dipping clinoforms, ii) erosional scours, and iii) large-scale sand waves, suggesting high depositional energy and potential erosion of (c.1 - 2.5 metre thick) shale interbeds. During deposition of the Utsira Formation differential compaction within the Upper Hordaland Group has down-folded, and rotated intra-Utsira reflectors onto underlying MMU mounded features. Løseth’s et al. (2003) and Jackson’s (2007) models for gas and fluid expulsion from the mobilized sediments during burial, leading to differential compaction, is the preferred hypothesis for this phenomenon. The result of collapsed sediments on reservoir architecture is folding, and the creation of the anticlinal internal geometries where the CO2 is injected today. CO2 reached the top of the reservoir by 1999, via a sequence of small accumulations beneath interpreted as intra-formational shale beds. It appears from this rapid ascent that shale layers are laterally discontinuous, and perhaps eroded by the high-energy depositional model inferred.

scholarly journals SHORELINE SAND WAVES AND BEACH NOURISHMENTS

2011 ◽  
Vol 1 (32) ◽  
pp. 102
Author(s):  
N. Van den Berg ◽  
A. Falqués ◽  
F. Ribas
Keyword(s):  
Large Scale ◽  
Incidence Angle ◽  
Wave Train ◽  
Shoreline Change ◽  
Sand Wave ◽  
High Angle ◽  
Wave Instability ◽  
Littoral Drift ◽  
Sand Waves ◽  
Change Models

The effects of the feedback between the changing coastal morphology and the wavefield on the generation and propagation of large scale (O(1-10 km)) shoreline sand waves is examined with a quasi-2D morphodynamic model. Traditional shoreline change models do not include this feedback and are only able to describe diffusion of shoreline sand waves and furthermore they are unable to describe migration. It is found with the present model that if there is a dominant littoral drift, the feedback causes downdrift migration of coastline features no matter if they grow or decay. Consistently with previous studies, simulations show that a rectilinear coastline becomes unstable and sand waves tend to grow spontaneously from random perturbations, if the wave incidence angle is larger then about 42o (θc) at the depth of closure (high angle wave instability). The initial wavelengths at which the sand waves develop are 2-3 km and this is similar to previous linear stability analysis. The implications of high angle wave instability for beach nourishments are investigated. The nourished shoreline retreats initially due to cross-shore transport because the nourished profile is steeper than the equilibrium profile. When a dominant littoral drift is present, the nourishment also migrates downdrift. If the wave angle at the depth of closure is below θc the alongshore transport contributes to the diffusion of the nourishment. However, if the angle is above θc (constant high angle wave conditions) the diffusion is reversed and the nourishment can trigger the formation of a shoreline sand wave train. Numerical experiments changing the proportion of ‘high angle waves’ and ‘low angle waves’ in the wave climate show that relatively small proportions of low angle waves slow down the growth of sand waves. These simulations with more realistic wave climates show shoreline sand waves that migrate downdrift maintaining more or less the same amplitude for years.

scholarly journals FORMATION OF DYNAMICALLY STABLE LAKESHORE UNDER SEASONALLY CHANGING WAVE DIRECTION

2011 ◽  
Vol 1 (32) ◽  
pp. 85
Author(s):  
Toshinori Ishikawa ◽  
Takaaki Uda ◽  
Toshiro San-nami ◽  
Shusuke Watanabe
Keyword(s):  
Numerical Simulation ◽  
Sandy Beach ◽  
Beach Nourishment ◽  
Lake Kasumigaura ◽  
Wave Direction ◽  
Spur Dike ◽  
Oblique Wave ◽  
The Stability ◽  
Wave Incidence

In the Ukishima region of Lake Kasumigaura, beach nourishment along with the construction of groins has been carried out to recover a sandy beach. After the beach nourishment, part of the nourishment sand was transported away from the beach, turning around the tip of the downcoast groin owing to the oblique wave incidence in winter. To enhance the stability of the beach, the groins were extended and a spur dike was constructed. To design these structures, a numerical simulation using the BG model was carried out, and the optimum shapes were determined by taking into account the seasonally changing wave direction. The effectiveness of the spur dike was numerically evaluated using the BG model.

scholarly journals A mechanism for sandbar straightening by oblique wave incidence

2013 ◽  
Vol 40 (11) ◽  
pp. 2726-2730 ◽  
Author(s):  
R. Garnier ◽  
A. Falqués ◽  
D. Calvete ◽  
J. Thiébot ◽  
F. Ribas
Keyword(s):  
Oblique Wave ◽  
Wave Incidence

scholarly journals MEASUREMENT OF WAVE PRESSURE ON PERFORATED CAISSON WALL UNDER OBLIQUE WAVE INCIDENCE

2014 ◽  
Vol 1 (34) ◽  
pp. 68
Author(s):  
Sang-Ho Oh ◽  
Chang-Hwan Ji ◽  
Young Min Oh ◽  
Hee Do Ahn
Keyword(s):  
Wave Pressure ◽  
Oblique Wave ◽  
Perforated Caisson ◽  
Wave Incidence
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