Katell Guizien | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)
Papers by Katell Guizien
Journal of Geophysical Research, 2003
1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model f... more 1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model for one-dimension vertical (1DV) oscillating bottom boundary layer in which a separation condition under a strong, adverse pressure gradient has been introduced and the diffusion and transition constants have been modified. This new turbulence model agrees better than the Wilcox original model with both a direct numerical simulation (DNS) of a pure oscillatory flow over a smooth bottom in the intermittently turbulent regime and with experimental data from Jensen et al. [1989], who attained the fully turbulent regime for pure oscillatory flows. The new turbulence model is also found to agree better than the original one with experimental data of an oscillatory flow with current over a rough bottom by Dohmen-Janssen [1999]. In particular, the proposed model reproduces the secondary humps in the Reynolds stresses during the decelerating part of the wave cycle and the vertical phase lagging of the Reynolds stresses, two shortcomings of all previous modeling attempts. In addition, the model predicts suspension ejection events in the decelerating part of the wave cycle when it is coupled with a sediment concentration equation. Concentration measurements in the sheet flow layer give indication that these suspension ejection events do occur in practice.
Journal of Geophysical Research, 2003
1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model f... more 1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model for one-dimension vertical (1DV) oscillating bottom boundary layer in which a separation condition under a strong, adverse pressure gradient has been introduced and the diffusion and transition constants have been modified. This new turbulence model agrees better than the Wilcox original model with both a direct numerical simulation (DNS) of a pure oscillatory flow over a smooth bottom in the intermittently turbulent regime and with experimental data from Jensen et al. [1989], who attained the fully turbulent regime for pure oscillatory flows. The new turbulence model is also found to agree better than the original one with experimental data of an oscillatory flow with current over a rough bottom by Dohmen-Janssen [1999]. In particular, the proposed model reproduces the secondary humps in the Reynolds stresses during the decelerating part of the wave cycle and the vertical phase lagging of the Reynolds stresses, two shortcomings of all previous modeling attempts. In addition, the model predicts suspension ejection events in the decelerating part of the wave cycle when it is coupled with a sediment concentration equation. Concentration measurements in the sheet flow layer give indication that these suspension ejection events do occur in practice.
Journal of Geophysical Research, 1999
An analytical model has been developed to describe the generation of a linear interfacial wave ov... more An analytical model has been developed to describe the generation of a linear interfacial wave over a steep ocean margin by a barotropic tide propagating toward the shelf break with a variable angle of incidence. The stratification is reduced to a two-layer system, and the model uses step-like shelf geometry. In both shallow and deep regions an open boundary is assumed (this implies particularly that there is no reflection at the coast). The model is forced with the amplitude and direction of an incident barotropic Poincar6 wave propagating toward the shelf break. With this forcing, the model gives the amplitude, direction of propagation, and wavenumber of both barotropic and baroclinic Poincar6 waves transmitted onto the shelf and reflected into the deep region in the vicinity of the shelf break. After comparison with Baines' [1973] model, our model is compared with internal tide observations made in July 1996 on the Malin Shelf within the U.K. Land Ocean Interaction Study-Shelf Edge Study program. The observations are from moored thermistor chains and acoustic Doppler current profilers sited at two locations, one near the shelf break and the other 47.5 km onto the shelf. Observations at this latter mooring are not described by the generation model because of nonlinear changes and damping as the internal wave propagates through shallow water. Baroclinic displacements of the thermocline of 8 m amplitude were observed close to the shelf break, and total baroclinic energy was estimated at 2.4 J/m 3 during neap tide and 3 J/m 3 during spring tide. Both amplitude and energy of the shoreward propagating internal tide waves are compared with the model. Using a barotropic forcing taken from bibliographical data, good agreement with observations is found during neap tide (when the density structure is close to being two-layer) for an incident barotropic tide of 1 m amplitude and propagation direction on a bearing of 23øT (T means from True North in a clockwise sense).
Within the MORSE project of the CEC-MASTIII, LEGI investigates the interaction of long gravity wa... more Within the MORSE project of the CEC-MASTIII, LEGI investigates the interaction of long gravity waves with the continental shelf. It is well known that internal tides are primarily generated at these dramatic topographic features. Propagating onshelf they desintegrate to “shed” solitary waves and highly nonlinear waves that very often give signatures on SAR images of the ocean surface. Moreover off-shore operators have shown recent concern in predicting internal wave fields that they regard as hazards. The present authors analyze the generation and the refraction of these long waves. They extend the shallow water model for linear long waves devised by Rattray (1960), which accounts for the stratification of the ocean water column (2-layer), for the earth rotation (f-plane approximation), for free surface boundary conditions, to take into account the oblicity of the wave crest with respect to the shelf break (modelled as a step shelf). The long wave assumption implies that the pressure on the vertical is hydrostatic. The horizontal component of the velocity is much larger than the vertical one due to the shallow water assumption. The equations reduce to vertically integrated (in each layer) 2D equations for the 2 horizontal velocity components, the interface displacement and free surface one. This system of equation yields for instance Poincare waves, Kelvin waves and standing waves for the 2 modes sustained by the two layer stratification. Long wave models of this type have been shown to be limited to the description of wave propagation on short time scales. The results of the model are used to describe how an internal solitary waves is refracted by a step and how internal tides are generated at the shelf break by an incoming surface tide modelled as a free Poincare wave
Continental Shelf Research, 2010
Experimental and field studies were carried out to quantify the hydrodynamic mobility under swell... more Experimental and field studies were carried out to quantify the hydrodynamic mobility under swells of a circalittoral epifauna species. The spatial distribution and structure of one population (NW Mediterranean) of the serpulid polychaete Ditrupa arietina was assessed before and after a moderate swell event in late winter 2006 with the two readings separated by a seven-week interval. The overall density in the bay did not change significantly. However, in certain locations, significant but heterogeneous changes occurred: at some stations, D. arietina disappeared, at others it appeared with high densities while at others, densities remained fairly constant, although in this third case, the population size structure was different. In addition, no trend was observed along a cross-shore gradient. Experimental studies were conducted to determine bed friction velocity thresholds for incipient motion, bed load transport and suspension transport for different sizes of D. arietina. The minimum friction velocity required to transport D. arietina as bed load over a smooth rigid bed ranged from 1.5 to 2:5 cm s À1 for tube lengths ranging from 6 to 25 mm. Thus, calcified worms (more than 6 mm long) cannot be destabilized by ordinary currents. Conversely, during the moderate swell event, the maximum bed friction was large enough to mobilize D. arietina, making probably all sizes available for bed load transport, while only worms with a tube length of less than 12 mm were transported in suspension at 27 m water depth. Wave statistics in Banyuls Bay indicate that D. arietina transport under moderate swell events should not be a rare phenomenon (28 days per year at 20 m water depth). Thus, the spatial scale for population dynamics studies should account for the extent of D. arietina spatial redistribution by the hydrodynamics. It is also recommended D. arietina be discarded from biotic quality index computations as this species is sensitive to natural hydrodynamic conditions.
The design (location and size) of sustaining, no-take reserves was investigated by combining real... more The design (location and size) of sustaining, no-take reserves was investigated by combining realistic numerical simulations of larval dispersal from a sedentary marine species with a population dynamics model. The method explored, a priori: (1) the planktonic larval duration (PLD) of self-persistent populations within no-take reserves with radii from 1 to 20 km, (2) the size of a no-take reserve reaching self-persistent recruitment of the reserve population, and (3) offspring spillover to adjacent fisheries for PLDs from 1 to 6 weeks. In the Gulf of Lions (northwest Mediterranean), as the radius of a no-take reserve increased to 20 km, the median PLD of a selfpersistent species within the reserve increased from 2 to 6.5 d. No unique relation between PLD and sustaining notake reserve size could be established because of large spatial and temporal variabilities, thus precluding any general guidelines for marine protected area sizes. For species with mass spawning lasting , 3 d, variability due to spawning timing yielded twice the spatial variability, reflecting strong wind variability. In contrast, when spawning lasted more than 10 d, the spawning location became more important. Thus, a biological process (spawning duration) can trigger deterministic and stochastic effects of environmental variability. Finally, some unprotected areas (Narbonne to Agde and the Camargue) clearly appeared to be better locations than the existing no-take reserves for maximizing biodiversity persistence within a reasonable no-take reserve size (10 to 20 km) and for producing offspring spillover important for regional fisheries (80%).
Journal of Geophysical Research, 2003
1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model f... more 1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model for one-dimension vertical (1DV) oscillating bottom boundary layer in which a separation condition under a strong, adverse pressure gradient has been introduced and the diffusion and transition constants have been modified. This new turbulence model agrees better than the Wilcox original model with both a direct numerical simulation (DNS) of a pure oscillatory flow over a smooth bottom in the intermittently turbulent regime and with experimental data from Jensen et al. [1989], who attained the fully turbulent regime for pure oscillatory flows. The new turbulence model is also found to agree better than the original one with experimental data of an oscillatory flow with current over a rough bottom by Dohmen-Janssen [1999]. In particular, the proposed model reproduces the secondary humps in the Reynolds stresses during the decelerating part of the wave cycle and the vertical phase lagging of the Reynolds stresses, two shortcomings of all previous modeling attempts. In addition, the model predicts suspension ejection events in the decelerating part of the wave cycle when it is coupled with a sediment concentration equation. Concentration measurements in the sheet flow layer give indication that these suspension ejection events do occur in practice.
Journal of Geophysical Research, 2003
1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model f... more 1] On the basis of the transitional k-w turbulence model, we propose a new k-w turbulence model for one-dimension vertical (1DV) oscillating bottom boundary layer in which a separation condition under a strong, adverse pressure gradient has been introduced and the diffusion and transition constants have been modified. This new turbulence model agrees better than the Wilcox original model with both a direct numerical simulation (DNS) of a pure oscillatory flow over a smooth bottom in the intermittently turbulent regime and with experimental data from Jensen et al. [1989], who attained the fully turbulent regime for pure oscillatory flows. The new turbulence model is also found to agree better than the original one with experimental data of an oscillatory flow with current over a rough bottom by Dohmen-Janssen [1999]. In particular, the proposed model reproduces the secondary humps in the Reynolds stresses during the decelerating part of the wave cycle and the vertical phase lagging of the Reynolds stresses, two shortcomings of all previous modeling attempts. In addition, the model predicts suspension ejection events in the decelerating part of the wave cycle when it is coupled with a sediment concentration equation. Concentration measurements in the sheet flow layer give indication that these suspension ejection events do occur in practice.
Journal of Geophysical Research, 1999
An analytical model has been developed to describe the generation of a linear interfacial wave ov... more An analytical model has been developed to describe the generation of a linear interfacial wave over a steep ocean margin by a barotropic tide propagating toward the shelf break with a variable angle of incidence. The stratification is reduced to a two-layer system, and the model uses step-like shelf geometry. In both shallow and deep regions an open boundary is assumed (this implies particularly that there is no reflection at the coast). The model is forced with the amplitude and direction of an incident barotropic Poincar6 wave propagating toward the shelf break. With this forcing, the model gives the amplitude, direction of propagation, and wavenumber of both barotropic and baroclinic Poincar6 waves transmitted onto the shelf and reflected into the deep region in the vicinity of the shelf break. After comparison with Baines' [1973] model, our model is compared with internal tide observations made in July 1996 on the Malin Shelf within the U.K. Land Ocean Interaction Study-Shelf Edge Study program. The observations are from moored thermistor chains and acoustic Doppler current profilers sited at two locations, one near the shelf break and the other 47.5 km onto the shelf. Observations at this latter mooring are not described by the generation model because of nonlinear changes and damping as the internal wave propagates through shallow water. Baroclinic displacements of the thermocline of 8 m amplitude were observed close to the shelf break, and total baroclinic energy was estimated at 2.4 J/m 3 during neap tide and 3 J/m 3 during spring tide. Both amplitude and energy of the shoreward propagating internal tide waves are compared with the model. Using a barotropic forcing taken from bibliographical data, good agreement with observations is found during neap tide (when the density structure is close to being two-layer) for an incident barotropic tide of 1 m amplitude and propagation direction on a bearing of 23øT (T means from True North in a clockwise sense).
Within the MORSE project of the CEC-MASTIII, LEGI investigates the interaction of long gravity wa... more Within the MORSE project of the CEC-MASTIII, LEGI investigates the interaction of long gravity waves with the continental shelf. It is well known that internal tides are primarily generated at these dramatic topographic features. Propagating onshelf they desintegrate to “shed” solitary waves and highly nonlinear waves that very often give signatures on SAR images of the ocean surface. Moreover off-shore operators have shown recent concern in predicting internal wave fields that they regard as hazards. The present authors analyze the generation and the refraction of these long waves. They extend the shallow water model for linear long waves devised by Rattray (1960), which accounts for the stratification of the ocean water column (2-layer), for the earth rotation (f-plane approximation), for free surface boundary conditions, to take into account the oblicity of the wave crest with respect to the shelf break (modelled as a step shelf). The long wave assumption implies that the pressure on the vertical is hydrostatic. The horizontal component of the velocity is much larger than the vertical one due to the shallow water assumption. The equations reduce to vertically integrated (in each layer) 2D equations for the 2 horizontal velocity components, the interface displacement and free surface one. This system of equation yields for instance Poincare waves, Kelvin waves and standing waves for the 2 modes sustained by the two layer stratification. Long wave models of this type have been shown to be limited to the description of wave propagation on short time scales. The results of the model are used to describe how an internal solitary waves is refracted by a step and how internal tides are generated at the shelf break by an incoming surface tide modelled as a free Poincare wave
Continental Shelf Research, 2010
Experimental and field studies were carried out to quantify the hydrodynamic mobility under swell... more Experimental and field studies were carried out to quantify the hydrodynamic mobility under swells of a circalittoral epifauna species. The spatial distribution and structure of one population (NW Mediterranean) of the serpulid polychaete Ditrupa arietina was assessed before and after a moderate swell event in late winter 2006 with the two readings separated by a seven-week interval. The overall density in the bay did not change significantly. However, in certain locations, significant but heterogeneous changes occurred: at some stations, D. arietina disappeared, at others it appeared with high densities while at others, densities remained fairly constant, although in this third case, the population size structure was different. In addition, no trend was observed along a cross-shore gradient. Experimental studies were conducted to determine bed friction velocity thresholds for incipient motion, bed load transport and suspension transport for different sizes of D. arietina. The minimum friction velocity required to transport D. arietina as bed load over a smooth rigid bed ranged from 1.5 to 2:5 cm s À1 for tube lengths ranging from 6 to 25 mm. Thus, calcified worms (more than 6 mm long) cannot be destabilized by ordinary currents. Conversely, during the moderate swell event, the maximum bed friction was large enough to mobilize D. arietina, making probably all sizes available for bed load transport, while only worms with a tube length of less than 12 mm were transported in suspension at 27 m water depth. Wave statistics in Banyuls Bay indicate that D. arietina transport under moderate swell events should not be a rare phenomenon (28 days per year at 20 m water depth). Thus, the spatial scale for population dynamics studies should account for the extent of D. arietina spatial redistribution by the hydrodynamics. It is also recommended D. arietina be discarded from biotic quality index computations as this species is sensitive to natural hydrodynamic conditions.
The design (location and size) of sustaining, no-take reserves was investigated by combining real... more The design (location and size) of sustaining, no-take reserves was investigated by combining realistic numerical simulations of larval dispersal from a sedentary marine species with a population dynamics model. The method explored, a priori: (1) the planktonic larval duration (PLD) of self-persistent populations within no-take reserves with radii from 1 to 20 km, (2) the size of a no-take reserve reaching self-persistent recruitment of the reserve population, and (3) offspring spillover to adjacent fisheries for PLDs from 1 to 6 weeks. In the Gulf of Lions (northwest Mediterranean), as the radius of a no-take reserve increased to 20 km, the median PLD of a selfpersistent species within the reserve increased from 2 to 6.5 d. No unique relation between PLD and sustaining notake reserve size could be established because of large spatial and temporal variabilities, thus precluding any general guidelines for marine protected area sizes. For species with mass spawning lasting , 3 d, variability due to spawning timing yielded twice the spatial variability, reflecting strong wind variability. In contrast, when spawning lasted more than 10 d, the spawning location became more important. Thus, a biological process (spawning duration) can trigger deterministic and stochastic effects of environmental variability. Finally, some unprotected areas (Narbonne to Agde and the Camargue) clearly appeared to be better locations than the existing no-take reserves for maximizing biodiversity persistence within a reasonable no-take reserve size (10 to 20 km) and for producing offspring spillover important for regional fisheries (80%).