Papers by Daniel Calvete Manrique
In this contribution a discussion is presented on the development of self-organized coastal morph... more In this contribution a discussion is presented on the development of self-organized coastal morphodynamic patterns which are due to the joint action of gradients in the depth-integrated concentration and the flow. This is done in the context of a depth-averaged shallow water model. Two physical mechanisms produce deposition-erosion patterns. Deposition either occurs where the current flows from high to low depth-averaged concentrations (1) or where the flow diverges (2). If flow conditions are quasi steady (i.e., the time scale on which bedforms evolve is much larger than the hydrodynamic time scales) only the former mechanism contributes to the formation of bottom patterns.
Journal of Geophysical Research, 2003
A morphodynamic model is analyzed to gain further knowledge about the finite amplitude behavior o... more A morphodynamic model is analyzed to gain further knowledge about the finite amplitude behavior of shore face-connected sand ridges observed on storm-dominated inner shelves. The present work elaborates on previous studies in which it was demonstrated that ridge formation may be due to an instability of a storm-driven current moving over a sandy inner shelf with a transverse slope. Here, the long-term evolution of the ridges is studied by performing a nonlinear stability analysis in which the physical variables are expanded in eigenmodes of the linear stability problem. New physical aspects are that the longshore pressure gradient in the momentum equations and settling lag in the suspended load sediment transport are incorporated. Furthermore, along-shelf uniform shelf modes and subharmonic eigenmodes are accounted for. The model shows that after the transient stage the competition between the modes results in saturation behavior that is dominated by a few modes only. The characteristic height of the final bed forms increases with increasing transverse slopes of the shelf, while the timescale of transient behavior decreases. The longshore uniform modes, pressure gradient, and settling lag effects only have a minor effect on the dynamics. A process analysis reveals that the mechanism responsible for the saturation behavior is the sediment transport related to the bottom slope and the effect of small-scale bed forms. Subharmonic modes significantly affect the transient behavior of the ridges and cause the final bed forms to have larger amplitudes and longer wavelengths.
the meaning and significance of self-organization processes in coastal morphodynamics is presente... more the meaning and significance of self-organization processes in coastal morphodynamics is presented. Two types of coastal self-organized patterns are discussed: crescentic bars in the surf zone and free shoreline sand waves emerging along coastlines where the wave incidence is very oblique to the shore. The coupling between wave breaking and bathymetry in the surf zone is presented as the mechanism which is responsible for crescentic bar formation. Numerical modelling illustrating this process is presented. Shoreline sand waves are described and numerical model results showing their growth and propagation are shown.
EGU General Assembly Conference Abstracts, Apr 1, 2009
Multiple sandbar systems have been observed in a variety of settings worldwide. The changes in mu... more Multiple sandbar systems have been observed in a variety of settings worldwide. The changes in multiple sandbar systems sometimes result in rhythmic patterns, usually called crescentic bars. The nature of their occurrence has been studied both through observations (e.g. Short and Aagaard, 1993) and numerical studies (e.g. Klein and Schuttelaars, 2006). The development of crescentic bars in multiple sandbar systems is part of sequential beach changes (Short and Aagaard, 1993) displaying a range of configurations that can involve coupling between the sandbars and, sometimes, also the shoreline (Ruessink et al., 2007). Here we use a numerical model based on linear stability analysis to study the role of hydrodynamic conditions and initial cross-shore sandbar profile on the evolution of the double sandbar system. Preliminary results shows various configurations that have been observed in the field and that can be related to a combination of offshore hydrodynamic conditions and initial cross-shore beach profiles.
Waves are the dominant forcing of the nearshore system and, in order to understand and predict be... more Waves are the dominant forcing of the nearshore system and, in order to understand and predict beach morphological evolution, it is crucial to have a reliable source for wave characteristics at shallow water (about 20 m depth). The best sources of wave conditions are measurements devices (e.g., a wave buoy or AWAC) located directly in front of the study site. However, wave buoys are scarce and deploying and maintaining an AWAC is expensive. This means that wave conditions often have to be taken from a buoy located far from the study site or from a large-scale global hindcast model and wave propagation is necessary. Mostly, propagation is done either by using linear wave theory and ray approximation or by using more advanced models such as SWAN. Such methods often lead to errors in quantifying wave conditions, especially in small fetch, complex geometry coasts such as the Catalan coast (Pallares et al., 2014). In particular, the reliability of the obtained wave angles is often questionable (see e.g. Amrutha et al., 2016 and Pallares et al., 2014), which is unfortunate because it is nowadays accepted that the wave angle plays a crucial role in nearshore evolution (e.g., Price and Ruessink, 2011).
Effect of surface rollers on the formation crescentic bars
The effect of surface rollers on the formation of crescentic bars/rip channel systems is examined... more The effect of surface rollers on the formation of crescentic bars/rip channel systems is examined with a morphodynamic model. A linear stability analysis is applied to find the fastest growing bottom patterns that develop as a result of morphodynamics self-organization. Explorations of sensitivity of model results to varying wave conditions have been performed. Special attention has been paid to off-normal wave conditions. There are noticeable differences in growth rates for large/intermediate angles of wave incidence with respect to shore normal conditions. The effect of the rollers is to increase the e-folding times with increasing the angle of incidence. For angles large enough the formation of crescentic bars is even inhibit. The effect of the rollers in wavelengths, migration velocities of the bedforms and bed morphologies of the FGM is minor. Flow velocities on the rips are a factor 2 smaller in the models with rollers than in the model without rollers.Postprint (author’s final draft
Formation of shoreface-connected sand ridges: effects of rigid-lid approach, quasi-steady approach and wave-topography feedbacks
The initial- and long-term evolution of shoreface-connected sand ridges (sfcr) is investigated wi... more The initial- and long-term evolution of shoreface-connected sand ridges (sfcr) is investigated with a new nonlinear model (MORFO56) that employs finite difference methods, rather than spectral methods. MORFO56 uses depth-averaged shallow water equations, including sediment transport and bed updating. Moreover, it includes full wave-topography feedbacks, wave shoaling and refraction, and wave radiation stresses. First, effects of relaxing the rigid-lid assumption and quasi-steadiness on the initial growth and migration of sfcr are quantified, by conducting a series of short-term runs. It turns out that assuming a free lid and unsteady flow results in larger wavelengths and larger migration speeds of sfcr. Furthermore, the new model is able to simulate the finite amplitude behaviour of sfcr for more realistic bottom slopes than earlier spectral models. Finally, the role of wave-topography feedbacks in the initial formation of sfcr is examined. Model simulations show that sfcr in the presence of these feedbacks are more trapped to the shoreface, with an offshore extent of approximately 1 km. Moreover, growth of sfcr is enhanced considerably by wave-topography feedbacks. The specific inclusion of radiation stresses does not affect this result.
Remote Sensing, 2021
Following the path set out by the “Argus” project, video monitoring stations have become a very p... more Following the path set out by the “Argus” project, video monitoring stations have become a very popular low cost tool to continuously monitor beaches around the world. For these stations to be able to offer quantitative results, the cameras must be calibrated. Cameras are typically calibrated when installed, and, at best, extrinsic calibrations are performed from time to time. However, intra-day variations of camera calibration parameters due to thermal factors, or other kinds of uncontrolled movements, have been shown to introduce significant errors when transforming the pixels to real world coordinates. Departing from well-known feature detection and matching algorithms from computer vision, this paper presents a methodology to automatically calibrate cameras, in the intra-day time scale, from a small number of manually calibrated images. For the three cameras analyzed here, the proposed methodology allows for automatic calibration of >90% of the images in favorable conditions ...
Waves are the dominant forcing of the nearshore system and, in order to understand and predict be... more Waves are the dominant forcing of the nearshore system and, in order to understand and predict beach morphological evolution, it is crucial to have a reliable source for wave characteristics at shallow water (about 20 m depth). The best sources of wave conditions are measurements devices (e.g., a wave buoy or AWAC) located directly in front of the study site. However, wave buoys are scarce and deploying and maintaining an AWAC is expensive. This means that wave conditions often have to be taken from a buoy located far from the study site or from a large-scale global hindcast model and wave propagation is necessary. Mostly, propagation is done either by using linear wave theory and ray approximation or by using more advanced models such as SWAN. Such methods often lead to errors in quantifying wave conditions, especially in small fetch, complex geometry coasts such as the Catalan coast (Pallares et al., 2014). In particular, the reliability of the obtained wave angles is often questi...
Remote Sensing, 2021
Measuring the nearshore bathymetry is critical in coastal management and morphodynamic studies. T... more Measuring the nearshore bathymetry is critical in coastal management and morphodynamic studies. The recent advent of Unmanned Aerial Vehicles (UAVs), in combination with coastal video monitoring techniques, allows for an alternative and low cost evaluation of the nearshore bathymetry. Camera calibration and stabilization is a critical issue in bathymetry estimation from video systems. This work introduces a new methodology in order to obtain such bathymetries, and it compares the results to echo-sounder ground truth data. The goal is to gain a better understanding on the influence of the camera calibration and stabilization on the inferred bathymetry. The results show how the proposed methodology allows for accurate evaluations of the bathymetry, with overall root mean square errors in the order of 40 cm. It is shown that the intrinsic calibration of the camera, related to the lens distortion, is the most critical aspect. Here, the intrinsic calibration that was obtained directly du...
Analysis of the long-term behaviour of shoreface-connected sand ridges: a nonlinear model study
Comparing observed surfzone transverse finger bars with model results
Proceedings of the 5th IAHR Symposium on River, Coastal and Estuarine Morphodynamics, Enschede, NL, 17-21 September 2007, 2007
ABSTRACT The results of a self-organization model for surfzone transverse bar formation are compa... more ABSTRACT The results of a self-organization model for surfzone transverse bar formation are compared with field observations in Noordwijk beach (the Netherlands). Two events of bar formation and subsequent evolution in June-July 2000 and in August-September 2002 are studied. The wave length of the patches is 35 m and 46 m, respectively, and the mean celerity is 3-4 m/d in the direction of the longshore current. Bars have an oblique orientation, deviating some 30 degrees from the shore-normal against the longshore current. Bars persist up to 2 months, coexisting with obliquely incident waves of intermediate heights. Application of the model to Noordwijk conditions yields wave lengths, crest orientations and growth rates that are in agreement with observations, but the model overestimates the migration rates. The clue to obtain up-current oriented bars is the assumption that the depth-integrated suspended sediment concentration is constant across the inner surf zone.
Modelling the interaction between transverse and crescentic bar systems
Proceedings of the 5th IAHR Symposium on River, Coastal and Estuarine Morphodynamics, Enschede, NL, 17-21 September 2007, 2007
ABSTRACT It is nowadays increasingly recognized that different types of surf zone sand bars and m... more ABSTRACT It is nowadays increasingly recognized that different types of surf zone sand bars and morphological patterns can emerge from free instabilities of the coupling between topography and water motions. Among them, the surf zone exhibits rhythmic features as (1) transverse bars attached to the shore and (2) crescentic bars farther off-shore which develop from the deformation of a longshore bar. By using the 2DH morphodynamical numerical models, (1) linear (MOKFO60) and (2) nonlinear (MORFO55), the stability analysis of a planar and a barred beach is given. This allows an understanding of the possible interaction between transverse and crescentic bars.
Reviews of Geophysics, 2015
This review highlights the important role of the depth‐averaged sediment concentration (DASC) to ... more This review highlights the important role of the depth‐averaged sediment concentration (DASC) to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern: beach cusps, surf zone transverse and crescentic bars, and shoreface‐connected sand ridges. We present a formulation and methodology, based on the knowledge of the DASC (which equals the sediment load divided by the water depth), that has been successfully used to understand the characteristics of these features. These sand bodies, relevant for coastal engineering and other disciplines, are located in different parts of the coastal zone and are characterized by different spatial and temporal scales, but the same technique can be used to understand them. Since the sand bodies occur in the presence of depth‐averaged currents, the sediment transport approximately equals a sediment load times the current. Moreover, it is assumed that waves essentially mobilize the sediment, and th...
Ocean Dynamics, 2014
The occurrence and characteristics of transverse finger bars at Surfers Paradise (Gold Coast, Aus... more The occurrence and characteristics of transverse finger bars at Surfers Paradise (Gold Coast, Australia) have been quantified with 4 years of time-exposure video images. These bars are attached to the inner terrace and have an oblique orientation with respect to the coastline. They are observed during 24 % of the study period, in patches up to 15 bars, with an average lifetime of 5 days and a mean wavelength of 32 m. The bars are observed during obliquely incident waves of intermediate heights. Bar crests typically point toward the incoming wave direction, i.e., they are upcurrent oriented. The most frequent beach state when bars
Morphodynamic Modeling of Rip Channel Growth
ABSTRACT The morphological evolution of a rip channel system is investigated using two different ... more ABSTRACT The morphological evolution of a rip channel system is investigated using two different approaches. The first approach is a state-of-the-art commercial 2DH Coastal Area Model, and the second is a linear stability analysis. Both modeling efforts begin by considering an alongshore uniform, barred beach and then impose an alongshore perturbation on the initial bathymetry and then allow the system to evolve in time. Both approaches predict the evolution of a system of rip channels with a similar alongshore spacing linked to the distance from shoreline to the crest of the alongshore bar. Furthermore, both approaches appear to predict similar initial growth rates for these systems.
Generation and Nonlinear Evolution of Nearshore Oblique Sand Bars
Coastal Dynamics 2005, 2006
The morphodynamic instability of a plane sloping beach for oblique wave incidence has been studie... more The morphodynamic instability of a plane sloping beach for oblique wave incidence has been studied by using a nonlinear numerical model based on a wave and depth averaged shallow water equations solver with wave driver, sediment transport and bed updating. The depth integrated sediment flux formulation is defined as a stirring factor times the depth averaged current plus a downslope term. Two formulae for the stirring factor have been selected: a constant and a function based on the Soulsby and Van Rijn formula. In each case, oblique bars appear with a specific orientation (up- current or down-current), with specific shapes and with specific migration velocities. Not only the initial formation is described but also the finite amplitude dynamics and, in particular, the saturation of the growth.
Dynamics of small amplitude shoreline sand waves
Large scale undulations of the shoreline propagating down drift along the coast have been reporte... more Large scale undulations of the shoreline propagating down drift along the coast have been reported from many sandy shores. At a particular site they result in alternating periods of accretion/erosion. Depending on their origin they have different lenghscales ranging from hundreds of meters to tens of km. At large time and space scales of years and km's the dynamics of
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Papers by Daniel Calvete Manrique