Search

In the light of challenges raised by a changing climate and increasing population pressure in coastal regions, it has become clear that theoretical models and scattered experiments do not provide the data we urgently need to understand coastal conditions and processes. We propose a Dutch coastline observatory named ICON.NL, based at the Delfland Coast with core observations focused on the internationally well-known Sand Engine experiment, as part of an International Coastline Observatories Network (ICON). ICON.NL will cover the physics and ecology from deep water to the dunes. Data will be collected continuously by novel remote sensing and in-situ sensors, coupled to numerical models to yield unsurpassed long-term coastline measurements. The combination of the unique site and ambitious monitoring design enables new avenues in coastal science and a leap in interdisciplinary research.

In the light of challenges raised by a changing climate and increasing population pressure in coastal regions, it has become clear that theoretical models and scattered experiments do not provide the data we urgently need to understand coastal conditions and processes. We propose a Dutch coastline observatory named ICON.NL, based at the Delfland Coast with core observations focused on the internationally well-known Sand Engine experiment, as part of an International Coastline Observatories Network (ICON). ICON.NL will cover the physics and ecology from deep water to the dunes. Data will be collected continuously by novel remote sensing and in-situ sensors, coupled to numerical models to yield unsurpassed long-term coastline measurements. The combination of the unique site and ambitious monitoring design enables new avenues in coastal science and a leap in interdisciplinary research.

Infragravity (hereafter IG) waves are surface ocean waves with frequencies below those of wind-generated “short waves” (typically below 0.04 Hz). Here we focus on the most common type of IG waves, those induced by the presence of groups in incident short waves. Three related mechanisms explain their generation: (1) the development, shoaling and release of waves bound to the short-wave group envelopes (2) the modulation by these envelopes of the location where short waves break, and (3) the merging of bores (breaking wave front, resembling to a hydraulic jump) inside the surfzone. When reaching shallow water (O(1–10 m)), IG waves can transfer part of their energy back to higher frequencies, a process which is highly dependent on beach slope. On gently sloping beaches, IG waves can dissipate a substantial amount of energy through depth-limited breaking. When the bottom is very rough, such as in coral reef environments, a substantial amount of energy can be dissipated through bottom friction. IG wave energy that is not dissipated is reflected seaward, predominantly for the lowest IG frequencies and on steep bottom slopes. This reflection of the lowest IG frequencies can result in the development of standing (also known as stationary) waves. Reflected IG waves can be refractively trapped so that quasi-periodic along-shore patterns, also referred to as edge waves, can develop. IG waves have a large range of implications in the hydro-sedimentary dynamics of coastal zones. For example, they can modulate current velocities in rip channels and strongly influence cross-shore and longshore mixing. On sandy beaches, IG waves can strongly impact the water table and associated groundwater flows. On gently sloping beaches and especially under storm conditions, IG waves can dominate cross-shore sediment transport, generally promoting offshore transport inside the surfzone. Under storm conditions, IG waves can also induce overwash and eventually promote dune erosion and barrier breaching. In tidal inlets, IG waves can propagate into the back-barrier lagoon during the flood phase and induce large modulations of currents and sediment transport. Their effect appears to be smaller during the ebb phase, due to blocking by countercurrents, particularly in shallow systems. On coral and rocky reefs, IG waves can dominate over short-waves and control the hydro-sedimentary dynamics over the reef flat and in the lagoon. In harbors and semi-enclosed basins, free IG waves can be amplified by resonance and induce large seiches (resonant oscillations). Lastly, free IG waves that are generated in the nearshore can cross oceans and they can also explain the development of the Earth's “hum” (background free oscillations of the solid earth).

International audience; This paper describes the main results of MICORE - WP4 (xbeach modelling) and was presented by Dr. Ap Van Dongeren during the AGU Conference in San Francisco.

Information on the actual state of the nearshore zone - in terms of topographic variability, surface waves, and circulation patterns - is crucial in many naval and civilian applications. Spatial scales of interest generally span distances on the order of hundreds of meters to a few kilometers. Obtaining this information form in situ measurements or model predictions alone is not feasible. This paper presents results of the first efforts in assimilating high-resolution video observations of the surf zone with a 2DH morphological model to map 3D bathymetry in the surf zone. Two pilot applications demonstrate the model's potential, returning a realistic rip channelled beach topography at Monterey (CA, USA) and preserving the characteristic bar-trough configuration at Egmond (NL) throughout the entire 9 month simulation period. Being fully embedded in the Delft3D modelling system, the assimilation model can be combined with any regular hydrodynamic or morphological model run. This sophisticated use of high-resolution video observations in combination with a 2DH morphological model opens the door towards the nowcasting of nearshore bathymetric evolution. Copyright ASCE 2006.

Existence of the estuarine turbidity maximum (ETM) zone is ubiquitous in partially mixed estuaries. It is characterized by high suspended sediment concentration. The position of the TM usually corresponds to the head of the salt instruction. In the Yangtze Estuary, the ETM zone is extremely large in spatial scale, spreading over the entire mouth zone downstream the South Branch and inside the 10 m isobaths. The ETM is aslo accompanied by a board shallow area (basically around 6 m) in the mouth zone, namely the mouth bars. The presence of the mouth bars hampers the navigation significantly. Thus extensive engineering works are implemented to achieve deeper water depth with the help of dredging activities in the North Passage in the Yangtze Estuary. However after the completion of the engineering works, high siltation appears in the middle segment of the North Passage. The hypothesis is that the location of high siltation (expressed in the morphology) falls in the range of ETM zone modified by the completion of the engineering works. The formation and development of ETM and consequent morphodynamic development is focused on.A three-dimensional z-layer model Delft3D is employed. This study clearly shows that salinity gradients can be better simulated using the z-layer model, where the stratification at the upper limits of the salt wedge is better resolved. Afterwards, the consequent morphological changes are qualitatively demonstrated. The study shows the capability of this z-layer model to exploit the mechanism of generation and development of ETM, thus to explain the complex phenomenon of the high siltation in the North Passage of Yangtze estuary

For an efficient protection of the north coast of the Dutch Waddensea island Texel, a long dam was constructed in 1995. The position of this dam is on the southern swash platform of the ebb tidal delta of the Eijerlandse Gat: the tidal inlet between the two Waddensea islands Texel and Vlieland. The long dam changed the hydro-morphological conditions in this tidal inlet. The changes in the inlet's morphology have been monitored through regular bathymetry surveys. This paper describes some of the most remarkable changes that occurred in the inlet after the construction of the long dam. The impact of the long dam on the inlet's morphology and the adjacent shoreline stability has been examined with the use of a medium-term morphodynamic model. From a comparison between the observed and predicted morphological changes it followed that the model was able to simulate the large scale morphological response of the inlet system. However, on a smaller scale there were still important discrepancies between the observations and the predictions.

Coastal 3D nearshore processes were considered with an emphasis on the effects of oceanic forcing and beach characteristics on sediment transport in both cross- and alongshore directions, as well as on foreshore bathymetry changes. In our numerical experiments, we combined the FLOW module of the Delft3D model with the WAVE solver of Xbeach models. k-ε turbulence closure was used to resolve the three-dimensional Navier-Stokes equations for incompressible flow and the beach morphology. The sediment transport module simulates both bedload and suspended load transport of non-cohesive sediments. A series of numerical experiments was performed for a range of control parameters. For each case, the general morphological response was determined in the shore-normal and shore-parallel directions. The simulations confirmed that the sole wave forcing is sufficient to drive a sediment circulation pattern that results in bar and berm formation. The wave characteristics have a considerable effect on the cumulative erosion/deposition, cross-shore distribution of longshore sediment transport, and the sediment transport rate across and along the beach face. For the same oceanic forcing, beach morphology exhibits different erosive characteristics depending on grain size. Fine beach sands were transported offshore, whereas coarse sands moved onshore-wards. Sediment movement increases with wave energy, which was shown to be the most dominant factor controlling the beach face shape. In the surf zone, the sediment transport rate increases towards the shore until the wave collapses whereas in the swash zone it decreases. The present model is able to reproduce complicated flow and sediment transport processes and estimation of beach face dynamics.

Two major parameters that determine the beach type are sediment grain size and beach slope. Intermediate beaches normally have steep slopes and are associated with coarse-grained sands and narrow surf zones, while dissipative beaches generally have mild slopes and are related to fine sands and wider surf zones. In numerical experiments, the Delft3D and Xbeach models were combined to resolve the 3D Navier-Stokes equations for incompressible flow and beach morphology. The sediment transport module supports both bed-load and suspended load transport of non-cohesive sediments. Numerical simulations were run for different hydrodynamic conditions, but with a focus on different beach slopes and grain sizes, and considering hydrodynamic processes, sediment transport in cross- and alongshore directions, as well as foreshore bathymetry changes. Larger grain sizes tend to generate more complex nearshore hydrodynamic patterns. The transformation of incoming waves as they reach shallow water occurs closer the shoreline for steeper profiles. Consistently, the peaks in eddy viscosity, turbulence dissipation rate (TDR), turbulent kinetic energy (TKE) and wave set-up are shifted onshore for steeper slopes. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. The TDR is an order of magnitude smaller for the coarsest grains compared with other cases. The numerical results showed that TKE, sediment concentrations and sediment transport rate are greater on steep beaches than on mildly sloped beaches. The beach morphology exhibits different erosive characteristics depending on grain size (e.g., foreshore profile evolution is erosive and accretionary on fine and coarse sand beaches, respectively). The results confirmed that wave energy, beach grain size and bed slope are the main factors influencing sediment transport and beach morphodynamics.

Dissertação de mest., Eco-Hidrologia, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2012 Ria Formosa lagoon, Southern coast of Portugal is considered as a very dynamic system. Current and water level data measurements of tidal dynamic in the main channels of Ria Formosa lagoon had been carried to figure out the hydrodynamic water circulation patterns. The aims of this study in general is to generate a recent hydrodynamic water circulation patterns based on tidal analysis, with the output of tidal dynamic characteristic (tidal propagation, tidal asymmetry and tidal distortion, energy flux and dissipation, water level and velocity longitudinal gradients, phase lag, tidal prisms, water discharge, etc) and residence time, which are used to identify the most suitable areas for seashell to grow. Several time series of water level and longitudinal component of velocity variations data during completed tidal cicles in the 12 station points of the main channel in Ria Formosa were analyzed using harmonic analysis methods and obtained the average errors of 7.5 % velocity root mean square and 6.75% elevation root mean square, respectively. The tidal analysis results when projected in GIS platform enabled to highlight water circulation patterns in the main channel of Ria Formosa and showed the significance role of Faro-Olhão inlet and Armona inlet in term of energy, volume, and discharge, and less significance role of Sao Luis inlet. The spatial variability of residence time in each stations was obtained and showed that in the west and middle regions of Ria Formosa, a good water exchange were indicated, while in east region, a high residence time magnitude was discovered especially in the inner part of east region with 6.7 days of residence time. This finding result was combined with the average current velocity and maximum flood current and found that Nave Pegos, Culatra, Cações, and Bela Romão stations and adjacent areas are the most suitable area for seashell to grow. The comparison study between inlet tidal cycle volume and geometric volume calculation was carried out and showed that volume difference represent in average a -38 cm of water level height difference estimation for all lagoon. The future development of this work will allow introducing a quality level of understanding of the system in Ria Formosa and can give contribution for the fisherman as a preliminary step to find the suitable place for doing seashell aquaculture/ harvesting. Hence, from the Eco-hydrological perspective, the result of this study could be used for the decision maker as a management tool that related to anthropogenic activities such as dredging activity, inlet opening, and other activities that can give impact to the biota life in Ria Formosa. O sistema lagunar da Ria Formosa localiza-se na zona costeira Sul de Portugal. Este trabalho teve por principal objectivo estudar os principais padrões de circulação da água nos canais principais, tendo por base leituras de velocidade da corrente e da variação da superfície livre, medidos em vários locais na Ria Formosa. Pretendeu igualmente estudar a propagação e a dissipação de energia da maré, os gradientes longitudinais referentes à variação da superfície livre e à velocidade da corrente, os atrasos da maré em diferentes locais, os prismas de maré, os volumes de água em circulação nos canais principais, os tempos de residência e as potenciais áreas para um melhor crescimento de bivalves tendo por base vários parâmetros hidrodinâmicos. Para o efeito foram medidas série de dados referentes à variação da superfície livre e variação da velocidade na coluna de água, ao longo de ciclos de maré, em 12 estações distribuídas na Ria Formosa, que foram submetidas a uma análise harmónica. Para a componente vertical da maré foram obtidos erros RMS médios de 6.75% e para a componente horizontal de 6.75%. Os resultados obtidos desta análise, quando projectados num sistema SIG permitiram realçar a importância das barras de Faro-Olhão e da Armona na circulação hidrodinâmica deste sistema lagunar em termos energéticos, volume e caudais, bem como uma menor importância relativa por parte da barra de S. Luís. Quando analisados os tempos de residência nas várias estações em estudo, verificou-se que as regiões Central e Oeste da ria foram caracterizadas por uma boa troca de água, enquanto nos sectores mais interiores da região Este por tempos de residência elevados de aproximadamente 6.7 dias. Estes resultados quando conciliados com as respectivas velocidades médias e velocidades máximas de enchente, permitiram definir as estações de Nave Pegos, Culatra, Cações e Bela Romão (e zonas adjacentes) com as mais indicadas para o crescimento de bivalves. Quando comparados os volumes referentes aos prismas de maré obtidos através das séries de dados maregráficos medidos nas barras em análise, com os prismas de maré geométricos obtidos pela plataforma GIS, constatou-se haver uma diferença entre eles que se materializou numa diferença media da altura da água na laguna da ordem dos -38cm. Este trabalho para além de contribuir para melhor conhecimento do funcionamento hidrodinâmico da Ria Formosa, e dar um contributo para as associações de mariscadores locais com estes resultados preliminares sobre as melhores localizações para os viveiros de marisco neste sistema lagunar, poderá permitir introduzir em trabalhos futuros outros parâmetros que ajudarão a definir as melhores áreas para a implementação deste viveiros. Os resultados obtidos neste trabalho no âmbito da Eco-hidrologia, poderão ser usados não só como uma ferramenta de decisão para as entidades locais, mas também dar informações primordiais para a gestão deste sistema costeiro no que diz respeito a actividades antropogénicas, tais como a gestão de trabalhos de dragagem, a abertura de novas barras, e outras actividades que possam ter impactes no Biota da Ria Formosa.