Tidal Network Research Articles

Dynamic evolution of tidal networks under the combined effect of de-reclamation and decrease of sediment supply

De-reclamation is a common strategy used for the restoration of tidal flats. In this study, we investigate the morphodynamic response of tidal channel networks and tidal flats after de-reclamation initiatives using the Delft3D numerical model. We find that tidal channel networks that have undergone reclamation and retreat projects have a lower drainage density (8.95 km−1) than that of channel networks that formed naturally (11.33 km−1), and the drainage efficiency of natural formed channel networks is almost three times greater than restored channel networks. These findings indicate that de-reclamation alone cannot fully erase the imprinting of the previous reclamation. We also find that the ultimate effectiveness of de-reclamation is affected by the geographical layout and unchanneled path length of the inchoate main creek system. In addition, following the implementation of de-reclamation, the immediate opening of previously enclosed areas amplifies the tidal prism, thereby intensifying tidal scouring and resulting in significant erosion, with erosion rate reaching hundreds of millimeters per day. Such losses can be remediated under sufficient sediment supply and prevented through the construction of artificial channels. However, this severe erosion may escalate under an insufficient sediment supply or a heightened tidal prism, potentially leading to permanent loss. These findings constitute an important reference for future engineering practices that support the safety and sustainability of coastal resources.

The Sensitivity of Tidal Channel Systems to Initial Bed Conditions, Vegetation, and Tidal Asymmetry

AbstractIn tidal environments, channel networks act as essential drainage pathways. Although the complex interactions between environmental factors have been studied extensively, the effects of the initial bathymetry on tidal network ontogeny are poorly understood. In this contribution, we used a numerical model to mimic a schematic tidal basin subjected to tidal forcing. The effects of the initial bathymetry and vegetation growth are analyzed by changing the features of randomly generated bed perturbation and the intertidal platform slope. Different perturbation densities mildly affect the growth of tidal networks, which, at equilibrium, share similar values in terms of channel length, tidal prism, and cross‐sectional area. The complexity and structure of channel networks are more sensitive to variations in the perturbation distribution. Increasing the initial bathymetry slope can shorten channels and reduce the tidal prism and drainage efficiency. Vegetation growth is found to invariably promote channel lengthening and narrowing, increasing the complexity and drainage efficiency of the system. An asymmetrical tidal forcing generally leads to longer channels and smaller unchanneled lengths. Under ebb‐dominant conditions, channels get deeper, and the increased channel length ensures a higher drainage efficiency. The insights of our study provide a deeper understanding of the environmental factors controlling the equilibrium morphology of tidal channel systems and their overall resilience. Further implications concern the restoration and management of coastal areas through the informed use of topographic changes and planting arrangements. Finally, accounting for the uncertainties associated with initial conditions is relevant when modeling other earth systems and comparing them with real systems.

Characteristics of Tidal Zone in Kalubhar Island, Gulf of Kachchh, Gujarat and Its Geomorphological Implications

Tidal networks, tidal flats and mangroves are some of the important features of tidal areas in the Gulf of Kachchh. Insight on the patterns of tidal networks, vegetation and sedimentation is useful in understanding geomorphological processes active on the region. In the present study features of tidal zone of Kalubhar island, located in the south-central part of the Gulf have been studied with emphasis on tidal networks using Sentinel-2 Multispectral Imager (MSI) data having spatial resolution of 10m. Typology of tidal network is described for the first time. The typology of tidal network pattern, their density, presence of mangroves and beaches indicate low energy depositional setting in eastern, south-eastern and southern parts. This coupled with continued sedimentation and long sub-aerial exposure during low tides may not be ideal environmentin future for live corals present in the intertidal zones. Keywords: Tidal Network Pattern, Sentinel-2 MSI, Kalubhar Island, Gulf of Kachchh

Managing dyke retreat: Importance of century‐scale channel network evolution on storm surge modification over salt marshes under rising sea levels

AbstractA hybrid coastal defense consisting of a salt‐marsh system at the seaward side and dykes on the landward side has been globally implemented to improve coastal resilience. In this approach, marshes are valuable ecosystems that dampen storm surges and have an intrinsic ability to keep up with sea‐level rise (SLR). Dykes instead, prevent the surge from penetrating inland. Therefore, dyke retreat is now considered a valuable option that allows the creation of new marshland in front of the relocated dyke, thus maximizing surge damping. The studies investigating the effect of dyke retreat on surge modification do not incorporate the morphodynamic expansion of tidal networks in the de‐reclaimed land, which is modeled as an unchannelized marsh. Here, we use the morphodynamic model Delft3D and a marsh evolution module to study the formation of tidal networks in a de‐reclaimed land after dyke retreat and evaluate their effect on surge modification (damping or amplification), and thus, the maximum water level reached at the dyke during a storm surge event. For this purpose, we consider different combinations of hydrodynamic (storm surge peak and duration, SLR), and morphodynamic (sediment input, dyke retreat distance, and de‐reclaimed land slope) parameters. Our results suggest that an increase in tidal prism, which depends on retreat distance, de‐reclaimed land slope, and SLR, drives the century‐scale morphodynamic evolution of the marsh. Results also show that surge damping is overestimated if the morphodynamic evolution of the tidal network after dyke retreat is neglected since the new creeks favor the landward propagation of the surge. Finally, a genetic algorithm is used to determine a relationship between surge modification, marsh morphology, and the morphodynamic and hydrodynamic parameters of the simulations. The relationship indicates that relative surge damping increases for shallower tidal networks, smaller surge peaks, higher marsh platforms, and smaller percentages of channelized area.

Muography for a dense tide monitoring network

Sub-hourly to seasonal and interannual oceanographic phenomena can be better understood with high special resolution and high frequency tidal observations. However, while current tidal measurements can provide sufficiently high observational density in terms of time, the observational density in terms of space is low mainly due to the high expense of constructing tide gauge stations. In this work, we designed a novel tide monitoring technique with muography that could be operated in near-shore basements (or similar structures on land below sea level) and found that more practical, stable, robust and cost-effective high-spatiotemporal-density tide measurements are possible. Although the time resolution, sensitivity, and the distance between the detectors and the shorelines are tradeoffs, hourly and annual sensitivity (ability to detect the tide height variations) of less than 10 cm and 1 mm can be statistically attained, respectively. It is anticipated that the current muographic technique could be applied as an alternative, cost-effective and convenient dense tidal monitor network strategy in coastal areas worldwide.

Influence Mechanism of Geomorphological Evolution in a Tidal Lagoon with Rising Sea Level

A tidal lagoon system has multiple environmental, societal, and economic implications. To investigate the mechanism of influence of the geomorphological evolution of a tidal lagoon, the effect of critical erosion shear stress, critical deposition shear stress, sediment settling velocity, and initial bed elevation were assessed by applying the MIKE hydro- and morpho-dynamic model to a typical tidal lagoon, Qilihai Lagoon. According to the simulation results, without sediment supply, an increase of critical erosion, deposition shear stress, or sediment settling velocity gives rise to tidal networks with a stable terrain. Such an equilibrium state can be defined as when the change of net erosion has little variation, which can be achieved due to counter actions between the erosion and deposition effect. Moreover, the influence of the initial bed elevation depends on the lowest tidal level. When the initial bed elevation is below the lowest tidal level, the tidal networks tend to be fully developed. A Spearman correlation analysis indicated that the geomorphological evolution is more sensitive to critical erosion or deposition shear stress than sediment settling velocity and initial bed elevation. Exponential sea level rise contributes to more intensive erosion than the linear or the parabolic sea level rise in the long-term evolution of a tidal lagoon.

Exchange Flows in Tributary Creeks Enhance Dispersion by Tidal Trapping

The North River estuary (Massachusetts, USA) is a tidal marsh creek network where tidal dispersion processes dominate the salt balance. A field study using moorings, shipboard measurements, and drone surveys was conducted to characterize and quantify tidal trapping due to tributary creeks. During flood tide, saltwater propagates up the main channel and gets “trapped” in the creeks. The creeks inherit an axial salinity gradient from the time-varying salinity at their boundary with the main channel, but it is stronger than the salinity gradient of the main channel because of relatively weaker currents. The stronger salinity gradient drives a baroclinic circulation that stratifies the creeks, while the main channel remains well-mixed. Because of the creeks’ shorter geometries, tidal currents in the creeks lead those in the main channel; therefore, the creeks never fill with the saltiest water which passes the main channel junction. This velocity phase difference is enhanced by the exchange flow in the creeks, which fast-tracks the fresher surface layer in the creeks back to the main channel. Through ebb tide, the relatively fresh creek outflows introduce a negative salinity anomaly into the main channel, where it is advected downstream by the tide. Using high-resolution measurements, we empirically determine the salinity anomaly in the main channel resulting from its exchange with the creeks to calculate a dispersion rate due to trapping. Our dispersion rate is larger than theoretical estimates that neglect the exchange flow in the creeks. Trapping contributes more than half the landward salt flux in this region.

Onset of runaway fragmentation of salt marshes

Summary Salt marshes are valuable but vulnerable coastal ecosystems that adapt to relative sea level rise (RSLR) by accumulating organic matter and inorganic sediment. The natural limit of these processes defines a threshold rate of RSLR beyond which marshes drown, resulting in ponding and conversion to open waters. We develop a simplified formulation for sediment transport across marshes to show that pond formation leads to runaway marsh fragmentation, a process characterized by a self-similar hierarchy of pond sizes with power-law distributions. We find the threshold for marsh fragmentation scales primarily with tidal range and that sediment supply is only relevant where tides are sufficient to transport sediment to the marsh interior. Thus the RSLR threshold is controlled by organic accretion in microtidal marshes regardless of the suspended sediment concentration at the marsh edge. This explains the observed fragmentation of microtidal marshes and suggests a tipping point for widespread marsh loss.

Piracy-controlled geometry of tide-dominated point bars: Combined evidence from ancient sedimentary successions and modern channel networks

Establishing critical comparisons between fluvial- and tidal-channel morphodynamics is a major goal in the study of coastal landscapes. Freely migrating meandering rivers are known to produce laterally extensive, sand-prone point-bar bodies which commonly exhibit width:thickness ratios up to 250. Meandering channels are widespread in tidal channel networks draining intertidal plains, where they exhibit planform dynamics similar to their fluvial analogues. However, tidal networks are characterized by a high channel density that likely hinders tidal meanders from migrating laterally for long distances without interacting with other channels. In order to better understand how the interaction between adjacent meandering channels controls the development of tide-dominated point bars, two point-bar bodies from the Eocene Castigaleu Formation (Spain) are investigated and compared with the geometry of a modern tidal point bar of the northern Venice Lagoon (Italy). The Eocene bars are characterized by a low width:thickness ratio (<30), interpreted as the result of premature deactivation of their parent-channel migration. Such deactivations were likely related to avulsive piracy operated by adjoining tide-dominated channels, and likely prevented the parent channel bend from depositing a laterally extensive, tabular sand body along its inner bank. This analysis is corroborated by direct time-lapse observations of similar dynamics in modern tidal networks, and from morphodynamic and sedimentological evidence from recent deposits of the Venice Lagoon. We conclude that, in densely drained tidal networks, meander bends often interact with adjacent channels, thereby triggering piracy events and premature channel abandonments that generate point-bar architectures distinct from those produced in fluvial meandering rivers.

Extracting tidal creek features in a heterogeneous background using Sentinel-2 imagery: a case study in the Yellow River Delta, China

ABSTRACTOwing to difficulties accessing areas where tidal creeks develop and the frequent morphological changes they undergo, there are very significant advantages in using remote sensing methods to effectively monitor conditions and the dynamics in these zones. The Yellow River Delta, which is the research area of this study, exhibits a very irregular tidal flat, with tidal creeks that vary in width and experience water current anisotropy. This study proposes a method for extracting tidal creeks based on a digital image processing technology that can carry out accurate characterization of tidal creeks against heterogeneous backgrounds. First, the normalized difference water index (NDWI) and Maximum Between-Class Variance (Otsu) classification are used to delineate the wide tidal creeks. Second, the modified fuzzy c-means clustering algorithm (MFCM) is used to suppress the difference between the target and background caused by spatial heterogeneity of the tidal flat environment. Next, the Gaussian matching filter (GMF) is used to enhance the narrow tidal creeks and suppress the influence of anisotropy. Then, adaptive threshold segmentation is conducted to delineate the narrow tidal creeks. Finally, the complete tidal creek networks are delineated by combining the wide and narrow tidal creeks. The overall performance was evaluated by visual interpretation and the result is excellent. In the four test areas, the kappa coefficient (κ) was greater than 0.79, the error of Commission was less than 22%, and the error of omission was less than 15%; the proposed method performed better than the Maximum Likelihood method, Support Vector Machine, and k-means algorithms. The results show that the proposed method can differentiate tidal creeks from different research areas, with good extraction accuracy and stability. The method can provide reference data for real-time dynamic monitoring of tidal creeks and has potential for application to other tidal zones in different regions.

Simulating the impacts of land reclamation and de-reclamation on the morphodynamics of tidal networks

The morphodynamic responses of tidal networks to anthropogenic reclamation and de-reclamation projects are investigated through a three-stage numerical simulation. In the first stage, the natural development of tidal networks is modelled in an open coast without any anthropogenic interventions. At the beginning of the second stage, parts of the computational domain are enclosed by sea dikes, which represents the implementation of the reclamation project. These sea dikes are removed or opened in the third stage to simulate the recovery of the tidal networks after de-reclamation. Each stage was set to last 100 years. The model results indicate that land reclamation can lead to three effects on tidal network morphology: (i) completely terminating the development of channels inside the projected area, (ii) hindering the development of the channel network in front of the dikes, and (iii) turning the channel direction near the corners of the dikes. When removing all the sea dikes, the previously reclaimed areas are quickly occupied by tidal networks. However, the morphology cannot be fully restored to its original natural state, although the entire reclaimed areas are returned. The effects of opening breaches are relatively slow, and tree-like network structures are formed inside the reclaimed areas.

Optimization of the electrical connection topology of a tidal farm network

This article presents an approach to optimize the electrical connection topology of tidal energy converters in a tidal farm. The methodology is based on a genetic algorithm (GA). The main purpose is to present a technique of coding to find the best electrical connection topology of the tidal farm network. The optimization model takes into account the energy loss in the submarine cables. The model gives as its output the optimal number of turbine clusters connected to each offshore substation, the number of turbines in each cluster, the cross-section of MV and HV cables, the connection design for each cluster of turbines as well as the number and the locations of the offshore substations. A particle swarm optimization algorithm (PSO) is used to confirm the results obtained with the GA. The optimization approach is applied to the Fromveur Strait (France).

Ocean Tidal Models and Tidal Gravity Observation

Abstract—Tidal ocean corrections for gravity observation play an important part in monitoring studies. Tidal ocean models were tested by Transcontinental Tidal Gravity Profile (TTGP) results. This part of the global tidal network was used for study the influence of the Atlantic and Pacific oceans up to coastline. Our tidal result agrees with static theory and had a weak ocean dynamic influence (Schiwiderski and other models) into the center of the Eurasian continent. Near the coast, where ocean effects were strong, the influence increases. In the East part of TTGP, we obtained observation results for Khabarovsk region, for Sakhalin Island and for Primorye region (Sea of Okhotsk and Sea of Japan). In the South part of the Primorye observation (Russian Far East) long-term measurement was completed at the Posyet Bay level station and Cape Shultz gravity station. Based on the results, a selection of ocean tidal models was made and a number of unresolved issues were determined.

Assessing the relative contributions of the flood tide and the ebb tide to tidal channel network dynamics

ABSTRACTFlood and ebb currents provide different contributions to the initiation and evolution of tidal channel networks, generating diverse network structures and channel cross‐sections. In order to separate the effects of these contributions, a physical model of a sloping tidal‐flat basin was set up in the laboratory. Depending on the degree of tidal asymmetry imposed offshore, either flood or ebb currents can be enhanced. The experimental results show that the ebb current has a higher capability to initiate and shape tidal networks than the flood current. Headward erosion is mainly induced by the ebb flow. The slightly inclined flat surface tends to reduce the energy of the flood current and to enhance the ebb current, thus prolonging the duration of morphodynamic activity as well as sediment motion. Overall, flood‐dominated tides favour the formation of small‐scale channel branches in the upper basin zone, while long lasting ebb‐dominated tides result in more complex, wider and deeper tidal networks. © 2019 John Wiley &amp; Sons, Ltd.

Flow Reorganization in an Anthropogenically Modified Tidal Channel Network: An Example From the Southwestern Ganges‐Brahmaputra‐Meghna Delta

We examine variations in discharge exchange between two parallel, 1‐ to 2‐km‐wide tidal channels (the Shibsa and the Pussur) in southwestern Bangladesh over spring‐neap, and historical timescales. Our objective is to evaluate how large‐scale, interconnected tidal channel networks respond to anthropogenic perturbation. The study area spans the boundary between the pristine Sundarbans Reserved Forest, where regular inundation of the intertidal platform maintains the fluvially abandoned delta plain, and the anthropogenically modified region to the north, where earthen embankments sequester large areas of formerly intertidal landscape. Estimates of tidal response to the embankment‐driven reduction in basin volume, and hence tidal prism, predict a corresponding decrease in size of the mainstem Shibsa channel, yet the Shibsa is widening and locally scouring even as the interconnected Pussur channel faces rapid shoaling. Rather, the Shibsa has maintained or even increased its pre‐polder tidal prism by capturing a large portion of the Pussur's basin via several “transverse” channels that are themselves widening and deepening. We propose that an enhanced tidal setup in the Pussur and the elimination of an effective Shibsa‐Pussur flow barrier are driving this basin capture event. These results illustrate previously unrecognized channel interactions and emphasize the importance of flow reorganization in response to perturbations of interconnected, multichannel tidal networks that characterize several large tidal delta plains worldwide.

Natural and Human-Induced Flow and Sediment Transport within Tidal Creek Networks Influenced by Ocean-Bay Tides

Improving current understanding of hydrodynamics and sediment dynamics in complex tidal embayments is of major importance to face future challenges derived from climate change and increasing human pressure. This work deepens the knowledge of the hydro-morphodynamics of complex creek networks that connect basins with different characteristics, identifying their morphodynamic trends and the potential impacts of channel deepening. We selected two tidal creeks which flow through salt marshes and tidal flats of the Cádiz Bay (SW Spain) in a singular network due to their double connection to the Atlantic Ocean and the inner bay. We study the interactions between tidal waves that penetrate into the creeks from these two different bodies of water, analyzing the tidal asymmetry and the morphodynamic tendencies of the system. For the analysis, we set up a hydro-morphodynamic model specifically developed for areas with very shallow and complex channels. Results show that the tidal wave penetrates within the tidal network both from the inner Bay and the open ocean with different amplitudes, phases and flow velocities. There is also an asymmetric pattern for the tidal flows caused by the deformation of the dominant astronomical tidal constituents, M2 and M4, due to the non-linear interaction of tidal currents with the irregular creek geometry and bottom topography. Tidal asymmetry promotes the progressive infilling of the area where the tidal waves meet closing the connection between the open ocean and the inner bay, such an infilling trend being accelerated by human interventions.

Modelling, simulation and real-time control of a laboratory tide generation system

Small-scale experiments allow to reproduce and understand phenomena and to draw inferences about large-scale processes. In this paper, we consider a peculiar experimental apparatus which is aimed at reproducing a typical lagoonal environment subject to tidal forcings. This apparatus is useful for performing morphometric analyses of synthetic tidal networks. The quality of these kind of experiments strongly depends on the behaviour of the artificial tide that has to exhibit predefined characteristics. To this aim, the height of the artificial water wave is controlled in real-time. The experimental apparatus has an intrinsic complexity and it represents an example of a multi-domain physical system. In order to design and to assess suitable control strategies, we have developed a Matlab-based simulation environment which is able to reproduce the behaviour of the artificial tide generation system. The dynamic model is calibrated and validated by using real experimental data and it can be seen as an extremely useful tool in the decision making process of the real control system development. In particular, we have designed, tuned, and tested a model-free control algorithm, that is the intelligent-PI (i-PI). Finally, the proposed controller has been implemented on a real-time hardware and then its performance has been compared with that of a standard regulator for different type of experiments.

Model-free Control of an Artificial Tide Generation Experimental Apparatus

Small-scale experiments allow to reproduce and understand phenomena and to draw inferences about large-scale processes. In this paper, we consider a peculiar experimental apparatus which is aimed at reproducing a typical lagoonal environment subject to tidal forcings. This apparatus is useful for performing morphometric analyses of synthetic tidal networks. The quality of these kind of experiments strongly depends on the behaviour of the artificial tide that has to exhibit predefined characteristics. To this aim, the height of the artificial water wave is controlled in real-time. Due to the intrinsic complexity of the system, the development of a control algorithm as simple as possible but able to ensure suitable control performance over a wide range of operative conditions, is a non-trivial task. In this paper, we have developed and tested a model-free control algorithm, that is the intelligent-PI (i-PI). Finally, the performance of the i-PI controller are compared with those of a standard regulator for different type of experiments.

Source identification of accidental water pollution in a tidal river network based on a water environment model and database

Source identification of accidental water pollution in a tidal river network based on a water environment model and database

A numerical study of equilibrium states in tidal network morphodynamics

The long-term morphodynamic evolution of tidal networks on tidal flats is investigated using a two-dimensional numerical model. We explore the physical processes related to the development of the morphology and the presence of equilibrium configurations. Tidal networks are simulated over a rectangular domain representing a tidal platform, a different setting compared to estuaries (subject to riverine influence) and lagoons (offshore bars constricting the flow). In the early and middle phases of the tidal network evolution, large sediment patches with rhombus-like shape form and gradually migrate in the flood direction, even though the overall sediment flux is ebb-directed. A cross-section-averaged “equilibrium” state is asymptotically approached after about 500 years. The area and peak discharge of the lower flat cross-sections at year 500 approximately show a 1:1 relationship, which is in agreement with field observations. We also show that model results are consistent with the Q-A relationship (peak discharge Q versus cross-sectional area A), which is obtained under the assumption of a constant Chezy friction.