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"Tidal inlets"
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Monitoring the Topography of a Dynamic Tidal Inlet Using UAV Imagery
Unmanned Aerial Vehicles (UAVs) are being increasingly used to monitor topographic changes in coastal areas. Compared to Light Detection And Ranging (LiDAR) data or Terrestrial Laser Scanning data, this solution is low-cost and easy to use, while allowing the production of a Digital Surface Model (DSM) with a similar accuracy. Three campaigns were carried out within a three-month period at a lagoon-inlet system (Bonne-Anse Bay, La Palmyre, France), with a flying wing (eBee) combined with a digital camera. Ground Control Points (GCPs), surveyed by the Global Navigation Satellite System (GNSS) and post-processed by differential correction, allowed georeferencing DSMs. Using a photogrammetry process (Structure From Motion algorithm), DSMs and orthomosaics were produced. The DSM accuracy was assessed against the ellipsoidal height of a GNSS profile and Independent Control Points (ICPs) and the root mean square discrepancies were about 10 and 17 cm, respectively. Compared to traditional topographic surveys, this solution allows the accurate representation of bedforms with a wavelength of the order of 1 m and a height of 0.1 m. Finally, changes identified between both main campaigns revealed erosion/accretion areas and the progradation of a sandspit. These results open new perspectives to validate detailed morphological predictions or to parameterize bottom friction in coastal numerical models.
Journal Article
Towards enhancing tidally-induced water renewal in coastal lagoons
In order to address the problem of limited water renewal in restricted lagoons of moderate size having at least two tidal inlets, a method is proposed to enhance water exchange between the lagoon and the open sea. The method consists of altering either the amplitude or the phase of the tide in one of the inlets. It is shown in the paper that this will result in an alteration of the function of the lagoon, from a lagoon periodically exchanging water equal to a tidal prism within each tidal cycle with the adjacent water body, towards an effectively flow through system, substantially improving the flushing rate of the lagoon. The method is confirmed by running a series of numerical experiments simulating tidal hydrodynamics in the Papas lagoon. The question of how to alter the tidal amplitude is briefly touched upon, by numerically testing the performance of artificially macro-roughening an inlet and alternatively, designing an inlet to have a meandering shape. It was found that both modifications produce a diminished tidal amplitude, providing positive evidence for the applicability of the proposed method.
Journal Article
Recent Advances in Tidal Inlet Morphodynamic Modelling
Bertin, X.; Mengual, B.; de Bakker, A.; Guérin, T.; Martins, K.; Pezerat, M., and Lavaud, L., 2020. Recent advances in tidal inlet morphodynamics modelling. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1016–1020. Coconut Creek (Florida), ISSN 0749-0208. Tidal inlets connect the ocean to inner water bodies and are present worldwide. Complex interactions between tides, waves and shallow bathymetry often drive fast morphological changes but the underlying processes remain only partly understood. To better understand these processes, the development and application of morphodynamic models represents a unique perspective. This paper evaluates the impact of recent developments in the modelling system SCHISM, which include: a WENO method to solve the Exner Equation, a 3D coupling between waves and currents using a vortex force formalism, an adaptive parameterization for the dissipation of short waves by breaking and improved representations for wave-induced sediment transport. In order to evaluate the relevance of these developments, SCHISM is applied to the Maumusson Inlet, a mixed-energy inlet located on the Western Coast of France. Model-data comparison reveals firstly that complex wave-current interactions take place over the inlet ebb-delta, that include partial wave blocking during the ebb. Compared to classical 2DH approaches, our improved modelling system better reproduces the dynamics of adjacent beaches, inlet migration under oblique waves and sediment infilling of the main channel under storm waves. The relevance of these developments is demonstrated at the mixed-energy Maumusson Inlet (France).
Journal Article
Controls on Shoreline Changes at Pluri-annual to Secular Timescale in Mixed-energy Rocky and Sedimentary Estuarine Systems
Chaumillon, E.; Cange, V.; Gaudefroy, J.; Mercle, T.; Bertin, X., and Pignon, C., 2019. Controls on shoreline changes at pluri-annual to secular timescale in mixed-energy rocky and sedimentary estuarine systems. In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 135-156. Coconut Creek (Florida), ISSN 0749-0208. This article examines the morphological evolution of 27 beaches, including sandy and mixed sandy and rocky beaches, located along a 460 km-long complex shoreline, indented by four incised-valleys. The wave climate, simulated numerically from 1999 to 2017 in front of each beach, allows distinguishing between exposed and sheltered beaches. The morphological changes are quantified at two time scales: the last two centuries, from old maps and aerial photos, and the last two decades, from topographic profiles, aerial photos and satellite images. The first-order parameters explaining most of the spatial variations in the shoreline evolutions are the presence or absence of bedrock outcrops in the foreshore and/or shoreface and the presence or absence of tidal inlets close to the beach. The fastest shoreline changes are observed along exposed sandy beaches close to tidal inlets, whereas moderate to slow evolutions are mainly observed along exposed beaches with rocky foreshore and sheltered beaches. Huge shoreline changes located close to tidal inlets are related to changes in littoral drift orientation and intensity, themselves related to changes in beach orientation. Maximum erosion rates at a decadal time scale are not associated with isolated exceptional storms, but rather with clusters of storms. Beaches evolutions on this indented shoreline are controlled by geological factors (coastal orientation and the basement topography) and display complex patterns that cannot be clearly related to past changes in wave climate and sea level rise, complicating the prediction of their future evolutions.
Journal Article
Following the Sand Grains
When longshore transport systems encounter tidal inlets, complex mechanisms are involved in bypassing sand to downdrift barriers. Here, this process is examined at Plum Island Sound and Essex Inlets, Massachusetts, USA. One major finding from this study is that sand is transferred along the coast—especially at tidal inlets—by parcels, in discrete steps, and over decadal-scale periods. The southerly orientation of the main-ebb channel at Plum Island Sound, coupled with the landward migration of bars from the ebb delta to the central portion of the downdrift Castle Neck barrier island, have formed a beach protuberance. During the constructional phase, sand is sequestered at the protuberance and the spit-end of the barrier becomes sediment starved, leading to shoreline retreat and a broadening of the spit platform at the mouth to Essex Bay (downdrift side of Castle Neck). Storm-induced sand transport from erosion of the spit and across the spit platform is washed into Essex Bay, filling channels and enlarging flood deltas. This study illustrates the pathways and processes of sand transfer along the shoreline of a barrier-island/tidal-inlet system and provides an important example of the processes that future hydrodynamic and sediment-transport modeling should strive to replicate.
Journal Article
Lessons Learnt from Restoring a Tidal Marsh by Enlarging the Intertidal Basin (Zwin Inlet, Belgium/The Netherlands)
Tidal inlets regulate the exchange of water and sediment between the open sea and adjacent basins. In many locations, engineering interventions combined with coastal protections and polders have intensified erosion and scouring. This study reports on a three-year monitoring program following the implementation of a Nature-based Solution (NbS) at a previous engineering tidal inlet in the Zwin, located along the Belgian–Dutch coast. In 2019, large-scale modifications to the intertidal zone and the opening of a dyke doubled the surface area of the tidal inlet and its associated tidal marsh. Results revealed rapid and substantial morphological adjustments: the main channel deepened, widened, and migrated eastward. Sediment balance analyses showed stability at the inlet entrance but material loss further inland. Tidal prism and cross-sectional measurements indicated a fourfold increase in tidal prism immediately after NbS implementation, triggering strong channel responses. Within a year, the channel cross-sectional area reached a new equilibrium, which remained stable in the following years. These patterns highlight active sediment transport driven by coupled hydrodynamic and morphodynamic processes. Using an extensive data set, a conceptual model is presented to illustrate how the NbS influenced tidal inlet dynamics through the interaction of flow and sedimentation processes.
Journal Article
Sediments and bedforms of the Harle tidal inlet (Wadden Sea, Germany)
The paper presents a map of sediment surface distribution and bedforms in the Harle tidal inlet, German Wadden Sea. Data collection, processing, and map editing were realized within the sublittoral mapping program of Lower Saxony national waters carried out by the NLWKN - Coastal Research Station. The map is the result of the combined use of multibeam echosounder, sub-bottom profiler, and ground-truth data. The sediment characterization is achieved by an unsupervised approach using an Object-Based Image Analysis (OBIA) on a normalized backscatter mosaic, verified by nineteen sediment samples. Morphometrical parameters and sub-bottom data provided important information to identify hard substrates and bedforms.
Journal Article
Spatiotemporal Change Patterns of Coastlines in Xiangshan Harbor (Zhejiang, China) During the Past 40 Years
Li, J.; Pu, R.; Yuan, Q.; Liu, Y.; Feng, B.; Guo, Q.; Jiang, Y., and Ye, M., 2018. Spatiotemporal change patterns of coastlines in Xiangshan Harbor (Zhejiang, China) during the past 40 years. As special and important landscape bodies, tidal inlets possess many coastal resources. Consideration of the maintenance and protection of coastline resources and the environment is a challenging research topic, i.e. how to reasonably and scientifically exploit and use coastal resources. In this study, multitemporal Landsat images were used to explore and quantify relationships between the intensity of human activities and coastline changes. Specifically, (1) the spatial location, length, and tortuosity of coastlines in Xiangshan Harbor (XH; Zhejiang Province, China) tidal inlets, from 1974 to 2014, were extracted from satellite images; (2) the coastline change indices and the intensity of human activities in the tidal inlet areas of XH were calculated and assessed; and (3) the relationships between coastline change characteristics and human activities during the past 40 years were explored and analyzed. The results demonstrated that, during the past four decades, as human activities have intensified, the natural coastlines in XH continuously shrank, whereas artificial coastlines increased and then gradually became stable. Various human activities have changed the morphology of local coastlines in XH, and the overall coastline tortuosity has been continuously reduced. The intensity of human activities increased from 1974 to 1998, and the intensity slowed after 1998. However, the impacts of human activities are extensive and almost cover the entire coastlines of the harbor. The correlations between the intensity of human activities and the overall length and tortuosity of the coastlines were significantly negative, which means that, as human activities intensified, the length and tortuosity of the coastlines decreased.
Journal Article
Analysis of the Impact of Hydraulic Gates on a Stabilized Tidal Inlet Structure: Mathematical Model and Data Measurements
Tidal inlet structures are engineering projects with associated benefits related to flood control, water quality enhancement, and coastal protection. This study analyzes the performance of hydraulic gates on a stabilized inlet in estuarine systems by developing a simplified hydraulic model that considers inlet and outlet water levels. The proposed model was applied to the stabilized tidal inlet structure in Cartagena de Indias, Colombia. This model offers a practical tool for engineers and designers operating estuarine systems. The analysis focuses on the coastal lagoon of Ciénaga de la Virgen. The proposed model was successfully calibrated using two water sensors, with extreme input and outlet flow rates of approximately 260 m3/s and 110 m3/s, respectively. The average daily output volume in the system is 3,361,000 m3, while the average daily input volume is 3,200,000 m3. Consequently, the manipulation of the opening gates results in a decrease in the estuarine water level, potentially by as much as 25 cm, which local authorities can use to make decisions to reduce extreme water levels during flooding events.
Journal Article