Understanding ebb-tidal delta (ETD) dynamics and interactions with adjacent shorelines provides valuable information for coastal management. This study analyzes and quantifies the evolution of the New Pass ETD (Florida, USA) using multi-temporal bathymetry (2004–2024), satellite-derived shorelines, and analyses of delta rotation, chronostratigraphic evolution, and volumetric change. Results show a persistent counterclockwise rotation of the delta (−1.67°/yr), consistent with the regional net southward longshore sediment transport regime. This rotation controls ebb-channel migration and sediment redistribution across the delta, promoting shoal accretion in downdrift sectors and episodic shoal attachment to the adjacent Lido Key shoreline. Chronostratigraphic analysis indicates that offshore shoals function as temporary sediment reservoirs that migrate landward and drive pulses of shoreline progradation. Shoreline analysis identified six shoal-attachment events, with recurrence intervals ranging from 3 to 15 years and a mean of 6.8 years. The estimated total ETD volume remained relatively stable between 2004 and 2022, despite substantial internal morphological reorganization and repeated dredging. This pattern suggests that longshore sediment supply may have contributed to maintaining sediment storage within the delta.
Tidal bores are common in tide-dominated estuaries, but their sedimentary products remain less well constrained than their hydrodynamics. This study examines the spatial transformation of tidal-bore hydrodynamics and associated flood-tide deposits across the inshore tidal flats of the Sittaung River estuary, Myanmar. Breaking bores approaching 1 m in height were directly observed along the main channel and lower sand flats, where bore passage was accompanied by abrupt water-level rise, strong flow acceleration, enhanced vertical motion, and high suspended-sediment concentrations. Bore height decreased landward within sandy blind tidal channels (BTCs). In BTC2, tidal bores less than 0.1 m high were directly observed, whereas at BTC1 a weak or cryptic bore-related hydraulic disturbance is inferred from the timing of water-level, velocity, and turbidity changes. Importantly, the strongest flood currents in the blind channels occurred after bore passage and were locally enhanced by channel geometry and scour-pool morphology. At BTC1, maximum turbidity preceded maximum local flood-current velocity by approximately 40–50 min, indicating that suspended-sediment concentration was not controlled solely by instantaneous local current speed and likely reflected a combination of local resuspension and landward sediment advection. The preserved bore-related flood-tide deposit commonly comprises an erosional base overlain by structureless to faintly laminated very fine sand, followed upward by more distinct parallel lamination and ripple cross-lamination. We interpret the basal structureless and lower faintly laminated interval as the portion most closely associated with bore passage and its immediate aftermath, whereas the overlying deposits primarily record the subsequent flood current. The complete succession is therefore regarded as a bore-related flood-tide deposit rather than a tidal-bore deposit sensu stricto. Spatial variability of these deposits reflects not only bore attenuation but also sediment advection, post-bore flow acceleration, local accommodation, scour-pool morphology, and subsequent ebb-tide reworking. High-elevation sand shoals are excluded from the bore-related facies succession and are interpreted primarily as river-flood deposits. These observations complement existing tidal-bore facies models by emphasizing the importance of blind-channel morphology and spatial separation between sediment entrainment, transport, and deposition in morphologically complex intertidal environments.
Iceland is one of the most geodynamically complex coastal settings on Earth: glacial isostatic adjustment, present-day glacial unloading, volcanic deformation, and mid-ocean-ridge spreading all act at once, so tide gauges there record a mix of land motion and ocean change rather than ocean change alone. The land-motion component is isolated by comparing tide-gauge sea-level trends with satellite altimetry trends at five Icelandic stations spanning contrasting geodynamic settings over 1997–2023, using the DUACS L4 reprocessed altimetry product. Tide-gauge trends range from −3.71 ± 1.02 mm/yr at glacially-rebounding Hofn–Hvanney up to +10.10 ± 1.12 mm/yr (Olafsvik) and + 9.10 ± 0.60 mm/yr at volcanically-subsiding Sandgerdi, while altimetry trends are far more uniform, from +2.43 to +3.59 mm/yr. The resulting land-motion estimates are evaluated against independent GNSS velocities and three glacial-isostatic-adjustment models. At Hofn–Hvanney the land is rising by +6.72 mm/yr by this estimate; the nearest GNSS velocity exceeds the glacial-isostatic-adjustment prediction by +10.32 mm/yr, consistent with a substantial elastic response to present-day Vatnajokull ice loss, a process the standard models do not capture. At Sandgerdi the land is subsiding by −6.41 mm/yr, consistent with independent radar-interferometry velocities of −5.26 mm/yr and with the volcanic unrest that began on the Reykjanes Peninsula in 2020. The spread across the three glacial-isostatic-adjustment models themselves ranges from 0.39 mm/yr at Olafsvik to 2.65 mm/yr at Hofn–Hvanney. These results show that reliable coastal sea-level monitoring in geodynamically active regions requires decomposing the land-motion budget separately for each geodynamic setting, rather than applying a single regional correction.
Estuarine channel-shoal structure integrates the effects of river discharge, tidal forcing, sediment sorting, and human modification, yet its along-estuary transition remains difficult to define objectively. This study establishes an integrated framework for the Xijiang mainstream in the Pearl River Delta by combining decomposition of residual water level and its gradient, cluster analysis of surface sediments, bankfull-stage determination, and channel-shoal morphometrics. Residual water level decreases seaward from 0.81 m near Xijiaokou to 0.10 m downstream, with a mean of 0.46 m. Decomposition of residual water level and its gradient identifies a river-dominated reach from 0 to 73.5 km, a river-tide coupling reach from 73.5 to 106.5 km, and a lower reach with enhanced tidal effect from 106.5 to 123.0 km. Surface sediments become finer downstream. The upstream cluster is sand-rich, with a median grain size of 2.01 Φ and 88.14% sand, whereas the downstream cluster is finer, with a median grain size of 2.98 Φ and 56.98% sand. Bankfull stage decreases from 3.13 m upstream to −0.02 m downstream. Independently delineated morphological reaches, separated at approximately 47.5 and 77.5 km, have mean channel-shoal relief values of 20.6, 16.0, and 11.9 m, respectively. These patterns indicate a transition from a narrow, deep, high-relief channel-shoal configuration to a configuration with a higher aspect ration and lower relief. The proposed framework links hydrodynamic dominance, sedimentary environment, and channel-shoal morphology and provides a process-based basis for navigation maintenance, bank stability, and shoal conservation in engineered estuaries.
This study investigates transient shoreline adjustment and sediment redistribution within an uplifted pocket bay on the northern Noto Peninsula, Japan, following the Mw 7.5 Noto Peninsula earthquake of 1 January 2024. Using high-frequency PlanetScope imagery and the CoastSat.PlanetScope toolkit, shoreline positions were extracted from 2022 to 2025, providing two years of observations before and after the earthquake. Shoreline evolution was analyzed at bay-wide and transect scales through mean shoreline comparison, quarterly fluctuation analysis, and harmonic regression of tidally corrected shoreline-position time series. Comparison of the mean pre- and post-earthquake shoreline configurations showed a pronounced seaward shift along the entire bay, ranging from approximately 60 to 250 m and averaging about 140 m. Shoreline variability increased markedly during the first half of 2024 and subsequently showed an overall tendency to decrease, although elevated variability recurred in early 2025. Transect-based analysis revealed strong alongshore heterogeneity, with adjacent sectors exhibiting contrasting erosional and accretional trends and localized changes in seasonal variability. Importantly, the magnitude of earthquake-associated shoreline offset did not uniquely determine the subsequent shoreline trajectory. These results indicate that coseismic uplift imposed an abrupt relative sea-level fall and reset the coastal boundary conditions, whereas subsequent shoreline evolution was spatially heterogeneous. The observed correspondence between contrasting shoreline trends and uplifted rocky areas, fishing ports, river-mouth sectors, and local morphology is consistent with localized sediment redistribution and suggests that these features may have influenced sediment connectivity. The results demonstrate that uplifted pocket-bay coasts can undergo multi-year, spatially heterogeneous reorganization after coseismic emergence.
