Tidal inlets

An archaeological survey of Back Bay was conducted along coastal Virginia immediately south of Virginia Beach for the Virginia Department of Historic Resources. The fieldwork was conducted between October and December of 2015. The survey documented eleven actively eroding shorelines with archaeological deposits. The archaeology, geology and soil profiles for each site were evaluated. During the late prehistoric period through the early 19th century, Back Bay was a high salinity barrier island lagoon with a high-tidal amplitude.  When the "new" and "old" Currituck Inlets closed in the early 19th century, the salinity of Back Bay plummeted and the tidal amplitude was greatly reduced.  Not only did the ecology of Back Bay change, the reduction of tidal amplitude greatly increased the rates of shoreline erosion and associated archaeological site loss.  The results of this research will help future researchers prioritize and assess the loss of archaeological sites within a coastal lagoon system that has very low tidal amplitude.

The availability of nearly 100 years of bathymetric measurements allows the analysis of the morphodynamic evolution of the Dutch Wadden Sea under rising sea-level and increasing human constraint. The historically observed roll-over mechanisms of landward barrier and coastline retreat cannot be sustained naturally due to numerous erosion control measures that have fixed the tidal basin and barrier dimensions.  Nevertheless, the large continuous sedimentation in the tidal basins (nearly 600 million m3), the retained inlets and the similar channel-shoal characteristics of the basins during the observation period indicate that the Wadden Sea is resilient to anthropogenic influence, and can import sediment volumes even larger than those needed to compensate the present rate of sea-level rise. The largest sedimentation occurs in the Western Wadden Sea, where the influence of human intervention is dominant. The large infilling rates in closed-off channels, and along the basin shoreline, rather than a gradual increase in tidal flat heights, render it likely that this sedimentation is primarily a response to the closure of the Zuiderzee and not an adaptation sea-level rise. Most of the sediments were supplied by the ebb-tidal deltas. It is, however, unlikely that the sediment volume needed to reach a new  equilibrium morphology in the Western Wadden Sea can be delivered by the remaining ebb-tidal deltas alone.

A series of regular bathymetric surveys of Texel Inlet and its ebb-tidal delta spanning a period of over 400 years forms a unique long-term morphodynamic dataset of this largest inlet of the Wadden Sea. The substantial changes in ebb-tidal delta evolution provide a clear example of the response of the inlet system to the cumulative effects of human intervention.
Analysis of the evolution of the ebb-tidal delta morphology shows different stages, each characterized by specific orientations of the main channels and shoals. Prior to construction of extensive coastal defense works on the southern shore of the inlet in 1750 A.D., the ebb-tidal delta showed a downdrift asymmetry. Periodic shoal breaching and downdrift channel relocation were the dominant mechanisms for sediment by-passing (major shoal bypassing). After construction of the coastal defence works, a stable ebb-tidal delta with a westward stretching main ebb-channel developed over a period of ca. 60 years. Damming of the Zuiderzee, the major part of the back-barrier basin in 1932 A.D., distorted this stable state and over a period of about 40 years the main channel switched to a southward course, remaining stable ever since. During the pre- and post-damming stable states the sediment bypassing took place as minor shoal by-passing; the main channel remained in position and smaller parts of the swash platform (periodically) migrated landward over the ebb-tidal delta.
The well-monitored large-scale changes on the ebb-tidal delta which were initiated by the construction of the coastal defence works and closure of the Zuiderzee show that incorporation of inlet modifications and back-barrier processes is vital for a correct description of the ebb-tidal delta dynamics and processes of Texel Inlet. A conceptual model is introduced to describe the process–response relation between intervention and ebb-tidal delta change.

The present paper tackles morphological modeling of a rare case of a re-migrating inlet to be used as the basis of a fishery port site selection study. The Tang inlet, located on the south-eastern shores of Iran, has so far been experiencing a cyclic migration with a return period of approximately a decade. In order to grasp the essence of the morphological behavior of the inlet, a two-fold site monitoring campaign was performed, consisting of a shoreline evolution study using aerial & satellite imagery for the outside of the bay as well as a sedimentation pattern comparison based on past hydrographical survey results for the inside of the bay utilizing ArcGIS software. Subsequently, numerical modeling of the inlet comprising of nearshore wave transformation, tidal regime of the bay, one-line coastline evolution and two-dimensional sediment transport within the bay was carried out utilizing MIKE 21 package. Ebb channel switching from a westerly to an easterly orientation is deemed to occur due to self-suffocation as a result of the presence of an existing offshore rock formation, as well as the salient making potential of the rock system. On the other hand, the closure of the east-facing channel is mainly attributed to diffraction currents due to Monsoon southerly waves helped by sedimentation load from inside the bay system due to floods & ebb currents.

In many parts of the Netherlands the transition from the Roman period (RP) to the Early Middle Ages (EMA) coincided with declining population. This contribution explores landscape dynamics of the Dutch coastal area in the first millennium AD and its possible influences on occupation patterns.
To achieve this, we developed a GIS containing geological-geomorphological elements from tidal systems (channels, tidal flats and salt marshes). Knowledge on the geological development of the tidal systems is documented in the GIS allowing mapping of coastal evolution. By comparing these coastal-evolution maps with archaeological data, interaction between landscape changes and settlements can be hypothesized.
At the onset of the Early Middle Ages, first results suggest silting up of tidal inlets along the Dutch coast coinciding with an increased settlement density in the waning tidal areas. Meanwhile, large-scale extension of tidal systems at the expense of habitable land occurred in the SW part of the Netherlands. Adversely, at the end of the Early Middle Ages the SW part of the Netherlands silted up and some large sea ingressions took place in the northern part of the Netherlands. In both of these regions the current archaeological data does not yet reveal a clear pattern.

Recently obtained high-resolution seismic records, collected offshore the western Netherlands in a kilometer-size grid across the lower shoreface and inner shelf, suggest the presence of a dense, previously unknown network of tidal-channel fills in the shallow subsurface of the North Sea. Seven channel fills constituting this network were analyzed in detail to infer relationships among the fills in time and space, and to identify factors governing channel development and tidal-basin evolution. The majority of the channels are oriented perpendicular to the coast, but parts of some have a strong coast-parallel component. Shell associations and sedimentological characteristics in most channel fills are typical of back-barrier depositional environments. All but one of the channel fills are part of an Atlantic-age tidal-channel system, draining a tidal basin protected by barrier islands. One channel fill, which is correlated to an incision recognized onshore, represents a younger phase in coastal development. The presumed barrier-island chain was positioned at least 12 km seaward of the present coastline in the northern part of the study area, and at least 6 km seaward of the present coastline in the southern part. The tidal channels grew and migrated actively before partially being filled in between 7300 14C yr BP and 5500 14C yr BP, reflecting an initial tidal-prism increase followed by a substantial decrease. The tidal-prism increase was governed by an upsurge of the tidal amplitude between 8000 14C yr BP and 7000 14C yr BP, and the subsequent decrease by a gradual decrease in the rate of sea-level rise. Rapid retrogradation of the coastline put a sudden end to the existence of the tidal basin. The ensuing shoreface erosion removed all but the deepest parts of the channel fills, which do not show any evidence of systematic landward migration. This field observation corroborates recent modeling results suggesting that rapidly rising sea level may create the conditions necessary for overstepping of sandy barriers.

Application of an one-dimensional numerical model for hydrodynamic simulation of a complex lagoon-inlet system in Vietnam is presented. Model results help to get a better understanding on the behaviour of the system. Based on the numerical model results and analytic solutions, stability of tidal inlets is evaluated. 1.

A series of interventions in the Guadiana River Basin (dam construction, increase in mining, deforestation, construction of jetties) have resulted in a reduction of average river volume, an increase of sediment load in the river, and ultimately a largescale change of the coastline and margins of the Guadiana Estuary. A series of maps and vertical aerial photographs were interpreted with the help of GIS in order to better understand and quantify the morpho-sedimentary evolution of the Guadiana Estuary mouth in the course of the 20th century.
The results show an average progradation of the western estuary margin by about 950 m since 1870, accumulating an estimated 4.6 x 106 m3 of sediments. About 20-25% of this accumulation was caused by the construction of the jetties, leading to the trapping of the entire littoral drift (estimated 180’000 m3/year) between 1974 and 1980. On the eastern estuary margin, a large marsh system protected by a long spit developed. Although the coastline showed average erosion at a rate of about 3 m/year, the total area of the eastern estuary margin increased because of the progradation of the system into the main river channel.
With the conclusion of the Alqueva dam project in the near future, a further significant reduction in average river volume is expected. Sediments originating from littoral drift will begin to bypass the western jetty, as the area west of it is infilled. Furthermore, as waves and tidal currents will dominate against a much reduced river flow, a further accumulation of sediments in the estuary mouth can be expected.

The availability of nearly 100 years of bathymetric measurements allows the analysis of the morphodynamic evolution of the Dutch Wadden Sea under rising sea level and increasing human constraint. The historically observed roll-over mechanisms of landward barrier and coastline retreat cannot be sustained naturally due to numerous erosion control measures that have fixed the tidal basin and barrier dimensions. Nevertheless, the large continuous sedimentation in the tidal basins (nearly 600 million m3), the retained inlets and the similar channel-shoal characteristics of the basins during the observation period indicate that the Wadden Sea is resilient to anthropogenic influence, and can import sediment volumes even larger than those needed to compensate the present rate of sea-level rise. The largest sedimentation occurs in the Western Wadden Sea, where the influence of human intervention is dominant. The large infilling rates in closed-off channels, and along the basin shoreline, rat...

The present paper tackles morphological modeling of a rare case of a re-migrating inlet to be used as the basis of a fishery port site selection study. The Tang inlet, located on the south-eastern shores of Iran, has so far been experiencing a cyclic migration with a return period of approximately a decade. In order to grasp the essence of the morphological behavior of the inlet, a two-fold site monitoring campaign was performed, consisting of a shoreline evolution study using aerial & satellite imagery for the outside of the bay as well as a sedimentation pattern comparison based on past hydrographical survey results for the inside of the bay utilizing ArcGIS software. Subsequently, numerical modeling of the inlet comprising of nearshore wave transformation, tidal regime of the bay, one-line coastline evolution and two-dimensional sediment transport within the bay was carried out utilizing MIKE 21 package. Ebb channel switching from a westerly to an easterly orientation is deemed t...