This discussion will update previous observations of Sudbourne Beach, near Aldeburgh, in Suffolk, in the United Kingdom. The update will consider the Saltmarsh and channel that run along the edge of the Shingle fan overwash, that formed around Autumn 2023. As well as briefly discuss the overall form of the beach system and erosion of the shingle ridge fronted by hard sea defences.
Firstly, the previous discussion to consider Sudbourne Beach, thought it might be possible for vegetation to begin to grow on top of the large Shingle Fan Overwash. It would appear this is beginning to happen. It is thought shingle washover fans can evolve to function as a base for new Saltmarsh to grow. As essentially Saltmarsh develops from the formation of an elevated reasonably solid accumulations of sediment.
But the appearance of the Saltmarsh and the Channel that runs along the edge of the shingle fan, seems to have altered with the saltmarsh seeming to look thinner, and with the channel looking like it has widened. It is thought that channels can be the main conduits for movement of sediment within saltmarsh systems. As it is hoped Saltmarsh landforms can increase in height above the regular flow of tidal water, to create a cohesive mass of vegetation sufficient to attenuate (lessen) wave energy.
In established saltmarsh systems, sinuous channels that intersect marshes can facilitate alterations in the flow of water, such that sediment held in suspension moves swiftly through the channels, whilst sediment at times of high water can be deposited when flows run over Saltmarsh. Accumulation of sediment on top of saltmarsh can encourage its growth and also aid the formation of deep channels. Similarly, it is thought Neap tides can flow within the channels and deposit sediment, whereas Spring Tides can erode the channel system, causing them to widen as well as deposit sediment onto the marsh surface.
It would seem the saltmarsh system adjacent to the shingle washover fan at Sudbourne Beach, is out of equilibrium as it would appear to lack cohesion. Rather than a dry elevated saltmarsh system, with channels winding through, saltmarsh appears to contain a substantial amount of tidal water within it. There is also a clear Tide Line seeming to show a meeting of estuary and Sea water.
It is not clear why the alteration to the saltmarsh system has occurred. Linked to this, it is interesting to observe that within the channel at the edge of the shingle fan, in addition to shingle, their appeared to be a layer of sand in the channel. It is thought that due to low-energy conditions more prevalent in saltmarsh systems, the predominant sediment type would be silt, clay or mud. The presence of sand could indicate higher energy tidal flows.
It is a puzzle however, as it is commonly thought that during a storm event, sand being a finer sediment, is transported offshore, perhaps to a nearshore sand bar. With courser sediment such as shingle moved as bedload, to be deposited further up the beach or as overwash if sufficient energy is present.
This moves the discussion to observations of the beach system itself. It is said that shingle beaches have a narrow Surf Zone, therefore the majority of sediment movement and influence of waves on the beach occurs in the zone where waves wash up (Swash) and move back down the beach, (Backwash). The succession of shingle ridges on the beach, reflects the reach of the Swash during Neap and Spring tides. With a tide line just visible towards the back ridge of the beach suggesting the presence of recent high water.
It would also appear the slope of the beach is reasonably steep; this could align with the description of shingle coastal locations having Reflective profiles. This can mean very little energy is lost when waves break on shingle beaches, so energy is transmitted and is shaped by the profile and sediment make-up of the beach itself.
Regarding the shingle fan itself, it could fit the description of a sluicing overwash, where substantial failure of the beach crest has occurred, but the overall height of the back beach and shingle fan has not substantially changed. Though this location is a dynamic environment, and it rarely stays stable for long.
This is also especially true of the section of remaining shingle ridge fronted by hard sea defences. The ridge certainly seems to have an airy feel as erosion continues.
It is also noticeable how erosion is especially concentrated around the back of the Groynes. Sea defences such as these are designed to trap and retain sediment. It is thought that in some circumstances, rip currents can form around Groyne structures, with approaching waves interacting with waves leaving the beach. This can generate rotating currents with powerful alongshore currents forming in both directions. Such rip/circular currents can facilitate the rapid removal of sediment.
In conclusion, ongoing changes observed at Sudbourne Beach can be summarised as a contrasting picture. With settlement of vegetation on the shingle fan, whilst processes that formed the shingle overwash, play out to a lesser extent around it.
The beach profile indicates the evolving shifting of shingle as if energy transmitted from wave action is constantly kneading away to erode and rework. As elements thought to be firm structures, beach, ridge and salt marsh, instead serve as dynamic fluid symbols of the fragility of this coastal location.
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