As Red House in Thorpeness on North End Avenue is been demolished, because of coastal erosion, this discussion will conclude the series to discuss whether large-scale events or small gradual processes contribute the most to erosion.
The previous discussion about Thorpeness, the penultimate in the series, looked at the acute erosion on the beach in the photo above, below North End Avenue. This is a high energy, rapidly changing location. Features of this erosion include the soft composition of the cliffs and the constant shifting shingle and narrowing of the beach width, exposing the base of the cliff at Mean High Water Spring. Additionally, waves arrive at the beach from a South-West or North-East direction, both can cause erosion, though NE waves are thought to contain the greatest potential to scour beaches and cliff. This discussion concluded high wave events cause the most erosion, as the change is so dramatic it is hard to see how beach and cliff can recover. Each simply become playthings for the waves of the North Sea.
However, between August 27th and 22nd of September 2022, and more recently, with the demolition of Red House, the beach has changed considerably. Large amounts of material have been stripped from the cliff frontage with big chunks of material slumped from the cliff. High steep ridges of shingle at the back of the beach, are indicative of even less space between sea and cliff.
In terms of the sea state in this time period, two wave events on the 31st of August and 16th September, saw a Maximum Wave Height (MHW) at Lowestoft exceed 3 metres, with Significant Wave Height (SWH) below 2 metres. There were several storm surges, with particularly high incidences on 13th, 16th, 15th of September.
Overnight on 30th September 2022, MWH at Lowestoft reached 4.22 metres and SWH reached 2.62 metres. Additionally, a storm surge of .833 was recorded on this date at Lowestoft. However, the conclusion to the penultimate discussion in this series, was that high wave events, not surges cause the severe erosion at Thorpeness. But recent events would indicate this isn’t necessarily the case. As the high wave events mentioned above were lower than the 31st March/1st April event that previously caused serious damage.
Elsewhere on the Suffolk coast, this series has discussed desiccated cracking in clay flood embankments and how it can be exacerbated by drought conditions. As the top of the embankment, above the water line, is exposed to meteorological conditions, it can experience tensile stress. This can alter the structure of the soil and cause cracks to form which can extend up to 1 metre deep into the embankment. Should water under flood conditions seep into these fissures, it could cause the inward slump of embankment material leading to a potential breach. Therefore, the process of desiccated cracking could itself be an early manifestation of erosion, which could ultimately lead to the collapse of a flood defence.
The series has also looked at Sudbourne Beach on the open coast near Aldeburgh and Hazelwood Marshes on the Alde Ore Estuary. Both locations are subject to large erosion events but are also being gradually worn away by the actions of the waves. A definition of erosion was used that described it as process in which sediment is removed by weather driven wave action and transported away from the area being eroded to another location. This discussion considered the stages of damage to a shingle bank or an estuary path and asked at what point is the damage assessed to have occurred. The moment a structure is breached or destroyed, or when incremental altering begins that can weaken and damage structures over time.
In a recent visit to Hazelwood, the work of the Suffolk Wildlife Trust, who manage the site, can be seen to fill in eroded edges of the path, leading to the bird hide, and buttress them with branches from old salt-water scoured trees.
Out on the inter-tidal area, it is evident the sea is eating away at the edges of the islands built up to enable Avocets to nest. It also wasn’t possible to examine the banks at the back of the reserve, as unusually, water from previous high tides prevented access. But scouring at the edges of the reserve can be monitored and repaired. What could be harder to quantify, is whether damage to the old sea walls enables greater quantities of sea water to access the reserve. Though as Hazelwood exhibits signs it can recover from erosion events, increasing frequent high tides could make continued maintenance of key features, harder to sustain.
Therefore, this series will conclude with a focus again on perceptions of damage. High Wave events, elevated tides and larger surges have elevated erosion processes, so that not only do they occur in a more dramatic ways, but they are now further developed. So perhaps it is a question of whether the actual act of erosion, removing and transporting of sediment. Or the ultimate conclusion to this process, inundation of a storm surge or destruction by wave action that causes the most damage.
alteredcoast 