alteredcoast

This discussion will take an initial look at the extremely active winter storm season of 2023/2024. An enduring presence during the storms, Total Water Level (TWL) will be considered, alongside erosion common to both Sand and Shingle beaches in East Anglia.

Given the complex nature of the winter storms it might be simplistic to just identify one element, Total Water Level (TWL), when additional destabilising elements such as Wind Speed and atmospheric pressure also play a major role. But TWL can also play a major part, in agitated, elevated sea levels, extreme rainfall and extensive flooding of land and properties.

Winter Storms season of 2023 2024, begin with Storm Babet, the second named storm of 2023 on Friday 13^th October, it continued through Monday 16^th October until Friday 20^th October. Storm Ciaran followed 9 days later on Sunday 29^th and continued until November 4^th. A considerable storm surge of over 1 metre occurred on Friday 24^th November with a larger storm surge of just under 2 metres on Thursday 21^st and Friday 22^nd December 2023.

In 2024 on January 14^th/15^th, a Storm Surge measuring just under 1 metre hit the East Anglian coast. On 22^nd January, Storm Isha and then Storm Jocelyn occurred in quick succession with 3 storm surges occurring in a week, the largest on Wednesday 24^th January, measuring over 1 metre. On 30^th January/February 1^st, Storm Ingunn hit Norway, generating a Surge of over 1 metre. On Sunday 25^th and Monday 26^th February a storm, localised mainly in the Southern North Sea saw a 0.5 metre surge recorded for Lowestoft, with a surge of nearly a metre measured at Sheerness.  Finally, on the evening of February 29^th/March 1^st stormy conditions generated a surge of around 1 metre at Lowestoft.

Additionally, particularly High Spring Tides in March 2024, coupled with exceptionally high rainfall and strong winds, caused considerable erosion and flooding in places.

The list of storms above is a summary of a very intense period of activity. Therefore, this discussion will assess whether the TWL approach, can enable an assessment of the impact of storms on erosion of cliffs, dunes and beaches.

It is thought that in storms where TWL exceeds 3.9 m water levels can reach the dune or cliff toe, potentially causing hollowing of frontages and lowering of beach surfaces. Methods to assess TWL often use measures of Significant Wave Heights (SWH) that reach or exceed Storm Alert Thresholds. As it is thought that such thresholds, can initiate movement of beach material. The table below lists the SWH for Happisburgh, Lowestoft and Felixstowe for winter storm season 2023/2024.

SWH heights hint at TWL at points on the coast where measures are taken, but they also give a picture of the variability of agitated sea states and how local they can be at times. For example, for November 24^th, SWH of 3.6 metres is recorded for Happisburgh, above Storm Alert Threshold (STA), conditions that might contribute to the collapse of the road at nearby Hemsby. But SWH at Lowestoft remained below STA, close to where the road also collapsed at Pakefield.

However, it is interesting to consider how common erosion features appear on beaches, despite the sections of coast being comprised of different layers of sediment. Photos taken on 20^th January at Thorpeness and on 16^th February at Pakefield, could be said to show wave height reached when dune face scouring occurred and could suggest the TWL present on the beach.

The potential energy in the TWL present on beaches is suggested in the photo below, taken at Minsmere that shows old wartime sea defences that have been uncovered on a beach stripped of shingle, with signs of a Scarp or cliff appearing to form in the remaining Shingle on the Upper Beach.

Cliff-like Scarps on Shingle beaches are said to only be maintained if physical conditions, enable sand to infill spaces in between the Shingle, to sustain the steep feature. Waves can cut into the bottom of Scarps, which can also influence subsequent wave direction. Increasing transportation of sediment off-shore.

Another significant type of erosion that has occurred at several coastal locations in East Anglia is Cliff failure, due to rainfall. Instances of this erosion have been observed at Dunwich and Pakefield in Suffolk and Overstrand and Sidestrand in Norfolk. It has been found that in stormy weather it is the combination of TWL reaching the Cliff toe and high rainfall that can cause cliff collapse, but it is thought that heavy rainfall is the predominant cause of cliff collapse in East Anglia and other coastlines around Britain. Particularly as at Dunwich, it was said that foredune on the beach had accreted sediment, so waves were not hitting the toe of the cliff.

The two charts below from the Met Office show rainfall levels for January and February 2024.

In January there were around 75-125 mm of rainfall and in February East Anglia had its wettest February on record, with 106.4 mm of rainfall.

Rainfall can cause severe damage to cliff structures in the following ways. Referred to as a Terrestrial process, rainfall can affect elements that determine the volatility of cliff materials. On the beaches of Thorpeness and Pakefield, with cliffs partly comprised of Glacial Till and sands, two views on the impact of rainfall on these surfaces are suggested.  

For Moderately cemented sands in cliffs that resist wave attack collapse can occur due to the penetration of rainfall soaking through materials. This process is aided by Desiccated Cracking causing sections of material to develop an imbalance that can lead to failure.

For Weakly cemented sands, wave action succeeds at eroding the cliff base with erosion and instability progressing up though the dune structure. As material falls from the cliff surface due to wave action, volatility develops in the upper cliff and these combined weaknesses cause collapse.

At a British Geological site at Overstrand in Norfolk a 300m section of cliff was studied located roughly halfway between Overstrand and Trimlingham. In this location, rainfall is thought to be main driver in cliff retreat, due to the abundant presence of clay in cliff materials. In this context, rainfall is thought to have the following impact on cliffs in this area.

There is thought to be a greater likelihood of the formation of pathways across cliff sections without vegetation, with subsequent movement of sediment through the gullies. This could enhance the formation of mudslides which can transport sediment down the cliff frontage. The level of the water table within the cliff can also be elevated, causing water to percolate through the frontage. Water resistant layers of cliff material can also funnel groundwater through the cliff. Breakdown of lumps of sediment across these resistant layers is thought to be caused by the materials progression across the plane of these channels.

Regarding these failure processes, in addition to heavy intense rain fall, it is also thought the cumulative impact of moderate rainfall can build up weaknesses. Such frailties can cause landslides days or months after initial rainfall episode. This makes it very important that members of the public do not walk close to the edge of cliffs and dunes as coastlines may have not recovered from the effects of heavy rainfall. A sign on the Dunwich coast warns walkers that path is still closed following cliff collapse weeks earlier.

In this discussion, consideration has been given to the severe storms that have hit the East Anglian coast in Winter 2023/2024. With a consideration of whether the concept of Total Water Level (TWL) can act as a contributory factor to types of erosion that occurred. TWL can be measured in Significant Wave Height, which can potentially increase likelihood of wave contact with the dune or cliff face. With some erosion features displaying the level of wave height that hit the cliff. TWL is also present as a feature in cliff failure due to rainfall.

However, in considering the usefulness of TWL in assessing the effects of winter storms, TWL can suggest volumes of water likely to have been in contact with dune and cliff faces. But it could be said there needs to be an additional element present, to move, agitate and initiate water volumes. Therefore, it might be better to consider TWL as one factor amoungst several destabilising tensions within complex storm systems that can erode and weaken fragile coastlines.

A Storm Surge measuring just under 1 metre hit the East Anglian coast on the evening of 14^th/15^th January 2024 with the surge persisting for around 24 hours.

The Surge, which coincided with Spring Tides resulted in extremely High-Water levels causing flooding in places, with the Thames Barrier closing for the 211^th time, since its inception. High Waves also caused severe damage at Hemsby and other locations. Therefore, this discussion will continue the 2^nd part of a two-part look at whether Surges have a particular strength to cause serious damage. In this context, Damage is defined both as physical destruction as well as overtopping of structures and/or flooding.

The 1^st part of this discussion looked at the damage caused by two surges in November and December 2023. The two surges had slightly different characteristics, the first on Friday 24^th November was the lower of the two surges with high wind speeds and wave heights. It seems that this surge was also slow-moving with a longer duration and fetch, which is the surface area over which the wind blows over the ocean. The second Surge on 21^st & 22^nd of December was produced from much steeper pressure gradients with a deeper low-pressure system, but wave and wind heights were lower with a much shorter spike in the level and persistence of the surge.

It is generally accepted that determinants as to the magnitude of a surge include wind strength, direction, and distance over which the wind is blowing, the “fetch”. In addition to how these forces combine with atmospheric pressure, the track of a low-pressure system and how these influence the elevation and the velocity of the sea. But the level of a storm surge does not necessarily give an indication of the power of a surge. Surges are rarely similar, as they are produced from differing weather systems, and display different features. But is it the case that whatever their traits, Surges possess a particular strength to cause severe damage to coastal landscapes.

It is said the North Sea is particularly vulnerable to Storm Surges. One reason for this is the effect of Coriolis forces, which describe the way the earth rotates, which influence the acceleration of ocean currents. In the Northern Hemisphere this means movements of sea water are accelerated to the right. If a storm moves down the North Sea, elevated sea levels will be piled up against the coastline. This point is also relevant because the North Sea is rather shallow.

Therefore, it is thought that as two flowing elements connect with each other a transaction occurs between the quicker moving element and the slower element. If this process is translated to wind blowing over the ocean, a wind speed of 23 metres per second blowing over 200m of water, with a depth of 30 km, could cause a rise in sea level of 0.85m. If the gale force increases to 23 metres per second, sea level could increase to 1.60 m.

The effects of Wind tension on the surface of the sea, produces differences in the speed of the current in relation to the depth of the water. It is thought that water is propelled at around 3% of the wind speed applied to the ocean’s surface. As an ocean current runs down a coastline, it rises progressively in a manner that operates inversely with the depth of water. Movement of the current and alterations in ocean levels can be magnified if the tension of the wind on the surface moves water in the direction the wind is blowing.

But do these surge characteristics provide evidence regarding the particular destructive power of surges. Especially as Wind Wave storms with Significant Wave Height persistently above Storm Alert Thresholds also occur in the North Sea. Such storms can also cause severe erosion features and harm to coastlines.

Additionally, it is said, sea water elevated by storms can simply mean tidal water is kept longer on beaches between tides. Specific forceful sea water episodes produced by storms that coincide with a tide, could simply be the product of a collection of storms, A series of storms can generate wave power equal to a single extreme weather event. Is it possible within these tempestuous sea states, to pick out a surge, as the sole culprit, of a culmination of damaging coastal events.

It is valid to query the usefulness of isolating one type of agitated, sea state that predominantly presents itself simply as the high wave heights or water levels that cause the damage. It could be more useful to coastal communities and urban centres affected to warn of higher than usual tide levels, with faster wind speeds and waves than normal. However, it isn’t the case that such a sea state will remain as a volatile phenomenon to be viewed from a distance.

With the surges in late 2023 and in the last few days, it is the large scale, almost clean sweep, for want of another description, of the destruction, that marks these surges as significant. At the time of the largest surge on 14^th/15^th January 2024, wind speeds at Happisburgh were under 30 metres a second. At Felixstowe, measures were just above 20 metres per second around about the time of the highest surge on Monday 15^th January. Yet a Flood Warning was in place for Sunday 14^th /Monday 15^th January for flooding at Bawsdsey Quay and Felixstowe Ferry. With sea levels at mAODN (height above average sea level) of 2.92, which is 0.88m above tides tables.

Therefore, to conclude this debate, even though every storm surge can be different, generated, as they are, by numerous systems acting on the ocean’s surface. Each surge is a demonstration of the transfer of momentum between atmospheric systems and the sea. Alterations in pressure systems alter energies down though the surface of the sea which are felt at all levels. With wind tension applied to both the physical surface and as well as equidistant to it.

The deepening of low-pressure, the strength of the wind and size of the area over which it blows, and the duration can initiate systems outside of normal tidal processes. These mechanisms can elevate and give Surges a particular force. When this is ranged against coastlines and tidal estuaries it can generate abnormally high-water levels. It is the intensity of these energy processes that can cause severe disruption to coastal landscapes and infrastructure.

Few areas are more susceptible to large dangerous storm surges than the southern part of the North Sea.

Storm surges, 1967–1982. N. S. Heaps. Geophysical Journal International, Volume 74, Issue 1, July 1983, Pages 331–376.

This discussion will begin a two-part consideration to look at storm surges. The first part will discuss the effects on the East Anglian coast of two surges that occurred on 24^th November and December 21^st/22^nd 2023. The second part will debate the extent to which storm surges possess a particular strength with the ability to cause significant long-term damage on a coastline. This 2^nd part will debate contributory factors to the potential power of surges, with reference to the slightly different meteorological conditions that produced the surges in November and December.

On Friday 24^th November, a storm surge measuring over 1 metre was forecast for Lowestoft, with similar forecasts in place at Cromer and Felixstowe.

In the time period of the surge several significant erosion episodes were recorded. Particularly significant damage occurred at Hemsby in Norfolk and Pakefield in Suffolk, where large sections of access road used by residents at both locations, collapsed into the sea.

In other areas of Suffolk, At Minsmere RSPB nature reserve, the surge overtopped the dunes and temporarily washed into the nature reserve before draining out within 2 days. Sea water from the surge, flooded the beach fence line, with the sea seeming to break through sections of dunes in places.

At Thorpeness, the surge seemed to level the length of the cliff frontage, with a noticeable difference in beach profile from photos taken on November 5^th and 26^th November 2023.

At Sudbourne beach, the shingle ridge appears to have further flattened out, with two wide fans of shingle that appear to stretch towards the water channel behind the wall that protects the Alde & Ore Estuary. In the estuary itself, the surge caused a greater volume of water than usual to flood the saltings for prolonged periods of time both before and after high tide.

The second storm surge occurred as Storm Pia hit the UK. between midnight on Thursday 21^st December and the early hours of Friday 22^nd December 2023. A storm surge measuring around 1.7 metres was forecast for Lowestoft.

At Hemsby, damage from the surge included scouring of around 2 metres of sand from Hemsby Gap, and the formation of a 1-3 metres Scarp. Additionally, less than 2 metres of dune remains North of Hemsby Gap, with a car park and Hemsby Independent Lifeboat station, immediately behind this section of dune. The damage to the slipway has meant that Hemsby Independent Lifeboat has been out of service.

Another significant feature of the December storm surge was the tide locking effect that occurred on the Norfolk Broads. This meant water that would naturally drain out into the sea from the Broads was prevented from doing so because of the volume of water coming up the rivers from the storm surge in the North Sea.

Two weather system maps for the storm surge on Friday 24^th November and Thursday 21^st December, provide a useful framework for the debate in part two of this discussion, as conditions show some similarities as well as significant differences.

On Friday 24^th November, a low-pressure system was located off the East Anglian Coast, whilst a high-pressure system was located over the Atlantic. At Happisburgh low pressure dipped to 1016 mb between 10:50 and 15:20 on Friday 24^th November. A Significant Wave Height of 3.6m was recorded at Happisburgh. 

On Thursday 21^st December, again a low-pressure system was located off the East Anglian Coast, whilst high-pressure was located over the Atlantic. However, the pressure gradient was much steeper, with low-pressure deepening to 997 mb between 07:30 and 08:00 am on Thursday 21^st December. SWH also remained below the Storm Alert Threshold on Thursday 21^st and Friday 22nd December 2023.

It would seem to be apparent that the two storm surges in November and December, were produced in slightly different weather conditions, but both surges had a significant effect on the coast and inland tidal estuaries. Therefore the 2^nd part of this discussion will consider the potential specific strengths of a storm surge and debate this phenomenon with reference to meteorological conditions and likely sea state features that can make surges so damaging.

Storm Ciaran hit the Southern half of England on the evening of Wednesday 1^st November and further intensified to a severe storm on Thursday 2^nd November.

One distinct feature of Storm Ciaran was that it seemed to be a Wind Wave Storm. A characteristic of a storm of this nature is the Significant Wave Height (SWH), the average height of a third of all waves. It is thought if SWH, reaches above a certain threshold, waves of this height have the potential to move significant amounts of beach material.

The SWH at Hemsby was forecast to be 2.4-3 metres, with wind speeds of 50/70 km/h, with a southerly/south-easterly direction. At Felixstowe SWH was forecast to be 2.4-3 m, with wind speeds of 65-75 km/h, with a southerly direction. At Lowestoft SWH was forecast to be 2.4-3 m, with wind speeds of 50-70 km/h, with a southerly direction. At Lowestoft the general, long-term SWH Storm Threshold measurement is 3.11 metres and at Felixstowe it is 1.94 metres.

The Met Office Surface Pressure Charts indicate the presence of weather conditions likely to produce disruptive sea states. The charts showed the Low-Pressure values for Storm Ciaran to be around 980 mb off the Southwest Coast at midnight on Thursday 2^nd November, deepening to 972 mb at 12 pm on Thursday 2^nd November. The Shipping Forecast produced by the Met Office gave the status as Low 100 miles west of FitzRoy 972 expected Humber 956 by midday tomorrow.

Low-Pressure systems have the potential to raise the sea level, potentially producing damaging storm surges, strongly influenced by the meteorological conditions at the time. A small surge was forecast for Lowestoft, with a surge of over 0.5 metres forecast at Cromer.

Another interesting feature of Storm Ciaran was that it was forecast to be a very slow-moving storm, likely to cause heavy periods of rain or strong winds to remain over Southern England, and the coasts of the South West, the English Channel and the North Sea for some time. Not to draw any parallels, but one of the features of the 1953 Storm was that it was extremely slow moving over the North Sea, which expanded the length of the wind area, increasing the surface capacity of the wind to produce damaging waves.

As in a storm of this magnitude, Wind, Waves, Rainfall and Sediment can dynamically interact to unleash intense damage on vulnerable, fragile coastlines.

In addition to concern about destruction, is the sudden sense of loss caused by erosion. The rapid destruction or diminution of landscapes, changed potentially forever by the wind & the waves.

This discussion will continue previous considerations looking at Tide data from Lowestoft for the months of January and July, from 2015 to the present day. The two months were selected to give a contrasting snapshot of tidal values in a winter and a summer month in the year. A chart is updated twice a year with data from the 1^st, 15^th and 30^th of the month, to indicate the highest tide values for these dates in January and July, for each year being considered.

The highest Surge (or residual) value is also collected and displayed in a Table below. This relates to the tendency for an elevated bulge of water, generated by meteorological conditions and separate from the tide, to arrive a few hours either side of tidal high water.

To begin by looking at Tide data for July 2015-2023 for the dates 1^st, 15^th and 30^th of the month. The chart below shows the Highest Tide Value for the dates mentioned.

The chart shows fairly regular tide heights for the years and dates selected. With the most noticeable features being the slight dips in tide levels in 2016, 2020 and 2023, which seem to occur uniformly on the 15^th of the month. However, it seems that there is nothing particularly significant about the 15^th of the month, as the higher values for tide heights for 2018 and 2021, occurred on the 15^th of July for both these years. It is noticeable that highest tide value occurred on 15 July 2021, in same year that saw exceptionally high tides for January 2021.

Additional data for surge values for 2023 on the dates mentioned above has been collected alongside tide heights for these dates, and this data includes the tide values above.

Consideration of Tidal levels and surge are useful to provide a snapshot of noticeable trends over time. As the basic data collected can provide a backdrop to observations or events on the coast. Additionally, these considerations can help to identify any significant alterations in the patterns of the ever-changing, ever-restless North Sea.