alteredcoast

This discussion will combine analysis of annual January tide data from 2015 to the current year, with further consideration of the 1953 storm event, to consider the usefulness of a Skew Surge. The total difference between Maximum Predicted Astronomical Tide and Maximum Observed High Water.

To begin with a look at annual observed Tidal High Water (HW) data for Lowestoft, from January 2015 to the present, each year the chart is updated to show annual tide data for the dates of 1^st, 15^th and 30^th of January. The data for 2023 can be seen towards the end, on the right-hand side of the chart. For the 1^st January, maximum observed tidal HW was 2.665 metres, for 15^th January, it was 2.918 metres and for 30^th January, the value was 3.019 metres.

To consider the skew surge, for the dates in January 2023, the table below shows the values for Maximum Predicted Astronomical Tide and Maximum Observed HW, and the Skew Surge for these dates. The figure for the skew surge is obtained by calculating the difference between the Maximum Predicted Astronomical tide and Maximum Observed HW.

It is interesting to note how values for 1^st January and 30^th January, occur quite close to predicted tidal HW, though a skew surge value applies whatever time it occurs within the tidal cycle. This useful to note, as recent flood warnings at the end of February highlighted that a storm surge can occur either side of predicted high tide. A diagram from a paper to discuss tide and surge independence illustrates the position of a skew surge, in a tidal cycle.

A skew surge can occur on any tide, and occurs independently, as the value only shows the difference between predicted and observed HW. So a Skew Surge could be framed as analysis of what constitutes the elevated portion of HW, the factors that create this elevation, and its significance in storm analysis.

To consider this, the Skew Surge on 15^th January 2023 can be used as an example. Maximum Predicted Tidal HW of 2.37 metres, occurred at 02:12 am, and Maximum Observed HW at 15:45 pm. Low pressure dominated, ranging from 995 to 1993 mbar, winds blew from a Southwest to Northeast direction, wind speeds increased from 18-20mph at the start of the day to 24 mph around 09:20-11:20 am.

Weather conditions can help explain a rise in observed sea level. Especially because on the January 2023 dates, all three tides were Neap Tides, when tides are smaller than usual. Regarding the 1953 storm, the scholar Steers in 1953 wrote that surge conditions in 1953 could have been even more serious had the surge occurred on a high Spring Tide. Steers states predicted Spring Tides were around 1-3 ft less than occur at other times of the year. This suggests the main cause of damaging sea levels in 1953 were meteorological conditions on the night. The Skew Surge on 31^st January 1953 was 2.41 meters at Lowestoft, whereas in 2013, the skew surge was 1.98 metres, even though the astronomical Spring Tide was higher in 2013.

A Skew Surge can contribute to analysis of a storm by indicating likely presence of specific, local conditions capable of generating dangerous surge conditions. But further information is still needed to ascertain its significance. Predicted tide height, levels of low pressure the breadth and duration of a surge, whether high water was still or agitated, wind speed and direction, all important indicators of the severity of a storm.

Values for Observed Tidal HW, in the January chart and the Skew surge for the January dates, show elevated sea levels and indicate the particular nature of a surge. These characteristics can contribute to an understanding of troubled sea levels and the power of the infamous surges of the North Sea.

Anyone who has been among mountains knows their indifference, has felt a brief, blazing sense of the world’s disinterest in us. In small measures, this feeling exhilarates. In full form, it annihilates.” –

Quote from film Mountain.

The sea inspires fascination, its otherness captivates and evokes awe and a sense of calm. But it is also a wild, phenomenon governed by natural influences, independent of people and homes and daily life. Storms like the 1953 surge, are a concern, because they remove the distance between humans and the weather. Normally, the weather happens around us, but it doesn’t directly impede daily life, or place people, and homes in peril. Storms operate as a natural force, acting according to rules, which may align with the laws of physics and meteorology, but operate with a force and ferocity, incomprehensible to humans and completely indifferent to their presence.  

Analysis by Wadey, Haigh, & Nicholls et al. identify particular characteristics that made the 1953 storm so destructive. The Low-Pressure epicentre, (known as Low Z) (Pollard, 1977), which at one point, dropped to 964 mb, produced extremely strong northerly winds over the North Sea. The storm’s trajectory from Ireland to Europe, featured an abnormally slow journey to the coast of the Netherlands. This created a lengthy north-south wind system over the North Sea, widening the area in which the wind could generate waves. This strengthened storm surge formation, and gradual amplification of northerly winds severely enhanced wave heights causing the sea state to deteriorate further. These conditions hit East Anglia severely because the rotation of the earth, deflects water to the right of tidal currents. As tide and surge travel in a southerly direction, the height of both, and shallower bathymetry (depth) in the southern North Sea, push large volumes of water towards its coastlines.

Ferocious conditions on the night of the 1953 storm, set the scene for the assertion in the book North Sea Surge, by Michael Pollard, in which he writes:

“It is not journalistic fancy to write that the North Sea went mad on the night of 31^st January 1953”

It is also claimed the insane rage of the North Sea had a return period of around 1-3000 years in some places. With a storm of such a size, and intensity, how can humans be expected to develop comprehensive, resistance, with warnings and defences to manage such a force of nature. Especially as Michael Pollard also writes that for several hundred years, at least, it has been very difficult to know without consulting maps and records, and sometimes, even then it is not clear where sea and land begin and end according to early archives. History has always told of a constant battle between land and sea.

It is perhaps, then not useful to draw inferences with today and the preparedness of coastal areas for future storms, by considering insights from Pollards book. In which he writes that tides can be predicted years ahead with some accuracy, but surges, tend to disrupt this accuracy. Reports describe how the inner landward facing walls of embankments failed, enabling the sea to overcome communities from the rear, sometimes many hours after sea facing defences many miles away had withheld the sea.

In the days before the storm, observers, noticed the tides were not completely leaving the estuaries, before the next tide came in. It was also said the motion of the sea seemed strange, and there were concerns about winds. In parallels with today, concerns exist about the robustness of clay embankments and flood warnings regularly refer to the tide locking affect, when the previous tide is preventing from leaving as the next high tide comes in.

The wildness of the sea, came crashing through people’s doors without warning on the night of 31^st January 1953. The magnitude of a storm of such severity invokes a constant tension between balancing the perception that coastal conditions can be made measurable and manageable. With the awareness that the enormous violence of storms makes them unpredictable, with communities increasingly aware of the restless, unruly neighbour, that dominates the coast.

The insights from Pollards book that describe the behaviour of the sea before the night of the storm, suggest that perhaps part of remembering the storm surge of 1953, is a realisation that there are natural systems and processes, the strength of which we do not totally comprehend. Phenomenon we can never totally get the measure of.

The characteristics of the 1953 storm described above, describe the basic meteorological conditions for the storm. But they don’t describe the human story of how communities comprehend the feeling of the raw fury of the sea and its indifference. People who lived through the 1953 storm, convey the sense that a grave injustice surged through streets once thought familiar and safe. Leaving a tragic, indelible memory of broken homes, boats and dampness in the walls that cannot be removed.

The 1953 storm was a severe assault on the coastline and the people and animals that live along it. Storms and high seas have plagued the North Sea Coastline for hundreds of years. In 2013, a storm which equalled if not exceeded the extreme conditions in 1953, hit the North Sea coast, only this time damage was not as severe as defences and warning systems were much more advanced. But on the dynamic, storm driven, East Anglian coastline, it is still perhaps, the unknown power of storms, indifferent to their effects, which prove that you can never underestimate the power of the sea.

This discussion will look at tides and surges to consider whether the data suggests the presence of conditions likely to cause beach erosion. This will follow-up a previous debate concerning big vs small erosion events, that looked at the transformation of Thorpeness beach, below North End Avenue between 27^th August and 1^st October 2022.

Values from Spring and Neap Tides will be examined. Spring Tides occur during Full and New Moon, when the Sun and moon align directly with the earth, this considerably increases the height of the tide. Conversely, when the sun and the moon are at 90 degrees, to the earth, a Neap Tide occurs, with an especially small range. Both Spring and Neap tides occur once a fortnight.

Data for five dates selected in the table below, show in the first line for each date, the highest tide value and in the second line the highest surge value. One 13^th September the highest tide value is 3.212 metres, and the highest surge value, 0.398 metres. The surge (residual) as it is called is calculated from observed sea level value minus predicted sea level, for the time they occurred.

Data obtained from the National Tidal and Sea Level Facility, provided by the British Oceanographic Data Centre and funded by the Environment Agency. The source is the Port, P024 at the site of Lowestoft, with the Latitude of 52.47300 and Longitude of 1.75083 with the start date of 13th September 2022-00.00.00 and end time of 23:45:00 for each date analysed. The Contributor was the National Oceanography Centre, Liverpool and data refers to Admiralty Chart Datum (ACD).

One question to consider is whether surges are independent phenomenon that form as a result of particular conditions. For 13^th September, a Spring tide, the surge occurred 1 hour and 15 minutes before High Water. However, it could be said surges originate from the environment at the time, separately from the lunar cycle. On 16^th of September, a Neap tide, the highest surge value is 0.649, the third highest surge value in the data above. The surge occurred on a falling tide, at 8:30 am, with a tidal value of 2.194 recorded. The highest tide value occurred 6 and a half hours earlier at 1:00 am and was recorded as 2,683, with a smaller accompanying surge of 0.368. On 26^th September a Spring Tide of over 3 metres was recorded, but the two surge values are also both elevated. The highest surge value of 0.756 occurred at 17:45, four hours before high water, with another reasonably high surge of 0.629 recorded at 21:45 at the time of high water.

It is also useful to look at the meteorological conditions at the time the tide and surge values were recorded. A rise in atmospheric pressure causes a 1cm fall in sea level, low pressure causing a rise. As a rough guide, air pressure of 1022 mbar is considered to be High Pressure, 1022-1009 mbar Normal Pressure and 1009 mbar and below, Low Pressure. The table below shows atmospheric conditions for Lowestoft in September 2022.

Data of mbar values and weather conditions obtained from the website https://www.timeanddate.com/weather/uk/lowestoft/historic?month=9&year=2022

For 13^th– 20^th September, Normal or High Pressure was recorded with air pressure fluctuating around 1012-1027 mbar. However, on 26^th and 30^th September, there is a noticeable drop in Air Pressure, from 1007 mbar to 998 mbar on the 26^th and 996 mbar on the 30^th. A significant drop in pressure can indicate storm conditions. On the 26th, air pressure at the time the highest surge was recorded was 1000 mbar and by the time of the highest tide it was 1001 mbar, the drop in Low Pressure recorded earlier in the day. On the 30^th, air pressure at the time the highest tide was recorded was 1008 mbar and by the time of the highest surge of 0.833 it was 998 mbar.

The tide and surge data in this discussion, offers some evidence that certain tides were elevated during September, and it can be seen surges can occur separately from High Water on both Spring and Neap tides. However, for three of the dates considered, it was not obvious conditions were present to produce a surge. But for dates, towards the end of September, noticeable drops in low pressure and stronger winds could have generated surge conditions.  Tide and surge values in September and atmospheric conditions don’t provide a causal link between beach changes at Thorpeness and elevated sea states. However, values for 26^th and 30^th September could suggest an agitated sea state that could move beach material. Though it should be noted tide and surge measurements at Lowestoft are recorded an hour or two before they arrive at Thorpeness. Though it is interesting to consider whether photos of the cliffs at Thorpeness taken on 1^st October, show a high-water mark at the top of the cliff. Perhaps concluding the examination of data, atmospheric pressure and the evolving movement of the sea and the land it interacts with.

This discussion will travel down the east coast with the tides and surges of East Anglia and will consider how the features of the North Sea influence tidal patterns. Along the way, it will also consider the tendency of surges to occur around 3 to 5 hours before peak high tide.

The shape and position of the North Sea can be said to contribute to the tidal ranges on this coastline. At its northern end, the North Sea links to the North Atlantic through a large channel that passes by Scotland and Norway. At its southern end, the North Sea squeezes through a narrow strip to the English Channel. The tidal system is created predominantly by astronomical, semi-diurnal tides from the Atlantic. Semi-diurnal tides are those which see two high and two low tides of roughly equal size every lunar cycle. Tides rotate around centres, known as Amphidromic Points, and thanks must go to the Environment Agency in providing information about these points, of which there are three in the North Sea. The 1^st Amphidromic Point is located in the Southern North Sea near the English-channel, the 2^nd in the centre of the North Sea and the 3^rd, close to the coast of Norway.

At the centre of Amphidromic Points, the sea is almost stationery with barely any tide. However, tides circulate round these points, as Kelvin waves in a counter-clockwise direction, southward down the coast of East Anglia, every 12 hours, 25 minutes. Each line of the Amphidromic Point represents 1 hour and 2 minutes of travel by a tidal wave, and the furthest from the centre of the Amphidromic Point, higher the tide. For example, at Immingham, placed further away from the centre of the Amphidromic Point in the centre of the North Sea average tide height is around 6-7 metres. Whereas at Lowestoft, located very near the Amphidromic Point in the southern North Sea, average tide height is around 2.5 metres.

The North Sea, is said to be a splendid sea for storm surges.  

(Heaps, 1983).

The position of the North Sea attracts extratropical storms which pass from west to east with the capability to generate energy in the sea. A ‘Storm Surge’, can be formed by atmospheric level pressure acting on the surface of the sea, for example, a 1 millibar reduction in air pressure causes a 1 cm rise in sea level. Another contributory factor, is the effects of wind blowing over large areas of shallow water, with the depth of the southern North Sea said to be around 35 metres.

A‘ storm surge’ is therefore a transitory increase in sea level originating from a depression generated by a weather system. The shape of the North Sea influences this process, because when a surge travels down the coast in a southerly direction, it is accentuated by the concentration of storm energy water being driven through the narrow funnel into the English Channel.

A related concept is the extent to which surges occur a few hours before peak high tide. In a paper by K. J. Horsburgh  and C. Wilson, data from 5 tidal gauges, spaced equally along the North Sea Coast at Aberdeen, North Shields, Immingham, Cromer and Sheerness, found the surge frequency to be around 3-5 hours before high tide. This assertion can be tested by looking at significant surges on the Suffolk coast, such as during the storm on 5^th/6^th December 2013 and the surges that accompanied high tides in January 2022.

Regarding the 2013 surge, it is interesting to note that with a large event like this, it could be problematic to focus on data from 5 specific sites, as you only know when a surge impacted these areas at a given time, whereas outside of these focus points data could show the surge at some locations arrived within between 2 hours or 30 minutes before High Water.

Figures in the table below show peak tide levels and maximum surge heights at Lowestoft for 5^th and 6^th December 2013 and the 6th December 2022.

Data obtained from the National Tidal and Sea Level Facility, provided by the British Oceanographic Data Centre and funded by the Environment Agency. The source is the Port, P024 at the site of Lowestoft, with the Latitude of 52.47300 and Longitude of 1.75083 with the start date of 05Dec2013-00.00.00 and end date of 23:45:00 for each date analysed. The Contributor was the National Oceanography Centre, Liverpool and data refers to Admiralty Chart Datum (ACD).

The table shows that peak high tide on 5^th December 2013 was at 22:30, but the maximum surge height of 2.179 was recorded at 22:00, half an hour before peak high tide. Interestingly, on 6^th December 2013, whilst the peak high tide of 4.228 was recorded at midnight, the maximum surge height of 1.856 metres was recorded at 03:15, over 3 hours after peak high tide. Elsewhere during the December 2013 surge, a report by Kenneth Pye Associates Ltd, commissioned by the Alde and Ore Association, gives figures from the Environment Agency tidal gauge at Orford Quay in the Alde Ore Estuary. On 6^th December 2013, maximum high water was 3.06 m OD at 01:45 am around 71 minutes before predicted High Water and the surge was 1.66 m.

However, in relation to the high tides and surges of January 2022, figures roughly concur with K. J. Horsburgh and C. Wilson. On January 18^th 2022, the surge of 1.2 metres, that travelled up the Alde Ore estuary arrived around 2 hours before normal spring high tide. Similarly, during the high tide and surge on 30^th January 2022, peak high water was recorded at 06:15 in the morning with tide height of 3.659 and a surge height of 1.370 m, but the highest surge occurred 3 hours earlier at 03:45 am with a tide height of 3.391 and surge height of 1.728 m. All data is from the British Oceanographic Data.

Discussion of these figures of surges in December 2013 and in January 2022, should in no way detract from the in-depth, analytical work undertaken by K. J. Horsburgh and C. Wilson. Instead, it just serves to demonstrate how the processes of tides and surges are both fixed describable features and fluid dynamic elements. As our journey concludes with tides and surges of the North Sea, it has revealed the complexity of the everchanging forces that move the water in the ocean.