East Head Spit

East Head Spit, West Wittering.
By Steven Hall

During undergraduate studies at the University of Brighton, and as part of Coastal Geomorphology studies, an examination of East Head Spit in West Sussex was undertaken. The below report was produced by myself following a field trip to the location and subsequent remote analysis of historic data.

Coastlines and estuaries are amazingly rich areas of biodiversity whilst also demonstrating incredibly dynamic and rapidly changing geomorphology. Because of this, our coastlines are an amazing natural resource, and as our climate changes so these areas will come under greater and greater stresses. I hope this report helps to demonstrate what an amazing place our coastlines and estuaries are, and please feel free to contact me for more information.

Evolution of East Head.
Located in West Sussex, East Head Spit is the Eastern boundary to the entrance to Chichester Harbour (Figure 1). The estuary is a submerged valley originating during Quaternary interglacial periods (Bates et al, 2003). Consisting of predominantly Tertiary and Quaternary sediments (Duvivier, 1961), little resistance to erosion and redistribution by coastal forces is present.

Figure 1. East Head, at the Eastern edge of the entrance to Chichester harbour and its location within the United Kingdom. Source: modified from Bray, 2010 and Google Maps.

The entrance to an historic port, the area has been mapped extensively in the past with their accuracy being examined in previous papers (Carr, 1980: de Boer and Carr, 1969), and methods developed to reduce inaccuracies (Thieler and Danforth, 1995), but the quality of the expertise and equipment available must always be borne in mind. Early maps of the area date back to 1585 (Figure 2), but Yeakell and Gardner in 1778 (Figure 3) show a tremendous improvement in the definition of features, with a clear recurve feature present in the drawing and a general alignment of NW to SE orientation for the spit.

Figure 2. 1585 map of the entrance to Chichester harbour, , from the British Library’s collection of maps by William Cecil Lord Burghley, Secretary of State to Elizabeth I.
Source. British Library
Figure 3, right. 1778 map of the entrance to Chichester harbour by Yeakell and Gardner. Clearly showing a recurve feature.
Source: University of Portsmouth

Maps produced in 1797 by William Heather (Figure 4), 1810 Ordinance Survey (OS) map (Figure 5) and 1848 Sheringham map (Figure 6) show the continued presence of the spit in a predominantly NW to SE orientation, and the continued presence of an earlier recurve feature, suggesting a period of stability with minor geomorphological changes.

Figure 4. 1797 map by William Heather for Trinity house, detailing the navigable channel and water depths.
Source: Norman B. Leventhal Map Center Collection
Figure 5. 1810 Ordinance survey map of Chichester harbour.
Source: British Library
Figure 6. Map of Emsworth and Chichester Harbours by Captain Sheringham, 1848.
Source: Chichester harbour Conservancy (www.conservancy.co.uk)

Maps detailing the spits characteristics in 1879 (Figure 7) and 1903 (Figure 8) show the spits orientation on a roughly NW to SE orientation, but with the presence of a recurve feature no longer present. By 1909 (Figure 9), the mapping of the area shows East Head spit turning to an almost north–south orientation, with an extensive area of intertidal sands directly west of the spit (the winner).

Figure 7. 1879 Ordinance survey map of Chichester harbour showing no recurve feature.
Source: National Library of Scotland
Figure 8. 1903 Ordinance survey map.
Source: National Library of Scotland

From 1909 to 1934 a continued migration of the spit produced alignment on a NE-SSW orientation (Figure 10). The area to the East of the spit, enclosed on three sides except to the north is labelled as ‘Saltings’ and ‘Mud’, with very low energy conditions producing high depositional conditions.
Continued OS mapping in 1945 (Figure 11), 1960 (Figure 12) and 2018 (Figure 13), show consistency in the shape and size of East Head Spit, with possible accretion on the distal end of the spit.

Figure 9. 1909 Ordinance survey map indicating a change of orientation to almost North/South.
Source: National Library of Scotland
Figure 10. 1934 Ordinance survey map indicating a change of orientation, and an enclosing of the area to the east of the spit.
Source: National Library of Scotland

Left to right: Figure 11. 1945 OS map survey. Figure 12. 1960 OS map. Figure 13. 2018 OS map.
National Library of Scotland

The reorientation of the spit between 1860 and 1909 is pronounced (Figure 14) and graphically demonstrates the migratory aspect of the spit over relatively short geological time periods. The introduction of sea defences around ~1900 AD, causing the interruption of sediment supply can be seen as a major factor affecting the development and maintenance of the spit (May, 1975: Bird, 2011).
Combining the changes to sediment supply with the cyclic nature of the tidal influences on accretion and deposition (Bray et al, 2007) (Figure 14), the migration and shape change of East Head spit can be seen to be influenced by wave action, aeolian transportation, tidal currents, sea defences, and storm events.

Figure 14. Orientation of East Head spit over time. Source: May, 1975.

Coastal Landforms – West Wittering and East Head
The area from West Wittering Beach eastwards to East Head has been separated in to key zones (Figure 15), with the characteristics witnessed on the day of the field trip (25th April 2018) described in detail for each section. Weather conditions on the day were bright and mainly dry, with some light rain early afternoon. A steady southerly breeze (force 3) was present, with 13-15°c.

Figure 15. Map showing the sections of coastline to be discussed. Source modified from OS 1:10,000.

West Wittering Beach
The eastern section of the area examined, West Wittering Beach, is an area of gently sloping sandy beach, backed by lightly vegetated sand dunes ~6m high, which then lead on to residential housing and low lying flat land ~5m above sea level.
Sea defences have been installed, but are almost completely submerged beneath sand (Figure 16), additionally fencing is installed to areas of the dunes to try to prevent anthropogenic damage, which extends landward for ~30m and gently rise in height to their maximum as you travel eastward.

Figure 16. West Wittering Beach with photos (clockwise from top left): sand dune face showing deposition stratification and current erosion; extensive intertidal, gently sloping sandy beach; historic sea defences (groynes) inundated, and recent fencing-off to protect dune vegetation. Source: Base map – Ordinance Survey; Photos, S. Hall.

No gravel was seen on the beach in this area or the dunes backing it, but some seasonal erosion could be seen on the seaward face of the dunes (Figure 16 top left), with a ~45cm vertical face being exposed at the high-water mark (HWM). As the intertidal beach area dried out, so aeolian transportation of sand from the beach on to the dunes was observed, driven by steady southerly winds.

The Hinge
Height and extent of the sand dunes diminishes rapidly westward and the beach gradually becomes gravelly (Figure 17). The sea defences continue along the beach in the upper reaches of the intertidal zone, and moving westward so the degree of inundation reduces and the groynes become more exposed. With the exposure of the groynes, so asymmetrical deposition of sediment on the groynes indicates wave sediment transport along the beach westward.
Additional defences have also been installed in this area, with wind breaks placed on the upper beach. Slatted fence structures have been orientated facing south west, perpendicular to the prevailing wind direction. Fine sand build up can be seen accumulating behind them (Figure 17).
Other historical sea defences are also present, perpendicular to prevailing wave direction (south-westward facing) and where these have decayed the mud/gravel matrix landward can be seen (Figure 17).

Figure 17. ‘The Hinge’ with photos (clockwise from top right): upper beach area showing increasing gravel content; recent defences to combat aeolian transported sand; historic sea defences (groynes) increasingly exposed, with increased gravel content; perpendicular sea defences destroyed exposing the soil matrix of the area landward. Source: Base map – Ordinance Survey; Photos, S. Hall.

At the time of examining the hinge, the tidal state was relatively high, therefore shore parallel swash bars, which have been monitored migrating shoreward (Bray et al, 2007 ;Bray 2010) were only visible as breaking waves; reduced water depth forcing waves to break (Figure 18)(Pinet, 2006).

Figure 18. Highlights (yellow lines) showing locations of consistent but brief cresting of waves. Source: S. Hall.

At the hinge itself (Figure 20), gravel and cobbles are dominant, but still retain some sand coverage. Groynes are exposed, and combined with the change in beach substrate, demonstrates a marked increase in energy levels (Masselink et al, 2011). Immediately landward of the hinge, a cobble berm is present to protect the saltmarshes to the north. Vegetation is also present helping to reinforce the natural defences, but the steep angle of the beach at this point highlights the eroding processes underway, continuing historical regression of the coastline northward (Figure 19).

Figure 19. Historical changes to the coastline. Source: Associated British Ports, 2001)

East Head Spit
Northward from the hinge, the spit can be described in three distinct zones: spit neck, body and tip (Figure 20). With a marked change in beach material apparent as you head away from the hinge, the dominance of shingle is replaced by sand, as the alignment of the beach changes dramatically.

Figure 20. Segregation of the areas of East Head Spit. Modified from google maps.

The spit neck is an area of low relief (~2m above HWM), and displays a marked narrowing. The intertidal zone consists of a sand bank which gently slopes seaward, and immediately behind the spit neck are salt marshes.
The spit body increases in both height (~8m) and width (~250m) of the dune system, with light vegetation coverage helping to maintain form. No sea defences are present in this area except for some roping to prevent damage to the dunes.
Seasonal erosion is evident at the HWM with ~1m high sheer faces present in the sand dunes (Figure 21), clearly showing seasonal deposition episodes in the density and colour stratification of the sand.

Figure 21. Eroded face of sand dunes – spit body area, with the box showing stratification of the sand. Source S.Hall.

The northern end of the spit (spit tip), has significant quantities of shingle and pebble beds which may be the re-exposed original deposits (Figure 22) (ABP Research and Consultancy, 2000). The intertidal zone continues to be predominantly sand with small quantities of shingle and pebbles visible (Figure 23).

Figure 22, northern tip of the spit, with shingle and pebble beds visible.
Source: S. Hall
Figure 23, intertidal zone of the northern tip of the spit.
Source: S. Hall

Proceeding eastward from the tip of the spit, shingle and pebble beds prevail, which are overlaid with sand. The very low energy environment created by the lee of the spit enables depositional accretion and the extending of the spit East-South-East (Figure 24). At the HWM, erosion is present with ~3m high sheer faces in the sand being present. Clear depositional features can be seen, with aeolian processes clearly visible in the stratification of the deposits (Figure 25).

Figure 24. Shingle and pebble banks to the north and east of the tip of the spit. Source S. Hall

Figure 25. Sand face in the northern bank of East Head spit showing depositional processes within the strata.
Source: S. Hall

Over-topping of the spit
Storm events and changes in topography have caused over-topping of the spit, (Wallingford, 2000: Bray and Teasdale 2007), and it has been recognised that salt marshes and mud flats are becoming a diminishing ecological resource (Pethick, 2002). When a spit is breached with an over topping event, two key issues are raised: the first issue is the immediate inundation of the salt marsh by storm carried debris. This layer of sediment is how we can then identify historical instances of over topping; the second issue is that of permanent breach of the spit, and a realignment of water channels (Robins et al, 2011).
During the examination of East Head spit, a feature at the northern end of the spit neck was identified, where a cutting through the dunes was visible (Figure 26). An eroded channel shows the possible location of the 1963 over-topping (SCOPAC, 2018). To support this, cores were taken to the leeward side of the spit. To try to identify the source of the sediment inundation, four samples of beach sand were taken on a transect from the HWM, seaward to the low water mark.

Figure 26. An eroded channel through the dunes on the spit neck appears visible.
Source. Modified from google maps.

All samples were dried at 100°c for 3 days, then weighed and passed through a particle size sieve, with each particle size category weighed and recorded (Uden and Wentworth particle size scale). Data analysis using the Method of moment (arithmetic) method (Figure 27) shows the cored (sand) layer falling between the middle and lower beach values, suggesting predominantly composed of these two sources.

Figure 27. Mean grain size of samples collected by ourselves (Left), and combined with previous surveys (Right) using the method of moment (arithmetic method) analysis.

Analysis of the data using the Folk & Ward geometric method produces data that implies sources for the sand layer being from the middle beach and dune sand (Figure 28), but when compared to data from previous surveys the data implies middle and upper beach sources.

Figure 28. Mean grain size analysis using the Folk & Ward geometric method. Left, samples collected during the field trip. Right, results from previous field trips.

The variety and ambiguity within the data may be explained by the uncertainty surrounding the location of samples. No specific methods were used to identify locations between sample sets, and tide times influence available beach expanse to sample.
The clearly defined layer within the core taken does demonstrate the presence of an over-topping event, and our data implies middle to lower beach sources.

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