Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.25: Head to Worms Head: large scale and local scale boundaries.

C1-70 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: MUMBLES HEAD TO SOUTHGATE

Interactions: This coastline is cliffed and composed of early Carboniferous limestones with north-west to south- east trending embayments, controlled by faults with the same orientation (Halcrow, 2002). Generally the cliffs are fronted by a narrow rock platform with intermittent and gravel pocket beaches located within individual embayments, and sand embayments at the mouth of stream valleys. Mumbles Head is composed of two limestone islands connected at low water. , , Bay and comprise limestone rock platforms backed by sand and shingle beaches. is a wide flat sandy beach with a shingle strewn rock platform; is characterised by a small gravel beach at the head of the embayment. These beaches act as local sinks for medium-sized due to the shelter created by the surrounding headlands (Posford Duvivier and ABP Research, 2000). West of Pwlldu Head, raised beaches may be found along the frontage at about 8m above present sea level.

Sections of shore between Mumbles Head, Caswell Bay, Pwlldu Head and Burrows are directly exposed to south-westerly swell waves, resulting in an eastward transport of sediment. Around Mumbles Head and to the west of Oxwich Point there are strong tidal currents adjacent to the shore. There are, however, few contemporary sources of sediment due to the seabed being sediment-poor and the updrift coastline containing limited sediment. Sediments have tended to accumulate in the more sheltered embayments created between headlands. The indented nature of these pocket beaches means that there is little connectivity between beaches, with sediments only able to move outside of the bays when sediments move offshore during storm events.

Complex tidal currents operate within Bay, with residual flows creating a weak anti- clockwise gyre. This results in a strong offshore residual flow running southwards from Mumbles Head, the interaction of which with waves has led to the development of a small sand bank which dries at low tide, known as Mixon (Shoreline Management Partnership, 2001). There may be potential sediment exchange between Mumbles Head and Mixon Shoals (Shoreline Management Partnership, 2001), but there is no data on direction or volume of any sediment flux. Posford Duvivier and ABP Research (2000) reported variable sand transport through the White Oyster Ledge and Mixon Shoals area, with westward transport occurring as a result of tidal influence, reversing under storm conditions, during which this region is part of the main transport route for sediment into .

Movement: These resistant cliffs have historically retreated very slowly with any erosion only affecting limited areas, sediment either being deposited on adjacent areas of accumulated sediment or being transported eastwards (coarse materials), westwards (fine sediments) or offshore. Futurecoast (Halcrow, 2002) suggested that the cliffs along this section typically exhibit ‘very low’ (less than 0.1m/year) rates of erosion, but that there is the potential for single cliff failure events to result in 10m to 50m erosion.

Generally the beaches have remained stable due to their indented nature enabling sediments to be retained within the bays, although the dominant cross-shore transport of sediments during storms does cause short-term volatility.

C1-71 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Coastal defences have been built within Bracelet Bay, Limeslade Bay, Rothers Bay, Langland Bay, Caswell Bay, and Port-Eynon Bay. These provide small-scale protection to the shoreline and their impacts on the wider coastline are limited. At Pwlldu Bay a shingle barrier beach provides the main defence to a couple of isolated properties. The barrier contains a number of sand and shingle beach ridges, indicating beach position during the period of progradation. The oldest (and thus most landward) ridge is aligned in a southwest to northeast orientation, with each successive ridge turning towards the current orientation nearer to a direct west to east alignment (May, 2003d).

Existing predictions of shoreline evolution: Under an ‘unconstrained’ scenario, Futurecoast (2002) predicted that low rates of erosion would continue, with ‘negligible/ no change’ (less than 10m erosion) predicted over the next century. The study concluded that beaches would remain stable, although with sea level rise there could be a landward movement of the water line resulting in beach narrowing as the cliffs will continue to prevent shoreline retreat. As only a small proportion of the frontage is defended, the Futurecoast (2002) prediction for ‘with present management’ is similar, although beach steepening and lowering was predicted in those bays where defences are present, but this was not predicted to affect adjacent sections of coastline.

LOCAL SCALE: OXWICH BAY (SOUTHGATE TO OXWICH POINT)

Interactions: Oxwich Bay is a wide sandy embayment that formed as a result of differential erosion, over geological timescales, of the underlying geology, due to both different cliff resistances and the presence of faults. The Bay can be split into three parts: , Nicholaston Burrows and Oxwich Burrows. Three Cliffs Bay is a small pocket beach lying between Great Tor and the resistant Three Cliffs outcrop, controlled by south-west to north-east trending faults and surrounded by limestone rock platforms which are partially covered with shingle. Climbing and cliff top dunes are present at the back of the Bay, known as Pennard Burrows. Sand for these dunes originated from the sandy beach, although this was historic and erosion of the fringing dunes means there is little current source of sediment (Pye et al. , 2007). Pennard Pill, a small , discharges across the beach. This river meanders across the beach and foreshore before reaching the sea. At the back of the Bay there is a narrow shingle beach. The meandering nature of Pennard Pill has meant that an area of low-lying land is enclosed at the top of the beach. Nicholaston Burrows is characterised by a fringing dune system backed by the western cliff of Great Tor. Nicholaston Burrows and Oxwich Burrows are separated by a river, Nicholaston Pill, which drains the marshland behind and dissects the dunes before discharges across the sandy beach. These dunes are generally natural although the stream has been partly trained.

Oxwich Burrows is characterised by a sand dune barrier which encloses low-lying marshland at the mouth of a small valley, cut into less resistant mudstones. It is bordered to the west by Oxwich Point, a limestone cliff, and a raised-beach platform is exposed around the base of Oxwich Point.

C1-72 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

The shoreline is protected from direct exposure to south-westerly swell waves by the substantial limestone headland of Oxwich Point, but the coast is exposed to locally-generated waves from the south and south-east (Halcrow, 2002). Net littoral drift is weak as wave diffraction and refraction caused by the prominent headlands results in local drift reversals. There are limited contemporary sources of sediment, and therefore the beaches within the bays are thought to be predominantly relict (Halcrow, 2002). There is, however, believed to be a sediment link, albeit fairly weak and involving small volumes of sand and fine sediment, between East Helwick area (eastern part of Helwick Bank) and the adjacent beaches, such that sediment can be transported between the Bank and nearby beaches (NAW, 2006).

Movement: It is thought that the main beach ridge within Oxwich Bay developed around 2,500 years ago, enclosing a brackish lagoon (Ratcliffe, 1977). Similar to the system within Swansea Bay, it is likely that low dunes gradually built up due to reworking of glacial deposits laid down on the seabed. During the 12 th and 17 th centuries, there was a period of increased storminess resulting in active dunes and sand sheets migrating inland and this probably also occurred at this site. Since the end of the 18 th century, there has, however, been little further change in the dune position (Pye, et al. , 2007).

The beach at Oxwich steepened during the early part of the 20 th Century, becoming more stable since 1970; although Halcrow (2002) note that there may be cyclical variations in local sediment movements. The dunes at Oxwich were also affected during World War 2 when US troops used the Gower to practice for the D-day landings. This resulted in the dunes becoming very bare due to trampling, and thus subject to reshaping and erosion. However, a policy of no grazing followed, allowing vegetation to become re-established and the dunes to recover (CCW, date unknown).

The marsh behind Oxwich Burrows was originally saltmarsh and open to the sea, but in 1790 a seawall was built, to enable construction of a serpentine ornamental lake and water meadows for grazing, over the former saltmarsh area (CCW, date unknown).

Until the mid-1960s, the Penmaen Burrows sand dune system extended across the western side of Three Cliffs Bay diverting the stream to the east across the beach. These dunes have eroded recently, but the stream still outflows on the eastern side, adjacent to the limestone outcrop to the east that form the three cliffs after which the bay is named (Bridges, 1997). It has been suggested that erosion at the western end of Oxwich Bay may be due to recreational pressure leading to instability in the dunes, rather than any change in the sediment budget (May, 2003a).

The cliff outcrops along this frontage are very resistant. The Futurecoast cliff classification (Halcrow, 2002) suggests that these cliffs typically experience between ‘low’ (0.1 to 0.5m/year) and ‘very low’ (less than 0.1m/year) rates of erosion.

There are no defences along the majority of this shoreline, apart from a very short stretch of gabions along the western side of Pennard Pill, which helps maintain the river outlet at this location, and a seawall along the western side of the bay, which reduces the risk of flooding to the highway and hotel.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predicted that under an ‘unconstrained’ scenario this frontage would remain relatively stable, although continued sea level rise could result in landward migration of the beach. Should this occur, there could be increased exposure of the Holocene back-barrier sediments, causing erosion of the foreshore through water draining through the back-barrier on

C1-73 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding ebb tides. The dunes at Oxwich Burrows could rollback, influencing the route of the stream; whilst at Nicholaston Burrows rollback would be prevented by the cliffs behind resulting in dune erosion and eventually their loss; however eroded sediment should be retained within the bay.

LOCAL SCALE: PORT-EYNON BAY (OXWICH POINT TO PORT-EYNON POINT)

Interactions: Port-Eynon Bay is a deeply indented embayment surrounded by Carboniferous limestone headlands, formed due to the faulted nature of this coastline. The cliffs on the south-western side of Oxwich Point are fronted by a gravel strewn rock platform, whilst to the west the rock platform fronting Port-Eynon Point is bare. The limestone headlands of Oxwich Point and Port-Eynon Point are very resistant and around Oxwich Point a raised beach deposit is still preserved at the base of the coastal slope.

The dunes and sandy beach at Port-Eynon are backed by a low-lying back barrier which is underlain by a platform of softer Holocene clays, silts and peats. At the western end of the beach the dunes are adjacent to the cliffs of Port-Eynon Point. The beach is covered by a thin veneer of sand overlying Holocene bedrock which is exposed in places. This bedrock consists mainly of peats and clays, known as the Submerged Forest Series , and lag gravels (Davies, 2001). The bay is predominantly exposed to locally-generated wind waves approaching from the east and westerly and south-westerly swell waves refracted and diffracted around the headland at Port-Eynon Point. Helwick Bank is also thought to provide some protection to the beach at Port- Eynon by dissipating some of the wave energy before it reaches the shoreline (Halcrow, 2002), especially during low tide conditions. The combination swell waves, strong tidal currents and scarcity of sediment has resulted in the lack of beach development along the base of the cliffs at Oxwich Point and Port-Eynon Point (Shoreline Management Partnership, 2001).

Sediment supply to the beach and dunes is thought to come from remobilisation and aeolian transport of sediments in the bay. Net littoral transport within the bay is low although there is some movement of sediment from one end of the bay to the other during storms. There is also potential for sand to be moved in an offshore direction during storm conditions, resulting in the periodic exposure of the underlying intertidal clays and peats, with the subtidal zone (i.e. the zone just below low water) potentially being a temporary store of such sediment. Some of this sand is then returned to the beach during more typical wave conditions. Although under normal conditions, the indented nature of Port-Eynon Bay means that sediment transport into or out of the bay around the headlands to west and east is unlikely, studies suggest that, once mobilised during storm conditions, there is potential for medium sand to be moved around Port-Eynon Point, in either direction, as both bedload and suspended load (NAW, 2006; Document 8.1). There is, however, a lack of quantitative information on sediment dynamics, and this possible sediment pathway has not been supported by specific work at Port-Eynon Point (NAW, 2006).

Movement: This movement of sand from one end of the bay to the other affects the exposure of intertidal older clays and peats (Submerged Forest Series) on the western side of the bay. It has been suggested that exposure of these peats and clays have only been a recent occurrence associated with

C1-74 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding dredging activities on Helwick Bank, others, however, argue, based on historical Ordnance Survey maps, that such outcrops have been exposed to varying extents pre-dating dredging activities (Davies, 2001; George, 1930). An Inspector’s Report (NAW, 2006), which examined available evidence relating to the possible impact of offshore dredging activities, concluded that the overriding reason for any deterioration in the beaches has been the loss of sand to the dune area behind.

The dunes have experienced erosion in the past, and became increasingly bare of vegetation during the middle part of the 20 th Century when a large number of blow-outs developed. Much of this is thought to have been a result of human use, and, as at Oxwich, US troops rehearsed the D- day landings here during World War 2. During the 1960s and 1970s a major programme of dune repair was undertaken, which, according to anecdotal evidence, included the use of significant amounts of beach sand (Davies, 2003). Marram planting and dune fencing were used to stabilise the dunes and they were almost fully regenerated by the early 1990s. It has been suggested (NAW, 2006) that the dunes have been transformed into a state so stable that sand movement is a one- way mechanism , with sand being moved from the beach into the dunes, to the detriment to the beach in front of the dunes.

Beach cleaning was carried out in the early 1990s, involving the removal of rubbish and debris, but also removed some shingle. This practice has also been suggested as a contributing to the destabilisation of the upper foreshore and some losses of sediment offshore (Davies, 2003). This practice has since ceased; however, photographs taken in March 2009 as part of this SMP show some continued undermining of the seawall at the western end of the beach.

The exposure of the intertidal peats and clays means that these deposits can be readily eroded by wave and tidal action. The fine sediments released are carried away from the beach in suspension and not returned, resulting in an irreversible lowering of the foreshore.

Although much of the bay is backed by dunes, there are cliffs exposed at Horton, towards the eastern end of Port-Eynon Bay. The Futurecoast cliff classification (Halcrow, 2002) suggested that, based on their geology, the cliffs could typically experience a ‘low’ (0.1 to 0.5m/year) rate of erosion.

Existing predictions of shoreline evolution: Under an ‘unconstrained’ scenario, Futurecoast (2002) predicted that the beach would remain generally stable with cyclical changes in beach volume due to onshore-offshore movements. Continued sea level rise is predicted to result in landward retreat of the beaches and dunes, with associated exposure and erosion of the Submerged Forest Series on the foreshore.

As the frontage is generally undefended, with the exception of localised defences at the car park, slipway, residential house, youth hostel and Salt House, the Futurecoast predictions for a scenario of ‘with present management’ are similar to that for the ‘unconstrained’ (Futurecoast, 2002); the exception being at Port-Eynon Salt House, where the seawall would continue to prevent shoreline erosion, although Futurecoast suggested that there would only be a localised impact of this.

C1-75 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: PORT-EYNON POINT TO WORMS HEAD

Interactions: This is an entirely cliffed frontage comprising early Carboniferous limestone cliffs that are indented with minor south-west to northeast trending embayments, which formed due to the presence of faults along this orientation. The cliffs are fronted by a narrow rock platform which is intermittently covered with sand and localised gravel deposits. The cliffs and platform vary in form (and height) dependent on local variations in geology (Halcrow, 2002). Worms Head itself is a rock island, with a low water causeway connecting it to the mainland which stretches westwards from . Small sand and gravel beaches backed by gravel storm beaches may be found within the embayments, with more substantial intertidal sand beaches at Fall Bay and .

The shoreline is exposed to westerly and south-westerly swell waves, although some shelter is provided by Helwick Bank which is believed to dissipate wave energy during periods of low tide (see Annex D for further discussion). It is thought that, although there may be sediment pathways between Helwick Bank and the shoreline, this frontage is too exposed for any significant accumulation of sediment to occur.

Swell waves and strong alongshore tidal currents result in a strong eastward drift (Shoreline Management Partnership, 2001). Halcrow (2002), however, suggested that gravel would be driven eastwards along the upper foreshore, with sand being transported westwards offshore and eastwards in the nearshore zone as a result of the circulatory gyre around Helwick Bank.

Due to the alignment, exposure and limited sediment availability along much of this coastline there are few beaches. Sediments tend to accumulate only where they become trapped in more sheltered embayments. At Mewslade Bay and Fall Bay the embayments are deep enough to allow the retention of sand and gravel sized sediments, although dominant cross-shore processes result in very volatile beaches. Longshore sediment linkages are believed to be minimal, although there is potential for sand sized sediment to be mobilised during storms and moved past Port-Eynon Point through both bedload and suspended transport; however, there are no studies that quantify this possible sediment pathway (NAW, 2006).

Movement: Historically there have been very low rates of cliff retreat due to the resistant geology of the area: the cliff classification in Futurecoast (Halcrow, 2002) suggested that these cliffs typically experience ‘very low’ rates of erosion (less than 0.1m/year). This trend is evident from the preservation of the raised beach rock platform around the base of the cliffs. Beach levels are susceptible to short-term changes, but generally these indented beaches have remained relatively stable. There are no defences along this stretch.

Existing predictions of shoreline evolution: Futurecoast (2002) predicted that for an ‘unconstrained’ scenario, the frontage would continue to experience very low rates of cliff erosion. It was considered that gravel may remain within pocket beaches or be transported eastwards during storm events, but sand could be transported westwards and offshore. The headland of Worms Head was predicted to remain stable and will continue to protect Mewslade Bay.

C1-76 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LARGE SCALE: BAY (WORMS HEAD TO GILTAR POINT)

Plate C.5: Tenby North Beach.

Interactions: Carmarthen Bay is a relatively wide (30 km), shallow (10 km deep) embayment bounded by the in the east and Giltar Point and Caldey Island in the west. The western side of the bay is characterised mainly by rocky cliffs and small bays which contain pocket beaches. The northeastern and eastern sides of the bay are dominated by large and associated sand barrier beach and dune systems. These estuaries are, from east to west, the (Afon ) and the Three Estuarine Complex (Gwendraeth (Afon Gwendraeth), Towy (Afon Tywi) and Taf (Afon Taf)).

The Bay is largely controlled by geology, being cut into softer Carboniferous rocks. The Tenby and Gower peninsulas are characterised by rocks folded in an east-west direction; with resistant Carboniferous limestones forming headlands such as Worms Head and (Halcrow, 2002). The pocket beaches and embayments have formed as a result of differential erosion of the softer mudstone-rich Carboniferous Coal Measures and Millstone Grit.

Due to the overall orientation of the Bay it is exposed to the dominant south-westerly Atlantic swell waves and storms. The shape of the modern coast is dominated by the high-energy, south-westerly

C1-77 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding wave regime (Barber and Thomas, 1989). Exposure and therefore littoral transport rates and directions vary around the bay, with beaches along the western end of the bay tending towards swash-alignment and beaches along the northern and eastern end of the Bay tending towards drift-alignment. Caldey Island and Woolhouse Rocks also influence localised shoreline conditions by refracting and diffracting waves. Similarly Helwick Bank is believed to play a role in dissipating wave energy during low tide conditions (see Annex D for further discussion).

Waves are refracted within the Bay, especially over the shallow areas of the estuaries (May, 2003b). Work undertaken by Barber and Thomas (1989) indicated that there have been significant changes in bathymetry within Carmarthen Bay and that such changes can have a dramatic effect on localised patterns of erosion and accretion at the shoreline, through altering the direction of approaching waves and the magnitude and direction of tidal streams. As well as affecting areas of most severe wave attack such changes can also affect the sediment transport patterns (Barber and Thomas, 1989). The combination of tidal and fluvial influences at the mouths of the estuaries results in periodic growth of sand banks along the coast, followed by breach (by fluvial flows) with associated impacts on the alignment of intertidal channels at the mouth of the estuaries and further upstream, which is complicated further by interactions between the Gwendraeth , Towy Estuary and Taf Estuary (Barber, pers comms, 2009).

The influence of the Three Rivers Estuarine Complex is an important control on the sediment transport regime along the adjacent open coasts (Barber and Thomas, 1989). Based on sediment grain size trend analysis, Posford Duvivier and ABP Research (2000) concluded that there is net sediment transport out of the Taf and the Towy but net import into the Gwendraeth estuary; however Bristow and Pile (2003) analysed historic maps and changes in estuarine area between 1876 and 2000. This suggested that the Taf and Gwendraeth are currently significant sediment sinks, whilst the Towy is near equilibrium. A complex sediment circulation pattern within Carmarthen Bay was suggested, involving radiating sediment transport pathways which emanate from three major sediment parting zones and three major meeting zones. These are situated within the Bay, two of the meeting zones are coastal; along the and Tenby frontages. It was suggested that extreme events are required to load the parting zones with sediment, following which regular transport processes produce the observed patterns of transport (Posford Duvivier and ABP Research, 2000; Cooper and McLaren, 2007). It was also suggested that extreme events are responsible for dispersing sediment from the convergence zones, and that the existence of the parting and convergence zones may be related to resonance features produced by the prevailing hydrodynamics (tidal, wave and wind-driven) in the as a whole. Locally the estuaries may also act as barriers to drift.

Carmarthen Bay is a potential sink for sediments due to its position sheltered from the main tidal streams. Sediment cover, predominantly sands resting on a gravelly layer, is up to 10m thick in the centre of the Bay, thinning towards the shoreline. However the seabed is not considered to be smooth, instead there are a series of ‘sinks’ and ‘sumps’ which are thought to be flattened periodically during severe weather (Posford Duvivier and ABP Research, 2000). Overall, the Bay is thought to contain a fairly constant volume of sediment, which is reworked during storms. The potential sediment exchange between Carmarthen Bay and the Bristol Channel remains, however, an unresolved issue with various hypotheses in existence.

Movement: Carmarthen Bay was formed prior to the Holocene and only subsequently filled with sediments during the Holocene. Exposures of submerged forest beds along the Gower coast indicate that the

C1-78 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Bay was subject to subaerial exposure and erosion during glacial periods, and that the shoreline features seen today have developed following post-glacial submergence.

The estuaries of the Loughor, Gwendraeth, Towy and Taf were excavated during glacial and early Holocene periods when sea levels were much lower and rivers flowed over what is now Carmarthen Bay. As sea level rose, following the last ice age, these valleys were flooded by tidal water and reworking of seabed deposits resulted in the development of the extensive dune fields that occur along the northern and eastern flanks of Carmarthen Bay. The relatively recent Holocene development of these dune systems reflects the abundance of sand stored within the Bay, which was available to aid their development.

Over the last 150 years, evolution along the northern and eastern shores of the Bay has been affected by changes within the estuaries. Construction of defences and reclamation of intertidal areas has generally led to a reduction in tidal prism, enhancing the long-term trend of infilling within the estuaries and also leading to the extension of dune barriers at Whiteford Burrows, Pembrey Burrows and Burrows, into the mouth of the estuaries. Overall there was a net trend of progradation along the dune systems during the early part of the 1900s, but more recently a general trend has been for the central sections of the barrier systems to exhibit erosion, with continued progradation and extension at the lateral ends.

Along the more rocky western side of the Bay, there has been more limited morphological change over the last century and generally the coast has remained relatively stable, with only localised accretion or erosion.

Modifications: Evolution of this open coast shore has been affected by changes within the estuary systems, which has led to a reduction in tidal prisms. This has affected both sedimentation within the estuaries themselves and the open coasts on either side. As discussed above the estuaries also play an important role in the sediment circulation pattern within the whole Bay and therefore their impacts are far-reaching. Specific details on the modifications within the estuaries are discussed in the separate statements for the Loughor Estuary and Three Rivers Estuarine Complex.

The coastline is generally undefended; localised open coast defences exist along coastal settlements, namely Pendine, Amroth, Wisemans Bridge, Saundersfoot and Tenby. At Wiseman’s Bridge, the coastal path and tunnels were originally developed as a tramway that carried coal to Saundersfoot (Shoreline Management Partnership, 2000). Generally the impacts of these interventions have been restricted to the local areas. During the Medieval period, a river outflowed through the Ritec valley, and this is still apparent on the earliest Ordnance Survey maps (1809 – 1833). The subsequent development of a bar across the estuary mouth, together with the construction of the road between Penally and Tenby (between 1830 and 1856) and railway embankments (in 1886) led to substantial training of the River Ritec and the subsequent development of South Beach, Tenby (Posford Duvivier, 1993; Halcrow, 2002). The river now flows through a culvert to the beach. A tidal exclusion gate has also been installed upstream of the railway embankment, which reduces the risk of tidal flooding to caravans and low lying properties during high tides.

Wider-scale interactions: Carmarthen Bay is believed to be largely self-contained, with limited interactions with the wider coastal frontage, although the potential sediment exchange between Carmarthen Bay and the Bristol Channel remains an uncertainty. One theory is that the main east-west sediment transport

C1-79 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding pathways, driven by the dominant ebb tidal flow across the main Outer Bristol Channel, generally by-pass Carmarthen Bay (Posford Duvivier and ABP Research, 2000). Sand-sized sediments may also be potentially transported westwards from the foreshores of Port-Eynon, Rhossili and Saundersfoot into the Bay; although the majority is thought to originate locally (Posford Duvivier and ABP Research, 2000). There is, however, little quantitative information relating to these potential sediment pathways (NAW, 2006).

Sediments typically tend to be reworked and recirculated within the Bay. Both the Loughor Estuary and Three Rivers Estuarine Complex have historically been major sinks for sediment and have been infilling since sea level reached approximately present day levels in the mid Holocene. At the present time, within the Three Rivers Estuarine Complex, the Taf and Gwendraeth are understood to be significant sediment sinks, whilst the Towy appears to be closer to a net sediment balance. The Loughor Estuary is also currently a net importer of sediment from the floor of Carmarthen Bay (Bridges, 1977a) and the adjacent open coastlines. Although limited sediment is supplied to Carmarthen Bay by rivers, these estuaries are major geomorphic features exerting a strong influence upon the coastal system. As such, any interventions within the estuaries have the potential to have a considerable impact upon wider shoreline evolution. Amongst the biggest uncertainties in future evolution are the potential effects of possible changes in bathymetry, average wind-wave conditions and the frequency and magnitude of major storms. While an increase in the frequency of moderate storm events may lead to further beach and dune erosion on exposed sections of the coast, increased incidence of major storms could potentially increase the transfer of sandy sediment from the deeper parts of Carmarthen Bay, towards the coast. Previous studies have suggested that major storms are the main mechanism through which sediment is transported into Carmarthen Bay from deeper water, while smaller magnitude events are responsible for re-distributing sediment in nearshore and intertidal areas (Posford Duvivier and ABP Research, 2000; Cooper and McLaren, 2007). The likelihood of either scenario occurring is highly uncertain and further studies would be required to consider this. The various dune systems will also be sensitive to any changes in the future long-term wind-wave climate.

The interdependencies between different features illustrate the importance of considering this area as a single system. However, the evolutionary responses within this system differ throughout Carmarthen Bay, and this shoreline is therefore described in the following sections (see Figure C.26): (1) Worms Head to Burry Holms; a swash-aligned beach and dune backed by hard cliffs and lower lying marsh located between two headlands.

(2) Burry Holms to Whiteford Point; a dune-capped barrier. (3) Pembrey Burrows ( to Tywyn Point); characterised by a large barrier dune system at the mouth of the Gwendraeth

(4) Pendine Burrows (Ginst Point to Gilman Point); characterised by a large barrier dune system (5) Saundersfoot Bay (Gilman Point to Monkstone Point); a resistant cliffed coastline

(6) Tenby North Beach (Monkstone Point to St Catherine’s Island)

(7) Tenby South Beach (St Catherine’s Island to Giltar Point) (8) Caldey Island

C1-80 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

The Loughor Estuary and the Three Rivers Complex (between Tywyn Point and Pendine) are discussed in separate large-scale statements.

C1-81 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.26: Carmarthen Bay: large scale and local scale boundaries.

C1-82 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: WORMS HEAD TO BURRY HOLMS

Interactions: This shoreline is controlled by the resistant Carboniferous limestone headlands of Worms Head to the south and the anticline islet of Burry Holms to the north. The dramatic change in the orientation of the coastline at Rhossili results from a north to south oriented fault which down-throws Old Red Sandstone rocks in Rhossili Bay whilst the resistant Carboniferous limestone at Burry Holms forms a headland to the c. 450m wide sweeping sand beach. North of Rhossili Down the cliff line curves to the northeast around Moor; this corresponds to the position of the relatively weak Lower Limestone Shales.

The southern boundary to the Bay is formed by the high limestone cliffs of Worms Head, which plunge directly into the sea on the northern side of the headland. Around Worms Head a shore platform is well developed and raised beach deposits are preserved on top of the shore platform; these are cemented and known as ‘Patella’ beach deposits, typically reaching up to 0.3m in height. Moving north from Worms Head, at the southern end of Rhossili Bay the wide sandy beach is backed by a low cliff of glacial and periglacial origin (Campbell and Bowen, 1989), thought to be a solifluction bench (Bridges, 1997; Mullard 2007), which forms a narrow platform of land, approximately 8m in height, extending along the foot of the Rhossili Downs. The platform has a steep scarp slope down to the beach and consists of unconsolidated material, which can be fairly readily eroded. There is a narrow fringing cobble beach at the toe of this slope. To the north the original cliff line trends inland and here the coast is characterised by a barrier dune system which fronts the low-lying area of Llangennith Moors. A stream discharges across the foreshore near Hillend, draining Llangennith Moor. Further north there are two larger dune systems known as Llangennith Burrows and Broughton Burrows, which rest on bedrock and reach heights of about 50m ODN (May, 2003b). Llangennith Burrows consists partly of climbing dunes and partly of hummocky dunes and transgressive parabolic dunes which cap the sand barrier system linking the headland east of Burry Holms with the northern end of Rhossili Down.

This north-south trending coastline and wide flat sandy beach is exposed to swell waves from the west and south-west, although some protection from waves is provided by Helwick Bank, during low tide conditions, which extends in an east-west orientation to the south of Worms Head. The ebb tidal delta at the mouth of the (Afon Llwchwr) may also influence the northern bay (Halcrow, 2002). Within Rhossili Bay, the coast is tends towards swash-alignment, but the beach has a high degree of exposure to waves from the west and south-west which generate net northward littoral drift. Towards Burry Holms, the pathway moves westward and into a local circulation system which combines with the strong tidal currents to transport sand-sized sediment southwards to Worms Head (Posford Duvivier and ABP Research, 2000). The rock-bound embayment at the northern end of the system has acted as a long-term local sediment sink for sand and finer-grained sediment (Llangennith Burrows, Hillend Burrows and Llangennith Moors).

It has been postulated that some sand may have arrived on the beach from offshore during periods of increased storminess between the 12th and 17th centuries, as was the case elsewhere in South (Bridges, 1997). Erosion of the solifluction terrace deposits which form cliffs in the

C1-83 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding southern part of Rhossili Bay has provided a local contemporary source of sediment which compliments a second source of sand from Carmarthen Bay which approaches the shore from the northern side of the Helwick Bank. Cliff slides along the slope fronting Rhossili Downs also contribute a small volume of boulders and cobbles to the narrow fringing beach (May, 2003b). Carmarthen Bay is believed to be largely self-contained, with sediments generally derived from recycling within the Bay; however, the potential sediment exchange between Carmarthen Bay and the Bristol Channel remains an unresolved issue with various hypotheses in existence. One theory is that the main east-west sediment transport pathway, driven by the dominant ebb tidal flow across the main Outer Bristol Channel, generally by-passes Carmarthen Bay (Posford Duvivier and ABP Research, 2000). However there is a possibility that sand which is transported westwards along the southern side of Helwick Bank may enter Carmarthen and Rhossili Bays (Posford Duvivier and ABP Research, 2000). Similarly, sand from Rhossili Bay may be transported south and south- eastwards and be deposited on the sand wave trains (Davies, 2005). There is evidence that littoral sand is able to by-pass Burry Holms and move from Rhossili Bay, around into and Whiteford Sands. There is, however, little quantitative information relating to these potential sediment pathways (NAW, 2006).

In summary, based on available information, there is believed to be little new input of sediment to this beach and dune system, but with a potential loss of sediment to Broughton Bay and Whiteford Sands and also offshore.

Movement: The modern configuration of this shoreline has evolved as a result of pre- and post-glacial processes and there is evidence that Carmarthen Bay has been affected by several phases of sea level rise and fall. Following the last ice age, as sea levels rose, glacial and periglacial deposits were reworked resulting in the development of beach and fringing dune systems.

During the Medieval Period (12 th to 17 th centuries) there was rapid dune development and shoreward migration of active dunes and sand sheets. Development of Llangennith Burrows enclosed the northern end of Rhossili Bay and apparently resulted in the burial of a Norman church there after AD1200 (Smithson et al. , 2002).

More recently, the shoreline has remained relatively stable and there has been little change in the shoreline evident from historical Ordnance Survey maps (which date back to the early 1800s). At Worms Head and Burry Holms, the resistance nature of the limestone headlands, means that erosion is limited, however occasional block falls result from marine undercutting of joint planes. The Futurecoast cliff classification (Halcrow, 2002) suggested that these cliffs could typically experience ‘low’ rates of retreat (0.1m/year to 0.5m/year), but with the potential for a single failure event to result in up to 10m to 50m erosion. Similarly at Llangennith and Broughton Burrows, erosion potential is limited as the dunes mainly consist of climbing and cliff top dunes, which rest on more resistant bedrock.

Along the southern section of Rhossili Bay, there is some erosion evident along the low cliffs, and this area is prone to slides and slippage. The vegetation along the cliff face suggests that these low cliffs are only exposed to wave attack during storms, although some additional erosion will occur due to sub-aerial processes and human activities (i.e. recreational use). Analysis of beach monitoring data (see Annex A1) has shown that there has been very little variability in beach levels in Rhossili Bay over the past decade, although there has been a slight landward movement of both HAT and MHWS.

C1-84 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Existing predictions of shoreline evolution: Under an ‘unconstrained’ scenario, Futurecoast (Halcrow, 2002) predicted that low rates of cliff erosion would continue at Worms Head. Rising sea level would result in the causeway between Kitchen Corner, Rhossili and Worms Head being submerged for longer periods of each tidal cycle, and could eventually lead to Worms Head becoming an island, although it would still exert a control over Rhossili Bay. Along the southern end of the Bay, Futurecoast predicted that sea level rise could cause lowering of the beach, where landward retreat is prevented by the solifluction terrace, and dune roll-back at the northern end of the Bay. Erosion at the front of the dunes may occur as the foreshore narrows and lowers, although there may be deposition on the landward face. The study suggested that along the Llangennith Moors frontage, where the dunes are narrower, there is a risk that the low-lying area would become increasingly vulnerable to occasional marine flooding, although this was not expected to result in a permanent breach.

LOCAL SCALE: BURRY HOLMS TO WHITEFORD POINT

Interactions: Burry Holms, a rocky island at high water, forms the southern boundary of Broughton Bay and this frontage. The shoreline between Burry Holms and Broughton Bay comprises low cliffs, partially buried by blown sand. There is a number of sea caves; these developed along joints in the Carboniferous limestone (May, 2003b). Between Twlc Point and Prissen’s Tor, the dunes extend to sea level and the outline of Broughton Bay appears to be fault controlled (May, 2003b). The dunes are fronted by the wide sandy beach of Broughton Bay. Further north the beach is backed by a raised beach dating from the last interglacial age, multiple till deposits of Devensian age, and overlying windblown sediments of Holocene age (Campbell and Bowen, 1989).

To the north of Hills Tor, a three kilometre long dune-capped shingle barrier extends to Whiteford Point, which is founded on a glacial moraine of Late Devensian age (Bridges, 1987; Bowen, 1995; May 2003b). From Whiteford Point, a spit feature extends into the Loughor Estuary. A 'scar' of residual cobbles is exposed in the intertidal zone north-west of Whiteford Point. The main line of highest dunes is located 50m to 100m inland from the shore and reaches up to 16m in elevation. Seaward of this ridge is a line of dune slacks and a second ridge of lower, younger dunes (Davies et al. , 1987). Within this slack area, cobbles and shingle deposits are exposed, showing that the dunes lie on an older shingle feature.

The intertidal zone fronting Broughton Bay and the southern half of Whiteford Bay is characterised by a series of large sand bars which are oriented at an oblique angle to the high water mark. Migration of these features plays an important role in transporting sand alongshore towards the mouth of the Loughor Estuary.

The blown sand in this frontage is a mixture of sediment derived from Broughton Bay and sand transported by south-westerly winds across the headland south of Burry Holms from Rhossili Bay. There is also some evident leakage of littoral sand from Rhossili Bay, around Burry Holms into Broughton Bay and Whiteford Bay. There is significant longshore drift along the beach, with sediment deposited in the form of a series of recurves at the Whiteford Point end of the system.

C1-85 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

At a larger scale, Carmarthen Bay is believed to be largely self-contained, with sediments generally derived from recycling of reworked material within the Bay; however, the potential sediment exchange between Carmarthen Bay and the Bristol Channel remains an uncertainty. Loughor Estuary is a key sink for sand and mud-sized sediments and is also a strong influence on the evolution of this shoreline. A reduction in the tidal prism, resulting from the construction of defences and reclamation of former intertidal areas within the estuary, probably enhanced the long-term trend for barrier extension at Whiteford Burrows and the development of the sand spit which extends into the mouth of the estuary.

The long-term development of the barrier dune system at Whiteford Burrows over the last few thousand years has had an important impact on the estuary; since the mouth of the estuary previously extended to Hills Tor. Any major change in the dune system (which is considered unlikely to occur naturally over the next century) would therefore have implications on the intertidal mudflats and saltmarshes which have developed along the north coast of Gower.

Movement: Evolution of this area is likely to have been similar to that along adjacent areas, with glacial and periglacial deposits becoming reworked as sea levels rose following the last ice age. Following final ice retreat, Carmarthen Bay was flooded by the sea which probably reached its maximum inland extent around 5,000 to 5,500 years ago. Around this time a barrier beach, probably with overlying dune system, formed in a position a few hundred metres seawards of the present Whiteford Burrows barrier. Freshwater peat deposits formed behind this barrier today outcrop in the sub-tidal zone, seaward of the modern barrier, and wave eroded peat blocks are commonly washed up on the shoreline. Detailed investigation of the stratigraphy and age structure of the barrier has not been carried out, but evidence suggests that a significant part of the dune system sits on a basement of glacial till which strongly influences the hydro-geology of the system (Davies et al ., 1987). As the barrier dune system developed, it linked Hills Tor with the glacial drift scar at Whiteford Point, which caused a reduction in the mouth width of the Loughor Estuary and encouraged the development of Marsh and Llanrhiddian Marsh. The dunes are thought to have been in existence by Roman times (around 2,000 years ago) and the subsequent dune activity in Mediaeval Period resulted in the development of the dune-capped shingle barrier which is present today (Lees, 1982; 1983).

By the mid 17th century the more landward parts of the marshes behind the barrier were already embanked and reclaimed, a process which probably began in the Middle Ages (James, 1991). A major sea bank, known as ‘The Bulwarke’, was probably constructed in the early 17th century, possibly as early as 1629. Embanking of the active marshes further to the north was undertaken in the mid 18th century and in 1817-18 when another major bank, the ‘Banc–y-Lord’, was constructed (James, 1991).

More recently, the southern end of the Whiteford Burrows system has experienced a complex history of accretion, erosion and renewed progradation in the last 20 to 30 years. This is due to the net longshore transport of sediment northwards from this location, followed by extension of sand ridges into this area from Broughton Bay to the south. However, most of the central and northern parts of the dune frontage have experienced slow erosion in recent decades (Pye and Saye, 2005; Saye and Pye, 2007). It is possible that the realignment of the outer Loughor Channel to a position closer to the Broughton shoreline about 50 years ago may have contributed to this change from accretion to erosion (Halcrow, 2002). The southern corner of the bay (at Twlc Point) has also been eroding for some time and toe protection measures have been installed (Shoreline Management Partnership, 2000). Here the foreshore is depleted of sand cover in places.

C1-86 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Over this period there has been further development and extension of the sand spit, which extends from Berges Island at the mouth of the Loughor Estuary; this is being fed by material eroded from Whiteford Sands and moved northwards by the strong littoral drift.

The spatial and temporal pattern of frontal dune erosion and accretion is closely dependent on changes in the nearshore bathymetry, notably movements of the low water channel leading in the Loughor Estuary. The past decade has seen offshore movement and infilling of this channel, leading to rising beach levels and foredune ridge development along the central and southern part of the barrier (see Annex A1); however, this trend could be reversed at any time. The 2003-08 LiDAR digital elevation model (see Annex A2; Figure 4), shows the main low water channel now taking an almost straight course between the training wall breach and just north of Whiteford Point. Development of this channel across the central part of the Middle Estuary in recent decades has lowered the average level of tidal flats on Llanrhidian Sands, leading to increased wave energy exposure along the edge of Llanrhidian and Landimore Marshes and the northern tip of Whiteford spit. The northern tip of the spit has been cut back by over 100m since 1968-72. In 1878, the dune toe along the central part of the barrier lay some 200m seaward of its present position, following apparent accretion in the period 1825/6 – 1878. Net erosion of the central part of the barrier occurred in all successive epochs after 1878. However, the seaward position of the northern end of the barrier system has not changed greatly over the period.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predictions for the ‘unconstrained’ scenario suggested that Burry Holms would remain stable due to the resistant geology and that, due to their elevated position; Broughton Burrows would remain protected from direct marine erosion, but that the sand beaches would narrow due to the landward constraints preventing roll-back. At Whiteford Burrows, the prediction was for sea level rise to lead to roll back of the spit and erosion of the dunes, but it was thought unlikely that the spit and burrows would be fully breached due the size of the system and the stability imparted to this area by the glacial moraine deposits beneath and seaward of the dunes.

LOCAL SCALE: PEMBREY BURROWS (BURRY PORT TO TYWYN POINT)

Interactions: This length of coast lies between the Loughor Estuary and the Three Rivers Estuarine Complex. It is characterised by a broad (one to two kilometres wide) belt of sand dunes. These dunes form a large barrier system (10 km long), aligned north-west to south-east. It is one of only three large barrier systems in England and Wales (May, 2003b). West of Pembrey village the belt of wind-blown sands is almost 3 km wide and is fronted by a wide flat sandy beach (Pembrey Sands and ). Seawards of the main area of dunes there is a cone of lower-lying sand hummocks, generally less than 2m in height, fringed by a narrow ridge of younger, mainly active dunes over 5m in height, which extend into both the Gwendraeth and Loughor estuaries (May, 2003b). Much of the area is now part of Pembrey Forest but the southern area, once the location of a Royal Ordnance factory, is occupied by Pembrey Country Park and the northern end comprises RAF Pembrey Sands, an air to ground bombing range. The beach at Pembrey is used a number of times

C1-87 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding per year by RAF Hercules transport aircraft for specialist training in landing on unconventional runways.

Like the other dunes systems within Carmarthen Bay, much of the sand along this frontage is thought to have been derived from reworking of glacial deposits on the seabed. It is thought that sand may have arrived on the beach from offshore during periods of increased storminess between the 12 th and 17 th centuries, as was the case elsewhere in South Wales (Bridges, 1997). Broughton Bay, Whiteford Sands and Rhossili Bay may also be contemporary sources of sediment to this coastline. There is significant longshore drift along the beach, with net littoral drift south-eastwards, resulting in sediment being deposited in the form of a series of recurves at the distal end of the spit.

At the large-scale, Carmarthen Bay is believed to be almost as a closed system, with sediments generally derived from recycling within the Bay; however, the potential sediment exchange between Carmarthen Bay and the Bristol Channel remains an unresolved issue. The two estuaries at either end of the frontage are key sinks for sediment and play an important role in sediment circulation within the Bay as a whole. As part of this large-scale sediment circulation, Posford Duvivier and ABP Research (2000) reported a sediment convergence point along this frontage.

Movement: The age and stratigraphy of the Pembrey dune complex have not been investigated in detail, but interpretation of LiDAR digital elevation models, aerial photographs and available geological and historical evidence suggests that the dune system may have originated from an emergent offshore bank during the Little Ice Age (c.1300AD to 1600 AD), superimposed on a thick sequence of Holocene marine sediments which extend up to 30m below sea level (Kahn, 1968). This would have subsequently grown both seawards and alongshore due to accretion of sand supplied from the seabed of Carmarthen Bay. Beach gravel deposits have been encountered at c. – 7mODN and – 12mODN in boreholes near Burry Port, suggesting high energy shorelines in this area around 7,000 years ago (Bowen, 1980, p155).

No radiocarbon or luminescence dates have been obtained from the Pembrey Burrows complex. The LiDAR digital elevation model of Pembrey Burrows shows the presence of four high dune ridges in the northern part of the complex; these merge into two main ridges in the central and southern parts of the barrier (see Annex A2, Figure 35). The exact time of formation of the individual ridges is uncertain, and they probably overlie aeolian sands of even greater age. However, the pattern of ridges bear testimony to alternating periods of shoreline progradation and erosion, with periods of partially transgressive high dune ridge building being coincident with periods of shoreline stability and/ or erosion (cf. Pye, 1990). middens are present but the earliest associated artefacts appear to be pottery shards from the late 13th or 14th century (James, 1991).

During periods of shoreline progradation new foredune ridges and sandplains would have formed in the centre of the barrier, with spits capped by low foredunes and intervening swales formed at the distal ends of the system. The morphological evidence provided by the LiDAR data suggests that initial development of the complex involved the development of a low spit which was attached to the mainland just to the north of Pembrey village. The landward end of the spit system was orientated broadly WNW-ESE and may have been composed of fairly coarse grained sediments which allowed only limited low dune development, while the more distal part of the spit had a more NW-SE orientation and was characterised by higher dune development. Subsequently, sediment brought onshore from sources in Carmarthen Bay was evidently drifted both to the north and south, forming new dune ridges with a broad NW-SE orientation. The greater width and greater

C1-88 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding spacing of the dune ridges in the northern part of the barrier complex testifies to greater long-term sediment accumulation in this area compared with the southern part of the complex.

Most of the area behind the dunes, Pembrey Marsh, was probably enclosed by the late 17 th century, if not earlier.

A map of 1762 date shows, however, that an area called ‘Black Marsh’, west of Pembrey village, was then not enclosed and may still have been subject to periodic tidal incursion (James, 1991). The northern limit of Black Marsh is defined on the LiDAR digital elevation model as an arcuate zone of slightly higher ground, approximately 500m wide (Figure 35), across which the access road from Pembrey village to Pembrey Burrows now runs. By the time of the first Ordnance Survey One Inch map this area had been cut off from the sea by the growth of a new arcuate beach and low dune ridge which had by then joined the southern end of the main Pembrey Burrows barrier complex to the narrow coastal plain near Burry Port. Although no direct dating evidence is available, it is possible that this secondary barrier system formed during a stormy period of the 18th century when erosion of the dunes further north occurred and significant quantities of sand were transported southwards and eastwards by longshore drift. This section of the shore then evidently remained fairly stable until the 1950’s, when the rate of longshore drift again increased, leading to rapid eastward movement of ‘The Nose’ and formation of the enclosed Pembrey Marsh.

In the 1850s embankments (south of the existing A484 -Carmarthen road and railway line) were constructed (Ludlow 1991, cited in Archaeological Trust, 2009). A series of canals were cut across this area, to export the anthracite coal of the South coalfield, from the early 18 th century onwards (Dyfed Archaeological Trust, 2009).

The development of new spit-like ridge extensions at both ends of the system between 1946-8 and 1968-69 suggests rates of longshore sand transport, in both directions away from the centre of the complex, were higher in this period than previously (or since). The late 1950s and 1960’s was a relatively cooler, stormy period which resulted in accelerated dune erosion and long-shore drifting at many British west coast localities (e.g. Pye & Blott, 2008).

Along Pembrey Burrows there has been more than a kilometre of progradation (see Figure C.27), much of it in the last 30 years, ranging from around 100m in the centre to more than 600m at the northern end and more than 1.5km at the southern end. In recent years there has, however, been erosion along the central section of dunes and in places an unstable, near vertical sand cliff face exists. The northern end of the Pembrey Forest frontage has been eroding for several decades. Erosion in this area is continuing, with dune cliffs up to 8m high along the northern part of the Country Park frontage. The current rate of dune erosion slows in a southwards direction and there is a transition to seawards dune accretion near the southern limit of the Pembrey Country Park frontage, with the eroded material transported south-eastwards by littoral drift. Analysis of beach monitoring data from 1999 - 2008 (see Annex A1) has shown that dune erosion (and landward movement of HAT) occurred along the northern part of the Pembrey Forest frontage, but there was accretion near Tywyn Point. Accretion also occurred along the central part of the Pembrey Forest frontage. Net erosion occurred along the north-central part of the Pembrey Country Park frontage, whilst accretion occurred between the southern end of the Country Park and Burry Port. Erosion along the Country Park frontage has undoubtedly been exacerbated by visitor pressure around the main beach access points, although this is unlikely to be the only cause. SMP1 (Shoreline Management Partnership, 2000) suggested that erosion tends to occur in ‘bites’, with several metres of shoreline lost over a high spring tide cycle accompanied with gales. The rate of erosion along the central part of the frontage is currently being reduced locally by rock armour buttresses.

C1-89 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

A sand spit feature, known as the ‘Nose’ currently extends eastwards across the entrance of Burry Port. Eastward drifting of sand from ‘The Nose’, past Pembrey Old Harbour and towards the western breakwater at the entrance to Burry Port has been occurring for decades but has become increasingly problematic in recent years. However, there has been recent erosion along parts of this shoreline,

Since the First Edition One Inch Ordnance Survey map, the tip of ‘The Nose’ has advanced approximately 3 km south-eastwards. Historical maps also indicate that the entire shoreline between Tywyn Point and Burry Port has experienced net seaward accretion of more than 200m since 1879. Therefore the original historic shoreline would have been several kilometres landward of the present foreshore, located between and Pembrey village (Shoreline Management Partnership, 2000).

Accretion in this area has been associated with recent erosion of the older central part of the barrier inshore of Cefn Sidan Sands, and strong littoral drift into the Loughor Estuary (May, 2003a). Accretion in this area was also been encouraged by the construction of Pembrey Harbour, Burry Port Marina and the railway line.

There has, however, been some recent trimming of the dune front at the eastern extremity of ‘The Nose’ (Pye, 2010; Annex A2). A small channel now runs from Pembrey Old Harbour parallel to the shore before turning along the western side of the Burry Port breakwater. This channel effectively limits the transfer of sand from the nearshore sand bank to the beach and dunes to landward. Hydrodynamic modelling results (Barber and Thomas, 1989) suggest that the change from accretion to erosion at the northern end of the Pembrey frontage (the central part of the Cefn Sidan Sands) may have been caused by changes in the bathymetry of neighbouring parts of Carmarthen Bay between 1977 and 1988, which has altered patterns of wave diffraction and focusing and also sediment transport patterns within Carmarthen Bay as a whole. This suggestion is to some extent supported by the historical chart and map evidence, which indicates that changes in the number and positions of low water channels in the Three Rivers confluence area have had a major effect on the timing and pattern of shoreline accretion and erosion on both sides of the estuary entrance; however, beach and dune erosion also affected the Pendine and Ginst Point frontages in the late 1960s and 1970s suggesting that increased storm forcing may have been a more significant factor (Pye, 2010; Annex A2).

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predicted that under an ‘unconstrained’ scenario, the dune-beach system would retreat slowly, although interaction between the dunes and beaches is likely to remain healthy, sediment that is eroded from the dunes is likely to be returned to the beach, or transported north or south and deposited on one of the spits. It was suggested that the forested nature of the dunes could constrain natural long-term evolution of the system, potentially causing greater amounts of dune erosion and cliffing of the dune face.

In SMP1, Shoreline Management Partnership (2000) recognised that the significant erosion in recent years tended to occur in ‘bites’, whereby several metres of shoreline could be lost over a high spring tide cycle accompanied with gales. It was suggested that under a do nothing’ scenario, a continuation of the current trend would be likely, resulting in further erosion and increased accretion adjacent to Burry Port. The report stated, however, that it is not possible to determine where the equilibrium line would be.

C1-90 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.27: Composite aerial photography of the Pembrey frontage and the adjoining Gwendraeth and Loughor Estuaries, flown in 2006. The dashed line defines the position of the dune toe or marsh edge from the first edition County Series OS Map, surveyed in 1879.

LOCAL SCALE: PENDINE BURROWS (GINST POINT TO GILMAN POINT)

Interactions: This frontage extends between the mouth of the River Taf (Afon Taf) at Ginst Point and the rocky headland of Gilman Point and consists of a large (10km long, 0.5km to 1km wide) barrier spit complex ( Burrows and Pendine Burrows). The dunes reach heights of over 15m, apart from in the vicinity of Little Burrows where there used to be a small stream, labelled as Whitegate Pill on the earliest Ordnance Survey maps (dating from 1809-1833), but subsequently known as Witchett Pill, which drained marshland and separated the dune systems of Laugharne Burrows and Pendine Burrows. Behind the dune belt is a belt of reclaimed former marshland up to 2 km wide, inshore of which is a degraded fossil cliff cut into Lower Old Red Sandstone. Regular tidal flooding at the eastern end of Laugharne East Marsh, to the north of Ginst Point, is prevented by a low ridge of dunes and an earth embankment, seaward of which is a narrow belt of active saltmarsh. The reclaimed marshes are extensive but are relatively high in the tidal frame (median surface elevation range 3.6mODN

C1-91 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding to 3.9mODN); consequently the tidal prism at MHWS level is less than might be expected (Pye, 2010; Annex A2).

The low tide beach at Pendine and Laugharne is wide (1km to 1.5km), relatively flat, and composed of medium to fine, well-sorted sand. The beach system can be classified as an energy dissipative system.

At a larger scale, Carmarthen Bay is believed to be largely self-contained, with sediments generally derived from recycling of reworked material within the Bay; however, the potential sediment exchange between Carmarthen Bay and the Bristol Channel remains an uncertainty. Therefore the main source of long-term sediment supply is likely to have been reworking of glacial and preglacial deposits laid down on the sea bed in Carmarthen Bay. Sand eroding from this shoreline is likely to be added to the linear sand banks at the entrance to the Three Rivers Estuarine Complex.

This shoreline is exposed to westerly and south-westerly swell waves. However, erosion of the beaches and sand dunes occurs mainly during storm conditions, as the wave energy during typical conditions tends to be attenuated across the gently sloping bathymetry of the Bay.

Movement: Evolution of this area is likely to have been similar to that along adjacent areas, with glacial and periglacial deposits becoming reworked as sea levels rose following the last ice age, resulting in the development of beach and fringing dune systems. Growth of the barrier beach and dune complex continued as a result of strong longshore sediment drift from west to east between 8,000 to 5,500 years ago (Walley, 1996; Higgins, 1933) enclosing low-lying marsh areas inshore. These marsh areas have evolved over the past 5000 years in response to the growth and accretion/ erosion history of the barrier system.

The inshore part of the western end of the dune-capped barrier system (Pendine Burrows) overlies glacial deposits and probably began to form around the time sea level reached its present position around 5,500 years BP (Walley, 1996). This area consists of a series of irregular hummock dunes and parabolic dunes which attain a height of more than 20m in places. The inner part of the eastern half of the system (Laugharne Burrows) is younger and may have formed in the later Holocene on a detached sand bank, separated from Pendine Burrows by a tidal channel. This channel (the Witchett ) was progressively blocked off, from the 17th century onwards, as the land inshore of the barriers was reclaimed and the dunes developed. Since that time new dune ridges have developed along the entire length of the Pendine - Laugharne frontage. Progressive eastward development of the spit system led to increasing shelter of the old cliff-line, a process which is reflected in the cliff morphology (Savigear, 1952).The presence of shell middens (deposits containing refuse that indicates the site of a prehistoric human settlement) within the dunes of the MOD/ Qinetiq site supports an early date for sand incursion (Cantrill, 1909, cited in Dyfed Archaeological Trust, 2009).

Analysis of historical maps and charts by Pye and Saye (2005) indicated seaward movement of the dune toe along most of the Pendine - Laugharne frontage between 1887 and 1970, except near Ginst Point (see Figure C.28). The present system of an unbroken chain of dunes between Pendine and the Taf estuary is modern: the earliest Ordnance Survey maps (between 1809/1833 and 1953) indicate that the two dune system were originally dissected by a stream known as the Whitegate, later known as the Witchett Pill, which drained the marshland inshore. These early maps show that the stream was being diverted eastwards due to the extension of the Pendine Burrows (formerly known as Great Hill Burrows). Further growth and extension of Pendine Burrows continued, with progradation of the dunes being particularly rapid along this section, forcing the mouth of the

C1-92 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding stream further eastwards. The 1970 Ordnance Survey map does not show the mouth of Witchett Pill with dunes forming a continuous barrier. However, the mouth was visible on the 1964 map and therefore the Pill is thought to have closed over in the 1960s. Since 1970 there has been variable accretion and erosion along the central and eastern ends of the system and a tendency for net erosion at the western end of the system.

Figure C.28 Historical changes in the position of the coastline, Mean High Water and Mean Low Water at Laugharne and Pendine Burrows from Ordnance Survey maps (1887, 1905, 1949 and 1970). The base map is dated 2002. The location of shore-normal profiles used to calculate the changes in width are also shown.

Analysis of beach profile data from 1999 to 2008 (see Annex A1) showed a net landward movement of the MHWS contour at most profiles along the Pendine - Laugharne frontage. Slight landward movement of the HAT contour occurred along most profiles, related to dune toe erosion, although recession was prevented or limited in areas where defences are present (e.g. near Pendine village). Further to the east up to 40m of frontal dune erosion occurred during this period. Along Laugharne Burrows the pattern and rate of dune toe erosion has been more variable, reflecting the local influence of slipways and rock armour placed by MoD/ Qinetiq. Although much of this coastline is undefended, evolution of this system has been affected by the intervention of man. The former Witchett Pill divided Laugharne Marsh into East and West Marsh. The latter was used as saltmarsh pasture in the Middle Ages before any sea walls were constructed. There may also have been Mediaeval settlements on the slightly raised sites of some of the present day farms on East Marsh (Dyfed Archaeological Trust, 2009). The first sea banks were constructed as early as 1660AD across the Witchett Inlet and between Sir John's Hill and the eastern end of Laugharne Burrows (Walley, 1996). Traces of 17 th century sea walls survive and the successive enclosures of the early 19 th century are well preserved (Dyfed Archaeological Trust, 2009). The Lower Marsh was embanked in the late 18 th century and further embanking and beheading of tidal creeks occurred in the 19 th century. The resulting loss in tidal prism encouraged sediment

C1-93 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding accumulation within the Taf Estuary and further eastward extension of the barrier system at the mouth of the estuary (Bristow and Pile, 2003).

Most of this coastline is undeveloped, with the exception of Pendine (Pentywyn) village at the western end of the Bay. The original village lies inland on higher land, but in the late 1800s, a hotel was built within the dunes and there has since been extensive development of dunes and former low-lying area inshore as a tourist resort, with significant modification the natural geomorphology at the very western end of the Bay, much of which has taken place since the 1950s. The village is fronted by seawalls and a revetment, which hold the coastline artificially seaward. Erosion affects the dunes to the east of the defences. Carmarthen District Council constructed a rock revetment fronting the seawall at the western end of the MOD/ Qinetiq frontage in the mid 1990s to prevent beach lowering and subsequent undermining of the seawall.

Much of the area of Laugharne Burrows and Pendine Burrows is currently owned and operated by the Ministry of Defence (MoD)/ Qinetiq as a weapons testing facility. Erosion of the dune frontage in the late 1960s and 1970s prompted the MoD to undertake dune creation works and place rock armour in several areas (Colquhoun, 1968). The lengths of rock armour now act as hard points which strongly influence the behaviour of the adjoining sections undefended shoreline. The remaining sections of dunes continue to evolve naturally and Ginst Point remains a dynamic area with continued growth of sand recurves into the entrance to Taf estuary.

Existing predictions of shoreline evolution: Shoreline Management Partnership (2000) predicted that the dunes would remain relatively stable, although this was subject to unknown inputs of littoral drift. However the study suggested that shoreline relocation may be necessary at Ginst Point which is increasingly vulnerable.

Futurecoast (Halcrow, 2002) predicted that for the ‘unconstrained’ scenario slow retreat of the dunes would occur in response to ongoing sea level rise, with potential breaching of the narrower dunes along the eastern end of this frontage, with associated flooding of the hinterland, towards Ginst Point. Future evolution would be dependent upon fluctuations in the alignment of the low water channels of the Taf, Towy and Gwendraeth Estuaries. Future development of these was considered uncertain.

For the ‘with present management’ scenario, Futurecoast (Halcrow, 2002) predicted that where defences have been constructed, along the MoD/ Qinetiq frontage and at Pendine village, there would be localised beach steepening, as a result of sea level rise.

LOCAL SCALE: SAUNDERSFOOT BAY (GILMAN POINT TO MONKSTONE POINT)

Interactions: Between Pendine (Gilman Point) and Monkstone Point the coast is mostly cliffed, with a series of intertidal sandy beaches and rocky shore platforms. Hard Carboniferous Limestone form the cliffs west of Pendine to near Ragwen Point, whilst resistant sandstones of Carboniferous Millstone Grit form the headlands of Ragwen Point and Telpyn Point. A faulted and folded mudrock-dominated sequence within the Millstone Grit cliffs between these promontories, and in Waterwynch Bay, has led to the formation of a series of bays. Carboniferous Coal Measures mudstones and coal bands

C1-94 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding with occasional sandstones extend around Saundersfoot Bay, with resistant sandstone beds forming the promontory of Monkstone Point. Raised beach deposits are present at Ragwen Point (Bowen, 1970; Campbell and Bowen, 1989), which suggest little change has taken place along this shoreline over the last 10,000 years (Bowen, 1973, cited in Bridges, 1997). Beach widths are greatest at Saundersfoot, Amroth and Marros Sands. At Wiseman’s Bridge and Amroth the sand beaches are backed by substantial shingle ridges. There are lengths of hard defences at Amroth, Coppet Hall, Wiseman’s Bridge and Saundersfoot which have had a limited impact on the adjoining shorelines.

Littoral drift is limited along this frontage, since numerous headlands act as a barrier to drift and as a result of the reduced exposure of this frontage to westerly and south-westerly swell waves and west-east tidal currents within the Bristol Channel. The beaches therefore tend to be swash-aligned. Shingle tends to be restrained from moving along the coastline by headlands. Any shingle bypassing headlands, such as Telpyn Point, is retained within embayments such as Marros Sands, between Telpyn Bay and Ragwen Point.

During typical conditions wave energy is much reduced, due to shoaling before it reaches the shore resulting from the shallow bathymetry of Carmarthen Bay. Onshore/ offshore sediment transport is typical, with offshore transport associated with storms and locally generated wind waves approaching from the east and south-east.

Movement: In general, the cliffs experience very low rates of erosion. There are areas where slight differences in lithology result in higher rates of erosion; e.g. the weaker shale cliffs to the west of Amroth are retreating at a relatively faster rate and in the 1930s there was significant erosion at Amroth which led to the loss of a number of houses, which were seaward of the existing shoreline road. The Futurecoast cliff classification (Halcrow, 2002) suggests that cliffs along this frontage typically experience ‘low’ rates of retreat, i.e. between 0.1m/year and 0.5m/year.

Some beach recession has also been recorded: Jones et al. (1992) reported 0.2m/year recession of the mean high water line between Amroth and Wiseman’s Bridge, although it is uncertain what period this relates to. Early in the last century and in the 19 th century ballast was dumped overboard by ships exporting coal from Saundersfoot harbour. Recent beach erosion has removed much of this ballast, returning the gravel beach to a largely sand beach.

Analysis of beach profile data (see Annex A1) has shown that along most profiles the position of the MHWS contour has moved landward between 1999 and 2008 (most notably to the north of Monkstone Point and at Summerhill). The central part of the beach, between the MHWN and MLWN lines, has shown a tendency for steepening along most profiles.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predicted that under an ‘unconstrained’ scenario the headlands would remain generally stable, although the softer mudstone cliffs within the embayments would experience higher rates of erosion, resulting in the embayments deepening and widening.

For a ‘with present management’ scenario, Futurecoast (Halcrow, 2002) predicted similar shoreline development, except where defences exist; defences were predicted to only have a local impact; with continued erosion either side which would result in outflanking.

C1-95 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: TENBY NORTH BEACH (MONKSTONE POINT TO ST CATHERINE’S ISLAND)

Interactions: Between Monkstone Point and Tenby (Dinbych-y-pysgod) the coast consists of a crenulated cliff- line cut into Millstone Grit and Lower Coal Measures, fronted by alternating intertidal rock platforms and small sandy beaches. At Tenby North Beach the cliff toe is protected by hard defences fronted by a sand beach.

Littoral drift rates along this frontage are low, due to the orientation of the coastline. The beach here is also influenced by locally generated wind waves from the east and refraction and diffraction of south-westerly swell waves around Caldey Island and Woolhouse Rocks. Onshore/offshore sediment transport is typical with infrequent offshore transport associated with storms and locally generated wind waves from the east and south-east.

Movement: The cliffs between Tenby and Monkstone Point are generally stable with low rates of retreat, although localised rock falls can occur along short sections of coast. Little or no change in shoreline position can be identified from historical maps. At Tenby, the harbour and seawall are shown on the earliest Ordnance Survey maps (1830s) and have fixed the backshore position along this frontage. Beaches have shown some temporal and spatial variability over the past decade, but little significant net change (see Annex A1). The Futurecoast cliff classification (Halcrow, 2002) suggests that cliffs along this frontage typically experience ‘low’ rates of retreat, i.e. between 0.1m/year and 0.5m/year, although there is a risk that 10m to 50m erosion could occur as a result of an isolated rock falls.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predicted, for the ‘unconstrained’ scenario, that the headlands would remain generally stable, although cliffs within the softer mudstones in the embayments would experience higher rates of erosion, resulting in deepening and widening of the embayments.

LOCAL SCALE: TENBY SOUTH BEACH (ST CATHERINE’S ISLAND TO GILTAR POINT)

Interactions: The area of high ground upon which Tenby and Giltar Point is situated is composed of Carboniferous Limestone outcrops. Between the two promontories lies Tenby South Beach, which is backed by a 50m to 300m wide dune barrier and the Tenby to Pembroke railway line. Behind the South Beach dune barrier is an area of low-lying land which comprises the former estuary of the River Ritec. The river now discharges through a culvert onto Tenby South Beach and a tidal exclusion gate has been installed upstream of the railway embankment, which protects the caravan parks and low-lying properties from tidal inundation at high tides.

C1-96 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Tenby South Beach faces south-east and is strongly influenced by wave refraction and diffraction of south-westerly swell waves around Caldey Island and Woolhouse Rocks, locally generated wind waves approaching from the east and south-east and strong tidal currents. The beach is relatively wide and flat and effectively swash aligned. Towards the south there is a shingle storm beach, which is thought to be mostly local in origin, although some of the material may have been derived from ship ballast dumped in the nineteenth and early twentieth centuries (Halcrow, 2002). Raised beach deposits ( patella beach deposits) are present at Giltar Point, suggesting relative inactivity over the last 10,000 years.

Sediment transport occurs mainly in an onshore-offshore direction; offshore sand movement is relatively infrequent and is associated mainly with storm events and locally generated wind waves from the east and south-east. Under such conditions sediment may also move south-west along the beach from Tenby towards Giltar Point.

Movement: Previously there was a small bar-built estuary at the mouth of the River Ritec. In the 11 th century the estuary extended upstream as far as St Florence (Halcrow, 2002). The earliest Ordnance Survey maps (dating from 1809 to 1833) show a large lagoon, Holloway Water, which extended inland to the present A4139, whilst the mouth of the estuary was partially enclosed by a sand and dune spit. By the mid to late 1800s this outlet had been blocked off following construction of the railway line and the river was diverted through a culvert, resulting in the development of an area of marshland, which at this time was still liable to flooding. Following this period, it appears that the dunes extended northwards, closing the former outlet and forming a much larger belt of dunes. There has since been the installation of a tidal exclusion gate, upstream of the railway embankment, which reduces the risk of tidal flooding to the low-lying caravan parks and properties behind the dunes. It has been postulated that the closure of the Ritec Estuary may have resulted in the movement of Giltar Spit (Posford Duvivier, 1993), a sand feature which originally extended seawards across Caldey Roads. Work by Posford Duvivier, (1993) suggests that following closure of the estuary, the spit became smaller and migrated inshore and that by 1932 the feature was a shore-connected bank. It is thought that this has affected exposure conditions; originally the spit may have provided shelter to the southern end of South Beach, allowing the wide belt of sand dunes to develop, but when the spit migrated onshore, there was a change in shoreline orientation and this southern end of the coast became more exposed, resulting the observed pattern of accretion and erosion along this shoreline. Evidence from later historical maps and air photographs indicates there has been very limited morphological change along the cliffed backed shoreline between Tenby South Beach and St Catherine's Island; this frontage appears to have a relatively low sensitivity to changes in environmental forcing factors and the intertidal beach seems to be a relatively stable feature.

Until the early 1990s the dunes were subject to heavy visitor pressure and exhibited a number of large blow-outs. There was loss of windblown sand inland, with lowering of the upper beach and erosion of the dune toe by waves during storms. Gabions and localised rock revetments were constructed in an attempt to limit erosion and a policy of dune management, including marram planting, fencing and boardwalks, was implemented in the 1990s. Since that time the seaward dunes have been stabilised and the old dune defence structures have been buried by sand. However, the dune belt remains relatively low at its southern end, where part of the landward dune area is occupied by Tenby Golf Club and the Penally MoD rifle range. Two former concrete groynes on South Beach have been removed in recent years.

C1-97 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Analysis of beach profile data between 1999 and 2008 (see Annex A1) has shown that Tenby South Beach has experienced relatively limited variability in levels and form over the past decade, and there has been little net change in the position of mean high water spring (MHWS) and highest astronomical tide (HAT). The position of the mean high water neap (MHWN) and mean low water neap (MLWN) lines have a shown a variable pattern of landward and seaward movement along different profiles, but the overall net change in the width and slope of the central section of the beach has been small.

The cliffs forming the headlands at Tenby and St Catherine’s Island, and Giltar Point are very resistant and experience negligible erosion over the century timescale. The Futurecoast cliff classification (Halcrow, 2002) defined these as experiencing ‘very low’ rates of erosion, i.e. less than 0.1m/year.

Existing predictions of shoreline evolution: The Futurecoast (Halcrow, 2002) prediction for an ‘unconstrained’ scenario was for Tenby South Beach to generally remain stable, with sufficient sediment available to maintain the beach. Some narrowing of the beach in front of cliffs was predicted to occur as a result of continuing sea level rise. The dunes were considered likely to retreat, particularly to the south, although the railway embankment would constrain landward recession.

LOCAL SCALE: CALDEY ISLAND

Interactions: Caldey Island is a fragment of the mainland, which became separated during the post-glacial rise in sea level. It is characterised by limestone and sandstone cliffs with headlands developed mainly along the strike of the geology, and intervening embayments, some containing pocket sandy beaches. The northern half of the island is composed of hard Carboniferous Limestone, Old Red Sandstone forms the southern side, whilst a band of thin Lower Limestone Shales separates the two. Pocket beaches and sand dunes are present in Priory Bay, on the north side of the island, and Sandtop Bay, on the western side of the island. Some sand eroded from mainland beaches may possibly reach the beaches on Caldey Island, however transport paths are complex due to swell waves, locally generated wind waves, refraction/ diffraction and strong tidal currents through Caldey Sound.

Movement: Rates of cliff recession on the island are low and therefore little change in the alignment of the coast is evident from a review of historic maps.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) predicted that future behaviour would continue to be dominated by low rates of cliff erosion, with beach steepening and narrowing and dune erosion within the pocket beaches in response to sea level rise, due to the lack of accommodation space for these to roll landward.

C1-98 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LARGE SCALE: LOUGHOR ESTUARY

Plate C.6:

Interactions: The Loughor (Llwchwr) Estuary is a large (area c. 45 km²), shallow inlet which owes its origin partly to structural control and partly to selective erosion of weaker Lower Coal Measures strata which form the southern side of the South Wales coalfield basin. It can be considered as a drowned coastal plain estuary whose limits are currently defined by a combination of steeply rising ground and defences (Moore, 1989). Extensive salt and brackish marshes occupy the north coast of Gower from inshore of Whiteford Point to Loughor, south of Pembrey and at the wildfowl and wetlands centre south of Llanelli.

Seaward of the estuary mouth is a well-developed ebb-tidal delta composed of medium to fine sand. The area immediately inshore of the estuary mouth shows many of the characteristics of a flood tidal delta (Elliott and Gardiner, 1981). Swell waves approach the mouth of estuary mouth from Carmarthen Bay but their energy is mostly dissipated by the ebb tidal delta. The few long- period waves which enter the estuary break on the most seaward bars. Within the mid and inner estuary the wave regime is dominated by short-period, locally generated wind waves. The sandy intertidal flats are dominated by megaripples and sandwaves produced by flood and ebb tidal currents (Elliot and Gardiner, 1981). Sediment trend analysis undertaken by Posford Duvivier and ABP Research (2000) and Cooper and McLaren (2007) suggests there is an active sediment transport pathway from eastern Carmarthen Bay into the Loughor Estuary, although the flux was not quantified.

C1-99 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Two principal river systems enter the Estuary; the largest is the River Loughor (Afon Llwchwr), and its tributaries, which flows into the head of the estuary from the north of . Approximately 2 km south-east of Loughor Bridge the Afon Lliw / Afon Llan river system flows into the estuary at Island Bridge, where the railway line/A484 highway forms the current normal tidal limit of the Afon Lliw.

The Loughor itself is tidal as far as , approximately 6km upstream from Loughor Bridge. On the east side of the Loughor estuary the limit of high water spring tide is defined by naturally rising ground, but on the west side the Llanelli to Pontarddulais railway embankment forms an artificial boundary. There are extensive areas of high saltmarsh and brackish marsh on both sides of the estuary, much of which remains undefended along the north coast of Gower (except at Crofty and Penclawdd). The lower intertidal zone is mostly sandy except near the head of the estuary. The combined average freshwater input (c. 1.10 x 10 3 m³ per tide) is small when compared with the volume of tidal water (c. 1.40 x 10 9 m³ on springs and 1.04 x 10 9 m³ on neap tides; Moore, 1976). Salinity characteristics (Moore, 1976) indicate that the estuary is relatively well mixed, with only minor freshwater input (400m³/day to 500m³/day) relative to the tidal exchange volume. The sediments of the intertidal flats and saltmarshes are predominantly fine sands (modal size 125 µm); muddy sedimentary facies are poorly developed (Carling, 1981). The presence of abundant sponge spicules, shell fragments and echinoderm spines amongst a predominantly quartzose sand indicates that the predominant sediment source is marine reworking of fluvio-glacial and glacial sediments from the seabed of Carmarthen Bay (Bridges, 1977a).

Modelling by BMT Ceemaid (1989) and Posford-Duvivier and ABP Research (2000) suggested a small residual ebb flow from the estuary. Other studies have indicated increasing ebb current dominance in the main channel upstream from the mouth (Moore, 1976). However, field measurements in the small channels and over the intertidal areas have indicated flood dominance, with surface flood and ebb velocities of 0.9m/s and 0.7m/s on neap tides and 1.7m/s and 1.2m/s on spring tides (Collins et al. , 1981; Elliot and Gardiner, 1981; Carling, 1981).

The tidal curve is generally symmetrical near the mouth but becomes progressively more asymmetrical towards the head; the asymmetry is accentuated on spring tides. Maximum flood and ebb tidal current velocities occur approximately mid way between low water and high water (Moore, 1976), which is characteristic of a standing tidal wave (Dyer, 1973). Towards the head of the estuary the tidal wave is modified slightly and takes on characteristics of a progressive wave, with the ebb tide much longer than the flood. The spring tidal length of the estuary from mouth to tidal limit is approximately 16 km.

The highest marshes (relative to mean sea level, 0mODN) are found in the Upper Estuary upstream of the Loughor A484 and railway bridges, in the Inner Estuary just west of , and in the Middle Estuary at Llanrhidian. In all of these areas the marshes are of considerable age and the median marsh elevation (Z 50 ) lies above the local level of MHWS tides (Pye, 2010; Annex A2). The lowest marshes are mainly of recent inception in the more seaward parts of the Middle Estuary (e.g. the outer parts of Landimore Marsh), where they equate approximately to the level of MHW.

The mean spring tidal prism is 219,571 x 10 3 m 3, approximately twice that of the Three Rivers estuarine complex (see Table 7, Annex A2 for further details). From the general relationship between tidal volumes and tidal height within the estuary, the tidal volume of the present active estuary is predicted to increase exponentially as a function of tidal level up to a level approximately 0.5m higher than MHWS, but thereafter increases almost linearly as a function of tidal height as the entire estuary area (within the defined limits) is flooded (Pye, 2010; Annex A2). In the event of a breach or overtopping of the defences, leading to a significant increase in the tidal

C1-100 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding storage capacity, a further steepening of the curve would be expected. The maximum rate of increase in tidal volume is predicted to occur at levels between 3.05mODN, just above MHW, and 4.35mODN, just above MHWS. This reflects the sudden increase in floodable area as the tide spreads over the relatively large saltmarsh area.

The length of the principal low water channel of the Loughor estuary was determined from the 2003-08 LiDAR data to be 25,673m, compared with a distance along the central line of the estuary of 20,445m (Pye, 2010; Annex A2). This gives an estuarine channel sinuosity index of 1.26, which is approximately the same as the values calculated for the Taf, Towy and Gwendraeth estuaries, and has not changed greatly over the last 130 years (Pye 2010, Annex A2).

Movement: The basic erosional forms of the area were probably established by weathering and fluvial erosion in Tertiary times, but the ancestral valley of the River Loughor was significantly modified by ice action during the Pleistocene. The area may have been influenced by Irish Sea ice moving up the Bristol Channel during the Wolstonian glaciation, but during the Devensian Welsh glaciation ice descended from the north and north-east to occupy the area (Bowen, 1970; 1995) The line of maximum Devensian ice extent lay NW - SE across the Gower Peninsula, passing through the Hills Tor area, across Carmarthen Bay and towards Saundersfoot. Following retreat of the ice, Carmarthen Bay was progressively flooded by the sea which reached its maximum inland extent around 5,500 years ago (Bridges, 1977a; Carling, 1978; Culver, 1980b). Since that time the Estuary has been progressively infilled with sand derived mainly from Carmarthen Bay, and (in a few more sheltered areas) by mud derived from the Bristol Channel and the rivers which enter the Estuary. The estuary is one of the main sediment sinks within Carmarthen Bay. The estuary is characterised by extensive saltmarsh, and has the largest saltmarsh area in Wales (2,121 ha which represents 32% of Wales’ total saltmarsh area) (May 2003b). Spartina anglica was introduced to Landimore Marsh in 1935 and has since spread throughout the estuary (Bridges, 1977b).

According to Bristow and Pile (2003), the tidal limit of the River Loughor moved 302m downstream between 1876 and 2000. The tidal area at MHWS and the tidal prism of the Loughor Estuary are much larger than those of the Three Rivers Estuarine Complex, despite a reduction in area from 8,254 ha in 1876 to 7,060 ha in 2000 (Bristow and Pile, 2003). Cramp et al. (1995) reported that net sediment flux within the Loughor Estuary is almost zero, but comparison of historical map data led Bristow and Pile (2003) to conclude a net reduction in area of the Inlet from 8,254 ha in 1876 to 7,060 ha in 2000. Part of this reduction was due to land reclamation (and the construction of embankments), but also partly due to net sediment accretion in the tidally active part of the estuary. The mineralogical and micro-faunal composition of the sediments strongly suggests that the principal source of sediment lies outside the estuary, in Carmarthen Bay (Carling, 1978; 1981).

The channels and intertidal sand banks of the Loughor Estuary have historically been highly mobile, and the channel pattern has changed considerably since 1830 due both to natural processes and human interventions (Cramp et al. , 1995). A detailed account of these changes is provided in Annex A2, and the variation in the alignment of low water channel positions is shown in Figure C.29 below. In 1872 it was possible to enter the estuary via either the north or south channel which combined to become the main inner channel in the centre of the estuary, approximately halfway between Burry Port and Whiteford Point, with the channel passing close to Llanelli Harbour (McMullen and Associates, 1982).

C1-101 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.29: Changing position of the low water channel in the Loughor Estuary, digitised from historical Ordnance Survey maps.

C1-102 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

In 1882 a training wall was built across the main channel to direct flows along the northern side of the estuary to maintain navigation channels into the docks at Llanelli and Burry Port, and by 1886, according to McMullen and Associates (1982), the main channel had moved northwards. A further ‘spur’ was constructed between 1908 and 1918, extending northwards from the main wall, just west of Careg-fâch scar, due to the original wall failing to fulfil its purpose, and a channel was dredged through the scar in 1911 to assist channel formation along the new alignment (McMullen and Associates, 1982). These structures encouraged sediment accretion on the southern side of the estuary and were a major contributing factor to the spread of the saltmarsh at Llanrhidian (Plummer, 1960). Downstream of the structures, the walls led to the river favouring the southern channel in the region of Whiteford and Broughton Bay, possibly leading to the accumulation of the sand beach at Broughton (Barber pers. comm, 2009.). This movement of the channel to the south at the estuary mouth and diversion of the main flows enabled the ‘Nose’ to migrated eastwards and southwards towards Burry Port. Eventually this migration resulted in a training wall between the West Breakwater of Burry Port Harbour and a navigation light 220m out into the channel being buried, leading to difficulties with navigation into the harbour. In 2008 the breakwater was extended along the route of the training wall to manage the sediment accumulation. Although the walls were constructed to be covered at half tide, they were constructed of slag or similar, and as such breached frequently, aided by the fact that the spur did not create a natural channel route, presenting a “veritable dam” to the river on the ebb (McMullen and Associates, 1982). These breaches were originally repaired although the walls fell into disrepair during World War 2. Serious breaches occurred in 1951 and 1965 and were not subsequently repaired (BMT Ceemaid, 1990). This major breach was adjacent to where the newer spur joins the main wall and allowed the main channel to migrate southwards, flowing through the training wall, moving to a position approximately 1 mile south of Llanelli harbour. This, along with the extension of the Nose spit, resulted in navigation problems at Burry Port. Eventually the northern channel reopened, although in a more braided form, resulting in safety issues at Pembrey Sands.

The channel leading to Llanelli docks upstream of Burry Port migrated landwards during the 1980s along Pwlch Gwyn and Llanelli. It was maintained by tidal flushing and the infilling of the earlier navigation channel forcing the channel northwards, and led to steepening of Llanelli beach and an increase in vulnerability of the seawall (Shoreline Management Partnership, 2000). The collapse of the wall in two places during storm events in the 1990s resulted in the construction of a series of rock breakwaters to divert the channel offshore and retain sand on the beach.

Currently the South channel has diminished, with the middle channel favoured, although further upstream this has moved northwards and now follows the shoreline of the , although away from the harbour shoreline resulting in recent dredging and harbour breakwater extension.

There have therefore been significant changes in channel geometry since abandonment of the training walls and SMP1 (Shoreline Management Partnership, 2000) concluded that there has been an associated increase in siltation and marsh growth. The general exposure of the Crofty frontage may have improved due to the reduction in nearshore water depths, although it remains exposed during high tides and Salthouse Point is occasionally affected by storms (Shoreline Management Partnership, 2000).

Modifications: The estuary is still adjusting to human interventions over the last 200 years, including extensive reclamation of intertidal areas, training wall construction, extension, abandonment and failure/

C1-103 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding breaching. The northern side of the estuary was formerly defined approximately by the 7mODN contour, but there has been extensive reclamation along the shore between Burry Port and Loughor Bridge over the last 150 years. According to Plummer (1960), some 1,800 ha had been reclaimed for industrial purposes on the north side of the estuary by 1850. Reclamation has been less extensive on the south side of the estuary, although Cwm Ivy Marsh in the lee of Whiteford Burrows was reclaimed for agriculture in the 17 th century (Kay and Rojanavipart, 1977). It is now considerably lower than the active marsh on the outside of the sea wall. There were also significant reclamations around the head of the estuary east of Loughor and Gowerton in the 18 th and 19 th centuries (Plummer, 1960). These reclamations have resulted in the construction of significant defences, which include seawalls, revetments and breakwaters. The Llanelli Millennium Coast has been developed extensively over the last 20 years and is now a major tourist attraction; however, the coastal cycle path remains at risk from erosion and tidal inundation.

The Cefn Padrig frontage is backed by the Pwll railway, which was constructed in 1844. The wall supporting the railway line comprises an original masonry structure in front of which armour stone has been placed. The wall continues to suffer periodic damage, with subsidence and damage to the coping stone on the top of the wall (Shoreline Management Partnership, 2000).

Wider-scale interactions: The estuary exerts some control on the open coastline to north and south, with changes in estuary regime resulting in changes to shoreline position and behaviour. Redistribution of sediments within the tidal deltas can affect the degree of shelter provided to Whiteford Sands and the southern shore of Pembrey Burrows; whilst channel migration leads to changes in sediment transport patterns and exposure conditions along the shore.

The estuary acts as a sink for sand and mud-sized sediments arriving from Carmarthen Bay from the north and south, and is gradually being infilled. Sediment transported north-eastwards from Burry Holms travels along Whiteford Sands, forming the distal recurves of the spit, and is eventually deposited in the estuary. Similarly, sand is transported southwards from the central Cefn Sidan frontage, deposited on the distal end of the spit, and eventually enters the estuary. The functioning of Burry Port is currently affected by the extension of the ‘Nose’, a sand spit that extends from the west and is affected by erosion of Pembrey Sands. The Loughor Estuary is still adjusting following significant human interventions over the last 200 years. The tidal channel system is current re-establishing a higher degree of dynamic behaviour following the breakdown and abandonment of the training walls. In recent decades the estuary has continued to show a tendency to import sediment, leading to a continuing reduction in tidal volume and marsh growth along the southern side. It is likely that this trend will continue over the next 50 to 100 years, although probably at a reduced rate, due to the combined effects of sea level rise and an overall flood-dominant sediment transport regime.

For the purposes of this study, the estuary has been further described in terms of: • Outer Estuary (defined as the area which is seaward of a line drawn between Whiteford Point and the eastern end of the Nose) contains a complex of banks and channels which effectively form an ebb-tidal delta, bordered by wide beaches and barrier dune systems on each side of the entrance (the Whiteford Burrows barrier on the southern side and the Pembrey Burrows barrier on the northern side).

C1-104 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

• Middle Estuary (defined to the west by Whiteford Point and the eastern end of The Nose and to the east by the Salthouse Point slipway at Crofty and the southern end of the Peninsula at Penrhyn Gwyn) is wide relative to its length and contains extensive intertidal tidal flats and saltmarshes, notably along the southern shore between Whiteford Burrows and Crofty.

• Inner Estuary (defined in the west by Salthouse Point – Machynys Peninsula, Penrhyn Gwyn and in the east by the Loughor A484 and railway bridges). The present tidally active area of the inner estuary is today considerably smaller than in the past due to land reclamation, mainly on the northern side around the Millennium Coastal Park, although significant areas of active saltmarsh remain on the southern shore between Penclawdd and Gowerton.

• Upper Estuary (extending upstream from the Loughor A484 and railway bridges to the normal tidal limit near Pontardulais) is narrow relative to its width and is flanked on both sides by active and reclaimed saltmarsh.

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