Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding erosion can be expected as tidal meanders migrate upstream and possibly develop greater sinuosity. This, along with variations in the alignment of the intertidal channels, will increase the risk of undermining of defences. There is also likely to be an increasing risk from overtopping during periods of extreme high water level and of flooding due to localised breaching if defences are not maintained. However, further marsh expansion and vertical growth can be anticipated, which could provide greater protection for flood defences within sheltered areas within the estuaries.

Modifications: The most significant modification that has taken place in the Three Rivers Estuarine Complex has been the reclamation of marshland for agricultural and industrial use. Bristow and Pile (2002) estimated that between the 16 th and 19 th centuries around 2,400 ha saltmarsh were lost due to land reclamation in the estuaries of Carmarthen Bay, including the Loughor estuary. Shoreline Management Partnership (1991) reported that sand winning was undertaken in the Towy, near Ferryside, until the mid-1930s, although the amounts removed were not stated. However the study suggested that this activity resulted in local stabilisation of the river channel. Otherwise the shoreline typically remains natural, with areas of localised defences, embankments, seawalls and revetments, along the railway line between St Ishmaels and Ferryside, Ferryside, Llansteffan, Laugharne and inshore of Laugharne Burrows. The railway embankment at Ferryside acts as a tidal defence for some properties, but can result in watercourses becoming tide-locked during high tides.

Wider-scale interactions: Sediment enters the estuarine complex from offshore and the barrier and dune systems to the west (the Laugharne-Pendine complex) and south-east (Pembrey and Cefn Sidan Sands). Sediment is deposited either within the saltmarshes of the estuaries, or on the spits and linear sand banks at the mouth of the estuaries. The estuaries act, in this way, as sediment sinks for Carmarthen Bay and exert a strong control over the Bay as a whole. They also act as local barriers to alongshore drift around the Bay, although drift within the closed system of Carmarthen Bay is generally weak (Halcrow, 2002). The alignment, extent, periodic growth and breaching of the outer banks and intertidal channels within the Three River Estuarine Complex has an influence on adjacent coastlines and within the estuaries and could result in localised beach steepening, increased exposure to waves and tidal currents, increased erosion and undermining of defences. Any changes in the flood / ebb regime of the estuaries will also potentially have an impact on the shoreline along the coast and within the estuaries. At the confluence zone, i.e. the area landward of the line between Ginst Point and Tywyn Point and the entrance to the individual estuaries, the estimated spring tidal prism within this area represents approximately 46% of the mean spring tidal prism volume for the combined Three Rivers estuarine complex. An appraisal of the potential effects of different UKCP09 sea level rise scenarios on the tidal prisms of the confluence area (see Annex A2 for further details) showed that for medium emissions scenario, the mean spring tidal prism in the confluence area could increase by 11% by 2100, compared to 22.4% for the currently active area of the estuarine complex as a whole. Under a more extreme scenario (assuming a high emission scenario), the mean spring tidal prism in the confluence area could increase by c. 35% and 77% respectively. The Gwendraeth Estuary, Towy Estuary and Taf Estuary are discussed below in separate statements (see Figure C.31).

C1-116 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.31: Three Rivers Estuarine Complex: large scale and local scale boundaries.

C1-117 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: GWENDRAETH ESTUARY

Interactions: The Gwendraeth Estuary is bounded by the spit of Tywyn Point to the south and St Ishmael’s Scar, Salmon Point Scar and Pastoun Scar to the north. Landward of the boulder scars is a narrow belt of dunes backed by a low-lying area of till and alluvium. These deposits represent a small barrier spit and back-barrier marsh area which has formed by north-west to south-east sediment drift into the mouth of the Gwendraeth estuary.

The estuary is fed by two small rivers: Gwendraeth Fach, which flows through Kidwelly, and Gwendraeth Fawr, to the south of Kidwelly. Gwendraeth Fawr is today little more than a stream, which is tidal only below Commissioner's Bridge, south of Kidwelly, which isolates a large area of reclaimed former marshland from tidal interaction. The Gwendraeth Fach is somewhat larger and is tidal as far as the A484 north of Kidwelly. The intertidal area of the estuary was considerably larger before canalization of the upper Gwendraeth Fawr and construction of the Llanelli to Carmarthen railway line in 1851-2 (James, 1991). The present tidally active estuary has a broadly rectangular form with an east-west long-axis. The width of the entrance has been significantly reduced over the past 60 years by the northwards and eastwards movement of Tywyn Point. At the present day the entrance is approximately 1.2km wide between Tywyn Point and the small sedimentary foreland currently the site of Carmarthen Bay Holiday Park. The maximum width of the estuary in its middle part is approximately 2.8km. The maximum length of the tidally active low water channel is 6,661m, a figure which has not changed significantly since 1879-87. The sinuosity index of the Gwendraeth estuary is low (1.31) by comparison with the Taf, Towy and Loughor. The area of the active estuary at the level of MHWS (839ha) is slightly larger than that of the Taf and the Towy, but the mean spring tidal prism is considerably smaller.

The north-west corner of the Gwendraeth estuary is exposed to swell waves and the shoreline is consequently dominated by a gravel and boulder upper beach backed by low dunes, with a foreshore composed of mixed sand and gravel. Further to the north, at confluence with the Towy estuary, wave erosion of glacial deposits in the intertidal zone has formed ‘scars’, intertidal platforms composed of glacial till with a patchy boulder or gravel surface lag deposits. The back- beach in this area was formerly characterized by more extensive estuarine dune development, banked against the steep slopes behind, but most of the dune sediments have now been eroded. Much of the estuary is shallow on account of extensive development of sandflats and saltmarshes. A large proportion of the active marsh area is comparatively recent and the surface elevations are relative low relative to the tidal frame. The older marshes near the landward margin of the active estuary have median surface elevations which are closer to, but still below, the level of MHWS (Pye, 2010; Annex A2). The reclaimed marshes on the landward side of the railway and A484 have median elevations ranging from below present MHW to just below MHWS (Pye, 2010; Annex A2).

Hydrodynamic modelling reported by BMT Ceemaid (1986, 1987, 1989), Barber and Thomas (1989) and Posford-Duvivier and ABP Research (2000) indicated a small residual ebb flow in this estuary and based on sediment grain size trend analysis, Posford Duvivier and ABP Research (2000) concluded that there is a net import of sediment into the Gwendraeth estuary.

C1-118 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

The tidal volume of the estuary above -0.5mODN shows a step increase at c. 3.5mODN due to sudden increase in tidally floodable area as the tide rises above the level of the marshes. The maximum rate of increase in tidal volume occurs midway through the flood on an extreme high tide, at the point where the tidally floodable area suddenly increases. Little information is available regarding hydrodynamic processes and sediment transport in the Gwendraeth estuary. Based on the morphology of the estuary and the major tidal channel features, flood flow dominance and net landward sediment transport would be expected. Historical evidence indicates long-term net sediment accretion in the estuary since the 17th century, when Kidwelly was a significant port.

Mineral magnetic studies of the Gwendraeth estuary sediments (Booth, 2002; Booth et al. , 2005) suggested that Carmarthen Bay was the dominant source of sediment (c. 77%), but that contributions from land-based sources via the Gwendraeth Fach and Gwendraeth Fawr are also significant (13% and 10%, respectively).

Movement: The intertidal area of the estuary was previously much larger but was restricted following the construction of the Llanelli to Carmarthen railway line and development of the A484 as a main highway. Large areas of the former estuary to the west of the railway line were also reclaimed and defended in the early to mid 19th century. An area to the south of the estuary was used for many years as an airfield (RAF Pembrey Sands). The entrance to the estuary has progressively narrowed over the past 120 years by the northward growth of the Tywyn Point spit. As a consequence of these changes, the tidal prism and associated tidal current velocities within the estuary have reduced and sedimentation in the remaining active outer estuary has increased, leading to significant expansion of saltmarsh (Bristow and Pile, 2002). Between 1876 and 2000, Bristow and Pile (2002) reported a downstream shift in the normal tidal limit of the Gwendraeth Fach by 60m and an increase in channel sinuosity. They suggested this may have been a consequence of canalisation in the upstream reach of the river. The main channel is today located close to the northern shore of the estuary where the intertidal profiles are generally steep compared with the much gentler gradients on the southern side of the estuary. Analysis of historical Ordnance Survey maps has shown that the main low water channel of the Gwendraeth Fawr has shown major lateral changes in position since 1879, although the upstream and downstream limits have remained almost fixed and there was less change between 1965 and 2003-08 (Pye, 2010; Annex A2). This was associated with significant growth of new marshes on the south side of the estuary in the later period.

The area of saltmarsh within the estuary has increased since 1876 (see Figure C.32), with Bristow and Pile (2002) reporting an increase of 142 ha. The extent of saltmarsh has increased on both sides of the estuary, although there are more areas of new saltmarsh development along the southern shore, since the northern shore is more exposed to south-westerly swell waves. Analysis of beach profile data (see Annex A1) showed that there has been slight net progradation along the north shore of the estuary between 1999 and 2008.

Existing predictions of shoreline evolution: There is very limited available information on how the estuary is evolving or predictions of how it is likely to change in the future.

C1-119 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Futurecoast (Halcrow, 2002) did not consider individual estuaries, but stated that the Three Rivers Estuarine Complex is still a very active sink and is capable of taking much more sediment. The study also recognised that changes in the estuary regimes are instrumental in locally modifying the shoreline either side of their mouths; either through redistribution of sediment within their tidal deltas, which can alter the degree of stability provided to the shoreline, or switching of channels and flows which can alter sediment transport as well as changing exposure conditions along the shoreline. The study predicted that further retreat of the beaches on either side of the mouth of the Three Rivers Estuarine Complex could lead to growth of the ebb tidal delta and the offshore sand banks.

As part of this SMP, in order to assess some of the possible implications of future sea level rise on the estuary, tidal areas and prisms were calculated for a number of future sea level rise scenarios based on the UKCP09 projections. A full description of the methodology used is provided in Annex A2. Two scenarios were considered: firstly using a medium UKCP09 emissions scenario and assuming MHWS increases at the same rate as MSL, and secondly an extreme ‘worst’ case scenario, using the High Emissions scenario and assuming MHWS rises at double the rate of MSL. Under the first scenario, the increase in tidally floodable area is projected to be 6.9% and the increase in MHWS tidal prism is projected to be 31.3% by 2100. Under the extreme scenario, the tidally floodable area at MHWS is likely to increase by 22.3% by 2100, with a corresponding increase in tidal prism of 106.3%.

LOCAL SCALE: TOWY ESTUARY

Interactions: The Towy (Tywi) Estuary lies to the east of the Old Red Sandstone promontory of Wharley Point. The river enters the sea via a glacially over-deepened valley cut into Old Red sandstone. The valley is partially filled with glacial drift and post-glacial alluvium. The Towy is the longest of the Three Rivers, with a length of 121 km, rising on the slopes of Crug Gynan in the Cambrian Mountains. It has a relatively large freshwater discharge, compared with the Taf and Gwendraeth and historically, the river has experienced significant floods following periods of heavy rain. However, since the construction of the Llyn Brianne dam and reservoir in 1972, 10km from the source, peak flows have been subdued to some degree. Nevertheless, high river flows continue to play an important role in determining movements of the low water channel, especially in the upper and middle parts of the estuary.

The river is tidal to a point approximately 3km upstream of Carmarthen and tidal elevations increase upstream from the estuary entrance. The MHWS level at Ferryside (4.2mODN) is approximately 40cm lower than at Carmarthen (Pye, 2010; Annex A2).

The central part of the estuary is confined between steep slopes cut into bedrock, and by the Llanelli to Carmarthen railway line, but the upper estuary widens to form a floodplain near Carmarthen. In this area the tidal river is confined by low flood banks, on either side of which are freshwater grazing marshes (Figure C.32). Saltmarsh occurs throughout the estuary, located in small embayments, on the inside of meander bends, and behind low sandy barriers in the lower part of the estuary. The median elevations of mature marshes increase up estuary in parallel with average tidal levels, and generally lie 0.2m to 0.5m above the level of MHWS. The lowest, immature marshes in the lower part of the estuary have median elevations in the range 3.68mODN to 3.75mODN, around 25 cm to 30 cm higher than the level of MHW (Pye, 2010; Annex A2).

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The Towy has a relatively small tidally floodable area at the level of MHWS and HAT owing to the restricted extent of tidal flats and saltmarsh within the estuary. The mean spring tidal prism (22,681 x 10 3 m 3) is similar to that of the Taf. The curve showing tidal volume above -0.5mODN shows a slight break of slope at a tidal elevation of c. 4.30mODN, slightly above the level of MHWS. The rate of change of tidal volume is relatively constant for much of the flood and ebb tide, reflecting the limited effect of saltmarsh ‘floodplain’ storage relative to the total estuarine tidal prism (Pye, 2010; Annex A2).

Only very limited information is available concerning hydrodynamic processes and sediment transport in the Towy estuary. Field studies were undertaken by Jones (1977) but the results have not been published. However, the available evidence suggests that the Towy, like the Taf, is flood dominated and that there has been long-term net-sediment movement into the estuary (Pye, 2010; Annex A2). Wave and wave-induced current transport is more important in the Towy than in the Taf on account of the greater exposure of the estuary mouth to the direction of prevailing winds and swell waves (south-westerly). Geomorphological evidence of long-term net northward longshore drift of sediment along the shores of the lower estuary is provided by spit features, capped by low dunes, at Llanstephan, Ferryside, and Morfa Urchaf. Due to the current position of the main low water channel, south-westerly waves propagate up the deep water channel of the estuary, at the margins the wave crests are refracted towards the east shore around Ferryside, facilitating net northward drift of sediment.

Movement: Analysis of historical maps has shown that the alignment of the main low water channel has varied in the lower estuary but has remained more or less constant in the middle and upper parts of the estuary (Jones, 1977; Bristow and Pile, 2002; Pye, 2010; Annex A2). Even in the lower estuary, the lateral shifts in channel position have been less marked than in the Taf estuary. However, such shifts have been significant in terms of erosion pressure at Ferryside and at the northern end of Morfa Uchaf. At the present time the main low water channel lies close to the shore at Ferryside near the slipway and pier.

The beach on the seaward side of the railway line has experienced net erosion in the past 40 years due to progressive eastward movement of the low water channel and increase in channel sinuosity in this length. However, considering the entire channel length between the estuary entrance and the normal tidal limit, the total channel length has increased only slightly and no significant increase in sinuosity is evident (Pye, 2010; Annex A2). A similar conclusion was reached by Bristow & Pile (2003).

Shoreline Management Partnership (1991) suggested that the channel and foreshore changes leading to erosion at Ferryside might be linked to variations in the balance between tidal forces and freshwater flows in the vicinity of Morfa Uchaf, with periodic times of high freshwater flow being capable of ‘flipping’ the channel meander pattern downstream, especially if coincident with storms from the southwest which drive tide and wave energy landwards. This is a reasonable hypothesis but has not been proven by direct evidence (Pye, 2010; Annex A2). Estuarine channel patterns are inherently unstable and, in the absence of training walls, often display oscillation on decadal time-scales due to both to intrinsic and extrinsic factors. Analysis of beach profiles within the estuary show variable movements in the position of MHWS between 1999 and 2008, although there was significant progradation at Ferryside, following the construction of rock revetments and groynes (see Annex A1). Bristow and Pile (2002) also reported

C1-121 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding a small increase of 19ha in the total area of saltmarsh within the estuary between 1876 and 2000. Saltmarsh growth is, however, limited by the constraining valley sides.

Existing predictions of shoreline evolution: As for the other estuaries in the Three Rivers Estuarine complex, there is very limited information available on how the estuary is evolving or predictions of how it is likely to change in the future. Futurecoast (Halcrow, 2002) did not consider individual estuaries, but states that the Three Rivers Estuarine Complex is still a very active sink and is capable of taking much more sediment. The study also recognised that changes in the estuary regimes are instrumental in locally modifying the shoreline either side of their mouths; either through redistribution of sediment within their tidal deltas, which can alter the degree of stability provided to the shoreline, or switching of channels and flows which can alter sediment transport as well as changing exposure conditions along the shoreline. The study predicted that further retreat of the beaches on either side of the mouth of the Three Rivers Estuarine Complex could lead to growth of the ebb tidal delta and the offshore sand banks.

As part of this SMP, in order to assess some of the possible implications of future sea level rise on the estuary, tidal areas and prisms were calculated for a number of future sea level rise scenarios based on the UKCP09 projections. A full description of the methodology used in provided in Annex A2. Two scenarios were considered: firstly using a medium UKCP09 emissions scenario and assuming MHWS increases at the same rate as MSL, and secondly an extreme ‘worst’ case scenario, using the High Emissions scenario and assuming MHWS rises at double the rate of MSL. Under the first scenario, a potential increase in spring tidal prism by 2100 of around 14% is projected. In comparison, under the extreme scenario, the spring tide tidal prism of the presently active estuary could increase by around 60%.

C1-122 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.32: Composite aerial photography of the Towy and Gwendraeth Estuaries, flown in 2006. The dashed line shows the position of the dune toe or marsh edge from the first edition County Series OS Map, surveyed in 1879.

C1-123 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: TAF ESTUARY

Interactions: The Taf Estuary is a funnel shaped sinuous estuary with saltmarsh development along both banks (Cousins et al. , 2008). The barrier beach at the entrance shelters the inner estuary, providing conditions for saltmarsh development. The estuary occupies a similar glacially-modified valley cut into the Old Red Sandstone as the Towy, which has been partially in-filled with glacial drift and post- glacial alluvium. Marine reworking of the glacial deposits has formed ‘scars’ (areas of till and outwash mantled boulder lags) near the river mouths (St Ishmael's Scar, Salmon Point Scar and Pastoun Scar). Elsewhere the intertidal zone is dominated by sandy sediments of varying thickness and texture (Jago, 1980). Salt and brackish marshes occur in more sheltered areas and consist mainly of sandy silt and silt.

The length of the principal low water channel in the Taf, determined from the 2003-8 LiDAR, is 14,883m, approximately two-thirds that of the Towy and more than twice that of the Gwendraeth (Pye, 2010; Annex A2). The sinuosity indices of all three rivers are similar to each other and to the Loughor (Pye, 2010; Annex A2). The low water channel presently lies on the eastern side of the estuary mouth, close to a steep slope formed of Old Red Sandstone, which terminates at Wharley Point.

The Taf is a macro-tidal estuary and is tidal up to the outskirts of St. Clears. Parts of the meandering tidal channel are backed by bedrock slopes while others are fringed by fresh to brackish marsh, which in places is offered partial protection from flooding by earth embankments. Significant areas of saltmarsh are restricted to the estuary downstream of the Taf - Afon Cywyn confluence. Between the confluence and Laugharne, new marsh has developed in recent decades seawards of older established marshes, mainly as a consequence of the introduction and spread of Spartina (Bristow and Pile, 2003). Tide levels increase upstream from the mouth of the estuary. The median surface elevations of active mature marshes also increase in an upstream direction, reaching a maximum of over 5.0mODN just upstream from St Clears on the Taf, whilst the youngest marshes near the mouth of the Taf have median surface elevations in the range 3.6 to 3.7mODN (Pye, 2010; Annex A2). The tidal volume above -0.5mODN in the Taf estuary shows a steep rise above c. 3.5mODN, reflecting the sudden increase in tidally flooded area as the marshes become immersed by the tide. The calculated maximum rate of change in tidal volume for a high spring tide reaching 5.19mODN occurs approximately 45 minutes before high water at the time when the highest marshes become flooded, whilst the maximum rate of tidal volume reduction occurs approximately 90 minutes after high water when water surface slopes are likely to be greatest and ebb velocities greatest (Pye, 2010; Annex A2).

The reclaimed marshes behind the Pendine – Laugharne barrier are extensive but are relatively high in the tidal frame (median surface elevation range 3.55 to 3.92mODN); consequently the tidal prism at MHWS level is less than might be expected (Pye, 2010; Annex A2).

Jago (1980) reported that the flood tide is considerably shorter than the ebb, with fast flood currents at the estuary mouth (1.8m/s) as the flood tide enters the estuary. Ebb currents were

C1-124 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding reported to reach 1.2m/s on spring tides as the flow becomes concentrated within the low water channel, 3 to 4 hours after high water.

The Taf is the most sheltered from waves of the three estuaries, with protection afforded by Laugharne and Pendine Burrows, and has a relatively low freshwater flow. Sediment is thought to arrive in the estuary from the marine environment rather than from fluvial sources (Cousins et al. , 2008), although a significant proportion of the mud fraction is probably derived from land-based sources (Jago, 1975, 1980). Sand-sized sediment, which is transported by alongshore drift from the adjacent open shoreline, accumulates at the mouth of the estuary either on the spit at the western side, or within tidal deltas and sand flats.

Movement: Analysis of historical maps and OS Landline data allowed Bristow and Pile (2003) to identify changes in the position and morphology of the tidal channels since 1876 (see Figure C.33). The normal tidal limit was found to have moved upstream by 368m, but little change in channel position was identified in the upper estuary. In parts of the mid and lower estuary reductions in channel width and position were identified, associated with spread of saltmarsh and a reduction in overall sinuosity. This is opposite to the expected effects associated with rising sea level, and indicates that sediment accretion in the Taf estuary has so far been able to outpace the effects of sea level rise. Repeated topographic surveys by Jago (1980) indicated that the Taf estuary is experiencing net vertical sediment accretion at a rate of 0.13m/yr. Short term process studies by Ishak (1997) also indicated that net flood-tide directed transport of suspended sediment in the Taf is 10% to 30% greater than the net ebb transport, which translates into a vertical accretion rate of 0.012m/yr to 0.016m/yr. Vertical sedimentation rates on active saltmarshes within the Taf were also found to range from between 0.004m/yr to 0.017m/yr. The available evidence therefore suggests that the sediment balance of the estuary in the later 20th century has been positive, with net import of sediment into the estuary.

Changes in saltmarsh area within the Three Rivers Estuarine Complex are the largest in the Taf since it is the most sheltered from waves (by Laugharne and Pendine Burrows) and has a relatively low freshwater flow, with a gain of 238 ha between 1876 and 2000 (Bristow and Pile, 2002). This accretion has occurred on both sides of the river, and in the tributary of the Afon Cywyn where previous agricultural land is thought to have naturally developed into saltmarsh.

There have also been changes in the position of the main low water channel of the Taf. Although the total length of the main low water channel (median line) has shown only limited variation over the period and there has been no significant net change in sinuosity index since 1879-87, the position of the channel within particular sections of the valley has varied considerably over time (Pye, 2010; Annex A2. For example, at Laugharne the low water channel lay only a short distance offshore in 1887 1949 and 2003-8, but was located towards the opposite shore at the time of the 1905 and 1965 surveys. However, with the exception of 1905, the low water channel was located close to Wharley Point at the time of all of the surveys. This has allowed the eastwards extension of Ginst Point and has encouraged saltmarsh development in the now more sheltered area in front of the St John’s Hill – Ginst Point embankment.

Existing predictions of shoreline evolution: As for the other two estuaries in the Three Rivers Estuarine Complex, there is very limited available information on how the estuary is evolving or predictions of how it is likely to change in the future.

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Futurecoast (Halcrow, 2002) did not consider individual estuaries, but states that the Three Rivers Estuarine Complex is still a very active sink and is capable of taking much more sediment. The study also recognised that changes in the estuary regimes are instrumental in locally modifying the shoreline either side of their mouths; either through redistribution of sediment within their tidal deltas, which can alter the degree of stability provided to the shoreline, or switching of channels and flows which can alter sediment transport as well as changing exposure conditions along the shoreline. The study predicted that further retreat of the beaches on either side of the mouth of the Three Rivers Estuarine Complex could lead to growth of the ebb tidal delta and the offshore sand banks.

Conversely, Bristow and Pile (2002) predicted changes in estuary morphology as a result of increasing rates of sea level rise, and predicted that erosion of the shoreline could cause landward retreat, whilst an increase in water levels could result in greater saltmarsh inundation and lead the tidal limit to be located further upstream. They also predicted that increased flows could also cause the estuary mouth to widen as the spits at either side become eroded; which together with increased water depths, could adversely affect the sheltered environment within the estuary, potentially resulting in shoreline erosion by waves. The study concluded that these effects could lead to a net loss of saltmarsh area in the outer estuary due to shoreline retreat and landward movement of remaining marshes due to water level increases.

As part of this SMP, in order to assess some of the possible implications of future sea level rise on the estuary, tidal areas and prisms were calculated for a number of future sea level rise scenarios based on the UKCP09 projections. A full description of the methodology used in provided in Annex A2. Two scenarios were considered: firstly using a medium UKCP09 emissions scenario and assuming MHWS increases at the same rate as MSL, and secondly an extreme ‘worst’ case scenario, using the High Emissions scenario and assuming MHWS rises at double the rate of MSL. Under the first scenario, the MHWS tidal prism is projected to increase by around 17%, by 2100 (Table 19). In comparison, under the extreme scenario, the spring tide tidal prism of the presently active estuary could increase by around 70%.

C1-126 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

C1-127 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.33: Composite aerial photography of Laugharne, Pendine Burrows and the Taf Estuary, flown in 2006. The dashed line shows the position of the dune toe or marsh edge from the first edition County Series OS Map, surveyed in 1887.

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LARGE SCALE: GILTAR POINT TO THORN ISLAND

Plate C.8: Freshwater West

Interactions: Geology is the main control on shoreline behaviour along the South Pembrokeshire coast. Carboniferous limestone headlands characterise this predominantly cliffed frontage. Indentations have developed along much of the shoreline due to differential erosion arising from local variations in geology. East of St Govan’s Head the heavily embayed shoreline has formed due to the differential erosion of shales and sandstones which are exposed within the folds of the more resistant limestones, whilst some bays, such as Manorbier, have formed due to erosion along fault lines (Halcrow, 2002). West of St Govan’s Head, to Linney Head, the south-south west facing coastline has a series of caves, blowholes and geos (deep steep-sided and narrow inlets in rocky coasts, such as Huntsman’s Leap west of St Govan’s Head), which have developed due to wave attack eroding areas of weak joints, faults and fissures in the Carboniferous limestone (Halcrow, 2002). Along this section of the coastline the cliffs have eroded back into karstic landforms which have combined with the processes of erosion to create dramatic features.

The cliffs are fronted by rocky shore platforms over much of the frontage to the east of St Govan’s Head and are only infrequently covered with sediment. Within the bays there are accumulations of sand and shingle, backed by dunes at locations such as Freshwater East, Barafundle Bay and Stackpole. There are wider sandy beaches at Frainslake Sands and Freshwater West.

In general, the shoreline is low in sediment, with few contemporary inputs, which tend to be localised. Fluvial inputs may contribute within bays such as Freshwater East and local landslides and

C1-129 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding rock falls may add some sand and shingle to adjacent shores. Halcrow (2002) suggested that a small supply of sand from offshore to the shoreline between Studdock Point and Linney Head feeds the dunes of Frainslake Sands and Freshwater West. There are no sediment inputs from further updrift, since the main Bristol Channel sediment transport pathways are thought to by-pass this coastline (Posford Duvivier and ABP Research, 2000). The bays are believed to be largely self- contained and to act as local sediment sinks. Milford Haven is the largest sediment sink in the area and is thought to store all of the sediment entering the Haven from the rivers which flow into it (Halcrow, 2002). Posford Duvivier and ABP Research (2000) suggested that sediment within the bays may be reworked and recycled during storm events.

The seabed in this region of the Bristol Channel was originally covered by unconsolidated sediments left from the glacial period. However sediments have gradually been removed from the area by the wave action, storms and strong currents, resulting in an irregular rocky seabed (Halcrow, 2002). This lack of sediment has resulted in the scarcity of beach material along the coast, with only a few embayments managing to retain sediment.

Littoral drift rates and directions vary along the frontage due to changing orientation and therefore exposure to dominant south-westerly swell waves and strong tidal currents. Drift is also hindered by the presence of the numerous limestone headlands which act as barriers to littoral drift. These factors, coupled with the small amounts of available sediment, result in little interaction between the bays. However, where littoral drift does occur, it is generally southwards on north-south orientated shorelines and eastwards on those shorelines aligned west-east. Posford Duvivier and ABP Research (2000) reported a potential sediment divide at St Govan’s Head, with sediment moving eastwards to the east, and westwards towards Linney Head.

Movement: This coast is predominately geologically controlled and therefore the fundamental shape of the coastline has not changed significantly for thousands of years, with the formation of bays and indentations having predominately taken place in the geological past, due to fluvial and glacial erosion (Shoreline Management Partnership, 2000). Raised beach and glacial drift (head) deposits were laid down over older, resistant geology during periods of higher sea levels. These were left stranded following periods of lower sea level during the last ice-ice. Reworking of glacial and preglacial deposits, both on the seabed and along the coastal fringes, commenced once sea level began to rise following the last ice age, forming beaches where sediment became trapped in embayments. A review of historic maps has shown that slow erosion has occurred along this frontage; the coastline has become more ‘nibbled’ in appearance since the early 1800s, following localised erosion events. These low rates of erosion are predicted to continue over the next 100 years with recession occurring in the form of localised landslips and rock falls (Halcrow, 2002). Any sand or shingle released would feed local beaches, but little sediment transport is predicted within bays. Sea level rise could result in narrowing of beaches which are backed by cliffs.

Modifications: There has been very limited human intervention along this resistant, cliffed coastline. Small-scale defences exist in bays such as Freshwater East and Lydstep Haven but these are not thought to have had any significant impact on the shoreline (Halcrow, 2002). Within the dune systems at Frainslake Sands and Freshwater West, there have historically been losses of dune area to

C1-130 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding agriculture, the use of the dunes for military purposes, damage by visitors and possibly sand quarrying (Liverpool Hope University, 2009). At Freshwater East, there has also been remedial works carried out within the dunes, including fencing and the construction of an artificial dune ridge (Pye et al., 2007).

Wider-scale interactions: The appearance and behaviour of this frontage is controlled largely by the resistant geology, particularly due to limited availability of sediment along this frontage and adjacent shorelines. Littoral drift is restricted by numerous headlands, including Giltar Point and St Ann’s Head at either end. Milford Haven also provides a barrier to drift, and acts as a sink for sediment arriving both from the rivers within the estuary (Rivers Cleddau (Afon Cleddau) and Pembroke (Afon Penfro). Therefore interaction with other areas along the coastline is thought to be limited. Sediment transport within the centre of the Bristol Channel is predominantly westwards, with the transport direction reversed along both the north and south banks. However, in the centre of the channel, there are few deposits of sand remaining, which have been removed from this high energy environment. There are limited contemporary sources of sediment (Halcrow, 2002).

For the purpose of this report, this frontage has been further divided into sections based on coastal processes (see Figure C.34): (1) Giltar Point to Old Castle Head; characterised by sandstone and limestone cliffs with small indented bays.

(2) Old Castle Head to Stackpole Head; a steeply cliffed coastline fronted by a rock platform. (3) Stackpole Head to St Govan’s Head; a vertically cliffed coastline with numerous caves and blowholes.

(4) St Govan’s Head to Linney Head; characterised by resistant cliffs and small embayments. (5) Linney Head to Sheep Island; characterised by the wide beaches and dune systems of Frainslake Sands and Freshwater West.

(6) Sheep Island to Thorn Island; comprising the beach at West Angle and sandstone cliffs of Studdock Point.

C1-131 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.34: Giltar Point to Thorn Island: large scale and local scale boundaries.

C1-132 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: GILTAR POINT TO OLD CASTLE HEAD

Interactions: This frontage is characterised by limestone and sandstone sea cliffs, along which have formed small crenulated bays. Along much of this coastline the cliffs plunge directly into the sea. Within the bays sand and shingle beaches have accumulated overlying the rock platform which fronts the cliff. The main bay along this frontage is Lydstep Haven where the foreshore is composed of slightly gravelly sand (Shoreline Management Partnership, 2000).

There is little sediment connectivity along this stretch, due to the barriers to drift formed by the headlands of Giltar Point, Lydstep Point and Old Castle Head, although there is a possibility of sediment leakage around Giltar Point (Halcrow, 2002).

Lydstep Haven is protected from the dominant south westerly swell waves due to its orientation and the shelter provided by Lydstep Point. The beach is near swash-alignment and is considered to be mainly self-contained; offshore losses are only likely to occur during storm events, when sediment could be drawn down outside the limits of the bay.

Movement: The resistant cliffs have historically been eroding very slowly, erosion occurs in the form of localised rock falls, as evident in the crenulated nature of the shoreline. As there is little sediment supply or transport to or from the beaches, Lydstep Haven and Skrinkle Haven have remained generally stable.

The Futurecoast cliff classification (2002) suggests, based on the geology of the cliffs, that typically ‘very low’ rates of erosion (less than 0.1m/year), should be expected.

Existing predictions of shoreline evolution: The Futurecoast (2002) prediction for an ‘unconstrained’ scenario were for the cliffs to continue to erode at historic rates, i.e. very slowly and with infrequent localised rock falls; any sediment released would remain in the individual bays. The only defences are localised and within Lydstep Haven, in the form of gabions and revetments. The prediction for a ‘with present management’ scenario (Halcrow, 2002) was very similar to the unconstrained scenario and stated that the effect of defences would not be felt outside of the immediate area.

Shoreline Management Partnership (2000) predicted ‘minor’ erosion along the south-facing coastline to the west of Giltar Head at the top of localised gullies and blowholes. In general, cliff erosion rates along this section of coast were predicted to continue at an average rate of 0.5m/year to 1.5m/year (Shoreline Management Partnership, 2000).

C1-133 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: OLD CASTLE HEAD TO STACKPOLE HEAD

Interactions: This frontage is characterised by vertical Carboniferous limestone cliffs to the west, which are replaced at Greenala Point by sloping Old Red Sandstone sea cliffs to the east, fronted by narrow rock wave-cut platforms (Shoreline Management Partnership, 2000). The cliffs are heavily indented, forming small crenulated bays, and contain numerous fissures and faults. There are blowholes in the limestone cliffs west of Stackpole Quay (Shoreline Management Partnership, 2000). On both sides of Manorbier Bay are gullies resulting from differential erosion. Along much of this shoreline the cliffs plunge directly into the sea, whilst beaches have developed within small embayments. Within these bays sand and shingle beaches overly the rock platform which fronts the cliff. There are a number of deeply embayed beaches along this frontage, namely Manorbier Bay, Swanlake Bay, Freshwater East and Barafundle Bay.

Freshwater East and Barafundle Bay are backed by dune systems, whilst Manorbier Bay is backed by a line of old vegetated cliff-top and climbing dunes. Remedial works have been undertaken to the dunes at Freshwater East in an effort to maintain the natural system following significant human pressure (Shoreline Management Partnership, 2000). Swanlake Bay is a sand bay lying at the foot of a large bank of overburden, which may be affected during storms and high tides (Shoreline Management Partnership, 2000). Stackpole Quay, north of Barafundle Bay, was built in the 17 th Century to transport limestone from the nearby quarry and land goods for Stackpole Court and is located in a natural indentation. There is little littoral sediment transport, due to the headlands that separate the bays. The bays are therefore likely to be mainly self-contained; offshore losses are only likely to occur during storm events when sediment could be drawn down outside the limits of the bay. Any sediment drift which occurs within the bays is likely to be eastwards (Shoreline Management Partnership, 2000), but generally the bays are swash-aligned.

Movement: Historically the resistant cliffs have eroded very slowly, due to localised rock falls, as evidenced by the crenulated nature of the shoreline. Very little change is evident from analysis of historical maps.

There are, however, localised areas where increased recession has occurred due to local landsliding (e.g. north of Stackpole Quay) and minor rock falls where the vertical limestone cliffs give way to horizontally bedded limestones between Greenala Point and Trewent Point. Jones et al. (1992; cited in Shoreline Management Partnership, 2000) reported minor rock falls of between 50 tonnes and 100 tonnes north of Greenala Point. Shoreline Management Partnership (2000) also noted minor rock falls (in the region of 20 to 100 tonnes) along the western cliffs of Swanlake Bay.

The Futurecoast cliff classification (2002) suggested that potential erosion rates were likely to be typically ‘very low’ (less than 0.1m/year) along the Manorbier and Trewent frontages, and low (between 0.1m/year and 0.5m/year erosion) at Stackpole and Stackpole Head.

Since there is not thought to be significant sediment movement either in or out of the bays, the beaches are thought to have remained generally stable. At Freshwater East, there was significant dune erosion in the 1980s and 1990s, due to recreational pressures on the dune system. This led to

C1-134 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding remedial works being carried out within the dunes, including the construction of an artificial foredune ridge, which is now a stable feature (Pye et al., 2007).

Existing predictions of shoreline evolution: The Futurecoast (2002) prediction for an ‘unconstrained’ scenario suggested that the cliffs would continue to erode at rates that have been observed to date, i.e. very slowly and with infrequent localised rock falls. The study suggested that local erosion of the dunes within Freshwater East could occur, which would result in landward migration of the system.

Shoreline Management Partnership, (2000) predicted general cliff erosion rates along this frontage to be between 0.5m/year and 1.5m/year on average.

LOCAL SCALE: STACKPOLE HEAD TO ST GOVAN’S HEAD

Interactions: This frontage is characterised by high vertical Carboniferous limestone cliffs which contain blowholes and caves (Shoreline Management Partnership, 2000). Although the cliffs are resistant, wave undercutting occurs in localised areas, which, along with the presence of caves, has resulted in the displacement of large blocks of cliff between Broad Haven and St Govan’s Head (Jones et al. , 1992, cited in Shoreline Management Partnership, 2000). Cliff erosion tends to be concentrated at faults or joints (Shoreline Management Partnership, 2000). There is a number of deeply indented bays and inlets along this frontage, some of which contain sand and shingle beaches, notably Broad Haven which is backed by dunes. These beaches overly the rock platform which fronts the cliff. The dunes at Broad Haven Bay, which are backed by man- made freshwater ponds, are thought to have originated from wind blown sand from Broad Haven beach and the pocket beach to the east of Saddle Point (Pye et al. , 2007) and have accumulated since the Bronze Age (Shoreline Management Partnership, 2000). The dunes are on average about 35m above sea level (Pembrokeshire Coast National Park, online). Pye et al. (2007) noted three distinct dune areas, namely bay fringing and transgressive dunes backing the beach at Barafundle Bay, climbing and cliff top dunes at Stackpole Warren and bay fringing dunes backing the beach at Broad Haven. The beaches are protected by headlands and are not exposed to the dominant south-westerly swell waves (Shoreline Management Partnership, 2000).

There is little sediment connectivity between the beaches, which are highly indented, and the exposed nature of this coastline means that sediment are not retained along the exposed cliffs. The embayments can therefore be considered as closed systems.

Movement: Historically the resistant cliffs have been eroding very slowly, and any erosion that has occurred has been in the form of localised rock falls, as evidenced by the crenulated nature of the shoreline. However, Shoreline Management Partnership (2000) noted erosion of the rock cliffs along this frontage, and suggested that erosion in the form of rock falls was minor but frequent. Approximately 10.5m³ rock was reported to have fallen from the cliffs bordering the western side of Broad Haven (Shoreline Management Partnership, 2000).

C1-135 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Futurecoast cliff classification (2002) suggested that these cliffs were typically eroded at ‘slow’ rates (between 0.1m/year and 0.5m/year), but with the potential for frequent (every 1 to 10 years) but small (less than 10m recession) cliff fall events to occur.

At Stackpole, three narrow valleys were flooded between 1780 and 1860 to create the lakes, known as Bosherston Lakes or Lily Ponds. Prior to being dammed, the valleys were probably flooded at high spring tides. The lakes are currently separated from the sea by a dam, and during the winter, overflow from the entire lake system to the sea occurs from the Central Lake via a weir at Broadhaven, set at 5.60mODN (Miller, 2007). Much greater quantities of water are, however, believed to be lost from the lakes through fissures within the lake bed (Miller, 2007).

Since there is little sediment supply or transport, the beaches are thought to have remained generally stable. The dunes at Broad Haven and Barafundle Bay, although sheltered from prevailing conditions, are under pressure from human activities, and some dune toe erosion has resulted. Pye and Saye (2005) used historical Ordnance Survey maps to determine average rates of change at Barafundle, Broad Haven and Stackpole. From analysis of four profiles, they concluded that overall the system appeared to show an average coastline (dune toe), advance of 0.6m/year between 1906 and 2002, with 0.6m/year advance of MHW, but 0.5m/year retreat of mean low water. These results have, however, been ‘skewed’ by apparent large change at a profile located at Broad Haven, whilst the remainder of the profiles actually showed little change in the coastline in mean high water and between 0 and 0.7m/year retreat of mean low water. Interestingly, the historical Ordnance Survey maps do not indicate any dunes at Broad Haven until the 1970 map edition, which seems unlikely; therefore it would seem sensible to reject the results derived from this data source.

Existing predictions of shoreline evolution: Futurecoast (2002) shoreline predictions for an ‘unconstrained’ scenario were for the cliffs to continue to erode at rates observed historically, i.e. very slowly and with infrequent localised rock falls. Shoreline Management Partnership (2000) predicted that the limestone cliffs on the western side of Broad Haven would continue to erode over the next several years, with a total loss of 72m³. However, following this, it was predicted that this section of the cliff would stabilise. Typical predicted rates of cliff erosion are between 0.5m/year and 1.5m/year (Shoreline Management Partnership, 2000).

Appendix A of Pye and Saye’s report (2005) used evidence from historical mapping to make predictions of future shoreline change. Using expert interpretation, the prediction was for no area change by 2080-2100 at Barafundle Bay and only minor adjustment at Broad Haven, leading to area gain. However, the conclusions at Broad Haven Bay are based upon the analysis of historical maps, which are considered unreliable for this bay.

LOCAL SCALE: ST GOVAN’S HEAD TO LINNEY HEAD

Interactions: This frontage is characterised by high, resistant limestone cliffs. There is a number of indented bays and inlets and two pocket beaches, Flimston Bay and Bullslaughter Bay, which are characterised by a thin veneer of sand overlying a rock platform.

C1-136 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

The cliffs along this coastline (known as the Castlemartin Peninsula) provide some of the finest examples of cliff forms in the UK, including geo, stack, cave and arch formations where faults and other weak points have been exploited by wave attack (May, 2007c). The cliffs are retreating into an area where karstic landforms dominate which has resulted in the combined effects of solution, collapse and reworking developing the distinctive features (May, 2007c). An example is the Castle, towards the south of this frontage, where there is a sequence of caves, arches and a blowhole. May (2003c) suggested that if their roofs collapsed, many of the features would become separated from the mainland.

The shoreline is exposed to the prevailing westerly and south-westerly swell waves. There is, however, little sediment transport due to the high exposure of this coastline. The indented nature of the two pocket beaches allows sediment to be retained at these locations.

Movement: The resistant cliffs have historically eroded very slowly, and any erosion that has occurred has been due to localised rock falls. The Futurecoast cliff classification suggested ‘low’ (between 0.1m/year and 0.5m/year) rates of erosion, with the potential for small (less than 10m recession) cliff failure events, occurring every 10-100 years.

The two pocket beaches are thought to have remained generally stable, with little input or loss of sediment.

Existing predictions of shoreline evolution: Futurecoast (2002) shoreline predictions for an ‘unconstrained’ scenario were for the cliffs to continue to erode at rates observed historically, i.e. very slowly and with infrequent localised rock falls.

LOCAL SCALE: LINNEY HEAD TO SHEEP ISLAND

Interactions: This frontage comprises limestone cliffs to the south and sandstone cliffs to the north, separated by the bays of Frainslake Sands and Freshwater West. The bays are characterised by wide sand and shingle beaches backed by the dune systems of Linney Burrows and Brownslade Burrows at Frainslake Sands and Broomhill Burrows at Freshwater West. Both Linney and Brownslade Burrows have some climbing dunes which have accumulated due to sand being blown upslope and inland of the main dune system (Halcrow, 2002). The dunes at Freshwater West are fronted by a beach ridge. The two bays are separated by the dune-topped cliffs at Little and Great Furzenip, which, along with the reefs fronting Linney and Gupton Burrows, may help stabilise the dunes and retain the beaches in their current position. The main supply of sediment to this frontage is from offshore, although some nearshore sediments may settle in the bay due to accelerating flows around the Castlemartin Peninsula (Halcrow, 2002). Atkins (2002) also suggested that erosion of the cliffs and dunes provides a source of sediment. The dune systems have developed due to shelter being provided by the headlands, although their seaward edges are eroding, and large blow-outs are visible at the seaward edge of Broomhill Burrows.

C1-137 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Movement: The dunes at Broomhill were formed by the prevailing onshore winds blowing sand inland; however Brownslade Burrows and Linney Burrows are bay dunes, formed by sand becoming trapped in the bay between the sheltering headlands of Linney Head and Gupton (Halcrow, 2002). This system formed as a bay-head barrier system and evolved during the Little Ice Age to become a transgressive climbing dune system (Pye et al., 2007).

Evidence suggests that all of the frontal dune systems have been generally stable, although Liverpool Hope University (2009) suggests that there may have been minor erosion at Broomhill – Kilpaison Burrows between 1906 and 2002, and slight accretion at Brownslade and Linney Burrows over recent years. The amounts of bare sand have reduced over the last 50 years, and Liverpool Hope University (2009) reported that there was 12% bare sand at Broomhill and Kilpaison Burrows in 1946, but that this reduced to 1.4% in 2006; whereas at Broomslade Linney there was 22% bare sand in 1946 and 6% in 2006. This is thought to be due to a number of factors including military activity during World War 2, which resulted in significant areas of bare sand at this time. At Brownslade Burrows a conservation practice of mechanically creating dune systems has been undertaken to encourage growth of rare dune slack species (CCW, 2005). To the north of Broomhill Burrows much of the former dune area is now used for agriculture (Liverpool Hope University, 2009). Pye and Saye (2005) concluded that at Brownslade and Linney Burrows generally little or no change in coastline or mean high water position was evident from historical Ordnance Survey maps for the period 1906 to 2002. The maps did, however, suggest between 0.8 and 1.9m/year retreat of mean low water. At Broomhill Burrows, Pye and Saye (2005) concluded little change in coastline position was evident, but an average of 0.2m/year advance in mean high water and between 1.8m/year and 1.6m/year retreat in mean low water. The headlands and cliffs that constrain the bays have historically eroded very slowly, due to their resistant geology. Futurecoast cliff classification (2002) suggested, based on their geology, that they are likely to experience a ‘low’ rate of erosion, i.e. between 0.1m/year and 0.5m/ year erosion.

Existing predictions of shoreline evolution: Futurecoast (2002) predicted that under an ‘unconstrained’ scenario, the beach would continue to be fixed by the reefs and resistant cliffs, which would continue to erode very slowly, resulting in a stable plan-form, although some retreat would be expected as sea levels rise. Wind and wave action might also be expected to periodically lead to some erosion.

Appendix A of Pye and Saye’s report (2005) used evidence from historical mapping to make predictions of future shoreline change. Using expert interpretation, the prediction was for a minor loss in dune area, but largely no change by 2080-2100 at Brownslade and Linney Burrows. Similarly at Broomhill Burrows, slight dune loss, but largely little change was predicted.

LOCAL SCALE: SHEEP ISLAND TO THORN ISLAND

Interactions: This frontage comprises the headland of Studdock Point, which is characterised by Old Red Sandstone cliffs, and the sandy beach at West Angle Bay, which has developed in a trough in the

C1-138 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding sandstone. Sheep Island prevents sediment entering the system from the west, but there is little sediment within this frontage due to the resistant nature of the cliffs. The beach at West Angle is generally considered to be a closed system, in terms of sediment transport, due to its heavily indented nature, although an eroding bank to the south of the bay is thought to supply limited amounts of sediment to the beach (Atkins, 2002).

Although Milford Haven, to the north, is a potential sink for fine sediments, there does not appear to be any connectivity with this section of shoreline, which, due to its exposure and geology, tends to be swept clean of sediments. The exception is West Angle Bay, where a more sheltered environment is provided due to the indented nature of the coast and the reduced exposure conditions provided by St Ann’s Head, the headlands of Rat Island and Thorn Island.

Movement: Little change in cliff line position is evident from the historical Ordnance Survey maps and therefore it is assumed that the cliffs have historically eroded very slowly due to their resistant nature.

Existing predictions of shoreline evolution: Futurecoast (2002) predicted that there would be very little change over the next 100 years under both the ‘unconstrained’ and ‘with present management’ scenarios. Similarly Atkins (2002) predicted that the beach at West Angle Bay would remain stable due to the indented nature of the bay, and the influence of St Ann’s Head, Rat Island and Thorn Island, which reduce the exposure of this bay.

C1-139 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LARGE SCALE: MILFORD HAVEN

Plate C.9: Milford Haven from the southern approach to the Cleddau Bridge

Interactions: Milford Haven (Aberdaugleddau) is a deep macrotidal ria-type estuary. The submerged river-valley is largely controlled by the underlying geology, in terms of structure and shape, with major east- west faults and folds running down the centre. The mouth is constrained by the resistant headlands of the Angle Peninsula to the south and St Ann’s Head to the north. Within the estuary, the shoreline is mostly comprised of cliffs and rocky foreshores. The cliffs are predominantly composed of Old Red Sandstone and although they are steeply sloping, they are generally vegetated. The lower estuary is highly industrialised (Atkins, 2002). The main tidal channel along the estuary is deep and sinuous, a legacy of the drowned river channel, with a typical depth of 20m between the mouth and the Cleddau Bridge and a typical depth of 10m upstream of the Cleddau Bridge to the confluence with the River Creswell and River Carew. The main channel is flanked by localised areas of intertidal sandflats and mudflats, which have generally accumulated where a more quiescent environment has been created, i.e. either in the shelter of headlands or man-made structures or within the subsidiary river channels. Saltmarshes are present, inland of the Cleddau Bridge, where the estuary has been subject to less modification.

Although the estuary has been heavily modified, there are few anthropogenic constraints on channel movement, and the resistant geology remains the main constraint. Tidal currents within the estuary are much lower than along the open coast. The estuary currents are higher within the main

C1-140 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding channel and lower within the embayments and over the shallower intertidal areas adjacent to the deep channel.

The estuary mouth is exposed to the prevailing westerly and south-westerly swell waves, but St Ann’s Head and the Angle Peninsula reduce wave penetration into the Haven. The dynamic, sandy beaches at Watwick Bay and Dale Roads are exposed to refracted southwesterly and southerly swell waves and locally generated southeasterly wind waves. To the east of South Hook Point, in the sheltered environment of the Haven foreshores are composed of a variety of sediments ranging from coarse cobbles and shingles, mixed shelly gravel and fine sands and muds. On the beaches there is evidence of ancient river channels across sub-tidal sediment plains.

Milford Haven has the capacity to be a large sink of sediment, based on its morphology (Halcrow, 2002); however, there is limited sediment input from offshore and the rivers are not believed to contribute significant volumes of sediment. River flows are low; therefore sediment discharges are thought to be small with any fluvial sediment entering the system thought to be deposited at the head of the tributaries (Halcrow, 2002). Bays such as Angle Bay, where sand and muds have accumulated, are understood to be largely closed sediment systems, due to the influence of the rocky headlands surrounding them.

Movement: The estuary is believed to have originated as a river valley which was drowned during the marine transgression at the end of the last Ice Age. It is cut into resistant geology and therefore its shape is predominately structurally controlled; this has meant that there has been limited accommodation space for the development of saltmarsh.

Historical Ordnance Survey maps show that (due to the geology of the estuary) the overall shape has changed very little over the last 200 years despite extensive industrial and urban development. Key anthropogenic changes are centred around the developments of Milford Haven (Aberdaugleddau), Neyland and Pembroke Dock (Doc Penfro) and include the construction of docks, ports, associated structures, construction of the A4139 road bridge and changes in upstream land-use, which have affected catchment run-off volumes. Countryside Council for Wales (2009) suggested that the latter has resulted in run-off entering the estuary during peak events rather than a steady rate. Increased erosion due to changes in farming methods has also resulted in increased sediment inputs. The geological structure of the estuary will restrict its ability to respond to future sea level rise, and little change in the overall structure anticipated over the next 100 years. The net impact is likely to be loss of intertidal area since the cliffs will not enable any roll- back of habitats.

Modifications: Humans have been modifying the estuary for centuries; ancient quays and quarry workings have been discovered along the shoreline, although these have generally since become partially or wholly naturalised. An Act of Parliament was passed in 1790 to develop a port at Milford and in 1797 a dockyard was established to build warships.

Over the last 150 years there has been considerable urban and industrial development, with the last 40 years seeing a loss of intertidal flats and an increase in defences along the foreshore associated with the port, oil and gas industry in the region (Countryside Council for Wales, 2009). Industry has not only affected the shoreline but the intertidal areas and the estuary bed through installation of features such as pipelines, cables, outfalls, harbour structures. There are large refinery jetties on both the north and south banks which are located about 800m and 300m offshore

C1-141 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding respectively. Countryside Council for Wales (2009) estimated that land reclamation and freshwater impoundment for the purposes of industry and recreation has resulted in the reduction of water area by 100 ha since the 1860s, 70 ha of which has been lost since the 1970s. This represents an overall lost of just under 2% of estuary area, assuming an overall estuary area of 55km² as suggested by Countryside Council for Wales (2009).

Wider-scale interactions: Milford Haven acts as a barrier between the open coast systems to the north and south of the estuary mouth. However, within this framework it is thought to be a self-contained system with little interaction with the coast. Although the estuary has the capacity to be a major sink for sediment, volumes entering the estuary from offshore are not considered to be significant (Halcrow, 2002). The indented nature and geology of the adjacent shorelines means that there is little littoral sediment transport.

For the purposes of this study, Milford Haven has been split into southern and northern banks (see Figure C.35).

C1-142 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

Figure C.35: Milford Haven: large scale and local scale boundaries.

C1-143 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding

LOCAL SCALE: THORN ISLAND TO CLEDDAU BRIDGE

Interactions: The southern shoreline of Milford Haven is characterised by Old Red Sandstone cliffs and rocky foreshores. There is a number of indented embayments where sand and mud have accumulated. As with much of the Pembrokeshire coastline, the estuary is constrained by the resistant geology. Angle Bay, near the estuary mouth, is controlled by the headlands to either side (Angle Point and Sawdern Point) and the reefs within the bay. Although the bay is similar in appearance to crenulated bays, Atkins (2002) consider that the bay has formed differently, simply being an accumulation of sediments within a naturally occurring bay.

The mudflats, such as those at Pwllcrochan Flats and west of Hobbs Point, have developed in sheltered areas and act as buffers between the coastline and the river channel, protecting the coastline from locally generated wind waves. However, they probably do not exert a significant influence over the surrounding features (Atkins, 2002).

The Pembroke River is a sheltered ria valley in the Milford Haven system. As such it is sheltered from direct wave action and therefore there has been an accumulation of mudflats and saltmarsh. There is little information on the sediment budgets for the area (Atkins, 2002), but the need for dredging at the Pwllcrochan power station suggests that there has been a process of infilling. To the east, the headland of Pembroke Ferry, which forms the southern end of the Cleddau Bridge, forces the river to make a significant meander. Carrs Rock is a submerged bedrock feature which deflects tidal currents and forces flows to the northwards side of the estuary. There is understood to be little sediment input into the estuary, with any new sediment generally entering the Haven from the various tributaries rather than from offshore. Sediments from rivers and tributaries, such as Pembroke River, are either deposited at the heads of the river or tributary or on the mudflats. The mudflats and pocket beaches therefore tend to act as sediment sinks. Sediment transport close to the shoreline is generally from west to east, and tends to be finer sediment, due to the low tidal currents in the estuary (Atkins, 2002). Atkins (2002) concluded that drift along the frontage varies, but is generally east to west, although there appears to be a drift divide along the Pembroke Dock shoreline, between the Tower and Carr Rocks, due to a difference in exposure conditions. Headlands, such as Carrs Rock and Hobbs Point appear to deflect tidal currents and providing shelter in their lee (Atkins, 2002).

The frontage has been heavily modified; there are coastal defences in a number of places (such as the seawall within Angle Bay) and jetties, piers and quay walls associated with Milford Haven’s industrial use. These structures may have minor localised impacts on adjacent areas.

Movement: A review of historical maps suggests that the intertidal area within Angle Bay has narrowed substantially since the 1830s, such that a much greater area of the bay remains submerged under normal tidal conditions. Additionally, the south-western side of the bay appears to have eroded to form a smoother, more rounded coastline. However, changes in mapping techniques and times of survey lead to means there is some uncertainty when considering trends in high and low water marks (Oliver, 2005). The resistant geology of the area would suggest there has been little historical

C1-144 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding change along the coast, except where there have been industrial developments. There has been some slow erosion of the cliffs, for example at Llanreath and Carrs Rock.

The Futurecoast cliff classification (2002) suggested that the cliffs at Angle could typically experience ‘low’ rates of erosion i.e. between 0.1m/year and 0.5m/year, but did not extend any further into the estuary.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) did not include Milford Haven, therefore no predictions are available from the source.

The SMP1 (Atkins, 2002) predicted that generally the shoreline would remain stable, with little change in regime, but that there would be continuation of the slow erosion of the cliffs and headlands, although no specific rates or recession data was provided. The report also emphasised the sensitivity to climate change, which could alter sediment deposition and cause some erosion of the mudflats and sand accumulations.

LOCAL SCALE: CLEDDAU BRIDGE TO ST ANN’S HEAD

Interactions: The northern shore, extending from the Cleddau Bridge to St Ann’s Head, has similar geomorphology as the southern shore, with the frontage controlled by the geology. The shoreline is characterised by Old Red Sandstone cliffs and rocky foreshores, with accumulations of sand and mud flats in sheltered areas. These mudflats and sand beaches act as a buffer region, protecting the coastline from tidal currents, swell waves and locally generated wind waves. There are a number of places where headlands influence coastal processes. For example, Neyland Point just west of the Cleddau Bridge, extends into the Haven and is thought to influence the direction of flood and ebb tidal currents (Atkins, 2002). A submerged spit at Wear Point extends into the Haven, forcing the main deep channel to meander. Gelliswick Bay represents the remains of one of the tributary valleys into the Haven which formed during the last Ice Age. The pocket beaches and shallow bays are generally aligned to the dominant waves, and some are susceptible to erosion as they are vulnerable to changes in wave direction. The northern shoreline is more exposed to the dominant wave conditions than the southern, particularly towards the estuary mouth, due to the orientation and geomorphology of the estuary.

There is little sediment input into the estuary, with any new sediment generally entering the Haven from the various tributaries rather than from the offshore (Atkins, 2002). Sediments from rivers and tributaries, such as Pembroke River, are either deposited at the heads of the river or tributary or on the mudflats. The mudflats and pocket beaches tend to act as sediment sinks. Sediment transport close to the shoreline is generally from west to east, and tends to be fine sediment, due to the low tidal currents in the estuary (Atkins, 2002).

The frontage has been heavily modified; there are coastal defences in a number of places (such as the seawall within Angle Bay) and jetties, piers and quay walls associated with Milford Haven’s

C1-145 Lavernock Point to St Ann’s Head SMP2 Appendix C: Baseline Process Understanding industrial use. Atkins (2002) considered that the oil jetties are unlikely to have a significant impact on coastal processes, even though they extend up to 900m out into the Haven.

Movement: A review of historical maps suggests there has been little net change in shoreline position, except where there have been industrial developments, and this would be expected due to the generally resistant nature of the coast. There has been some slow erosion of the cliffs, and a number of the more exposed beaches are subject to erosion, such as at Dale. These beaches may also experience periodic cross-shore variations in beach level with sediment being moved offshore during storm events and returning onshore during periods of calmer weather (Atkins, 2002).

Pickeridge, near Dale, is a shingle/sand barrier, which encloses the Gann Estuary and a tidal lagoon. Pickleridge Lagoon was established as saline lagoon between the 1950s and 1980s, following extraction of gravel in the area behind the ridge from the early 1900s. Prior to this, the 1887 Ordnance Survey map shows that the barrier enclosed an area of marshland known as Pickleridge Common. Since the 1887 there also appears to have been considerable siltation of the Gann Estuary, with development of extensive saltmarsh areas.

The Pickleridge Lagoon is dynamic over tidal cycles, as well as longer time scales, because of sediment accretion and erosion; historical aerial images of Pickleridge Lagoon indicate considerable temporal variation in sediment transport processes with a complex history of sediment accretion and erosion (CCW, 2009). The lagoon is gradually being infilled as sediment settles out into the basin, but there is a risk that the whole lagoon could be inundated and destroyed should a major breach of the Pickleridge barrier occur (CCW, 2009).

The Pickleridge Lagoon was protected from oil ingress by the construction of a temporary dam across the entrance channel. The removal of this dam created some instability of the boulder sill in the entrance, which resulted in the lagoon draining more rapidly and to a lower level than it had previously. Some refurbishment of the sill was carried out by Pembrokeshire County Council, but continued problems are still causing concern among the local community (Blaise Bullimore and Andrea McConnell, pers. comm.). The main effect appears to be a change in the flow regime, resulting in changes to the water levels in the lagoon and possibly some increased silting in places.

Existing predictions of shoreline evolution: Futurecoast (Halcrow, 2002) did not include Milford Haven; therefore, no predictions are available from the source.

The SMP1 (Atkins, 2002) predicted that the shoreline would remain generally stable, with some continuation of the slow erosion of the cliffs and headlands, although climate change could alter sediment deposition and cause some erosion of the mudflats and sand accumulations. Some areas, such as the low-lying land at Dale could become increasingly vulnerable to flooding.

C1-146 Swansea Bay and Carmarthen Bay Shoreline Management Plan Appendix C: Baseline Process Understanding

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