Berry Head to Hope's Nose, Tor Bay
1. INTRODUCTION - References Map
This unit coincides with the large, well-defined coastal embayment of Tor Bay. The confining promontory headlands terminating at Hope's Nose (Photo 1), to the north, and Berry Head (Photo 2), to the south, are developed on erosionally resistant Devonian limestones. Slates, mudstones and breccia outcrops occupy much of the recessed coastline between Torquay and Brixham. Due to their varied lithological composition these latter rock materials are characterised by differential response to both marine and sub-aerial denudation. Consequently, a sequence of headlands and embayments has developed, which vary in their scales of development. With the exception of Roundham Head (Photo 3), south of Paignton, headlands within the bay form relatively minor low elevation salients. Beach development is confined to the re-entrant bays and coves, with little obvious sediment exchange between them. Sand is the dominant beach-forming sediment, with coarser material mostly adjacent to eroding headlands.
Most of this shoreline is stable, recording low rates of recession over the past 100 years (Posford Duvivier, 1998). Urban development occupies over 60% of the frontage, with seawalls and revetments built to protect residential property, infrastructure and commercial (especially recreational) facilities. At locations such as Torquay, Paignton (Photo 4), Hollicombe and Brixham (Photo 5) protection structures form esplanades and also represent an amenity resource in support of the regionally important tourism industry. Breakwaters have been constructed at Torquay, Paignton and Brixham Harbours (Photo 5), thus adding strong, artificial structures approximately at right angles to local coastline orientation.
The effect of both natural and built salients has been to compartmentalise this coastline into a sequence of discrete sub-cells of sediment movement. Whilst a weak, approximately south to north littoral transport pathway is discernible, each sub-cell appears to operate as as a relatively independent coastal process system. This is especially evident from contrasts in beach morphodynamics within this unit as a whole.
1.1 Coastal Evolution - References Map
The arcuate form of the Tor Bay coastline is considered to be the product of structural control created by axial planes of folding and thrusting and the effects of differential faulting. The latter has been influential in shaping the Hope's Nose (Photo 1) and Berry Head (Photo 2) promontories; in the former case, there has been intrusion of igneous dykes, thus adding further strength (Perkins, 1971). These structures are inherited from complex tectonic events that occurred not less than 250 million years ago (Lloyd, 1933).
The modern coastal planform is, however, much more recent. The presence of raised beach platforms and associated sediments at Shoalstone Point, Hope's Nose, and on Thatcher Rock (Photo 1), at between 8 and 12m OD, is evidence of erosion associated with higher sea-levels (Mottershead et al., 1987). These palaeoforms have survived because of the relative resistance of the Devonian Limestone on which they developed. An absolute date for their origin is uncertain, but they are likely to represent high sea-levels during either the ultimate or penultimate interglacial period, i.e. not more than approximately 330-360,000 years before the present. Uranium series dating of speleothems from abandoned terrestrial caves beneath Berry Head (Proctor and Smart, 1991) suggests that their formation was approximately contemporary with the shore platforms, i.e. sea-level regulated the ground water table. It is therefore reasonable to assume that the ancestral forms of both headlands, and thus Tor Bay itself, existed at least some 400-500,000 years ago. Submerged platforms, and at least one cliffline at -40m OD off Berry Head, are indicative of lower sea-levels that may be early Pleistocene in age. It is not considered that there has been any significant post-formation isostatic or tectonic displacement of the above evidence for relative sea-level change, although direct evidence is lacking.
The detail of the modern coastline is the product of Holocene sea-level rise over the past 15,000 years. Submerged forests and interbedded marine, brackish and peat beds exposed on the foreshore at Goodrington Sands (Photo 6) and Torre Abbey, Torquay (Photo 7) are provide evidence of former marsh deposits now submerged by progressive early to mid-Holocene sea-level transgression (Jukes-Browne, 1911; Perkins, 1971). Nearshore buried channels, representing the seaward extension of contemporary rivers, e.g. the Torre Stream, further confirm transgression. It is hypothesised that sandy seabed sediments occupying Tor Bay provided material for barrier beach formation from mid-Holocene times. This would have commenced when sea levels were approximately -30 to -25m OD, with shoreward barrier migration occupying several subsequent millennia of steadily rising sea-level. As this 'super' barrier was driven towards the contemporary coastline, it encountered a series of headlands that formed the truncated interfluves between several west to east-orientated river valleys. These drain the coastal hinterland, and are long-established features that account for many of the embayments of both the pre-existing and modern coastlines. In response, the barrier segmented and sealed up the mouths of several rivers. Several former lagoons, now reclaimed and partly built over, provide evidence for this evolutionary stage. These include Torre Abbey Meadows (Photo 7), a site 1.5m below mean sea level, where there is a 5.2m thickness of estuarine and both saltmarsh and freshwater peat deposits (Perkins, 1971); the former Fleet Estuary, at the base of Abbey Road, Torquay, (now Cary Green), where a repetitive sequence of alluvial clays and silts, fluvial sands, peat and coarse beach sand is known (Doornkamp, 1988), and the low-lying areas behind Goodrington Sands (Photo 6), Broad Sands (Photo 8) and Livermead Sands. The sandstone outcrop in the centre of Goodrington Sands was surrounded by saltmarsh up until the 1860s, prior to its drainage and reclamation of landward parts as part of rapid urbanisation (Perkins, 1971).
1.2 Hydrodynamic Regime - References Map
There is a dearth of quantitative knowledge of contemporary wave and tidal process (although this study was unable to locate potentially helpful data in studies known to have been carried out for the managements of Torquay and Brixham Harbours). Mean tidal range at Torquay is 3.1m, but tidal currents are weak and are not considered capable of any significant independent sediment transport. The eastward - facing orientation of this coastline results in protection, by Berry Head from waves approaching directly from between west and south. However, long period Atlantic swell waves, refracted and diffracted around Start Point and Berry Head, do enter Tor Bay, but their energy at the coastline is greatly reduced by the width and shallowness of the bay. Waves approaching from between north-east and south-east are more energetic, and can generate mean significant wave heights of between 2.5 and 3.0m (Harwood, 1983). The mean significant wave height is, however, characteristically less than 0.5m. Given that higher energy waves only occur infrequently, and that most waves approach approximately normal to shoreline orientation, the potential for littoral transport is small. Most beaches are swash-aligned and show fairly modest seasonal changes in volume and profile form, though short-term winter storm losses and longer-term summer season gains are characteristic of some.
2. SEDIMENT INPUTS - References Map E1
Only small streams drain into the bay and these are regulated and reach the shoreline via culverts so that there is limited potential for any significant supply of fluvial sediments. There are no reports of offshore to onshore supply of sediments to beaches.
2.1 Cliff Erosion
The Devonian Limestones of Hope's Nose (Photo 1) and Berry Head (Photo 2) are relatively resistant to marine and subaerial denudation, although they exhibit a variety of up to 60m high rugged coastal slopes that are also adjusted to the presence of interbedded shales, intrusive dolerite sills and sandstone dykes. Wave action has exploited well defined joints and other parting planes and - as in earlier stages of the Quaternary period - is creating minor shoreline platforms. These occupy a height-range of several metres, with salt spray weathering being a probable contributory factor at higher elevations. On both Berry Head and Hope's Nose, nineteenth century quarrying has modified the natural coastal slope.
Between these two main "anchor points", sandstones, conglomerates, breccias and shales outcropping within the bay collectively offer relatively less resistance and support an intermittently cliffed coastline. Several small bays and coves are developed in weaker bedrock, defined by headlands of various degrees of prominence. Where present, harbour breakwaters and piers form strong, albeit artificial, salients. Narrow shoreline platforms are present, particularly where there are well developed near-horizontal joints or bedding planes. Several are subject to breakdown by sub-aerial weathering, particularly where poorly consolidated sandstone provides the local substrate.
Erosion is most active and rapid on sandstones, conglomerates and breccias, as evidenced by cave formation (e.g. Corbyn's, Livermead and Hollicombe Heads see Photo 9). Some cliff segments are protected by concrete walls (east Livermead and Corbyn's heads) or a rock revetment (Holliconme Bay), but most sections remain free to erode and there is an active blowhole in the grounds of the Livermead House Hotel. Harwood (1983) estimated a current mean rate of sandstone cliff recession of 0.15ma-1 at Hollicombe Head (Photo 9) based on weekly re-measurement of the exposure of monumented erosion pins placed on the cliff face, between October 1981 and April 1982. This study demonstrated that recession rates are spatially variable, depending on (i) aspect-related exposure to weathering above the wave-trimmed cliff base; (ii) microscale variations in rock resistance; and (iii) cliff height. At one site, a rate of cliff face retreat of between 75 and 100mma-1 appeared to be largely controlled by perennial overland flow fed by groundwater seepage.
Landslide and rock failures have been noted at several sites (Doornkamp, 1988). Occasional rockfalls have been recorded at most of the prominent sandstone/breccia headlands south of Corbyn's Head and on the cliffs south of Goodrington Sands. They are also known from some Devonian Limestone locations, e.g. Daddyhole Cove see Photo 10 (Kalaugher and Grainger, 1991), Fishcombe Point and close to Berry Head. The Meadfoot slates and grits also generate infrequent falls, one example occurring north of Saltern Cove. The slates and mudstones within Saltern Cove are also prone to this type of cliff failure, which is partially independent of wave-induced cliff erosion. Doornkamp (1988) has mapped over 80 different translational slides, both rock and debris slides around the bay, though most are not currently active. Deeper-seated rectilinear slides are also known from their diagnostic morphology and associated debris. There are examples between Hollicombe Head and Elberry Cove, mostly developed in the Oddicombe Breccia. In most cases, slides also detach head deposits overlying bedrock. This includes soliflucted material, overlain by silty loess.
Some of these slope failures may be long established, even possibly recently reactivated, features. Many, however, have been inactive over the past 50-70 years. There is a good possibility that there are several relict or 'fossil' failure surfaces inherited from previous (Pleistocene) morphoclimatic conditions.
A distinctive process that adds morphological variety to the Devonian Limestone cliffline is hydraulic erosion by waves of originally solution weathered caves. There are several around the Hope's Nose peninsula and on Berry Head. Features such as the London Bridge arch, Torquay, may be partly due to original solutional widening of joint planes. Several small caves between the Brixham breakwater and Shoalstone Point are regarded by Perkins (1971) as sites of original solutional pits, possibly opened up by roof collapse. There have been no systematic or site-specific studies of rates of cliff erosion for any sector of this coastline, with the apparently singular exception of that by Harwood (1983). An very broad historical rate of cliff top recession of between 0.3 and 3.0ma-1 for this entire length of cliffed coastline is proposed by Posford Duvivier (1998). This source suggests that long-term rates not exceeding 0.3ma-1 are characteristic of nearly 70% of the cliffline, with some sectors apparently stable in position over the past 100 years. No specific details of areas of higher rates are given, although they are likely to coincide with sites with a history of falls or slides, as detailed above. Potential rates of retreat are greatly reduced where there are seawalls and other protection structures, with toe stabilisation inhibiting the undermining that leads to falls and slides. These structures also reduce potential sediment input into the littoral transport system.
3. LITTORAL TRANSPORT - References Map LT1
LT1 Northward Transport within Pocket Beaches
Because of low wave energy along much of this shoreline and a prevailing wave approach from normal to shoreline orientation, rates of littoral drift are weak. There are several sectors where it is difficult to identify any net movement direction, but slight northwards directed pathways are apparent within most of the pocket beaches from sediment accumulations against the infrequent structures and harbour breakwaters that interrupt them. The weak nature of longshore transport is indicated by only very limited sediment accumulations against the updrift, southern sides of headlands. There are, no measurements or estimates measurements of drift rates at all within this unit. Both Hope's Nose and Berry Head are considered to be absolute boundaries to bedload longshore transport.
4. BEACH CHARACTERISTICS - References MapBeaches are composed predominantly of reddish pink sand, with some coarser material adjacent to headlands, and are confined to small bays and "pocket" coves contained by coastal salients. Input is presumed to derive from local cliff weathering and erosion, and from updrift when headlands are occasionally by-passed. The possibility of some net input from offshore is implied by Merefield (1984), who stated that 7% of the volume of Goodrington Sands was composed of carbonate material. This was all broken shell debris, and could only have derived from the nearshore or offshore seabed. However, abrasion and solution ensure this source has a short residence time, and its resupply is seasonal.
Several of the larger beaches have a postulated barrier origin (see Section 1.1), and have now been built over. Many are backed by seawalls and revetments, which prevent landward migration. Most beaches, such as Goodrington Sands, are trapped by enclosing headlands and appear to be effectively closed transport sub-cells. Cross-shore transport is a function of incident waves; beach volumes deplete and profiles flatten in response to higher energy waves, from the north-east, east or south-east (Posford Duvivier, 1998). They subsequently recover, usually at a slower rate, when modified swell waves from the south and south-west operate. These fluctuations are seasonal, with little apparent long-term change. In the absence of data from beach monitoring, it is currently difficult to add any further observations on beach morphodynamics. Visual evidence, such as the presence of some gravel in coves between Brixham and Broad Sands, at Livermead and immediately east of Corbyn's Head, but with finer more silty sediments at Paignton, Broad Sands and Goodrington Sands (Doornkamp, 1988) indicates scope for research into the sorting and provenance of beach material. Transfer of local accumulations of boulders, gravel and cobbles in coves and beaches (e.g. Meadfoot, Torquay) along the Devonian Limestone cliffs to the beaches of central Tor Bay seems inherently unlikely. Thus, the presence of isolated gravel beach berms is more probably related to nearshore outcrops of Permian conglomerate and breccia at these sites.
Significant foreshore depletion of Torre Abbey Sands occurred between about 1920 and 1960 (Perkins, 1971), although it has been stable since then. The result has been the complete loss of any remaining beach at high tide at this amenity location The reason for this behaviour is uncertain, as it post-dates the cessation of beach mining known to have occurred at several Tor Bay sites during the second part of the nineteenth century.
Some of the land behind the Broad Sands Goodrington Sands, Paignton and Torre Abbey beaches has been reclaimed from marshland and a lagoon still remains behind Goodrington Sands (Photo 6). As a consequence, these frontages may be susceptible to subsidence due to (i) uneven partially compacted fill materials used and (ii) compression of soft estuarine and freshwater marsh sediments. Problems of subsidence have been clearly identified affecting Princess Gardens immediately behind Torquay Harbour and a need for remedial actions has been highlighted (Bolitho, 2003). Due to their low-lying nature hard defences that prevent beach profile adaptation by landward migration protect these reclaimed areas. This could result in some narrowing and steepening of the beaches by 'coastal squeeze.'
5. SUMMARY - References MapThis appears to be a self-contained unit characterised by relatively slow rates of sediment flux and shoreline change. The following issues are significant:
6. COASTAL DEFENCE AND HABITAT INTERFACE ISSUES - References MapThe main habitats present include vegetated sea cliffs and rocky foreshores, which are relatively unaffected by the existing arrangement of defences. Due to their proximity to urban areas, good access and the high coastal amenity, there could be opportunities for interpretation and educational projects focusing upon the ecology of the rocky shores.
7. OPPORTUNITIES FOR CALCULATION AND TESTING OF LITTORAL DRIFT VOLUMES - References MapThe discontinuous nature of the shoreline of this unit with its numerous headlands, nearshore reefs, boulder aprons and pocket beaches means that it is unsuited for definitive studies of drift. There are, however, opportunities to study drift occurring on the major pocket beaches e.g. Broad Sands, Goodrington Sands, Paignton and Torre Sands where each bay would appear to operate as a relatively closed system for sand and gravel. A possible approach would be to compare the sediment accretion/depletion (based on profile measurements) against confining headlands within each bay with estimates of transport derived from modelling based on hindcast waves. Potentially, a beach plan shape model could be set up to simulate the beach responses to SW and SE waves that would tend to cause significant beach re-orientations within the confined bays. It should also be understood that the bays are swash-aligned so that cross-shore transport could predominate over longshore transport.
8. KNOWLEDGE LIMITATIONS AND MONITORING REQUIREMENTS - References MapMuch of the preceding account is based on descriptive statements in the very limited literature, together with field knowledge. There are no quantitative estimates of sediment yield from cliff or platform erosion, nor is there any monitoring data of beach behaviour. Such information will, in future, be required for effective beach management, especially in light of the very high amenity values of the beaches. Given the combination of future sea-level rise, climate change (including wave climate) and the apparent absence of more than minimal fresh sediment inputs, it would be advisable to consider the following:
9. REFERENCES - References MapBOLITHO, J. (2003) Sinking garden shock. Herald Express, page 1.
DOORNKAMP J C (Ed) (1988) Applied Earth Science Background: Torbay, Geomorphological Services Ltd. Report to the Department of the Environment, 109pp and 10 maps.
HALCROW, (2002) Futurecoast: research project to improve the understanding of coastal evolution over the next century for the open coastline of England and Wales. Report and CD-ROM produced by Halcrow-led consortium for DEFRA.
HALCROW MARITIME, UNIVERSITY OF PORTSMOUTH and the METEOROLOGICAL OFFICE (2001) Preparing for the Impacts of Climate Change. Report to SCOPAC, 110pp.
HARWOOD L N (1983) Observations Made Regarding Cliff Erosion at Hollicombe Head, Torbay, Reports and Transactions of Devonshire Association for the Advancement of Science, 115, 71-78.
JUKES-BROWNE A J (1911) The Making of Torbay, Reports and Transactions of Devonshire Association for the Advancement of Science, 39, 103-136.
KALAUGHER P G and GRAINGER P (1991) The influence of changes in sea level on coastal cliff instability in Devon, in: Forster A, et al. (Eds) Quaternary Engineering Geology, Geological Society (London), Engineering Geology Special Publication No. 7, 361-367.
LEE, E. and CLARK A. (2002) Investigation and Management of Soft Rock Cliffs. Report to DEFRA, Tunbridge Wells: Thomas Telford, 382p.
LLOYD W (1933, 2nd Edition) Geology of the Country Around Torquay, London: HMSO. Geological Survey of Great Britain.
MOTTERSHEAD D N, GILBERTSON D D and KEEN D H (1987) The Raised Beaches and Shore Platforms of Tor Bay: A Re-Evaluation, Proceedings of Geologists' Association, 98(3), 241-257.
PERKINS J W (1971) Geology Explained in South and East Devon, Newton Abbot: David and Charles, 192pp.
POSFORD DUVIVIER (1998) Lyme Bay and South Devon Shoreline Management Plan, 3 Volumes. Report to Lyme Bay and South Devon Coastal Group.
PROCTOR, C J and SMART P L (1991) A Dated Cave Sediment Record of Pleistocene Transgressions on Berry Head, Southwest England, Journal of Quaternary Science, 6, 233-244.
RENDEL GEOTECHNICS (1998). The Investigation and Management of Soft Rock Cliffs in England and Wales. Report to Ministry of Agriculture Fisheries and Food. 236p.
MMIV © SCOPAC Sediment Transport Study - Berry Head to Hope's Nose