About the Study

SCOPAC Committee

Chairperson Councillor Mrs M Penfold MBE, West Dorset District Council.

Vice-Chair Councillor Jackie Branson, Havant Borough Council.

Technical assistance provided to Councillors by Mr Lyall Cairns (Southern Coastal Group Chair) and Dr Samantha Cope (SCOPAC Research Chair).

The STS 2012 update

The 2012 update of the SCOPAC Sediment Transport Study (STS) was funded by the Environment Agency under FDGiA, grant number LDW 41230, with additional contributions from SCOPAC.  

It is referenced as: New Forest District Council (2017). 2012 Update of Carter, D., Bray, M., & Hooke, J., 2004 SCOPAC Sediment Transport Study, www.scopac.org.uk/sts.

Sediment Transport Study 2012

North West Isle of Wight

The Needles to East Cowes

1. Introduction

The north-west coast of the Isle of Wight forms the southern margin of the West Solent, with which it has evolved contemporaneously. The West Solent occupies part of the valley of a formerly more extensive Pleistocene river system, the Solent River, which has experienced a complex history of change (refer to separate text on Quaternary History of the Solent for full details). Three critical stages can be recognised in the evolution of the West Solent seaway, namely:

1. Breaching of the Chalk ridge previously existing between the Needles (Photo 1) and Handfast Point (Isle of Purbeck) (Everard, 1954). Subsequent rapid marine erosion of soft Tertiary strata in the early to mid-Holocene created Christchurch Bay as a result of rapid sea-level rise. This in turn allowed refraction of dominant southwest waves around remnants of the protective ridge to attack the northwest coast of the Isle of Wight. Infilled palaeovalleys south of the eastern sector of the Chalk ridge fail to breach this feature, suggesting that fluvial denudation did not initially play a significant role in admitting the ingress of marine conditions at this point (Velegrakis, et al., 1999).
2. Linkage between the Western Solent and Christchurch Bay was probably initiated between 8,000 and 7,500 years BP (Nicholls and Webber, 1987; Dean, 1995; Velegrakis, et al., 1999; 2000). This interpretation is corroborated by dating of organic horizons in Holocene sediments that accumulated in the Western Yar estuary - see Photo 2 (Devoy, 1987). The isthmus of land connecting the shorelines of the northwest Isle of Wight and Hampshire may not have been finally removed until approximately 4,500 years BP. This tentative conclusion is based on evidence of submerged Mesolithic trackways and other archaeological features indicating human occupation at this time in the vicinities between Newtown and Yarmouth (Tomalin, 2000). Momber (2000a, 2002b) has given a description of a submerged cliffline, approximately 500m offshore the present coastline at Bouldnor, with a base between -11.2 and -11.4mOD. It truncates three peat horizons, interbedded between silty clays, that record relative sea-level fluctuations between approximately 6,000 and 4,500 years B.P. Dating has been determined by radiocarbon 14 (see separate text on Quaternary History of the Solent).
3. Eastward littoral drift of coarse sediments in Christchurch Bay created Hurst Spit, a transgressive coarse clastic barrier spit built on a basement of late Pleistocene gravel terraces and extending south-east from the mainland (Nicholls, 1987; Nicholls and Webber 1987). This spit has several effects on hydraulic conditions in the Western Solent. It provides shelter from dominant southwest waves and its progressive growth has constricted the channel at Hurst Narrows, thus deflecting tidal currents towards the northwest Wight coast (Brampton, et al., 1998). Coarse sediment is lost from the distal part of the spit and is transported offshore by high velocity dominant ebb currents to feed the Shingles Bank (Nicholls and Webber, 1987; Velegrakis and Collins, 1992). This bank interferes with west and south-west waves approaching the open northwest Wight coast between the Needles and Fort Albert, and thus provides an additional element of dampening of the wave regime.

Between Alum Bay (Photo 3) and Fort Albert, Cliff End (Photo 4), the coast is exposed both to tidal currents and modified open sea, including swell waves. Maximum significant wave heights of up to 2.36m (Webber, 1969; Posford Duvivier, 1990, 2000; HR Wallingford, 1999) might occur at a 1 in 50 to 1 in 100 year frequency south of Fort Albert. Between Fort Albert and Cowes, the coast is sheltered from the open sea and incident waves generated in the West Solent are fetch-limited and generally are less than 1m in height. However, exceptional storm and tidal surge events, such as occurred in March 2008, can raise water levels in excess of 1m above those predicted (Yarmouth Coastal Defence Working Group, 2010). Dyer (1971) has shown that ebb and flood tidal streams have sinuous courses in the West Solent; thus the relative effectiveness of tidal currents varies spatially, with strongest flows adjacent to meander bends. Full details of the hydraulic regime of the main channel are given in the Unit Report covering the West Solent mainland. Locally strong currents are generated by exchange of tidal waters at the mouths of the Western Yar, Newtown Harbour and Medina Estuaries.

In conjunction with these spatially variable hydraulic influences, the major factors influencing coastal morphology are geology and topography (Royal Haskoning, 2010). The narrow Chalk ridge exposed along the south of Alum Bay is relatively resistant to erosion and forms high cliffs, rising to 100m (Photo 5). The remainder of the coast comprises Tertiary (Eocene and Oligocene) strata, a sequence of poorly consolidated sands, silts and clays interbedded with thin and mostly soft limestones. Strata immediately succeeding the Chalk to the north dip almost vertically so that the Reading Clay and Thames Group formations have extremely limited outcrops in Alum Bay. Younger Palaeogene strata dip more gently towards the northeast and these comprise the main geological formations outcropping on this coast between Headon Hill and Old Castle Point. The coastal topography is undulating with high points at Headon Hill (120m - see Photo 3), Bouldnor Cliff (61m - see Photo 6), Burnt Wood (57m) and Gurnard Cliff (45m - see Photo 7). Small estuaries are developed in former tributaries of the Solent River that have been inundated by the Holocene transgression. These comprise the Western Yar (Photo 2), Newtown Harbour (Photo 8) and the Medina, all of which have sediment – filled palaeovalleys between 14 and 22m in depth. Other minor tributaries have been truncated by post mid-Holocene recession of the coast and form short, steep gradient coastal valleys e.g. Alum, Brambles and Widdick Chines, or the marshy valleys of the Gurnard and Thorness streams (Photo 9). The latter have been partly blocked, or deflected, by the eastward growth of small gravel spits.

The combination of relatively non-resistant rock material and a spatially varied exposure to waves and currents has resulted in the formation of a predominantly eroding coastline characterised at several locations by well-developed cliffs and landslides. Headlands occur on more resistant strata that also outcrop on the foreshore to form protective ledges or platforms. In places the prominence of headlands has been accentuated by nineteenth century construction of forts and associated coast protection structures e.g. Fort Victoria, Fort Albert and Warden Point (Photo 10) (McInnes, 2008). The shoreline exhibits a varied and complex sediment transport pattern due to both coastal configuration and hydraulic regime. Transport sub-cells on the open coast are separated by headlands, and each of the three estuaries has distinct, albeit small scale, circulation patterns (Halcrow, 1997).

A major new source of coastal data is from the Defra-funded National Network of Regional Coastal Monitoring Programmes.  The Programmes consist of topographic beach surveys, nearshore bathymetry, aerial photography, lidar, coastal hydrodynamics (waves and tides) and terrestrial habitat mapping. Specifications for data collection are consistent for all regional programmes and the data and analysis reports are made freely available under the Open Government Licence from www.channelcoast.org. 

The Southeast Regional Coastal Monitoring Programme commenced in 2002. The Lead Authority is New Forest District Council, with data collection, analysis and reporting led by specialist teams at the Channel Coastal Observatory (CCO), Canterbury City Council and Adur and Worthing Councils. (See CCO Annual Survey Reports for further details).

Three high resolution, 100% coverage swath bathymetry surveys were commissioned by the Southeast Regional Coastal Monitoring Programme. The nearshore zone of Christchurch Bay (completed 2010) and the northern coast of the Isle of Wight (completed 2011), extending 1km offshore from the MLW, and an extensive area extending between Lee-on-the-Solent and Selsey Bill and offshore to abut with the northeast Isle of Wight survey boundary, between Cowes and Bembridge, was completed in 2013.

2. Sediment Inputs

Analysis of Coastal Monitoring Programme 2008 to 2012 lidar and aerial photography datasets and 2003 and 2012 topographic baseline survey data, combined with other datasets, academic research and historical studies has enabled sediment budgets, transport rates and directions to be identified or verified.

2.1 Marine Inputs

» F1 · F2 · F3 · F4  

F1 Coarse Input at Hurst Narrows

Analysis and seabed mapping interpretation of a combination of extensive high resolution, 100% coverage swath bathymetry surveys of Christchurch Bay (2010) and the northern shore of the Isle of Wight (2011) collected through the Southeast Regional Coastal Monitoring Programme, indicate that coarse and mixed sediments are evident on the immediate fringe of Hurst Spit, south of the Castle to Hurst Point. A combination of high wave energy and a storm surge from the south-west coincident with peak flood tide velocities can be sufficient to transport pulses of coarse sediment into the West Solent against the prevailing net transport direction. This would certainly explain the growth of recurves and the extension of Hurst Point, although further lateral growth of the spit may be limited. Distal recurvature is the product of waves generated over local fetches, and refracted swell waves. Neither would have sufficient energy to move coarse sediment into the West Solent channel. (Further detail on the morphodynamics of Hurst Spit are provided in the unit on Christchurch Bay).

A series of three 10-20m high, steep angled, sub-marine terraces are located in 25-60m water depths between Fort Victoria and Hurst Point (Photo 15), associated with the formation of the Solent and the former position of the Solent River. These large-scale features restrict or inhibit bedload transport into the West Solent from Christchurch Bay, even under extreme hydrodynamic and tidal conditions. Examination of tidal curves for Lymington, Yarmouth (Isle of Wight) and Totland reveal marked asymmetry, because the ebb flow is concentrated into a shorter time period than the flood (Webber, 1980). The ebb flow is therefore considerably more rapid than the flood and transport of coarse bedload sediments (sand and gravel) is therefore likely to be parallel to the shoreline between Fort Albert and the Needles, determined by peak current velocities. The nearshore bathymetry in the Hurst Narrows channel indicates a scoured bedrock bed.

Studies of the Pot Bank dredging area by Hydraulics Research (1977) identified significant coarse sediment circulation from Hurst Narrows offshore to feed Shingles Bank and Dolphin Sand in Christchurch Bay and, to a lesser extent, Pot Bank. Although much of the analysis, involving comparison of successive editions of Admiralty hydrographic charts, concentrated on Pot Bank (located south-west of the Needles) it was concluded that sediments from this offshore directed pathway from Hurst Narrows did not directly feed the beaches of the north-west Wight coast. Evidence is not conclusive because sediment throughputs may occur with no net alteration in seabed levels. Coastal Monitoring Programme data indicates that the beaches in Alum, Colwell and Totland Bays are generally stable. A study of the potential effect on beach morphology of dredging of the Shingles Bank (Bradbury, et al., 2003) did not identify any onshore supply of sediments to these beaches, although it did highlight the important function of the Shingles Bank in providing shelter against waves approaching from the west.

F2 Suspended Sediment Input at Hurst Narrows

Aerial photography collected in 2013 through the Coastal Monitoring Programme and observations confirm the transport of suspended fine-grained sediments from Hurst Spit, into the West Solent. Thus, it is likely that fine marine sediments and suspended clay sediments derived from cliff erosion of the west Isle of Wight and Christchurch Bay coasts become drawn into the West Solent. Remote sensing studies of suspended sediments within Christchurch Bay and the Western Solent support these conclusions (Strisaenthong, 1982; McFarlane, 1984).

F3 Onshore Transport to Newtown Spits

Analysis and seabed mapping interpretation of Coastal Monitoring Programme swath bathymetry data of the northern nearshore zone of the Isle of Wight indicates a shallow exposed rock platform which extends for the majority of the northwest shoreline, and offshore between 1-800m. Where it is not exposed, it is covered in a relatively thin veneer of sediments, suggesting a limited or a lack of sediment is available. Groundtruthing indicates sediments include coarse, mixed sand and clay. The sediment along the platform transitions from coarse sediment between The Needles and Fort Albert to finer sediments further east, and mud to the east of Newtown Creek. Offshore of the platform, bedforms are ubiquitous along the deeper, wider channels of the West Solent. The symmetrical or slightly asymmetric bedforms indicate bed current directions and velocities consistent with tidal movements in the West Solent. Surficial seabed sediment within the West Solent is transported in separate ebb and flood pathways (Dyer, 1980) so these inputs are not immediately moved back offshore by subsequent ebb tidal currents.

Twin gravel spits flank Newtown Harbour entrance (Photo 8) and comparison of a time series of both OS maps and Admiralty hydrographic charts revealed significant changes in morphology, as well as shoreline retreat, over the period 1879-1951. The sediment source for periods of spit growth was attributed to net onshore supply, involving complex sediment circulation between Solent Bank, Newtown Gravel Banks and Newtown Spits (Hydraulics Research, 1977). However, onshore transport and/or exchanges of sediment between Solent Bank, inshore gravel banks and onshore spits is not evident from analysis of Coastal Monitoring Programme bathymetry data. Possible transport mechanisms and pathways are poorly understood because a phase of spit recession between 1914-1951 occurred at the same time as major growth of Solent Bank. Significantly increased bed levels over Newtown Gravel Beds between 1963 and 1973 accompanied diminution of the size of Solent Bank (Hydraulics Research, 1977).

F4 Suspended Sediment within the West Solent Channel

Tidal regimes at the mouths of estuaries and inlets in the West Solent are characterised by a rapid short duration ebb current and a more pronged lower velocity flood (MacMillan, 1955, 1956; Webber 1969, 1980; Price and Townend, 2000). This regime favours net input of suspended sediments into inlets, so that tributary estuaries and creeks flanking the West Solent are subject to progressive infilling and are flanked by mudflats and accreting saltmarshes (Photo 2 and Photo 8).

Analysis and seabed mapping interpretation of Coastal Monitoring Programme swath bathymetry data of the northern nearshore zone of the Isle of Wight indicates a shallow exposed rock platform which extends for the majority of the northwest shoreline, and offshore between 1-800m. A thin veneer of fine-grained sediments and mud to the east of Newtown Creek suggest that sediment deriving from erosion of the local soft clay cliffs of the northwest Isle of Wight coast is also likely to contribute suspended sediments to the channel. Much of the lower foreshore between Newtown Harbour and Egypt Point comprises fine muds (Posford Duvivier, 1999).

A sequence of dominantly fine-grained estuarine sediments, up to 14m thick contained within a well-defined palaeovalley, has been described for the western Yar estuary (Devoy, 1987; Tomalin, 2000) representing pulsed (unsteady) sediment input over the past 7000 years of sea-level transgression. This may have a marine source, but no mineralogical analysis has been undertaken to confirm this. Dredging at 4,000m³ per year is required to maintain the approaches to Newport Harbour on the Medina estuary, which strongly suggests that suspended sediment input remains a contemporary process (The Harbour Master, Newport, 1991). Dredging has also been undertaken in response to slow but progressive siltation in Yarmouth Harbour (MacMillan, 1955; Western Yar Liaison Committee, 1998), although in this case the tidal prism, which has been reduced by piecemeal land claim since medieval times, provides a possible explanation (Pethick, 1999).

2.2 Fluvial Input

FL2 Fluvial Input to the Western Yar, Newtown Harbour and Medina Estuaries

Rivers on the Isle of Wight are small due to limited catchments and therefore contribute negligible sediment to the coast. Rendel Geotechnics and the University of Portsmouth (1996) estimate that all of the rivers discharging sediment to this coastline potentially contribute together some 2,450 tonnes per year of suspended load and 740 tonnes per year of bedload material. However, various barriers and regulation of flows reduce the delivery volume very substantially. The River Medina has a mean flow of 0.5m³s-¹ and this comprises only 0.67% of the tidal volume entering at the mouth during a corresponding tidal period (Webber, 1978). Thus, marine sediment input to estuarine mudflats and saltmarshes must be the dominant source of supply and fluvial sources are considered to be insignificant. Several small coastal streams, e.g. Gurnard and Thorness, have been partially or wholly infilled behind spits that have grown across their mouths. It is not clear if this represents marine or river-derived sediment. If present day spits are the product of breaching of medieval or earlier barriers then there could have been a significant earlier phase of trapping of fluvial sediment (Tubbs, 1999). Conversely, it could be that spits grow across inlets when marine infilling has reduced the flushing effect of their tidal exchange.

2.3 Coastal Erosion

» E5 · E6 · E7 · E8 · E9 · E10 · E11 · E12

Much of the northwest Wight coast is subject to active erosion, but its morphology varies spatially from simple high-angle cliffs, as at Colwell Bay, to compound slopes with multiple scarps and intervening degradation zones, e.g. Headon Hill (Bird, 1997). This is principally related to the mechanisms of mass movement and slope failure. A coastal landslide can be regarded as a transfer of sediment from an area of elevated topography to the foreshore. Slope instability and a semi-continuous sediment cascade is maintained by basal erosion (e.g. Photo 11) which can act in two ways: (i) degraded materials are removed from the base of the slope, which prevents a stable slope angle being achieved; (ii) basal erosion of in-situ strata can undercut the cliff toe so that the slope is steepened to a greater repose angle than would naturally be maintained by the ground-forming materials. From a coastal viewpoint the result is the same, in that sediment is supplied to the littoral zone, and, assuming it is removed thereafter, the coast retreats.

Overall, the longer-term retreat of this cliffed coastline has widened the West Solent estuarine channel and contributed a substantial input of fine sediment to its tributary estuaries. It is probable that much of the finer grained sediment stored in the West Solent itself comes from the same source. The type and rate of coastal slope retreat is controlled by the geology and hydrogeology of outcropping strata, and antecedent topography (height of the coastal slope), thus promoting slope failure through various slide and slip mechanisms (Hutchinson and Bromhead, 2002). All these factors vary spatially, so rates of retreat and volumes and grades of sediment input are also non-constant. Reports of past coastal erosion and landsliding reveal similar rates of activity and landform development to the present day situation (Norman, 1887; White, 1921; Colenutt, 1938; Moorman, 1939; McInnes, 2008). Thus, it is likely that this coast has retreated throughout much of the late-Holocene period following the establishment of interconnection between the West Solent and Christchurch Bay. Evidence of this is provided by recognition of an ancient landslide deposit, extending up to 100m offshore, from a foreshore lobe of boulders off Brickfield Farm (Munt and Burke, 1987).

Spatial variation in sediment yield from eroding cliffs is also, in part, a function of the contrast in hydraulic regime east and west of Fort Albert. To the east, dominant waves are fetch-limited, whilst westwards the more open coast receives attenuated and refracted swell as well as locally propagated waves. H.R. Wallingford (1999) undertook numerical modelling of modified swell waves for Totland Bay, using HINDWAVE applied to synthetic data. For an annual return period, Hs (mean) was computed to be between 0.22 and 1.71m, depending on wave approach. For a 1 in 10 year frequency values are between 0.33 and 2.05m.

The Coastal Monitoring Programme measures nearshore waves using a network of Datawell Directional Waverider buoys. The nearest measurement stations to this cell are at Milford-on-Sea and Hayling Island. The buoy deployed at Milford-on-Sea is in 10mCD water depth. Between 1996 and 2012 the prevailing wave direction was from the southest-by-south, with an average 10% significant wave height exceedance of 1.31m (CCO, 2012).

E5 Chalk Cliffs at Alum Bay (see introduction to coastal erosion)

These cliffs (Photo 5) comprise the northern face of the Chalk ridge, which terminates at the Needles. The Chalk is significantly more resistant than other geological units outcropping further northeast having been “hardened” by tectonic forces but is nevertheless subject to erosion, albeit at slow mean rates in the order of 0.1 to 0.3 m per year (May, 1966; Halcrow, 1997; Posford Duvivier, 1999). The Needles stacks have been isolated by the assailing forces of breaking waves exploiting near vertical joint and other fracture planes. It should be noted that recession is episodic with major cliff falls and intervening periods of little activity. Erosion takes place by basal undercutting followed by periodic localised falls that generate temporary accumulations of scree at the cliff toe. The cliff face then retreats slowly by sub-aerial processes until marine erosion removes the debris at the toe and another cycle of undercutting can begin. Several large falls have occurred in recent decades causing subsequent localised recession of up to 10m (Photo 5).

The significance of the Chalk is that it contains in situ flint nodule bands, which are released as angular gravels that become abraded to form beach pebbles. However due to the short frontage and modest retreat rate the overall supply is quite small. An estimated shoreface erosion rate of 3mm per year, combined with the above recession value, would yield approximately 100m³ per year of coarse flint debris (Posford Duvivier, 1999). The Coastal Monitoring Programme data indicates cliff erosion and falls are episodic and occasionally of significant scale, but is unable to quantify the proportion of flint gravel to the beach in Alum Bay, although it is estimated to be significantly less than 1,000m³ per year.

E6 Alum Bay and Headon Hill (see introduction to coastal erosion)

In the south of Alum Bay, Reading Beds and London Clay (Thames Group) dip steeply (75 degrees to 85 degrees), but the outcrops of the Bracklesham and Barton Groups are wider because of a rapid reduction in dip angles as the Isle of Wight monocline fold levels out northwards. All strata in Alum Bay are easily eroded, comprising clays, sandstones and occasional grit and pebble horizons. The near vertically inclined strata in the south of the bay are primarily sandy and form relatively steep simple cliffs that fail by rockfall. Exceptions are the Reading and London Clay outcrops immediately north of the Chalk where mudslides and slumps have created a less steep, but dynamic coastal slope. These materials are supplied to the foreshore by cliff falls, flows and mudslides (Hutchinson, 1965; Hydraulics Research, 1977) and gulleying (Gifford and Partners, 1994). Northwards, alternating sands clays and limestones form units of differing resistance and permeability generating deeper seated landslides and giving rise to a wide degradation zone incorporating benches and scarps towards and around Hatherwood Point on the western flanks of Headon Hill. Headon Hill rises to 120m and is underlain by Oligocene age Headon Beds, Osborne Beds, Bembridge Limestone, Bembridge Marls and a thin cap of Pleistocene Plateau Gravels. The varying resistance and permeability of these strata have led to the development of a complex coastal slope, with mudsliding over a series of partially concealed scarps and both translational and deep seated failures, especially towards the cliff top (Hutchinson, 1965, 1983, Hutchinson and Bromhead, 2002). The cliff top and toe environments are partially "decoupled" by the interposition of the degradation zone.

A wide range of sediment grades is supplied to the shore by these processes. Little quantitative work has been undertaken, but analysis of the lithology of Headon Beds yielded a composition of 20% sand, 20% limestone and 60% clay (Lewis and Duvivier, 1973). The other beds are predominantly clays and sands with a major limestone unit and small quantities of gravel from the superficial drift deposits. The limestones are of significance for they break down into joint-controlled boulders and thus provide some protection to the toe of the coastal slope (Hydraulics Research, 1977). Map comparisons covering the period 1868-1963 revealed long-term cliff retreat at Alum Bay and Headon Hill of between 0.2-0.5m per year (May, 1966). Corresponding estimates by Halcrow (1997) for 1909-95 are 0.24m per year for Alum Bay and 0.69m per year for Headon Hill. Posford Duvivier (1997; 1999) give a rate of between 0.35 and 1.1m per year for the sector between Widdick and Alum Bay Chines. Total erosion yield is calculated at 110,000m³ per year of which 22,500m³ per year is estimated to be sand, gravel and limestone boulders. It should be noted that the value for coarse materials is not based on field sampling and is rather uncertain, although 500m³ per year is estimated for flint gravel from superficial deposits that cap the hill. Analysis of Coastal Monitoring Programme indicates that the cliff erosion within Alum Bay yielded significantly less than 1,000m³ per year of shingle or sand grade beach material, as the potential availability of these materials in the cliffs is limited. The vast majority of the fine sands, silts and clays are transported offshore in suspension.

E7 Totland and Colwell Bays (see introduction to coastal erosion)

Totland Bay has historically been subject to basal and cliff-top erosion at mean rates of 0.1-0.3m per year (May, 1966) and a maximum of 0.56m per year was recorded for the period 1907-1961 (Lewis and Duvivier, 1962). Historical map comparisons by Halcrow (1997) indicate a long-term mean of 0.38m per year for the period 1909-1961 immediately preceding sea wall construction. A series of cliff falls induced by toe erosion in 1960-61 led subsequently to sea wall protection of the cliff base throughout the bay from Widdick Chine around Warden Point to Colwell Chine. Installation of cliff drainage at selected points to prevent or reduce future cliff top instability has been in progress since 1925, with further comprehensive cliff stabilisation in 1998 (Lewis and Duvivier, 1973; Posford Duvivier, 1989, 1991, 1993; HR Wallingford, 1999, Royal Haskoning, 2010). It should be noted that significant instability continues within some cliff sections and results in occasional extension of debris lobes across the esplanade e.g. winter of 2000/01. A significant landslide at Warden Point in the northern sector of Totland Bay occurred during winter 2012/spring 2013, and resulted in approximately 25m lateral (seaward) displacement of the seawall, promenade, toe protection and foreshore. The volume of silts and mud introduced to the nearshore from the 2012/13 landslide was in the order of 1-3,000m³ per year, however the volume of shingle or sand grade beach material is unquantified but considered to be extremely low.

The southwest part of Colwell Bay has been fully protected by a seawall since 1993. The Headon and Osborne Beds, which form the cliffline in the remainder of the bay, are subject to active erosion at their toes. The geological units of the cliffs comprise gently northward dipping sands and clays with occasional soft limestones, which promote seepage erosion and landsliding. In the south, cliff profiles are regraded and vegetated, but north of Linstone Chine simple steep eroding profiles are characteristic, with a tendency for increased landsliding and wider degradation zones towards Fort Albert. Cliff morphology may follow a cyclic pattern of response to marine undercutting of the toe that results in cliff failure. Marine processes must then excavate protective basal debris produced by failures before another cycle of toe undercutting and cliff failure can begin. Rising topography and increasingly clayey lithological units of the Cliff End Member of the Headon Hill formation complicate conditions towards Fort Albert, where slumps and shallow slides are active processes.

A variety of estimates are available for the mean long-term (100-120 year) recession rate: 0.3-0.6m per year (Hutchinson, 1965), up to 0.45m per year (Hydraulics Research, 1977), 0.10-0.60m per year (Lewis and Duvivier, 1962; 1981), 0.5m per year (Lewis and Duvivier, 1986; Posford Duvivier, 1989), 0.6m per year (Barrett, 1985) and 1m per year for cliff top retreat (McInnes, 1994). Historical map comparisons by Halcrow (1997) indicate a long-term mean of 0.32m per year in southern Colwell Bay for the period 1866-1975 covering the period prior to full protection. A mean of 0.52m per year is indicated for the central bay (1909-1975) with 0.93m per year for the section at Fort Albert.

Differences are due to measurement accuracies and the various time periods covered by map analysis, but all indicate consistent long-term retreat. Recent erosion rates suggest faster than average recession in the Brambles Chine area and especially towards Fort Albert (Posford Duvivier, 1991). Retreat between 0.5 and 1.0m per year was recorded for the period 1970-85 (McInnes, 1994; Posford Duvivier, 1997) and maximum short-term retreat of the cliff-top was recorded at 1-2m per year (Lewis and Duvivier, 1986; Posford Duvivier 1989, 1991). The fine sands and clays yielded have little stability on the beach and much of the estimated cliff erosion input (approximately 5,000m³ per year) is rapidly lost offshore (Posford Duvivier, 1999). An additional shoreface erosion rate of 17mm per year, yielding 7,000m³ per year of fine sediment is also proposed. Analysis of Coastal Monitoring Programme indicates the cliff-derived fine-grained sediment is not retained on the foreshore, being removed from the beach as suspended load by waves and currents. The lack of detailed study information regarding cliff sediment composition and proportions of sediment grain sizes means that it has not been possible to quantify volumes of cliff input yielding shingle or sand grade beach material.

E8 Fort Albert to Fort Victoria (see introduction to coastal erosion)

This coastal sector comprises a relatively low angle coastal slope degrading primarily by mudsliding in lower parts with some upper parts thickly vegetated and relatively inactive (Hutchinson, 1965; Lewis and Duvivier, 1973; Posford Duvivier, 1990b; Halcrow, 1997). A sea wall protects the cliff toe for 200m to the northeast of Fort Albert, but there is considerable instability of the slopes behind. Along the remainder of this unit, the soft clays at the cliff toe appear to be eroded faster than the rate of supply of material from mudslides, thus some lower slopes are oversteepened and controlled by shallow failures (Halcrow, 1997). Serial map comparisons do not indicate any discernible cliff-top erosion, possibly due to the thickly vegetated and complex morphology of the upper slope (Lewis and Duvivier, 1973). Despite this, long-term toe erosion at 0.5m per year has been calculated (Lewis and Duvivier, 1981; Posford Duvivier, 1989, 1990b, 1997; Halcrow, 1997). It would appear that aggressive toe erosion is leading to progressive reactivation of relict landslides upslope, so that the scale of landsliding is likely to increase in future as the full slope becomes active.

The geology of the coastal slope is obscured by vegetation and disturbed by landsliding (McInnes, 2008) but White (1921) and geological maps indicate Headon and Osborne beds overlain by Bembridge Limestone and Marls, so cliff erosion input must be predominantly clays with some sands and soft limestones (Halcrow, 1997). Posford Duvivier (1997) estimate an annual cliff erosion yield of 5,000m³. It is reported that small quantities of gravel are also supplied (Lewis and Duvivier, 1973, 1981). This coast is more sheltered from wave erosion than areas to the west, but is swept by rapid tidal currents of Hurst Narrows so relatively little beach material accumulates. The beach shoreface between Fort Albert and Fort Victoria (as opposed to the toe of the cliffs and slopes) is some 250m long and 20m wide; given an estimated 0.5m per year erosion rate, the yield of fine sediment is approximately 7,000m³ per year (Posford Duvivier, 1999). For the shoreface between Fort Victoria and Bouldnor, the respective values may be in the order of 1mm per year and 3,000m³ per year. Analysis of Coastal Monitoring Programme indicates the cliff-derived fine-grained sediment is not retained on the foreshore, being removed from the beach as suspended load by waves and currents. The lack of detailed study information regarding cliff sediment composition and proportions of sediment grain sizes means that it has not been possible to quantify volumes of cliff input yielding shingle or sand grade beach material.

E9 Bouldnor and Hamstead Cliffs (see introduction to coastal erosion)

Between Bouldnor and Hamstead Ledge, cliffs rise to 61m at Bouldnor Cliff (Photo 6) and 35m at Hamstead Cliff. The coastal slope is underlain principally by gently northward dipping clay-rich Hamstead Beds of the Bouldnor Formation (White, 1921; Daley and Insole, 1984; Hutchinson and Bromhead, 2002). It exhibits complex morphology and degrades by deep-seated rotational slides at the backscar and by mudsliding within extensive mid and lower mudslide dominated terraces. Morphology comprises a steep upper cliff, with several embayments associated with zones of past failures feeding small mudslides. These landforms have been classified as relatively shallow, multiple translational slides (Bromhead, 1979). Mudslide movement is seasonal and controlled by precipitation, groundwater availability and enhanced porewater pressures generated by undrained loading at the head of the mudslide (Hutchinson and Bhandari, 1971; Bromhead, 1979) and seepage erosion. It has been postulated that enhanced porewater pressure has greater effect on initiating a slide than toe erosion by the marine processes which prepare the slopes (Bromhead, 1979; Hutchinson and Bromhead, 2002). This could explain the historical and present day instability and rapid mudsliding despite limited wave energy available for toe erosion. However, active undercutting of the cliff toe operates in many places (Photo 11) and mudslide instability is maintained by marine erosion of lobes as they extend seaward. There may be some linkage between deep-seated failures of the terrestrial cliffs and past erosion of the 8 to 9m high submarine cliff located between -4 and -12mOD (Hutchinson and Bromhead, 2002).

The nature of landsliding varies spatially, with a zone of highly developed and active mudslides at Bouldnor Cliff, repetitively triggering deep-seated rotational base failures to the west, and less well developed, superficial mudslides to the east. The level of relatively resistant units at the base of the Hamstead Member and the top of the Bembridge series are identified as the critical control of this variability (Halcrow, 1997). Rock dips are locally reversed by faulting so that underlying Bembridge Marls and Bembridge Limestone rise to beach level in the northeast of this sector (White, 1921). Thus, at Bouldnor Cliff this horizon lies at 1 to 3m above mean sea-level and provides optimum conditions for mudsliding. This persistent tendency for shallow mass movement has apparently increased in both magnitude and frequency of events here since the mid-1980s (Posford Duvivier, 1995). To the west the resistant horizon is not exposed and the soft clays exposed at beach level are rapidly eroded at rates in excess of mudslide supply. The coastal slope becomes oversteepened, facilitating deep-seated failures. To the east, resistant strata rise well above beach level and increase the resistance of the base of the slope to marine erosion so that recession of is less rapid and mudslides less well developed (White, 1921; Hutchinson, 1983).

Mean long-term cliff-top retreat over the period 1868-1963 was 0.61m per year (May, 1966; Posford Duvivier, 1997), but a high rate of 3m per year was recorded for a part of the Bouldnor Cliff complex over the period 1922-1962 (Hutchinson, 1965). Historical map comparisons by Halcrow (1997) indicate long-term (1909-1995) mean cliff top recession of 1.13m per year for western and central Bouldnor and 0.84m per year for Hampstead Cliff. Although, map comparisons covering the period 1908-1971 indicated locally rapid recession of mudslide lobe toes at rates of up to 1.6m per year (Webber, 1977), it appears that cliff top recession has been more rapid than recession of mean high water at the toe leading to an overall flattening of the slope profile (Halcrow, 1997).

Cliff recession yields significant sediment volumes, but much is clay and silt so only a small proportion, estimated at 15% (Bray and Hooke, 1997), of total cliff input is stable on the beach. Some gravels are supplied from Pleistocene cliff-capping coarse deposits (Hydraulics Research, 1977; Posford Duvivier, 1995; Halcrow, 1997) and Moorman, 1939) reported gravel scree beneath the steep upper cliff. Mapping and sediment sampling of the gravel outcrops has not been undertaken so exact contributions remain unquantified although they could be significant on this low drift rate coast. The erodible shoreface materials may be scoured to a depth of 0.12m per year, yielding some 23-25,000m³ per year of fine sediment (Posford Duvivier, 1999), which is transported offshore as suspended load. Analysis of Coastal Monitoring Programme indicates minimal erosion, and the cliff-derived fine-grained sediment is not retained on the foreshore, being removed from the beach as suspended load by waves and currents. The lack of detailed study information regarding cliff sediment composition and proportions of sediment grain sizes means that it has not been possible to quantify volumes of cliff input yielding shingle or sand grade beach material.

E10 Newtown Harbour to Little Thorness (see introduction to coastal erosion)

For some 2km eastward of Newtown Harbour there are steep, but low eroding cliffs with basal landslide debris and fallen trees on the beach (Hydraulics Research, 1981). Cliffs increase slightly in height eastward and landsliding rather than rockfall becomes increasingly evident as the major cliff recession process. Historical map comparisons by Halcrow (1997) indicate a long-term mean retreat rate of 0.73m per year for the period 1909-1995.

Further east, the coastal slope rises in height to 57m near Burnt Wood. At this location there is active shallow translational landsliding and transport of debris in mudslides (May, 1966; Hutchinson, 1965; Halcrow, 1997). The lower part of the coastal slope at Burnt Wood is composed of the relatively more resistant Bembridge Limestone units, while the upper slopes are composed of the clayey Hampstead Member of the Bouldnor Formation and capped by Plateau Gravels. Retreat is generally slightly less rapid than at Bouldnor to the west, perhaps due to the outcrop of the Bembridge strata at beach level (similar geological sequence as at Hampstead). Some areas of localised severe erosion were nonetheless reported by Hutchinson (1965). Mean cliff top retreat of 0.36m per year was measured from map comparisons covering the period 1868-1963 (May, 1966). Posford Duvivier (1999) propose a higher rate of 0.6m per year. Historical map comparisons by Halcrow (1997) indicate a long-term mean of 0.99m per year for the period 1909-1995. These different estimates reflect considerable spatial and temporal variation in the recession process and also some uncertainty in the exact cliff top position due to the obscuring presence of woodland and scrub.

Material supplied is predominantly clay, but a limited gravel input is also reported (Lewis and Duvivier, 1981; Halcrow, 1997). The latter is probably limited to a deposit of Pleistocene Plateau Gravel at Burnt Hill, although it may also derive from erosion of in situ Pleistocene gravel-bearing deposits on the foreshore (Lewis and Duvivier, 1981). These materials may be similar in composition and age to those recognised offshore of Brickfield Farm (Munt and Burke, 1987). Posford Duvivier estimate a total cliff erosion sediment yield of 75,000m³ per year for the sector between Newtown Harbour and central Gurnard Bay. Estimates suggest that less than 500m³ is coarse material. Mapping and sampling of the gravel outcrops has not been undertaken so exact contributions remain unquantified, although they could be significant on this low drift rate coast. A shoreface erosion rate of 12mm per year, yielding 11,000m³ per year of fine material, has been calculated by Posford Duvivier (1999). Analysis of Coastal Monitoring Programme indicates the cliff-derived fine-grained sediment is not retained on the foreshore, being removed from the beach as suspended load by waves and currents. The lack of detailed study information regarding cliff sediment composition and proportions of sediment grain sizes means that it has not been possible to quantify volumes of cliff input yielding shingle or sand grade beach material.

E11 Little Thorness to Gurnard; Thorness Bay (see introduction to coastal erosion)

The entire coast between Whippance Farm (Thorness Bay) and Gurnard displays evidence of coast erosion, with cliffs up to 45m in height, much active mudsliding and shallow translational slides that supply debris accumulations on the foreshore - see Photo 12 (Hutchinson, 1965; Hydraulics Research, 1977, 1981; May, 1966; Bird, 1997; Halcrow, 1997; Posford Duvivier, 2000; Hutchinson and Bromhead, 2002; Moore and McInnes, 2002). The landform assemblage is comparable to that at Bouldnor and Burnt Wood, but smaller in scale. Recession has been measured at 0.36m per year for the period 1868-1963 (May, 1966) and 0.6m per year, 1862-1938 (Hydraulics Research, 1977). Some basal protection afforded by Bembridge Limestone ledges at Gurnard Ledge, and to the east, results in some increased cliff stability and slower retreat rates to the northeast of the Ledge compared to the cliffs to the south. These ledges eroded by 0.6m per year to 1.2m per year over the period 1862 to 1938 which suggests that their protective capacity is limited (Hydraulics Research, 1977; Posford Duvivier, 1997; 1999). Historical map comparisons by Halcrow (1997) indicate long-term (1909-1995) mean cliff top recession of 0.48m per year for the cliffs to the south of Gurnard Ledge (Photo 12) and 0.18m per year for those to the northeast.

Posford Duvivier (1997) estimated that the eroding cliffs and platforms between Sconce Point and Gurnard Bay currently yield 150-200,00m³ per year of fine sediment, very little of which is available to littoral transport, but which may provide (or provided) a source of supply to estuarine mudflats and saltmarshes in the Western Solent. By contrast, the annual yield of coarse sediment is considered to be less than 500m³.

Map and field evidence indicates that cliff erosion supplies material from (i) the Bembridge and Osborne Beds; (ii) Plateau Gravels, which cap the high cliffs immediately south of Gurnard Ledge (White, 1921). The solid strata contribute predominantly clay sediments that are transported offshore but also some limestone boulders, which temporarily remain on the foreshore as boulder arcs that mark the seaward, limit of former mudslide surges. Posford Duvivier (1997; 1999) estimate a total sediment yield of 75,000m³ per year for the sector between Newtown Harbour and central Gurnard Bay. Estimates suggest that less than 500m³ is coarse material, although mapping and sampling of the gravel outcrops has not been undertaken so exact contributions remain unquantified. The rate of inter-tidal shoreface abrasion is calculated at between 4 and 24mm per year (Posford Duvivier, 1999), providing a yield of rapidly removed suspended sediment of 2,500 to 14,000m³ per year. Analysis of Coastal Monitoring Programme indicates the cliff-derived fine-grained sediment is not retained on the foreshore, being removed from the beach as suspended load by waves and currents.

E12 Gurnard Marsh to West Cowes (Cowes Castle) (see introduction to coastal erosion)

North of the small valley occupied by Gurnard Marsh, a partly active wooded coastal slope, located on Oligocene clays, marls and interbedded limestones, up to 35m in height is protected by revetments and sea walls (Photo 13). The slope continues east to West Coves, but to the east of Gurnard slipway it becomes less steep, and is protected at its toe by seawalls and an esplanade (Photo 14). Slope morphology comprises numerous bench-like irregularities, which indicate intermittent past and active seepage erosion and the presence of relic deep-seated and shallow landslides together with associated debris (Posford Duvivier, 2000; Isle of Wight Centre for the Coastal Environment, 2000; Hutchinson and Bromhead, 2002; Moore and McInnes, 2002; Hodges, 2002). Although an average rate of cliffline recession of 1.5 to 3.0m per year between approximately 1850-1950 is suggested by Hutchinson (1965), present conditions do not support such rapid recession of the entire cliff. It could be that the rates quoted relate to local areas where formerly inactive landslides have rapidly reactivated upslope.

Geomorphological and ground behaviour mapping from Gurnard to Cowes (Isle of Wight Centre of the Coastal Environment, 2000) reveals several active mudflows and both superficial and deep-seated landslides that have intermittently extended downslope and surged across the foreshore of the southwestern sector of this frontage (Hydraulics Research, 1981; Posford Duvivier, 2000; Moore and McInnes, 2002). Cliff input to the sediment transport system is clearly indicated, and comprises clays and limestones from the Bembridge and Osborne Beds together with a limited quantity of Plateau Gravel and remobilised relict landslide debris.

Between Egypt Point and West Cowes the upper coastal slopes exhibit evidence of instability, but the toe has been protected by an esplanade and sea wall since 1894, so no contemporary sediment supply occurs (Hydraulics Research, 1977; Hutchinson, 1965; Halcrow, 1997; Posford Duvivier, 2000; McInnes, 2008) so long as it maintains its function. The reconstruction of defence structures at Gurnard Bay will reduce the historical recession rate of slightly less than 0.1m per year (Posford Duvivier, 2000).

Although the majority of this frontage is defended by a continuous seawall at the southern end of Gurnard Bay, and between Gurnard and West Cowes, preventing cliff input to the narrow depleted mixed sediment beach, analysis of Coastal Monitoring Programme indicates that for the undefended sections the slope or cliff-derived fine-grained sediment is not retained on the depleted beach, being removed from the beach as suspended load by waves and currents.

2.4 Beach Nourishment

Limited beach nourishment has been undertaken at several locations in response to falling beach levels so as to temporarily prevent undermining of coast protection structures and reduce the historical trend of inter-tidal narrowing (Halcrow, 1997). In all cases, volumes are small and designs governed by the perception of critical losses rather than through and systematic long term monitoring of beach profiles and volumes. The main sites are:

1. Yarmouth Pier to Yarmouth Common: Small scale gravel replenishment has been introduced in response to falling beach levels east of Fort Victoria (Hydraulics Research, 1977);
2. Norton Spit: Stabilisation of the spit by groynes and revetments and ad hoc reinstatement of beaches by gravel nourishment/replenishment (Lewis and Duvivier, 1981; Barrett, 1985; Posford Duvivier, 1989) has been undertaken over the past 25 years;
3. Fort Victoria: There has been co-ordinated shingle replenishment, seawall repairs and groyne construction immediately at and east of Fort Victoria, to prevent shoreline recession affecting the coastal access road (Lewis and Duvivier, 1981; Barrett, 1985; Posford Duvivier, 1989). The source materials have been predominantly rounded pebbles from Solent Bank, and other marine sources;
4. Colwell Bay: Replenishment by fine gravel and coarse sand of the extreme south-west corner of the bay to reverse falling beach levels occurred periodically between 1977 and 1993. Material is retained by groynes (Barrett, 1985; Posford Duvivier, 1991);
5. Old Castle Point to Shrape Breakwater, Cowes Harbour entrance: No information on quantities available, but are believed to be small.

3. Littoral Drift

» LT4 · LT5 · LT6 · LT7 · LT8 · LT9 · LT10 · LT11 · LT12 · LT13 · LT14

Both the potential for, and actual rates of, littoral drift vary along the North-West Wight coast due to spatial changes in wave climate and the role of tidal currents. Between the Needles and Fort Albert, the coast is subject to obliquely approaching refracted Atlantic swell waves, modified by the shallow water of the western English Channel and Christchurch Bay, especially the Shingles Bank. Drift potential is thus high (New Forest District Council, 1998). North-east of Fort Albert, the coast is sheltered by Hurst Spit and the mainland so that most incident waves are fetch limited (rarely in excess of height of 1.3m) and of relatively low energy (Webber, 1978; Posford Duvivier, 1990; Halcrow, 1997). Thus, actual volumes and rates of drift are well below their potential (Brampton, et al., 1998). Despite this, transport throughput is not uniformly low along this coast, for ebb tidal currents are rapid within the West Solent (Webber, 1980). Meandering of ebb and flood flow brings these tidal streams close to the shore at certain points so significant sediment transport is possible by tidal currents augmenting wave action (Dyer, 1971; Halcrow, 1997; Brampton, et al., 1998). Ebb and flood currents at the mouths of the estuaries have created local transport sub-cells (Bray, Carter and Hooke, 1995).

Analysis of Coastal Monitoring Programme 2008 to 2012 lidar, 2003 and 2012 aerial photography and topographic baseline survey data, has been combined with other datasets, academic research and historical studies to review and revise sediment budgets, transport rates and directions.

LT4 Alum to Totland Bay (see introduction to littoral drift)

Although previous authors report flints released from the Chalk (see E5), sand and limited quantities of gravel from Eocene rocks and cliff top Quaternary sediments are transported from the southern end of Alum Bay towards Headon Hill (E6) (Lewis and Duvivier, 1962, 1973, 1981; Hydraulics Research, 1977; Barrett, 1985; Posford Duvivier, 1989; Halcrow, 1997; Bradbury, et al., 2003), Coastal Monitoring Programme data indicates that there are no long-term drift trends within Alum Bay, as direction of gravel and sand transport is variable, depending on location, scale and frequency of cliff falls. Net offshore loss of fine sand in Alum Bay is suggested by Brampton, et al., (1998).

Previous authors agree that boulder aprons on the foreshore at Hatherwood Point appear to intercept drift significantly so that only relatively small quantities of coarser materials appear to reach Totland Bay (where they are intercepted by groynes installed in 1993 and subsequently upgraded). The transport discontinuity at Hatherwood Point, appears to confine the well-defined gravel upper beach in Alum Bay (Photo 3) whereas predominantly sandy beaches occur in Totland Bay. Transport of gravels or sand northeastwards from Alum Bay, around Hatherwood Point into Totland Bay is not evident from Coastal Monitoring Programme data. Study of nineteenth century engravings and paintings suggest that this distinction has been sustained for more than a century (McInnes, 2008).

Coastal Monitoring Programme data supports net drift from south to north within Totland Bay on a narrow beach, although very little gravel is available and only a low gradient intertidal sandy foreshore is present. Observations indicated that beach depletion was the dominant trend in Totland Bay between 1960 and 1990, but the first consistent programme of beach monitoring has revealed a gradual increase in beach volume over the period 1996-2002 (Bradbury, et al., 2003). The profile analysis revealed that the beach within Totland Bay varied significantly seasonally with a greater volume being evident in summer. Its profile was also considerably more volatile than at corresponding locations in Colwell Bay and it was reported that an equilibrium profile did not form. These latter features are believed to result from the initially depleted state of the beach and are indicative of interaction with the seawall (Bradbury, et al., 2003).

Warden Point at the northern extremity of Totland Bay is a natural headland resulting from an outcrop of resistant strata on the foreshore to form Warden Ledge, which partly intercepted littoral drift prior to sea wall and esplanade construction in the early 1980s (Photo 10). The prominence of this headland has been accentuated by the protection structures and the nearshore seabed has been lowered by beach drawdown, so that deep water now extends directly to the sea wall (Lewis and Duvivier, 1981; Barrett, 1985), including the section that collapsed in 2012 due to landsliding. Due to limited material availability it is probable that north-eastward drift of gravel into Colwell Bay is totally intercepted (Lewis and Duvivier, 1981; Barrett, 1985; Halcrow, 1997). Transport of sand northeastwards from Totland Bay, around Warden Point into Colwell Bay is not evident from Coastal Monitoring Programme data.

LT5 Colwell Bay (see introduction to littoral drift)

Coastal Monitoring Programme data confirms that Colwell Bay no longer receives coarse sediment input from Totland Bay by longshore drift, due to depletion of the latter and Warden Point acting as a drift barrier. The Programme also confirms that within Colwell Bay, low rates of net movement is from southwest to northeast, an observation also confirmed by beach sediment grading. Previous authors indicate that the beach in the southwest corner of the bay became severely depleted, an effect starting in the 1940s, whilst central parts maintained a relatively stable shingle and sand beach (Lewis and Duvivier, 1973; Posford Duvivier, 1989). This trend led to reinstatement of the beach by nourishment and the rebuilding of retaining groynes between 1966 and 1977 (Barrett, 1985), but these latter structures now restrict drift. The first consistent programme of beach monitoring has revealed a gradual increase in beach volume over the period 1996-2002 (New Forest District Council, 1997, 1998-2000; Bradbury, et al., 2003). The profile analysis revealed that the beach within Colwell Bay varied seasonally with a lower volume being evident in winter, but otherwise maintained a slowly increasing profile volume and an equilibrium form. The Programme data confirms the continuation of this seasonal variability.

The northeast extremity of Colwell Bay is marked by Fort Albert, which was constructed in the mid-19th century. Subsequent coast recession and foreshore lowering has created a prominent salient here with deep water adjoining the fort (McInnes, 2008). Transport of coarse sediments northeastwards from Colwell Bay, around the artificially strengthened headland of Fort Albert is not evident from Coastal Monitoring Programme data. Evidence suggests that Colwell Bay behaves as an isolated pocket beach, which may only receive sediment from local cliff or shoreface erosion and possible limited onshore transport. Although potential littoral transport is likely to be towards Fort Albert, negligible accretion has occurred against this barrier and sediments are concentrated in the central part of the bay (Lewis and Duvivier, 1973). Two possible explanations exist: (i) there is no net drift in Colwell Bay, except for a tendency for sediment to move away from the headlands; (ii) net drift is indeed north-eastward, but sediment is lost offshore in the vicinity of Fort Albert due to entrainment by strong tidal currents generated at Hurst Narrows.

LT6 Fort Albert to Fort Victoria (see introduction to littoral drift)

Analysis of Coastal Monitoring Programme indicates less than 1,000m³ per year of landslide and cliff-derived input yielding fine-grained sediment is retained on the 50m wide sandy foreshore, with the bulk of material being removed offshore by waves and currents. Sand accumulation is absent at Fort Victoria (Lewis and Duvivier, 1973). Coast protection structures restrict drift transport at Fort Victoria, but it has been suggested that limited eastwards movement of coarse sediment was possible around the fort before it was halted by construction of two groynes over the period 1870-73 (Lewis and Duvivier, 1973). This coastal segment has therefore functioned as a self-contained unit since the pathway around Fort Victoria was denied.

LT7 Fort Victoria to Tarmouth Harbour Entrance (see introduction to littoral drift)

Drift direction is presumed to be eastward, but Coastal Monitoring Programme data confirms beach levels are very low and transported volumes are less than 1,000m³ per year. Nourishment programmes have supplied a small quantity of beach material immediately east of Fort Victoria and at Norton Spit, but groynes were constructed here in the past to retain predominantly sandy sediment and thus net drift quantities are small or non-existent (Lewis and Duvivier, 1981; Barrett, 1985; Posford Duvivier, 1989; Halcrow, 1997). The alignment of Norton Spit and accumulation behind the western face of Yarmouth Harbour breakwater indicates that historically net drift has been eastward (Hydraulics Research, 1977; Dyer, 1980; McInnes, 1994; Royal Haskoning, 2010), although visual inspection of sediment distribution against groynes has failed to reveal a preferred drift direction.

LT8 Westward Drift at Yarmouth (see introduction to littoral drift)

Morphology of the mouth of the Western Yar estuary indicates littoral drift towards the inlet on both sides (Dyer, 1980; Halcrow, 1997). Due to the negligible volumes and drift rates of predominantly fine-grained sediment on this frontage, Coastal Monitoring Programme data provides no evidence for a weak net westward drift over the sector to the immediate east of the inlet mouth.

LT9 Eastward Drift east of Yarmouth (see introduction to littoral drift)

Due to the negligible volumes and drift rates of predominantly fine-grained sediment on the narrow foreshore, Coastal Monitoring Programme data provides no evidence for a weak net eastward drift. Beach levels are extremely low along this frontage and groynes are frequent (Hydraulics Research, 1977; Lewis and Duvivier, 1981) so it is likely that actual drift is currently nearly zero (Halcrow, 1997; Royal Haskoning, 2010).

LT10 Bouldnor to Newtown Harbour (see introduction to littoral drift)

Coastal Monitoring Programme data supports negligible net eastward drift of sand and gravel, with minimal variation in morphology and extent of the western spit (Hamstead Duver) at Newtown Harbour entrance (Photo 8). Eastward alignment of this spit is regarded as evidence of net eastward drift (Dean, 1995; Dyer, 1980; Hydraulics Research, 1977; Lewis and Duvivier, 1981; McDowell, 1990a and b; Posford Duvivier, 1989; McInnes, 1994; Halcrow, 1997). For the majority of this frontage, most beach sediment is derived from local cliff and foreshore erosion, and is often little more than a patchy veneer of gravel and coarse sand overlying an erosional surface cut into substrate materials (Photo 11). Observations of a major mudslide lobe, which temporarily extended across the beach beneath Bouldnor Cliff (Moorman, 1939), revealed beach accretion on its western side, and erosion of gravel and boulders from the mudslide toe. Coastal Monitoring Programme data suggests this mudslide has stabilised (Photo 6). It was stated by Moorman (1939) that these materials were transported eastwards from the lobe.

Hamstead Duver (the western spit) has shown significant morphological and planform variation according to analysis of maps and charts covering the period 1879-1973 (Hydraulics Research, 1977). Shorewards recession and recurvature into the harbour has been the dominant trend, although there are two features indicative of long-term gravel accretion. First, a relic spit is located in the harbour entrance behind the active one (Photo 8) and secondly, a gravel foreland has formed at Hamstead Point in front of low inactive cliffs. Such features would be consistent with accretion/erosion cycles at the shore caused by variation in littoral drift supply. Drift rates could have reduced due to a variety of reasons: (i) coast protection and correspondingly reduced supply along the updrift coast; (ii) temporary blockage of the foreshore by mudslides and debris accumulations between Bouldnor and Hamstead; and (iii) variation in cliff erosion input at Bouldnor and Hamstead Cliffs (Halcrow, 1997). Since the cliffs have been increasingly active in recent decades it is likely that supply to the shore has increased, although there may be a lag for materials to be released from mudslide lobes and contribute to drift towards Hamstead Duver. It should be recognised that other factors may also affect the dynamics of this spit, such as the tidal regime of the estuary and possible onshore-offshore sediment transfers involving gravel banks in the West Solent (Hydraulics Research, 1977, 1981; Dean, 1995; Tubbs, 1999).

LT11 Westward Drift at Brickfield Spit (see introduction to littoral drift)

Coastal Monitoring Programme data indicates that Brickfield Spit, to the east of Newtown River entrance, has extended westwards approximately 5m and rolled back 2-3m supporting a weak net westward drift (Dyer, 1980; Lewis and Duvivier, 1981; McDowell, 1990a and b; McInnes, 1994). It is suggested that westward drift is a local phenomenon associated with the hydraulics of the inlet entrance. Thus, there is a conjectured transient drift divide offshore Brickfield Farm. However, human modification of this coastline, involving previous attempts at land claim, may account in part for the present structure (Tubbs, 1999). The spit has a history of sediment depletion and has receded landwards over saltmarshes that subsequently became exposed and eroded on their seaward face (Halcrow, 1997). Timber groynes and revetments have been installed in past attempts to stabilise the spit, but has breached to form a small new inlet subject to tidal flows at high water (Photo 8).

LT12 Brickfield Spit to Gurnard (see introduction to littoral drift)

Analysis of Coastal Monitoring Programme data indicates that less than 1,000m³ per year of cliff-derived sediment is transported northeastwards, with the bulk of fine-grained material being removed offshore by waves and currents. Net north-eastward drift is indicated by eastward deflection of stream mouths by small, mixed sediment bars at Thorness and Gurnard (Hydraulics Research, 1977; Dyer, 1980; Posford Duvivier, 2000; Tubbs, 1999). A considerable quantity of gravel is stored on the upper and mid foreshore within Thorness Bay (Photo 9 and Photo 12), where it has formed a barrier across the stream and its low marshy valley. It is uncertain whether all of this material could have been supplied by drift from local eroding cliffs, or whether material could have arrived as small barrier beaches, or swash bars that have moved onshore, fed from relic gravel sources in the West Solent. Gurnard Ledge certainly functions as a partial impediment to drift tending to assist coarse sediment retention within Thorness bay, causing depletion of the beaches to its northeast.

LT13 Gurnard to West Cowes (see introduction to littoral drift)

Due to the negligible volumes and drift rates along the depleted beach from Gurnard (Photo 13) around Egypt Point, Coastal Monitoring Programme data provides no evidence for a weak net eastward littoral drift. Concrete rubble groynes at Egypt Point selectively intercept sediments (Photo 14), but quantities are small because of the presence of protection structures and a lack of available material (Halcrow, 1997; Posford Duvivier, 2000).

LT14 Old Castle Point to East Cowes (see introduction to littoral drift)

Analysis of Coastal Monitoring Programme indicates less than 1,000m³ per year of weak eastward drift occurs between a drift divergence at Old Castle Point and the Shrape breakwater, which prevents input into Cowes Harbour. Falling beach levels and lack of significant accretion against the breakwater indicate low drift rates, which have necessitated some recent beach nourishment. The paucity of supply is due to the small source area and the impact of protection structures in reducing cliff erosion (Posford Duvivier, 1994). Cowes Harbour entrance therefore represents a drift convergence boundary, although the very small quantities of sediment moved by littoral transport towards the Medina entrance, together with the effect of Shrape breakwater, makes this little more than a notional feature.

4. Sediment Outputs

4.1 Offshore Transport

Analysis of Coastal Monitoring Programme data provides no conclusive evidence of offshore transport although fine-grained sediment derived from cliff erosion is not retained on the foreshore. The majority of sediments are probably transported offshore in suspension, but it has not been possible to identify pathways or sinks, or quantify volumes.

O1 Bouldnor and Hamstead

Analysis and seabed mapping interpretation of Coastal Monitoring Programme swath bathymetry data of the northern nearshore zone of the Isle of Wight indicates a shallow exposed rock platform which extends for the majority of the northwest shoreline, and offshore between 1-800m. A veneer of fine-grained sediments suggest that sediment deriving from erosion of the local soft cliffs is likely to contribute suspended sediments to the Solent, and  notable but low rates of offshore transport of sand or coarser sediments. Localised banks of sand or gravel occur offshore of the rock platform in deeper water in the main Solent channel. However, offshore coarse sediment transport pathways from the foreshore is not evident from analysis of Coastal Monitoring Programme bathymetry data.

4.2 Estuarine Outputs

» EO2 · EO3 · EO4

Throughout the Western Solent the ebb tidal flow is of shorter duration than the corresponding flood (Webber, 1980). As a result, ebb currents are of greater velocity (up to 1.2ms-¹) than the flood, causing net offshore transport of coarse bedload sediments at the mouths of both larger estuaries and small tidal inlets, as well as at the western exit (see Unit Report for Western Solent). Well-defined ebb tidal deltas are not reported (excepting the possibility of Newtown Gravel Banks) and it may be that deposits have been inhibited by lack of available sediment or that they were small in quantity and have been removed by dredging.

EO2 Yarmouth Harbour (see introduction to estuarine outputs)

Dominant flow is during the ebb tide and it has been estimated that its sediment carrying potential is five times that of the flood (MacMillan, 1956; Price and Townend, 2000). No measurement of volumes of sediment transport has been undertaken to verify this statement. It is reported that sand can be transported into Yarmouth Harbour by strong northerly gales, but training of the ebb flow by breakwater structures (Photo 2) is generally successful in flushing such material back offshore (MacMillan, 1956). Maintenance dredging of the harbour and approaches is infrequent and comparison of hydrographic surveys for 1980, 1983 and 1987 revealed that bed levels were stable (Brogan, 1987). A major capital dredge in 2006 removed 380,000 tonnes of mostly fine sand and silt.  It is therefore concluded that the dominant flushing effect of the ebb current rapidly removes fine-grained sediments previously transported into the mouth (Western Yar Liaison Committee, 1998; Pethick, 1999). In the past, significant quantities of sediment may have been transported across the mouth to create Norton Spit, but this is now impeded by groyne and breakwater systems either side of the harbour entrance. There is currently no analytical data on mudflat and saltmarsh erosion or accretion specifically for Yarmouth Harbour, though aggregated data for the North-west Isle of Wight is presented in Bray and Cottle (2003).

EO3 Newtown Harbour (see introduction to estuarine outputs)

It is reported that sediment mobility is greatest at the entrance of Newtown Harbour, with fine silt and clay accumulating as mudflats and marsh sediments within the inner estuary (Hodgson, 1962; Hydraulics Research, 1981; Tubbs, 1999). The bed of the main channel is composed of coarse pebbles and ebb tidal currents exceeding 0.5ms-¹ have been recorded (Howard, Moore and Dixon, 1988). As a result, offshore flushing of coarse sediments may occur, fed by gravel driven by wave action along the spits flanking the harbour entrance. Although this has not been experimentally proven, the opposed alignment of these spits suggests drift convergence at the harbour mouth that would feed the losses seaward (Lewis and Duvivier, 1981). Previous research has not reported the existence of an ebb tidal delta, although the Newtown Gravel Banks surveyed by Hydraulics Research (1977 and 1981) may perform this function. It is uncertain whether coarse sediments are recycled back shorewards from these banks, although several distinctive bar-like features can be observed within the intertidal zone (see Photo 8 and also F3).

Saltmarsh erosion is currently occurring at a few sites (Howard, Moore and Dixon, 1988; Raybould, et al., 2000; Bray and Cottle, 2003) and the strong ebb current may remove silt released by this process. Spartina anglica 'dieback' can be traced to 1935 in the Solent, but its role in trapping and subsequently releasing sediment has not been researched at this site (Tubbs, 1999). In comparison to most other Solent estuaries, Spartina loss has been limited and some areas remain accreting. In Newtown Harbour S. anglica only appeared in 1932 and has spread slowly. Approximately 17 ha have developed since the breach of a seawall in 1954 (Isle of Wight Biodiversity Action Plan, 2004). This site is unique in the Solent in retaining a concentration of the native S. maritima, especially around the area of Walter's Copse, where it has a long established presence. Total area of all types of saltmarsh is estimated as being 120 ha. Die-back is not reported as occurring within Newtown Harbour, indeed slow colonisation by S. anglica appears still to be continuing in at least two locations. (Refer to Bray and Cottle (2003) for aggregate data on North-West Isle of Wight, most of which relates to Newtown harbour).

A proportion of the sediment stored in inter-tidal flats and saltmarsh is presumed to derive from input by the small rivers discharging into Newtown Harbour. Most input however, is likely to have been transported by the flood tide, and originate from cliff, platform and shoreface erosion of suspended sediment from the adjacent open coastline. The tidal prism of the harbour has not been constant, as a result of piecemeal land claim in the nineteenth and twentieth centuries, and the submergence of a previously reclaimed area resulting from a storm surge in 1954 (Halcrow, 1997).

EO4 Medina Estuary (see introduction to estuarine outputs)

Ebb tidal flow is of shorter duration (4 hours) than corresponding flood flow (5 hours) so ebb currents are more rapid (Webber, 1969). This produces a net offshore flushing effect of sand and gravel at the harbour entrance, which was enhanced by construction of the Shrape breakwater in 1936/37. Ebb and flood tidal flow is confined to separate channels, but the ebb flow has shifted westward as a result of the construction of the breakwater. Dominant transport of sand is thus out of the harbour except along the extreme west bank, where the flood current dominates and net transport is inward (Bunce, Gibbs, Goldsmith, Jones and Spence, 1987; Posford Duvivier, 1994; Carter, 1997; Webber, 1969, 1978; Pieda, 1994). Measurement of tidal currents in the adjacent area of the central Solent indicate westward flow at high water, thus ebb currents at the harbour entrance are deflected westward and sediment transport pathways shift accordingly (Bunce, et al., 1987; Price and Townend, 2000).

Examination of hydrographic charts dating back to 1856 indicate that some cyclic variations of outer estuary bed morphology may have occurred prior to construction of the Shrape breakwater, but subsequently it has been very stable (Bunce, et al., 1987; Webber, 1969; Carter, 1997). This can be attributed to net offshore transport of sediment, which maintains stable channel configuration and prevents siltation even in recently dredged berths (ABP Research and Consultancy, 1994; Webber, 1969). Small sand and gravel banks exist where dominant ebb and flood flows crossover; these are probably not sediment sinks but temporary accumulation zones for sediment subject to net offshore transport (Webber, 1969). In the Medina estuary upstream of Cowes, bankside erosion of marginal mudflats began to replace a longer-term tendency for channel accretion in the 1980s. Banks further offshore in the central Solent, such as Prince Consort Shoal and Bramble Bank, are probable sediment sinks (Dyer, 1980) in a confluence zone receiving both wave and tidally transported sediment (Velegrakis, 2000; Bray, Carter and Hooke, 1995). Prince Consort Shoal was probably previously supplied by fine sediment flushed out of the Medina, but quantities have been significantly reduced by breakwater construction and periodic maintenance dredging (Isle of Wight Development Board and Cowes Harbour Commissioners, 1990).

4.3 Dredging Outputs

Dredging for aggregate was practised at Pot Bank, Solent Bank and Prince Consort Shoal from the late 1940s until 1994 (Hydraulics Research, 1977, 1981; Webber, 1977). Pot Bank is located several kilometres southwest of the Needles and studies indicate no direct sediment supply connection with the coast of northwest Isle of Wight. Newtown Harbour entrance may have been affected by dredging of Solent Bank (see section on the West Solent), but its precise contribution is uncertain (Hydraulics Research, 1977, 1981) - see unit covering West Solent for full details. Dredging of coarse sands from Prince Consort Shoal has generally been at a relatively low rate. In 1977, a licence existed for removal of 60,000 tonnes per year, but less than 30,000 tonnes per year were extracted (Hydraulics Research, 1977). Webber (1977) quoted mean extraction of 50,000 tonnes per annum for the late 1960s and early 1970s. Comparisons of hydrographic charts dating back to 1912 indicate relatively stable conditions on the shoal (Hydraulics Research, 1977; Webber, 1977), which is thus most appropriately regarded as a sediment sink (Dyer, 1980; Bray, Carter and Hooke, 1995). Dredging at this site has thus had limited impact on adjacent shores, because of its small potential to supply sediment. The low energy wave climate also makes it unlikely that increased depths caused by dredging would have much effect on local sediment budgets (Hydraulics Research, 1977). Dredging close to Cowes Harbour, however, may be of more significance, because the configuration of the harbour tends to amplify and concentrate wave energy; extreme wave events coupled with high spring tides can cause flooding at both West and East Cowes (Bunce, et al., 1987; Lewin, Fryer and Partners, 1995; Webber, 1978, 1981).

Dredging is also periodically undertaken for navigation purposes at Yarmouth Harbour (MacMillan, 1956; Turton, 1982; Western Yar Liaison Committee, 1998; ABP, 2003), Cowes Harbour and Newport Harbour. In all cases dredged volumes are small and predominantly comprise muds and silts. At Cowes Harbour, regular dredging was necessary to offset siltation prior to construction of the Shrape breakwater in 1936/37, but subsequent sediment removal comprising maintenance dredging of the main channel, deepening of access channels and creation of new berths, has been modest (Webber, 1969). An approximate equilibrium between loss from this source and gain from flood tide sediment input may prevail.

Maintenance dredging of approximately 4,000 tonnes per year is undertaken in the Medina estuary upstream of Cowes Harbour to maintain the channel to Newport Harbour (Newport Harbour Master, 1991). It is reported that routine dredging began in the early 1900s but reliable historical data is lacking. For the most part, the main channel upstream to Newport is self-scouring.

Dredging at estuary entrances represents a net output from the sediment budget and may result in loss of sediments that might otherwise be transported to shorelines. Furthermore, operations close inshore potentially cause drawdown that could contribute to the steepening of local inter-tidal zones.

5. Summary of Sediment Pathways

1. This unit comprises the north facing valley side of the former Solent River that became occupied/re-occupied by marine inundation some 7,000 to 8,000 years before present. It is considerably more exposed than the corresponding mainland shore to the combination of waves and tidal currents. Erosion has therefore prevailed at the toes of coastal slopes formed in soft Tertiary clays and mantled by relict landslides. In this situation the slopes and cliffs are inherently sensitive to erosion and renewed landslide activity, even when the driving marine forces are relatively weak.
2. Cliffs to the west of Fort Albert are exposed to open coast wave action and undergo relatively rapid rates of recession. Between Yarmouth and Gurnard, recession is also locally rapid despite their more sheltered location within the West Solent. This is due to the soft predominantly clayey lithology and the combination of wave action with rapid tidal currents that removes stabilising (protective) debris from the cliff toe. Some coastal slopes in the east remain intact and mantled by relic landslides, although there is evidence at many locations that reactivations are in progress or imminent.
3. Substantial quantities of sediment are yielded by cliff erosion, but most are fine grained and are transported offshore so that they do not contribute to protective local beaches. Instead, it is likely that they are deposited within more sheltered regions such as the local estuaries, Southampton Water and the mainland shore of the West Solent. Significant quantities of sand are contributed in Alum Bay and small quantities of gravel are contributed from thin superficial deposits along much of the summit of the cliffline, especially Headon Hill, Bouldnor Cliff, Burnt Hill and Thorness cliffs.
4. Two distinct shoreline drift pathways appear to operate as follows: (i) From Alum Bay to Fort Albert and (ii) from Fort Victoria to Egypt Point. The linkages between the two are uncertain for their interface flanks Hurst Narrows and it is thought that ebb-dominated tidal transport dominates over shoreline drift, imposing a significant discontinuity. Between Fort Victoria and Egypt Point, coarse sediments drift eastwards and appear to be retained in spits at the mouths of the West Yar and Newtown Harbour estuaries, with some material moving onward to collect within Thorness Bay. Very little exits Thorness Bay to continue to Egypt Point. The quantities of drift involved are small so that the spits and barriers are sensitive to morphodynamic change. Between Alum Bay and Fort Albert drift is northeastward within a series of partly connected bays. It is thought that sand can move from bay to bay, although gravel generally cannot in any significant quantity. Intervening headlands between the bays inhibit transport. A potential uncertainty relates to the fate of the quantities of sand and gravel yielded from between the Needles and Fort Albert because there are no significant shoreline accumulations. In the absence of firm evidence the most likely explanation is that material is lost seaward entrained by the strong ebb tidal flows that exit Hurst Narrows. Losses would be most likely to occur at headlands such as Hatherwood Point, Warden Point and Fort Albert.
5. Exchanges of sand and gravel between the West Solent Channel and the shoreline are poorly understood. Some foreshore gravel bars would appear to be indicative of onshore supply between Thorness Bay and Bouldnor, but this has yet to be proven. Exchanges are indicated at the entrance to Newtown Harbour where gravels drifting along the convergent spits are flushed seaward and some return onshore directed transport back to the spits is indicated by foreshore morphology. It is uncertain whether this constitutes a closed circulation, or whether "new" material could be contributed from the West Solent channel e.g. Solent Bank.
6. Future increases in rates of sea-level rise and winter rainfall would have a clear potential to accelerate processes of landslide re-activation on the historically stable coastal slopes between Gurnard and Cowes. It would also accelerate the landsliding of currently active cliffs between Alum Bay and Fort Victoria and between Bouldnor and Gurnard (Halcrow Maritime, et al., 2001). Increased supply of sediments to the shore would be likely to occur as a result.
7. The Western Yar, Newtown and Medina estuaries appear to be capable of continuing to accrete fine sediments and their saltmarshes have been relatively stable, although trends for slow to moderate saltmarsh erosion have become apparent recently in the Western Yar and Medina. Since these are all valley type estuaries with relatively steeply sloping margins their saltmarshes are likely to be sensitive to future climate change and sea-level rise unless vertical accretion can compensate (Halcrow Maritime, et al., 2001).

6. Opportunities for Calculation and Testing of Littoral Drift Volumes

Data collected by the Defra-funded National Network of Regional Coastal Monitoring Programmes is pivotal for future improvement in estimating beach change.  The Programmes consist of topographic beach surveys, nearshore bathymetry, aerial photography, lidar, coastal hydrodynamics (waves and tides) and terrestrial habitat mapping.  Specifications for data collection are consistent for all regional programmes and the data and analysis reports are made freely available under the Open Government Licence from www.channelcoast.org.

The Southeast Regional Coastal Monitoring Programme commenced in 2002. The Lead Authority is New Forest District Council, with data collection, analysis and reporting led by specialist teams at the Channel Coastal Observatory (CCO), Canterbury City Council and Adur and Worthing Councils. Longer term Coastal Monitoring Programme data, when combined with other data sets, academic research and historical studies may enable sediment budgets, transport rates and directions to be identified and/or validated in the future.

The lack of significant wave energy, modest development of natural linear beaches and prevalence headlands, reefs/ledges and debris lobes mean that shorelines of this frontage are not well suited for definitive studies of drift. There are, however, opportunities to improve knowledge of drift and beach behaviour. In particular the provision of improved monitoring of beach profiles should allow calculations of changes in beach volumes from which estimates of drift can be made. Locations especially amenable to study include: Totland Bay; Colwell Bay; Thorness Bay. Difficulties to overcome in this work would include making allowances for gravel input from offshore, and estimating the transport efficiencies of the various foreshore obstacles that intercept or constrain drift.

7. Research and Monitoring Requirements

Notwithstanding results from the Southeast Regional Coastal Monitoring Programme and the Isle of Wight SMP (Haskoning, 2010; Halcrow, 1997), recommendations for future research and monitoring that might be required to inform management include:

1. To understand beach profile changes it is important to have knowledge of the beach sedimentology (grain size and sorting). Sediment size and sorting can alter significantly along this frontage due to variations in cliff supply, beach transport, sorting and beach management. Ideally, a one-off field-sampling programme is required to provide baseline quantitative information along this shoreline together with a provision for a more limited periodic re-sampling to determine longer-term variability. Examination of longshore and onshore-offshore grading of the various sediment parameters can be employed to indicate or confirm directions of transport, sources of sediment and possible residence (storage) timescales.
2. Understanding of inputs of beach-forming sediment from coast erosion, would be enhanced by cliff section mapping and sampling of deposits to reveal the detailed thickness, composition and variability of the lithological units (especially the Plateau and Valley Gravels - a major local source of beach gravel) occurring along the cliff tops. Sampling of such deposits could thus reveal particle size distributions, and be compared to similar analyses of stable beach materials. Quantitative information on cliff input should be coupled with details of beach sedimentology to assess the smallest size sediment grades stable on the beach and thereby determine the proportion of cliff input capable of contributing long term to beach volumes.
3. Comparisons could be made of sequential series of historical aerial photography to produce a definitive analysis of cliff and shoreline change from the 1940s to the present.
4. Interactions between tidal channel and beach sediments are poorly understood in the West Solent (see unit on the West Solent). Hydraulics Research (1977) suggested that onshore feed was the major supply to spits at Newtown Harbour entrance but evidence remains inconclusive. Further studies involving beach profiling, sediment sampling and hydrographic surveys have so far failed to verify this possibility. Proving supply links between Solent Bank, other offshore gravel banks and beach deposits is extremely difficult without resort to sediment tracing and time consuming and difficult underwater clast movement detection techniques. Preliminary analysis of sediment lithology, size, shape and roundness could be employed for comparison of offshore, nearshore and beach samples to test whether they are derived from the same source population(s).
5. Simultaneous beach profiling and hydrographic survey (extending up to MLWM) could be undertaken after major storms, when the most significant morphological changes might be expected to occur. Beach and offshore changes could be compared for evidence of onshore-offshore sediment transfers. Direct evidence of linkage might be obtained using low cost tracer techniques in conjunction with beach profiling and hydrographic techniques.