Copyright © MMXVII SCOPAC Sediment Transport Study. All Rights Reserved
Chairperson Councillor Mrs M Penfold MBE, West Dorset District Council.
Technical assistance provided to Councillors by Mr Lyall Cairns (Southern Coastal Group Chair) and Dr Samantha Cope (SCOPAC Research Chair).
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.
This sector of shoreline has a slightly arcuate planform, with a near west to east alignment. Its continuity is interrupted by the mouths of the Rivers Arun (Photo 1), at Littlehampton and Adur, at Shoreham-
The West Sussex Coastal Plain narrows progressively eastwards and consists of low gradient bevelled erosion surfaces resulting from successive Middle and Late Pleistocene sea-
A major new source of coastal data is from the Defra-
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).
Most of this coastline is open to a moderate to high-
The Southeast Regional Coastal Monitoring Programme measures nearshore waves using a Datawell Directional Waverider buoy deployed at Rustington in 10mCD water depth. Between 2003 and 2012 the prevailing wave direction is from the southwest-
Hydraulics Research (1989), Robert West and Partners (1991) HR Wallingford (1994) and Gifford Associated Consultants (1997) and Environment Agency (2012) all report that prevailing waves are from the west-
Shoreham and Middleton, east of Bognor, are locations for which wave modelling exercises were undertaken as part of the DEFRA Futurecoast Project (Halcrow, 2002). An offshore wave climate was synthesised based on 1991-
Although the tidal range increases from west to east, the inshore tidal current velocities decrease eastwards. Typical spring tidal range is 5.3m at Pagham increasing to 6.5m at Shoreham, with a neap range at the latter of 3.0m. Locally strong ebb and flood tidal currents are generated by the exchange of tidal waters at the Pagham, Arun and Adur inlets. At Pagham Harbour entrance, velocities range from 1.4m per second (springs) to 0.7m per second (neaps), whilst at Shoreham the corresponding speeds are 0.8m per second and 0.4m per second.
Net beach drift and nearshore longshore transport is from west to east. Evidence of this drift direction is provided by the development of Shoreham spit over several centuries, the probable formerly eastwards deflection of the mouth of the Arun and the pattern of sediment retention in the near continuous present day groyne fields (Robinson and Williams, 1993). A sequence of transport sub-
Previous to shoreline management, beaches were periodically very vulnerable to the impacts of high magnitude storm events. Examples include some 275m of shoreline retreat along the Worthing frontage in the eighteenth century, a 600m wide breach at Widewater Lagoon in 1908 and 20m of recession in less than 7 hours at Lancing in 1877. Although this type of catastrophic response has been constrained by defences since the early decades of the twentieth century, several locations have continued to experience overtopping and retreat during surge events (Halcrow Maritime, et al., 2001; Halcrow, 2006; Worthing Borough Council, 2009). Many of the original barrier beach characteristics such as a wide crest, backslope seepage cans and dissipative response to high wave energy and elevated water levels have now been lost as a consequence of intensive management (Cope, 2004).
Following increasing urbanisation of this coastline from the mid-
Three naturally occurring potential sources of sediment are identified for this coastline, comprising offshore to onshore transport, fluvial discharge and shore erosion. These have been supplemented in recent decades by beach replenishment and maintained by beach recycling at several sites.
Analysis of Coastal Monitoring Programme bathymetry data and sediment sampling provide no evidence of onshore transport by kelp rafted shingle, which was postulated to potentially constitute a small (not reliably quantified) but regular and significant gravel supply in certain areas (Jolliffe and Wallace, 1973; Jolliffe, 1978). The sandy lower foreshore extends sub-
Septarian nodules and reworked flint pebbles are released from nearshore outcrops of the London Clay (Aldwick Beds) between Bognor and Felpham, but this is probably a very small input into local beaches.
Analysis of Coastal Monitoring Programme bathymetry data provide no conclusive evidence of onshore transport in the nearshore zone to support F2 arrows in the 2004 SCOPAC study. The F2 arrows were based on experiments conducted between 4km and 10km offshore from Shoreham by Crickmore et al. (1972) and Jolliffe (1978), indicated a landward drift of gravel. No evidence of the sediment reaching the shore was presented, and therefore this information does not support the process of wave powered onshore shingle ‘creep’. The F2 arrows have been removed from this 2012 update, and where suitable, replaced by O arrows to represent sediment transport occurring offshore. Refer to section 4.1 for details of O arrows
Two regionally significant rivers, the Arun and the Adur, discharge at Littlehampton and Shoreham-
Quantities of fine sediment delivered at the coastline are estimated as being approximately 9-
Estimated potential input is 20,000 to 26,000 tonnes per year of suspended load, but actual delivery is reduced by the presence of various barriers to transport and by flow diversion at times of high discharge in the lower flood plains. The river is considered unable to contribute a significant gravel (bedload) input, due to the restricted source area and upstream and in-
Although some lengths of the beaches of this shoreline are currently, or have until recently, been either stable or accreting, the long-
Analysis of the relative movements of the positions of mean high and low water on successive Ordnance Survey maps from 1875 to 2004 reveals long-
Posford Duvivier and British Geological Survey (1999) have calculated that vertical wave erosion of the shoreface zone between Bognor and Rottingdean (east of this unit) yields between 1,900 and 4,000m³ per year of coarse material and 2,000 to 7,000m³ per year of fine sediment. Most of the latter is presumed to be lost to the coastal transport system as suspended load.
Several significant gravel beach nourishments have been completed by coastal defence authorities over the past 45 years with numerous local, small-
The table below provides data on approximate quantities of renourishment, by site and dates. It was compiled based on Gifford Associated Consultants (1997), Williams (2005) and Halcrow (2006), with additional information provided by Adur and Worthing Borough Council, Arun District Council and the Environment Agency.
Beach Renourishment/Replenishments are regarded generally as having been successful, although rapid initial diminution of beach fill volume by 20-
Material is lost even with well-
The most substantial recharge to date has taken place along the Shoreham to East Lancing beach frontage, where introduced shingle has been sourced from offshore reserves, in several phases. This has been accompanied by the construction of eleven rock groynes, designed to help retain this material (Environment Agency, 2012).
There are sites of periodic removal of accumulated beach sediments for recycling at other locations. At West Beach, Littlehampton, sediment being transported eastwards by longshore drift is retained at the West Pier breakwater. It is then removed for periodic beach recycling updrift along the Climping frontage (Elmer to Climping).
The Environment Agency conduct recycling and reprofiling of the foreshore at Climping/Atherington (Poole Place to The Mill) using a sand/shingle mix material recycled from West Beach at Littlehampton further downdrift. Records of this recycling are presented by Williams (2005) for the period 1993 and 2005. Recycling logs from the Environment Agency show this recycling has since continued, occurring twice in 2006 and then annually 2008-
Under the Shoreham Harbour Act, Shoreham Port Authority conducts periodic harbour inlet bypassing through extraction of sediment that accumulates in the 100m length of beach adjacent to the Old Fort West breakwater (Photo 2 and Photo 7) owned by Shoreham Port Authority. This material is then deposited immediately downdrift of the east breakwater along the frontage which is not the management responsibility of the Port Authority (East Shoreham and Southwick).
Based on a calculation of net input of 10-
Small quantities of sediment dredged from areas of Littlehampton and Shoreham harbours adjacent to their confining breakwaters are periodically used to recharge beaches immediately downdrift (e.g. 2,000m³ was placed on Littlehampton East Beach in 2004). Williams (2005) and Moses and Williams (2008) provide further background and a critical evaluation of recent (post-
Net longshore transport along the West Sussex coast from Pagham Harbour to Shoreham-
Many earlier accounts are general and fragmentary and offer only limited quantitative evidence. Much more substantial are the results of several site specific numerical modelling, documentary and field-
A general west to east net drift operates along this frontage.
Rock groynes (installed in the early 1990s to replace earlier timber structures), demonstrably inhibit potential drift rates, and the local transport system is further complicated by artificial beach crest elevation, replenishment and regrading in the areas of persistent erosion (Photo 8). In 2009-
Periodic onshore gravel migration from Pagham tidal delta and the Inner Owers is subsequently moved north-
The construction of eight shore-
Over 220,000m³ of mixed sand and gravel was used to replenish Elmer Beach between 1989 and 1993, with the main function of the breakwaters being to retain this by reducing nearshore wave energy. The gaps between breakwaters are designed to effect a longshore transport system that minimises the downdrift impact of the shore-
Littoral drift of gravel was calculated to be potentially between approximately 60,000m³ per year (Mouchel, 1997a, b, c) and 50,000m³ per year (Gifford Associated Consultants, 1997) at Felpham. The actual rate is likely to be significantly less, at approximately 20 to 40,000m³ per year; this estimate is proposed by HR Wallingford (2003) based on beach modelling. At West Beach, Littlehampton, Hydraulic Research (1987) using a calibrated wave power model based on a 15-
River training works and piers at the mouth of the River Arun have intercepted beach drift since the earliest constructions in 1736 and 1793 They caused accretion to the west resulting in increasing stability of what had previously been described as a low and marshy (presumed back barrier) area subject to frequent inundations. By 1830, beach accretion to the west had produced a distinct offset in the coastal planform and sand dunes (Photo 1) began to form behind the wide foreshore. Not all drift was intercepted, for a proportion of the sand and fine gravel moved around the western training wall and thus bypassed the Arun inlet. Much of this is likely to be sand (Hydraulics Research, 1987). The progressive accretion of Littlehampton West Beach, to the immediate west of West Pier, indicates that historically there has been greater input of littoral sediment than natural losses. However, detailed study of beach profiles measured over the period 1973 to 2002 identified a trend for accretion at West Beach from 1973 to 1993, but with a tendency for erosion thereafter, especially within a zone extending 300m to the west of West Pier (Harris, 2003; HR Wallingford, 2003; Jezard, 2004). It can be postulated that less fresh sediment is entering the system due to retention by the Elmer breakwaters and that the recycling operations at West Beach are possibly removing material at a more rapid rate than it can be replaced naturally by eastward drift.
The mouth of the River Arun at Littlehampton appears to form a partial barrier to bedload movement of shingle due to strong tidal flushing and the intercepting effect of river training structures. Posford Duvivier (1987) report some overflow of fine shingle into the channel of the Arun and Hydraulics Research (1987) and Environment Assessment Services (1997) report significant sand transport across the Littlehampton Bar further offshore. Therefore, it is likely that the River Arun inlet is a more effective barrier to shingle than sand. Indeed, if bypassing of sand did not occur, recession of Littlehampton East Beach would have been significantly greater than it has been in recent decades. Jezard (2004) has analysed the historical evolution of the mouth of the Arun since the late 16th century. The first piers date back to the early 18th century and were associated with river straightening operations to improve navigation. The first reliable map to show the offset alignment of the west and east beaches dates to 1830, although there are some documentary records of West Pier extension in 1793 and 1825, possibly arising due to accretion to the west. 110m of retreat of the position of low water along East Beach (Photo 12) occurred between 1875 and 1979 (Gifford Associated Consultants, 1997), but most of this adjustment to the effects of the piers and training works upon sediment bypassing had occurred by 1900. Indeed, some advance of low water mark has occurred since 1930 (Jezard, 2004), possibly in part reflecting the periodic (but largely undocumented) addition of fine gravel and sand obtained from dredging Littlehampton Harbour and its approach channel. HR Wallingford (2003) estimated up to 20,000m³ per year of sediment may by-
Although natural potential for littoral drift on East Beach, Littlehampton was estimated to be between 20,000 and 65,000m³ per year eastward (Hydraulics Research, 1987; Posford Duvivier, 1987; Scott Wilson Kirkpatrick, 2000c), the LITPACK figure (Gifford Associated Consultants, 1997) for East Beach was an actual rate of 37,500m³ per year.
Analysis of Coastal Monitoring Programme baseline topographic (2008-
For the Worthing frontage, the LITPACK figure for eastwards movement of 38,500m³ per year was based on observed and estimated storage in the numerous inter-
A major rock groyne and gravel replenishment scheme was completed in phases at Lancing over the period 1997 to 2003, with further subsequent additions, e.g. 117,000m³ between 2005 and 2007 (Photo 13 and Photo 14). Studies of the initial beach behaviour suggested that the new rock groynes intercepted drift and retained material effectively, but that they were partly permeable, allowing some throughput of gravel to Shoreham West Beach (Coates, et al., 1999). It should be noted that the studies were undertaken over a three month autumn season shortly following completion of one section of the scheme. Beach behaviour and groyne permeability have altered over the following years following subsequent recharges and the development of a new beach equilibrium. However, the continuing efficiency of the groyne field is apparent from modest changes in volume between 2003 and 2008 (Worthing Borough Council, 2009).
West Beach comprises the western portion of a shore-
The Shoreham Harbour Authority have by-
Analysis of Coastal Monitoring Programme baseline topographic (2008-
As part of the Shingle Beach Transport Project (funded by MAFF and the EA) undertaken at Shoreham West Beach between 1996 and 1999 (Coates, et al., 1999), the deployment of six different tracer types over a 700m frontage indicated a net eastward actual drift of between 15,000 and 20,000m³ per year. Van Wellen, et al. (1997, 1999) and Lee, et al. (2000) reported that there was preferential transport of larger particles, suggesting the operation of sorting process that could result in beach grading. Most transport was confined to the beach face, with negligible exchange with the nearshore zone. Transport rates were closely related to wave energy flux, with "bursts" of more rapid drift. (During the experimental period 48% of waves approached between west and south, with a maximum offshore wave height of 4m). Tidal currents are weak (0.1 to 0.7m per second) and of no significance in effecting sediment transport. It was additionally concluded that vertical mixing depths have a linear relationship to significant wave height (Lee, et al., 2000). Beach elevations were found to oscillate by as much as 1m during single tidal cycles. Sediment exchange rates of 10m³ per tide for low energy waves, and 150m³ per tide for medium to high energy waves were recorded for specific experimental areas. Especially large high energy events were found to result in exchanges of up to 3,000m³/tide (Bray et al., 1996; Stapleton, et al., 1999). Taking a longer perspective, Mason, et al. (1999) found reasonable agreement for both short-
Beach Plan Shape Models (Halcrow, 1990; Chadwick, (1988a, b, c and d, 1989a and b, 1990; Baily, 2001; Duane 1998) have been tested at Shoreham by comparing their predictions with observed beach accretion. Models were calibrated so that littoral drift volume and direction, together with its effect on beach plan/volume, could be determined from suitable wave climate data. Despite this, wave refraction and reflection from the artificial breakwaters protecting the harbour mouth were found to cause anomalous effects on the drift pattern and beach volumes nearby, which could not be consistently predicted. Additionally, sediment transport was measured in the field using shingle traps and related to wave power to create calibrated transport equations (Bray et al., 1996). Halcrow (1990) reported that wave reflection from the breakwater caused a progressive eastwards reduction in the rate of longshore transport. This was also apparent over the frontage west to Lancing, possibly because of a slight change in shoreline orientation.
Analysis of Coastal Monitoring Programme bathymetry data and sediment sampling provide no conclusive evidence of onshore transport by kelp rafted shingle, which was postulated by Jolliffe and Wallace (1973) and Jolliffe (1978) to potentially constitute a small (not reliably quantified) but regular and significant gravel supply in certain areas. The sandy lower foreshore extends sub-
There is an apparent trend for sediment to grade from coarser to finer in both shoreward and eastward directions (Halcrow, 2004). All possess a distinctive cross-
Binnie and Partners (1987 and 1988) report that the seabed 2km to 8km offshore Worthing consists of a thin cover of sand and medium to fine gravel. Faintly defined sub-
Potential shorewards transport of sand and gravel from the Inner Owers, 15km offshore Littlehampton is regarded as very unlikely (HR Wallingford, 1993), and this observation has provided some confidence that long-
A series of sand waves were mapped off Shoreham and Brighton by the British Geological Survey (1990) using information from seismic and echo sounder surveys. Sand wave morphology indicated a net eastwards sediment transport pathway. It was, however, uncertain whether these sand waves were permanent bedform features or were intermittently developed, indicating periodic transport. HR Wallingford (1993) report large areas of sand in shallower water, with dominant but thinly veneered gravel further seawards. Much of the seabed is colonised by various flora and sedentary marine life, and sediment transport potential was thus considered to be low. Gravel was presumed to be immobile below depths of 12-
In both areas, residual tidal currents provide the main transport mechanism for very fine sand, although waves are a significant process in maintaining movement of suspended fine grained sediment in the nearshore zone.
Experiments conducted between 4km and 10km offshore Worthing and Shoreham by Crickmore et al. (1972) indicated a landward drift of gravel. Crickmore et al. (1972) concluded that the 9m water depth onshore feed was measured at 1,000-
Jolliffe (1978) conducted painted pebble experiments 8-
Tidal flushing operates at the mouth of the River Arun, but as training walls (Photo 1 and Photo 12) inhibit gravel entering the inlet channel (Posford Duvivier, 1987) transport mostly involves sand. Sediment sampling by Hydraulics Research (1987) demonstrated that sandy ebb tidal delta deposits extend up to 1km seaward of the East Pier comprised of sediments that drift into the inlet channel and then become flushed seaward. A study of the estuary mouth regime (Environmental Assessment Services, 1997) estimated that return shoreward transport from the delta is possible so that by-
The mean tidal flow at Littlehampton Harbour mouth is 135m³ per second, with tidal current velocities of up to 2.5m per second. Tidal scour has thus maintained the inlet and the depth of clearance over the harbour bar, which consists of two parts, an inner component (West Pier Head to East Beacon, to about 150m seawards), and an outer component between 150m and approximately 500m seawards of the outer entrance channel. Although the inner bar is more dynamic, there has been little overall morphological change since the late nineteenth century. However, new shoals have appeared inside West Pier and on the seaward margin of the outer bar, the former tending to reform between dredging operations. A reduction of depth of clearance over the outer bar, of 0.5m between 1887 and 1993, could be due to weed growth stabilising the sandy surface of the bar, which overlies consolidated cobbles. Alternatively, this trend may indicate an increase in the volume of sediment in transit across the harbour mouth, though there are no sedimentary structures that are diagnostic of sediment mobility.
Beaches comprise the main zones of littoral sediment storage. Ebb tidal deltas associated with the inlets of the rivers Arun and Adur are relatively poorly developed, possibly due to the loss of tidal prism resulting from infilling and reclamation of these estuaries. It can be postulated that larger tidal deltas could have been maintained in the past when the estuaries were larger, but their sediments would presumably have been driven onshore to feed beaches following estuary infilling and reclamation. Further information may be found at http://www.scopac.org.uk/sediment-
Upper beaches are composed predominantly of coarse flint gravel and are relatively steep and flat-
There are sand dunes behind Climping Beach, to the immediate west of Littlehampton Harbour West Pier that have accreted since 1830 in apparent response to the interception of drift by the River Arun training structures and the wide sandy lower foreshore that has accreted as a result (Harris, 2003). Although stabilised in parts by vegetation planting, they remain an open, active deposition system. Former dunes to the east of the River Arun, at Littlehampton, are now concealed by urban development (Jezard, 2004).
These general statements are based on analyses of beach composition at several specific locations, e.g. Shoreham (Chadwick, 1989; Coates, et al., 1999), Middleton and Felpham (Lewis and Duvivier, 1973; Mouchel, 1997a, b and c), Elmer (Cooper, 1997), Littlehampton West Beach, (Harris, 2003), Worthing (Binnie and Partners, 1987) and Lancing to Shoreham (Scott, Wilson Kirkpatrick, 1995). Quantitative data on beach sediments based on significant field sampling is provided principally by Gifford Associated Partners (1997), Cooper (1997), Coates, et al., (1999), and Scott Wilson Kirkpatrick (2000b, c) and Harris (2003). Gifford Associated Partners (1997) present trends of mean grain size, sorting and skewness separately for the upper and lower beaches. Although there are some site-
Information includes a variety of site-
Beach thickness is available for the vicinity of Littlehampton Harbour, where 4 boreholes were drilled (Environmental Assessment Services, 1997). On the lower foreshore (East Beach), 0.2-
The gravel volume of Pagham Estate beach, east of Pagham Harbour entrance, is estimated at 2-
Scott Wilson Kirkpatrick (2000b, c) calculate a mean volume of 2.5 million m³ for central-
The volume of West Beach at Shoreham is approximately 2.5 million m³, calculated from analyses of beach monitoring profiles derived from Environment Agency annual aerial photo surveys (Gifford Associated Partners, 1997). Scott Wilson Kirkpatrick (2000a, c) calculate that there was a steady gross increase in volume, between 1974 and 1998, in the order of 470,000m³. Duane (1998) reports an earlier net gain of 15,340m³ per year from 1971 to 1986, some 4,000m³ less than subsequently, but with some natural inter-
A comprehensive review of beach volume changes between 1973 and 2000 has been provided from analysis of the Environment Agency (and predecessor organisations) Annual Beach Monitoring Survey (ABMS) by Gifford Associated Consultants (1997), Scott Wilson Kirkpatrick (2000b, c) and Jezard (2004). Harris (2003), HR Wallingford (2003; 2007), Halcrow (2004), Worthing Borough Council (2009) and Atkins (2010) provide analysis of beach volume and cross-
The major trends between the early 1970s and 2011 that have been identified are (i) narrowing and steepening of most inter-
Analysis of profile changes between Poole Place (Photo 11) and the River Arun identified a trend for cutback erosion, crest flattening and overall loss of volume between Poole Place and Climping and accretion at West Beach from 1973 to 1996 (Harris, 2003). Erosion continued at Poole Place thereafter up to 2002, but at significantly reduced rates. Between 2003 and 2007, erosion downdrift of Poole Place migrated eastwards, but accretion occurred to the immediate west of Climping Car Park (Atkins, 2010). At West Beach, the accretion rate reduced slightly from 1993 to 2002 with erosion being temporarily recorded within a zone extending 300m to the west of West Pier. It can be postulated that the Poole Place frontage suffered sediment shortfall for some time prior to construction of the Elmer breakwaters and that the recycling operations from West Beach since 1993 have provided compensation for this deficit. Erosion at West Beach and some marginal dune erosion at Climping between 1993 and 2003 could indicate that less fresh material has entered the system since the Elmer breakwater construction, although it could also indicate that the recycling operation may have been removing material at a more rapid rate than it can be replaced naturally by eastward drift. Between 2003 and 2008 the Elmer to West Beach sector recorded a net gain of 3,500m³ (Worthing Borough Council, 2009) suggesting that a condition of quasi-
Worthing Borough Council (1987) stated that beach levels along their western frontage were previously appreciably lower. Thus, there has been a general trend for accretion of all grades of sediment throughout much of the twentieth century at a rate calculated at 7 to 9,000m³ per year. This has been attributed to the effectiveness of successive generations of groynes at intercepting drift. This assessment is based on comparisons of old photographs, plus observations of groynes periodically exposed by storms and some survey records. Reliability is only low/moderate, because insufficient quantitative evidence was presented. This report mentioned that in the mid-
A consequence of shoreline management by groynes has been both narrowing and steepening of beach profiles between Goring by Sea, South Lancing and West Shoreham Beach (east to King's Walk). Dobbie and Partners (1990) and Scott, Wilson Kirkpatrick (1995) identified these trends to have been uninterrupted since at least the 1870s. Mean Low Water mark retreated 1.7m per year between 1875 and 1896 and continued at a mean rate of between 2 and 3m per year up to the early 1970s. In response to very substantial losses of beach volume in the winter of 1989/90, a recharge of 110,000m³ was carried out in 1991/2. At the same time, beach crest height and width was increased. Resulting from subsequent shoreline management strategic studies (Scott, Wilson Kirkpatrick, 1995; 2000b and c), further small recharges and the construction of a series of rock groynes have been undertaken (Photo 13 and Photo 14). Recharge in 2003, 2005 and 2007 provided a total of 390,000m³ of gravel to help restore depletion of coarse sediment, thus clearly indicating that loss of volume is an ongoing inherent problem that continues the behavioural character of the beaches of this frontage experienced during the past forty years.
Analysis of beach monitoring data by Chadwick (1989) showed that the beach immediately west of the Shoreham harbour entrance was subject to net shingle accretion (1973-
Baily (2001) has analysed Lancing and Shoreham beach profile data for consecutive years, and decadal periods, and has concluded that shorter-
Data collected by the Defra-
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.
Estimates of gross and net littoral drift derived from numerical modelling based upon wave hindcasting are available at numerous points along the shoreline due to previous studies in support of schemes and the decision taken within the Beachy Head to Selsey Bill SMP to routinely provide such information (Gifford Associated Partners, 1997). Difficulties encountered in applying these models included the problem of selecting a representative sediment gain size on the mixed sand and gravel beaches (sediment mobility is highly sensitive to grain size) and the need to estimate (or ignore) the extent to which groynes on the upper beach intercepted any potential drift. It has meant that the data generated from these studies has had to be interpreted carefully.
Shoreham West Beach provides some of the best opportunities in the region for calculation and testing of littoral drift volumes. This is due to due to its simple morphology and bathymetry, unconfined transport and abundant shingle available for transport. These qualities were recognised by a series of researchers who have attempted to measure sediment transport in the field, develop relationships with hydrodynamic forcing and undertake numerical model application, development and verification e.g. Chadwick (1989b); Morfett (1990); Bray, et al. (1996); Duane (1998); Coates, et al. (1999); Mason, et al. (1999); Stapleton, et al. (1999); Van Welen, et al. (1999) and Lee, et al. (2000). The presence of the breakwater was especially advantageous for much of this work because the shingle accretion that it promoted to its west offered an independent estimate of long-
Other comparative work has been undertaken on beaches controlled by rock breakwaters Elmer (Cooper, 1997; King, et al. 1996) and rock groynes at Lancing (Coates, et al., 1999). Although it proved possible to demonstrate that transport could occur through such schemes over short intervals it proved difficult to determine generic controlling relationships that would enable scaling up of results to longer time periods. The problems encountered related to the complex configurations of these features and the tendency for rapid initial sedimentological and morphological changes of the recently replenished beaches.
Notwithstanding results from the Southeast Regional Coastal Monitoring Programme, and the summarised information and assessments from the Beachy Head to Selsey Bill SMP2 (Halcrow, 2006), recommendations for future research and monitoring that might be required to inform management include: