Cliff Erosion Research Articles

Seasonal Quantification of Coastal Processes and Cliff Erosion on Fine Sediment Shorelines in a Cold Temperate Climate, North Shore of the St. Lawrence Maritime Estuary, Québec

Abstract A quantification of coastal erosion processes on a clay cliff in a cold temperate region was conducted. This study was based on a network of markers that were measured on a monthly basis from 1998 to 2003. During that period, the average retreat rate of the cliff was 1.5 m/y. Our results demonstrate that weathering is a more significant cliff retreat factor than hydrodynamic processes on fine sediment shorelines. This statement opposes conventional understanding. In fact, 65% of the annual cliff retreat took place through the winter season when the waves could not reach the foot of the cliff because of an ice foot. This erosion is caused by cryogenic processes in winter, particularly through freeze–thaw cycles, whereas desiccation and wave undercutting contributed respectively for 20% and 15% of the total annual retreat. The field measurements conducted before and after major storms, especially on October 29, 2000, illustrated that wave undercutting was negligible for the clay cliff. These result...

The main characteristics, problems, and prospects for Western European coastal seas

Located to the far West of Western Europe, France has a western maritime coastal zone of more than 3800 km, which is widely influenced by the North-eastern Atlantic. The English Channel, an epi-continental shallow sea with very strong tides, runs along 650 km of the French coast and 1100 km of the English coast. It is also a bio-geographical crossroad encompassing a much wider range of ecological conditions than other European seas. France’s Atlantic coast north of the Gironde estuary is a succession of rocky and sandy shorelines, including a sizeable intertidal zone, a wide continental shelf, and two major estuaries (Loire and Gironde). South of the Gironde, the 260 km of coastline is low, sandy and straight, with a narrowing continental shelf further on South due to the presence of the Cape Breton canyon in the bathyal and abyssal zones. Interface between the continental and oceanic systems, these bordering seas – North Sea, English Channel and Atlantic Ocean – have been the subject of many recent research programmes (the European Mast-FLUXMANCHE and INTERREG programmes; the national coastal environment programme and the LITEAU programme in France), designed to improve comprehension of the functions, production, and dynamics of these seas as well as their future evolution. Given the many conflicting practices in these littoral zones, integrated coastal zone management appears to be essential in order to cope with both natural phenomena, such as the infilling of estuarine zones, cliff erosion, and rising sea levels, and chronic anthropogenic pressures, such as new harbour installations (container dikes, marinas), sea aggregate extraction for human constructions, and offshore wind mill farms. This article provides as complete an overview as possible of the research projects on these bordering seas, both those that have recently been accomplished and those that are currently in progress, in order to highlight the main characteristics of these ecosystems and to underline the future challenges for European marine research in terms of the integrated coastal zone management of these highly significant coastal zones.

Patterns and rates of erosion produced by high energy wave processes on hard rock headlands: The Grind of the Navir, Shetland, Scotland

The Grind of the Navir is an ignimbrite headland on the exposed Atlantic coast of the Shetland Islands, Scotland. During storms, offshore wave heights exceed 20 m and deep water close inshore allows high-energy waves to impact on these cliffs. The cliff top at ∼ 15 m above sea level is awash with wave water when wave heights exceed 8 m, a condition met in storms in most years. Detailed mapping, ground photography and patterns of lichen colonisation and growth allow the processes, patterns and rates of erosion to be assessed on different parts of the headland over the past 100 years. Recent fractures in the rock of the cliff face and top indicate that wave impact forces exceed the 1.5 kPa tensile strength of the rock and fresh sockets low on the cliff face record the removal of fracture-bounded blocks that are lost to seaward. On the upper part of the cliff face, upward moving water flow is capable of removing blocks from both vertical faces and stepped overhangs. Clefts in the cliff face are extended inwards and upwards by crack propagation and block removal, leading to the development of slot caves. The movement of waves across the cliff top in fast-moving bores quarries blocks from the cliff face close to the edge and from rock steps on the cliff top, promoting further rock fracturing. Socket sizes and block characteristics indicate that blocks of > 1 m 3 are rotated from sockets on the cliff top platform and carried landwards for up to 60 m to be deposited in a series of boulder ridges on the cliff top. Multiple boulder movements during a storm in January 2005 generated impact marks and orientated striations that allow the pattern of water movement to be reconstructed across considerable areas of cliff top. The average rate of erosion at The Grind is estimated at 1.3–6.0 mm/yr on the cliff face and 5 mm/yr on the cliff top, although erosion rates vary in both time and space. Although block movement on the cliff top occurs in most years, erosion of rock by block removal is most active during major storms. Nevertheless, some parts of the cliff top and face remain blackened by lichen and so have experienced little recent erosion over the last 70 years or so. Although erosion occurs at the base of the cliffs, in recent decades it has been concentrated on upper part of the cliff face and top. Cliff-top erosion is most intense where stepped geos act as channels for waves to access the cliff-top. The most active features on the cliff top are the boulder ridges where substantial changes can be traced to storms over the past century. Unlike conventional models of cliff erosion where erosion is concentrated by wave attack at the waterline, wave impacts on this headland may occur on any part of cliff face and top and appear particularly effective on the upper cliff and cliff top platform.

Hierarchical random effect models for coastal erosion of cliffs in the Holderness coast

Prediction of possible cliff erosion at some future date is fundamental to coastal planning and shoreline management, for example to avoid development in vulnerable areas. Historically, to predict cliff recession rates deterministic methods were used. More recently, recession predictions have been expressed in probabilistic terms. However, to date, only simplistic models have been developed. We consider the cliff erosion along the Holderness Coast. Since 1951 a monitoring program has been started in 118 stations along the coast, providing an invaluable, but often missing, source of information. We build hierarchical random effect models, taking account of the known dynamics of the process and including the missing information.

Past and future forcing of Beaufort Sea coastal change

Changes to the Beaufort Sea shoreline occur due to the impact of storms and rising relative sea level. During the open‐water season (June to October), storm winds predominantly from the north‐west generate waves and storm surges which are effective in eroding thawing ice‐rich cliffs and causing overwash of gravel beaches. Climate change is expected to be enhanced in Arctic regions relative to the global mean and include accelerated sea‐level rise, more frequent extreme storm winds, more frequent and extreme storm surge flooding, decreased sea‐ice extent, more frequent and higher waves, and increased temperatures. We investigate historical records of wind speeds and directions, water levels, sea‐ice extent and temperature to identify variability in past forcing and use the Canadian Global Coupled Model ensembles 1 and 2 (CGCM1 and CGCM2) climate modelling results to develop a scenario forcing future change of Beaufort Sea shorelines. This scenario and future return periods of peak storm wind speeds and water levels likely indicate increased forcing of coastal change during the next century resulting in increased rates of cliff erosion and beach migration, and more extreme flooding.

Cliffed coasts of New Zealand: Perspectives and future directions

About one‐quarter of New Zealand's shoreline is composed of cliffs. In some areas erosion rates are sufficiently rapid to be of concern to planners, whereas other cliffs have eroded imperceptibly slowly over human timescales. This paper reviews work conducted on New Zealand's cliffed coasts, from the pioneering studies of Sir Charles Cotton, who used Davisian theoretical methods to elucidate the evolution of hard‐rock coasts, to Jeremy Gibb's nationwide benchmark measurements of historical erosion rates. This review is augmented with a description of state‐of‐the art methods in use globally for investigating processes of cliff evolution. Key methods identified include detailed measurements using the micro‐erosion meter as well as novel geophysical methods of studying cliff movement under wave loading. Such process‐based studies build on previous research that has been largely confined to explanatory description and observation. It is recognised that the combined impact of such studies has been relatively muted, owing particularly to the difficulty of unravelling ambiguous process‐form interactions. However, the increasingly widespread availability of terrestrial and aerial remote laser scanning systems now provides an opportunity to re‐invigorate such studies by extending the scale from local to regional. The paper concludes by outlining prospects within New Zealand for further research. In particular, the development and use of numerical models is seen as an important avenue both for clarifying some basic behaviours observed on cliffed coasts, and for studying the likely response of eroding cliffs to future climate change.

Sedimentary processes over an intertidal flat: A field investigation at Hythe flats, Southampton Water (UK)

The sedimentary processes acting over an intertidal flat (Hythe, UK) located in Southampton Water, Hampshire, UK are investigated on the basis of hydrodynamic, morphological and sediment transport field measurements. Bed level changes, patterns of suspended sediment transport and shell movement over the tidal flats were examined in order to identify sediment transport pathways and salt marsh–mudflat morphological changes. Overall, sediment transport patterns at Hythe can be described in terms of suspended sediment and bedload-shell transport. The hydrodynamic complexity of the tidal flow over the flats determines the patterns of suspended sediments transport. During the young flood phase, tidal currents present a SW orientation (shoreward). About 1 h into the flood, a change occurs and the currents start flowing in a SE direction (estuary mouthward). This veering of the tidal current controls the hydrodynamic pattern over the mudflat inducing sediment transport towards the estuary mouth. Conversely, shell tracer experiment showed a net landward movement. Shells are transported over the mudflat, deposited at the base of the cliff, and eventually transported over the salt marsh where they form extensive chernier deposits. Shell transport rates can reach up to 0.7 m/tide over the upper mudflat. Shell movement over the salt marsh (on cheniers) occurred only during storms (up to 3 m in a storm event). Shell-induced erosion can become an important parameter on morphological changes of a coastal area. Shell transport and deposition over the salt marsh surface can contribute to vegetation deterioration, as shell deposits migrate over the marsh surface. As a result, the seaward limit of the salt marsh showed deteriorated vegetation, which leads to scouring and consequent surface lowering. In terms of bed level changes, no seasonal pattern was observed. A relationship between mudflat bed erosion and cliff retreat is suggested. During periods of high cliff erosion there was a tendency for the mudflats to be stable and, conversely, mudflat bed erosion was greatest when cliff retreat rates were lowest. Hence, morphological characteristics of Hythe intertidal area appear to be controlled by a combination of prevailing hydrodynamic conditions and shell transport over the salt marsh.

Factors Controlling the Retreat of Drumlin Coastal Cliffs in a Low Energy Marine Environment—Strangford Lough, Northern Ireland

The erosion of low cliffs of glacial material has been investigated around the shoreline of an enclosed sea basin (lough) with a very low wave energy environment. Erosion pins used at 16 sites monitored cliff retreat rates at monthly or 6-monthly intervals over a 3-year period. The total erosion during the 3-year study period ranged from 164.4 mm a−1 to 8.2 mm a−1. Cliff height, cliff angle, and the length and bearing of maximum fetch were found to be the most important parameters controlling erosion. Variations in cliff materials did not emerge as a significant factor controlling erosion rates. The shoreline on the eastern side of the lough suffers more rapid erosion than that on the western side because of its greater exposure to storms from the southwest quadrant. Current rates of erosion are sufficient on the eastern shore for some drumlins to have been completely eradicated or reduced to boulder shoals by erosion in the time that sea levels have been at present elevations.

Cliff recession and behaviour studies, Hunstanton, UK

This paper presents the recent case study of cliff recession at Hunstanton, North Norfolk. The cliffs at Hunstanton are composite weak rock cliffs which have retreated by up to 30 m since 1885 in a series of failures of varying size and nature. The paper describes a programme of cliff monitoring and analyses the findings in the context of the available historical data. The geological control over the failure mechanisms, erosion cycle, and hence failure return period is investigated and discussed. Based on observations made, the cliffs have been mapped according to cliff behaviour characteristics, each cliff behaviour unit comprising a recession rate class and a failure type class. In this way the behaviour of the cliffs can be described semi-qualitatively, based on real recession data and the nature and extent of failures. The boundaries between units are seen to traverse the cliffs with time, reflecting the transient nature of the cliffs' response to erosion. The case study demonstrates the importance of high-resolution spatial data in understanding the mechanisms involved in the cliff erosion cycle. The detailed monitoring data collected have enabled a transition from macro-scale predictions of future recession rates for the entire cliff section towards real hazard-related predictions based on failure size and return period at specific localities such as vulnerable structures. The benefits of this approach to coastal managers and planners are illustrated through discussion of remedial options and the anticipated impact of those remedial options on the cliff behaviour.

Sea Cliff Erosion in the Eastern Part of the North Aegean Coastline, Northern Greece

The coastal zone is an area where many human activities are taking place. Erosion of the coast obstructs, in various ways, these activities creating occasionally serious socioeconomic and environmental problems. In this paper the coastal erosion problems encountered in the eastern Greek part of the North Aegean Sea Coast, a stretch of about 51 km long adjacent to the city of Alexandroupolis, are discussed. Given the observed type and location of erosion and other sea-action phenomena, the coast under study is divided in two parts/stretches. The western stretch, where the city of Alexandroupolis is presently extending, presents, mainly, cliff erosion problems and retreat of the coastline, very serious in some sections; whereas, the eastern stretch (to the east of the city) exhibits deposition and progression seawards due to the abundance of sediments supplied by Evros river delta. A classification of the coastline according to its relief, geologic material, erosion characteristics and rate, slope failure phenomena as well as the wave energy potential, is presented together with suggestions for case-appropriate mitigation and protection measures regarding the coastal erosion problems. The paper is focusing on the cliff erosion phenomena, since varying in height coastal cliffs made of soft rocks, cover the major part of the investigated coastline (western stretch).

Meeting report: Soft coastal cliff: understanding and managing retreat

This article reports on a seminar held at the Institution of Civil Engineers in May 2004. This, and a previous meeting in 2002, stemmed from Government-funded research into soft cliff erosion. While the previous meeting dealt with the theory, this one dealt with more practical issues by way of four papers. Dr Neil Dixon described work carried out on landsliding of unprotected London Clay cliffs at Warden Point on the Isle of Sheppey. Dr Alan Clark described practical examples of engineering schemes at Lyme Regis and at Castlehaven, Niton and the Military Road on the Isle of Wight. The final two papers described aspects of work on the Norfolk coast: Dr Mike Walkden presented a process-based regional model of shoreline recession while Peter Frew of North Norfolk District Council described the problems faced by his authority in managing a retreating coastline where property is under threat.

Dynamic simulation and visualisation of coastal erosion

A key requirement for effective coastal zone management is good knowledge and prediction of land erosion rates due to encroachment of the sea. However, in addition to demarcation of the hazard through modelling and mapping, a policy of risk mitigation necessitates significant attention should also be addressed to communicating the transient behaviour of the predictions and associated uncertainty. With climate change and sea level rise implying that historical rates of change may not be a reliable guide for the future, enhanced visualisation of the evolving coastline has the potential to improve awareness of this changing risk. This visual content is developed by linking scientific modelling with the transformation of digital elevation models, and then using GIS to integrate other spatiotemporal content. The resulting high-resolution visualisations may meet demands from decision-makers for tools to communicate scientific results more effectively, due to their realism and apparent authenticity. Nevertheless they can also produces a tension with the underlying scientific content because of the necessary extrapolation of extra detail, and the lack of established procedures to communicate the resulting uncertainty in the visualisation. Coastal managers also have concerns about releasing the visualisations to the general public. These issues are explored through analysis of future cliff erosion in Norfolk on the eastern coast of Great Britain.

Numerical modeling of suspended matter transport in the North Sea

Knowledge about the distribution of suspended particulate matter (SPM) is an important prerequisite for the description and prognostication of the ecological conditions of the North Sea. SPM concentrations in the water column regulate the penetration depth of light and, therefore, is an important parameter influencing the primary production of plankton. Fine sediment in the bottom acts like a dynamical buffer representing sources and sinks for nutrients simultaneously. Moreover, the determination of the distribution of SPM and fine sediment provides evidence of the disposition of pollutants, adhered to the particles. In cooperation with GKSS Research Center, the transport model for dissolved conservative substances of the Federal Maritime and Hydrographic Agency (Bundesanstalt fur Seeschifffahrt und Hydrographie, BSH) was extended by a Suspended Particulate Matter module to take into account the processes of vertical exchange and horizontal distribution of SPM due to currents and waves. The success of such a model depends on an adequate description of the physical processes, as well as a careful preparation of maps of fine-grained sediment in the bottom and other sources of SPM (e.g., fluvial input and cliff erosion). In this paper, we examine quantitatively and qualitatively SPM distributions during two periods in 2000 and 2001. The results of a simulation during a storm at the beginning of 2001 are examined in detail to show the role of single exchange processes. Another application of the SPM transport model is presented as the simulation of dispersion of suspended material after a big river flood.

The application of time-lapse azimuthal apparent resistivity measurements for the prediction of coastal cliff failure

The erosion of coastal cliffs is inevitable. The resultant cliff collapses are a hazard, a problem for coastal land use planners and limit the use of the coastline as an amenity. There has been very little research into physical property changes within the rock mass behind a cliff face prior to collapse. If any such changes could be monitored with geophysical techniques then it might be possible to identify sections of a cliff that are becoming unstable. In cliffs composed of a highly fractured rock, such as chalk, any sub-vertical fractures will gradually dilate with time until a collapse is initiated. Since fractures often occur in sets with a preferred orientation, they impose anisotropic physical properties on the rock mass. With care, azimuthal apparent resistivity can be used to map fracture orientations and a factor of anisotropy can be calculated that should vary with time if the fractures are dilating. Azimuthal apparent resistivity data have been collected at three cliff top sites over a period of 2 years in order to quantify any such effects. The results indicate that a cliff-parallel fracture set develops in response to the presence of a free surface at the cliff face. A large reduction in anisotropy near the cliff face was measured as a result of a cliff fall. This has been interpreted as a release of fracture dilatancy. However, it is likely that the tectonic fractures within the cliff limit the lateral extent of the cliff fall and the lateral extent of the fracture dilatancy. Hence a consistently high value of anisotropy near the cliff edge may constitute a long-term warning of impending cliff collapse. Many of the sites showed seasonal variations in anisotropy, with peaks in the summer and troughs in the winter. A correlation has been observed between these variations and changes in rock temperature. It appears that changes in rock temperature lead to an expansion and contraction of the rock mass, with a maximum expansion in the winter. The expansion leads to fracture contraction with associated minimum values of anisotropy in the winter.

Seasonal and annual variations in the volumetric sediment balance of a macro-tidal salt marsh

This paper examines the spatial and temporal variability in the volumetric sediment balance of Allen Creek marsh, a macro-tidal salt marsh in the Bay of Fundy. The volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin. Changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996–2002, and detailed margin surveys were conducted in 1997, 1999 and 2001 using a differential global positioning system. Changes in surface area were calculated using GIS overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system. Currently the volumetric sediment balance at Allen Creek marsh is positive. However the processes of erosion and accretion demonstrate seasonal, annual and spatial variability. Inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments. Sediment is deposited onto the marsh surface year round, even during the winter when vegetation cover is sparse, and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations. Based on the data from 1996 to 2002, the mid and high marsh zones experience mean accretion rates of approximately 1.4 cm year − 1 whereas accretion rates in the low marsh region are statistically significantly lower (0.8 cm year − 1 ). The absolute amount of accretion varies between seasons and from year to year. The main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters. The volume of material removed from the marsh margin almost tripled between 1997 (169 m 3) and 2001 (502 m 3) following breaching of the side of a tidal creek channel, altering the patterns of margin erosion and deposition in the marsh system. During this time, however, other sheltered areas of the marsh system, such as along the tidal creek banks, showed evidence of new vegetation growth, increasing the amount of vegetated surface area available for deposition. The processes of erosion and deposition on the marsh surface exhibit considerable spatial variability, with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system, namely wave activity, vegetation, ice and water depths. A key factor in predicting how a marsh will evolve and respond to a number of different controls, e.g. sea-level rise or reduced sediment supply, is to quantify both accretion of the marsh surface and erosion of the marsh margin, evaluating the marsh system as a volumetric whole. This study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation. This is particularly important for open coastal marshes exposed to the erosive action of waves.

Terrestrial laser scanning for monitoring the process of hard rock coastal cliff erosion

Hard rock cliffs represent approximately 75% of the world's coastline. The rate and nature of the mechanisms that govern the retreat of these cliffs remain poorly constrained, primarily because conventional approaches employed to monitor these processes are generally inadequate for describing cliff erosion processes directly. These techniques are usually centred upon the interpretation of data collected periodically from aerial sensors, including stereographic aerial photographs and more recently air-borne LIDAR. These methods are generally not capable of assessing the pattern of erosion on the cliff face due to the oblique viewing angles, and hence tend to concentrate upon the resultant recession of the cliff top rather than change on the cliff face. Thus, processes of undercutting and small scale iterative failures of localized sections of the cliff face are generally not recorded. It is only when a failure affects the cliff top that any retreat is recorded. It is therefore unsurprising that cliff erosion is commonly deemed to be episodic. This paper presents a new approach to detailed cliff process monitoring using terrestrial laser scanning (TLS), which directly monitors changes on coastal cliff faces. The method allows the quantification of failures ranging in scale from the detachment of blocks of a few centimetres in dimension through to large rock, debris or soil, falls, slides and flows over 1000 m 3 . The collection of data is on-site and rapid and hence cost effective, providing a detailed description of the nature of coastal cliff erosion. This paper describes the methodological approach and demonstrates the range of results which can be generated, here shown for 16 months of monitoring data collected for a near-vertical cliff section on the coast of North Yorkshire, UK. The results demonstrate that terrestrial laser scanning can be used to quantify cliff failures to a previously unobtainable precision. The results reveal a strong spatial and temporal pattern of cliff collapse which contradicts commonly held perceptions of the nature of coastal cliff development.

Wave overtopping at vertical and steep seawalls

Wave overtopping is the critical response of most sea defence structures and one of the more important responses for many coast defences around the UK and other developed shorelines. Sea defences in rural areas are commonly provided by embankment seawalls. Steep or vertical seawalls are more commonly used in urban areas to protect against erosion, flooding and local overtopping hazards, and to protect the base of eroding cliffs in urban or rural areas. Vertically faced breakwaters have been common around many European countries, and caisson-type breakwaters are heavily used in Japan. For simple slopes or embankments, overtopping performance can be predicted by simple monotonic empirical formulae. Overtopping of vertical or slightly battered walls is however rather more complicated, with substantial differences in overtopping volumes and velocities depending on the form of wave interaction at or close to the wall. The present paper draws together results from a number of UK and European research projects over the last 10 years. Their results improve and validate prediction methods for wave overtopping discharges and velocities for steep battered, composite and vertical seawalls/breakwaters. The methods presented herein support, extend and qualify guidance given in the UK Environment Agency overtopping manual. The present paper shows how the use of these methods can now explain why overtopping of some seawalls/breakwaters can be greatest at mid-water level, rather than at the highest water levels.

Estimating long-term cliff recession rates from shore platform widths

Coastal cliff erosion is a problem in many coastal areas. However, often only very limited data are available to quantify the rates of recession for the development of coastal management strategies. In the soft flysch deposits of the Waitemata Group, Auckland, New Zealand, coastal cliffs are associated with shore platforms. Two models exist for the profile evolution of shore platforms and associated cliffs: the first suggests that an equilibrium profile develops in response to erosive processes, and this profile subsequently migrates landward; the second model suggests that the seaward margin of the shore platform is relatively static, and the profile extends landward through a combination of cliff recession and platform lowering. Physical simulations and field measurements for mudstone and limestone lithologies indicate that the second model is more likely for soft flysch deposits. A eustatic sea-level curve for the Weiti Estuary, Auckland, suggests that up to 7120 ± 70 years have been available for shore platform development since sea level reached the present seaward margins of shore platforms. Shore platform widths were measured using GPS at two sites in Waitemata Group rocks: the North Shore of Auckland; and the southern side of the Tawharanui Peninsula, North Auckland. The long-term cliff recession rates estimated from shore platform widths (1.4 ± 0.1 to 14.3 ± 0.1 mm y − 1 ) are consistent with the lower end of the average range of cliff top and face recession rates published for Waitemata Group rocks using different methods (11–75 mm y − 1 ), and in agreement with cliff base recession estimates (∼3.5 mm y − 1 ). Shore platform widths were qualitatively related to the rock mass characteristics of the associated cliffs, and therefore platform widths could provide a method of identifying regions of potential hazard.

Vulnerability of Poland's Coast to Sea-Level Rise

Over the last decades, the Polish coast, about 500 km long and predominantly featured by sandy, low-lying beaches, has been exposed to various threats resulting from intensified climate change and Accelerated Sea-Level Rise (ASLR). This has manifested itself in the growing intensity of shoreline, dune and cliff erosion and by the increasing necessity of their protection.The current study is both a summary and an extension of the existing Polish studies and analyses on the present and predicted influence of ASLR on the coast. First, the Polish coast was divided into three basic area types (AREA I, II, III) according to their geographic and socio-economic background. Then, two different scenarios of accelerated sea-level rise (ASLR1 — 30 cm/100 yrs and ASLR2 — 100 cm/100 yrs) were assumed. After that threats of land loss and the risk of its temporary or partial inundation was analyzed in connection with the assessment of the material and social costs and losses. These analyses were made within the framework of two adaptation scenarios, i.e. retreat (do nothing) and full protection.The performed analyses have shown that the greatest threat of partial or full land loss and the associated material and social costs are expected to occur in two regions of the Polish coast. One of them is situated in the eastern sector of the Polish coast and covers the agglomeration of Gdańsk and the Żulawy polders. The other is located in the west and comprises low-lying areas around the Szczecin Lagoon and the vicinity of the Odra river mouth. These areas both require intensive care and protection efforts.

Terrestrial Methods for Monitoring Cliff Erosion in an Urban Environment

Terrestrial methods that may be used to quantify cliff erosion rates, and to qualify the real status of coastal areas currently zoned for building are described. The methods are fast, inexpensive and effective for relatively small terrains. Due to the use of modern methods and instruments, a very high (sub-centimetre) accuracy for measuring cliff recession can be reached. A computer model is derived to analyse data obtained through the measurement techniques. The model will, over time, supply data sufficient to project short to medium term volumetric changes in rock mass and will provide significant input in the development of a coastal hazards zoning protocol. A pilot study has been carried out in North Shore City (Auckland, New Zealand).