Cliff Recession Research Articles

Bayesian Statistical Methods for Modeling and Prediction of Major Landslides in Coastal Cliffs

The ability to predict coastline evolution in the long term is of great importance to coastal managers for social, economic and environmental risk assessment purposes. A Bayesian statistical approach to the problem of modeling and predicting the occurrence of major failure events in soft coasted cliffs is presented. This approach combines available data with expert judgement about the behavior of the cliff under study. Expert judgement is described in the form of expected values for cliff failure occurrences, confidence or degree of belief and subjective probability of occurrence of extremes. WinBUGS software is used to derive predictive probabilities, estimates of the rate of failure and standard deviations, which combine all information. The statistical method is illustrated in the cases of cliffs situated in Herne Bay and Scarborough, UK. The results can be used in a risk-based assessment of coastal cliff recession.

Rocky coast geomorphology and erosional processes: A case study along the Murgia coastline South of Bari, Apulia — SE Italy

Many sites along the Apulian coast (SE Italy) are composed of weathered and fractured carbonate rocks affected by intense erosion and the development of slope instabilities. Here, coastal morphology was mostly produced by Quaternary tectonics, the severe and selective action of modern erosion by sea waves, and locally, was strongly conditioned by human influences. In addition, due to the carbonate nature of rock masses, the role exerted by karst processes has to be considered. This paper provides a critical review of the common eroding processes and factors affecting coastal morphology in a typical Mediterranean coastal carbonate environment. A stretch of the Murgia coastline south of Bari (between San Vito and Polignano a Mare) made up of cliffs and shore platforms interrupted by small pocket beaches was considered. For qualitative and quantitative assessment of shoreline recession, the coastal stretch was monitored by means of field surveys between 1997 and 2003. Furthermore, a comparison of vertical aerial photographs covering the period 1966–1997 (scales 1:33,000, 1:10,000 and 1:5000), topographic maps (scales 1:5000, year 1987, 1:2000, year 1982), and archival terrestrial photographs taken since the 1930s was also employed. In some zones, characterised by a gently sloping shore platform, a significant shoreline retreat was calculated at about 20 m in the last 100 years (0.2 myr − 1 ), which was caused, above all, by human activity. Here, in fact, the presence of small ancient coastal quarries and artificial salinas is widespread; they are located where soft and porous calcarenites crop out. The cliffs are characterized by different types of landslides, with various complex mechanisms of rock slope failure. Cliff recession is episodic and discontinuous in time and space, and occurs in response to single large sea storms, such as that which occurred in January 1999. Between 1997 and 2003, the cliff retreat rates vary within a range of 0.01–0.1 myr − 1 and, in general, decrease where the coast is composed of fine-grained limestones and increase where medium-grained biocalcarenites crop out. Examples of erosion hazard indicators and mass movement typologies are illustrated.

The role of groundwater in cliff instability: an example at Cape Blanc‐Nez (Pas‐de‐Calais, France)

AbstractCliff retreat in northern Boulonnais is described. The distribution of the amount of retreat is related to structural and topographic factors. Both control the runoff–infiltration balance and therefore the mechanical behaviour of the rocks, which determines the modes of failure. The spatial variability of the retreat rate is explained, but predicting the temporal variability of the retreat rate, which is central to risk management, is much more difficult. Rainfall and piezometric surface data enhanced a ‘piston flow’ mechanism during November 2000. The result of its occurrence on the stability of the cliff and conditions of its recurrence are examined with a view to better understanding the rate of recession of coastal cliffs and wiser management of risk. Copyright © 2005 John Wiley & Sons, Ltd.

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.

Coastal cliff recession risk: a simple judgement-based model

To predict cliff recession rates, it is necessary to make judgements about the effects of changing environmental conditions and shoreline management practice on the recession process. A simple model is presented that allows judgements to be ordered in a systematic manner. The model can be used to generate single predicted values or a probability distribution of the possible recession rates, as illustrated by an example from the Covehithe cliffs, Suffolk. The output from the probabilistic model can also be used to support risk-based economic evaluation of the benefits of coast protection.

Frequency-Size Statistics of Coastal Soft-Cliff Erosion

Predicting the retreat of a coastal soft cliff is a difficult and uncertain operation, which has both theoretical and practical significance. Recession of soft cliffs occurs through a combination of processes, including slope failures and surface erosion, that are difficult to model jointly. Deterministic models for predicting coastal retreat are hampered by the complex nature of coastal erosion, which is highly nonuniform in space and episodic in time. To overcome these limitations, stochastic approaches have been proposed. These models assume distributions for the size and the time of the recession events. In this paper we investigate the frequency-size statistics of soft-cliff erosion based on two historical datasets of coastal retreat measurements at two sites in England. We find that the two datasets exhibit a similar behavior. The frequency of the recessions decreases with increasing size of the retreat. For small retreats the decrease is slow. For medium to large retreats the decrease is rapid and follows a power law. The frequency-size statistics of soft-cliff erosion is similar to the statistics of medium to large landslide areas, which are also power-law distributed. This is a significant but not conclusive result. More data are needed to confirm this finding.

Coastal processes and cliff recession between Gabicce and Pesaro (northern Adriatic Sea): a case history

Cliff recession on the high rocky coast between Gabicce and Pesaro Adriatic sea causes a wide range of mass movement processes on the whole slope, affecting both the bedrock and the overburden. The outcropping late Miocene rock formations are represented by marls, marly limestones, dark laminated mudstones and bedded sandstones and marls. Mass movements are common because of stratification and discontinuities in the rocks that, together with the presence of groundwater and weathering processes, reduce the overall strength of the slopes. A model for the evolution of this coastal area is proposed, which involves cyclic basal erosion, followed by mass movement that favours debris accumulation at the base of the cliff. The longshore currents have to then remove the material before a new cycle can begin.

Coastal profile modeling along the Russian Arctic coast

A morphodynamic model previously developed to predict the evolution of sedimentary coasts is extended to compare the effects of abrasion and thermal-abrasion processes on Arctic coasts. It is concluded that under the same storm impact, an unfrozen abrasion cliff loses almost the same sediment volume and retreats at almost the same rate as a thermal-abrasion cliff of corresponding effective height. Thermal impact itself presumably does not contribute to the volume of sediment losses significantly and only prepares the frozen material to be removed by waves and currents. Whatever the potential of thermal-abrasion determined by thermal effects, the volume of lost material would be limited mostly by the potential transport capacity of storm wave activity, as in the case of a pure abrasion. The long-term losses of sediments for both types of coast can be determined using an empirical relationship incorporating the effective height of the cliff, h ce, taking into account the subsidence of soil after thawing of ice. The proposed model is employed to predict the evolution of thermal-abrasion and accretionary coasts in the central and eastern Russian Arctic where the sea-ice conditions at present are more severe. The recession of the thermal abrasion cliffs is expected to accelerate by 1.4 to 1.5 times in the second half of the 21st century. Evolution of the accretionary coasts may lead to development of natural berms protecting the coast from erosion.

Soft Cliff Recession under Oblique Waves: Physical Model Tests

Laboratory experiments have been performed to investigate the recession of soft cliffs due to oblique wave actions. The experiments were conducted in a wave tank with irregular waves. A test cliff ...

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).

Lateglacial and Holocene talus slope development and rockwall retreat on Mynydd Du, UK

Modification of Lateglacial and Holocene talus sheets by debris flows and gully incision on Mynydd Du, Wales, has resulted in a convergence of upper slope form characterised by an upper rectilinear slope gradient of 36°±3° and a range of concavities of c. 0.1–0.2. In most cases, gully incision and accumulation of debris cones have led to an increase in slope concavity. Evidence for talus erosion, reworking and redeposition on the upper slope emphasises secondary reworking processes, as well as primary talus accumulation on the upper slope, and permits construction of a model of talus development at Mynydd Du. On the basis of talus volume, calculation of the first rockwall retreat data set for southern Britain suggests that c. 7.1 m (84%) of overall rockwall retreat (8.5 m) took place during the Lateglacial, and only c. 1.4 m (16%) occurred during the Holocene. These figures imply that Lateglacial retreat rates ranged from 1.01 to 2.44 m ka −1, with an overall mean rate of 1.23 m ka −1. In contrast, Holocene rockwall retreat rates range from 0.10 to 0.17 m ka −1, with a mean rate of 0.12 m ka −1. Approximately 27% of cliff retreat is attributed to microgelivation. While similar to Holocene and present-day alpine environments, these Lateglacial retreat rates are one order of magnitude higher than most equivalent values for arctic sites. This reflects both ‘alpine-style’ diurnal freeze–thaw activity on Mynydd Du during the Younger Dryas and paraglacial rock-mass instability following deglaciation. Assuming an exponential decline in rockwall sediment release, it is estimated that approximately half the talus had accumulated within c. 1 ka of deglaciation. At one site, paraglacial talus accumulation appears to have contributed significantly to the glacial sediment transport system of a subsequent ice advance. Present-day rates of rockwall retreat and talus accumulation by rockfall are estimated to be 0.014 and 0.022 mm yr −1 (m ka −1), respectively, similar to values for other British sites and markedly lower than Holocene rates of cliff recession due to microgelivation. By implication, the geomorphic significance of microgelivation may have been greatly underestimated in studies of inland rock-slope evolution in temperate, mid-latitude environments.

Coastal landslide activity: a probabilistic simulation model

A process-based simulation model of coastal landslide activity is described which uses Monte Carlo simulation to build up probabilistic predictions of cliff recession. The model, CLIFFPLAN, represents the principal nearshore, beach and landsliding processes that are instrumental in coastal cliff recession. Its potential is demonstrated by application to an eroding coastal cliff site on the east coast of the UK. This type of process-based simulation model could be used to make probabilistic predictions of cliff response to proposed engineering schemes, such as cliff toe protection or beach nourishment, and to model the consequences of potential climate changes such as sea level rise or changing hydrological regimes.

Stochastic simulation of episodic soft coastal cliff recession

Probabilistic methods provide a means of demonstrating the potential variability in predictions of coastal cliff recession. They form the basis for risk-based land use planning, cliff management and engineering decision-making. A range of probabilistic methods for predicting soft coastal cliff recession has now been developed, including statistical techniques, process-based simulation and structured use of expert judgement. A new episodic stochastic simulation model is introduced, which models the duration between cliff falls as a gamma process and fall size as a log-normal distribution. The method is applied to cliff recession data from a coastal site in the UK using maximum likelihood and Bayesian parameter estimation techniques. The Bayesian parameter estimation method enables expert geomorphological assessment of the local landslide characteristics and measurements of individual cliff falls to be combined with sparse historic records of cliff recession. An episodic simulation model is often preferable to conventional regression models, which are based on assumptions that are seldom consistent with the physical process of cliff recession.

Coastal cliff recession: the use of probabilistic prediction methods

A range of probabilistic methods is introduced for predicting coastal cliff recession, which provide a means of demonstrating the potential variability in such predictions. They form the basis for risk-based land-use planning, cliff management and engineering decision-making. Examples of probabilistic models are presented for a number of different cliff settings: the simulation of recession on eroding cliffs; the use of historical records and statistical experiments to model the behaviour of cliffs affected by rare, episodic landslide events; the adaptation of an event tree approach to assess the probability of failure of protected cliffs, taking into account the residual life of the existing defences; and the evaluation of the probability of landslide reactivation in areas of pre-existing landslide systems. These methods are based on a geomorphological assessment of the episodic nature of the recession process, together with historical records.

RISK-BASED BENEFIT ASSESSMENT OF COASTAL CLIFF PROTECTION.

Cliff protection schemes are designed to reduce the risk of damage or permanent loss of cliff-top assets as a result of coastal cliff recession and landsliding. To identify the most efficient scheme in economic terms requires an assessment of the beneficial risk reduction that each of the scheme options will achieve. This paper introduces a risk-based approach to evaluating the economic benefits of coastal cliff protection. The approach is applicable to economic appraisal of schemes for currently protected and unprotected coastal sites. Example appraisals of sites prone to progressive cliff recession, large catastrophic landslides and minor recurrent ground movement are included. Methods for including and structuring expert judgements of failure probabilities are explored. A risk-based approach is preferable to current practice, which is essentially deterministic, because it reflects the uncertainty that is inherent in recession predictions. Current deterministic methods can underestimate the economic risk associated with cliff recession.

Risk-based benefit assessment of coastal cliff protection

Cliff protection schemes are designed to reduce the risk of damage or permanent loss of cliff-top assets as a result of coastal cliff recession and landsliding. To identify the most efficient scheme in economic terms requires an assessment of the beneficial risk reduction that each of the scheme options will achieve. This paper introduces a risk-based approach to evaluating the economic benefits of coastal cliff protection. The approach is applicable to economic appraisal of schemes for currently protected and unprotected coastal sites. Example appraisals of sites prone to progressive cliff recession, large catastrophic landslides and minor recurrent ground movement are included. Methods for including and structuring expert judgements of failure probabilities are explored. A risk-based approach is preferable to current practice, which is essentially deterministic, because it reflects the uncertainty that is inherent in recession predictions. Current deterministic methods can underestimate the economic risk associated with cliff recession.

Talus accumulation and Rockwall retreat, Trotternish, isle of Skye, Scotland

Calculations based on the volume of talus accumulations at the foot of a basalt cliff indicate that 4.3–7.8 m (mean 5.6 m) of rockwall retreat has occurred since deglaciation at 17.5 Cal ka BP, implying average rockwall retreat rates of 0.25–0.45 m ka‐1 (mean 0.32 m ka"') over the last 17,500 years. The composition of the talus sediments indicates that approximately 70 % of total cliff retreat reflects rockfall, and that the remainder has been due to granular weathering of the face. However, radiocarbon‐dated soil horizons within the talus suggest that rockfall has been very limited since the end of the Loch Lomond Stade at c. 11.5 Cal ka BP, implying that about 80% of total rockwall retreat occurred between 17.5 Cal ka BP and 11.5 Cal ka BP. Rockwall retreat rate during this period is estimated to have averaged c. 0.75 m ka"1. This relatively high rate of cliff recession probably reflects stress release following deglaciation and/or frost shattering under periglacial conditions. Current rates of cliff retreat due to granular weathering are estimated to average 0.10 m ka"1, and probably exceed those due to rockfall.

Coastal cliff behaviour and management: Blackgang, Isle of Wight

Abstract In January 1994 coastal erosion and landslide activity at Blackgang, Isle of Wight, resulted in a dramatic retreat of the coastal cliffs and landward extension of ground movement. The initial impact of the event involved the destruction of two cottages, an access road, several cars and caravans, and around 12 homes had to be evacuated. The event raised considerable local and national media attention. The initial landslide response was co-ordinated by South Wight Borough Council, with advice from Rendel Geotechnics, and was aimed at ensuring public safety and security in the area. A detailed investigation was subsequently carried out to identify the extent and causes of coastal instability and cliff recession in the context of ‘cliff behaviour units’. An understanding of the characteristic cliff behaviour units has proved the key to assessing future landslide and cliff recession potential as well as identifying options for coastal cliff management at Blackgang. The coastal cliffs have been significantly oversteepened by the latest events and appear to be very sensitive to rainfall, with only relatively moderate to high winter rainfall totals expected to cause further cliff-top retreat and landslide reactivation. Consequently, in the absence of a financially and environmentally acceptable slope stabilization and coast protection scheme, continued managed retreat of cliff-top development and land use is seen as the only viable option.

Present‐day periglacial processes and landforms in mountain areas

AbstractThis paper outlines recent advances in our understanding of periglacial processes and landforms in mountain areas, as reported in the literature over the last 8 years. Landforms investigated include rockwalls, screes, avalanche paths, bedded slope deposits and patterned ground phenomena. Processes subject to quantification include cliff recession, rock displacements on slopes, rock thermal and moisture regimes, frost creep, mass wasting and solution. Laboratory experimentation and modelling studies have also been undertaken.

Stability and recession of the chalk cliffs at Compton Down, Isle of Wight : Barton, M E Proc International Chalk Symposium, Brighton, 4–7 September 1989P541–544. Publ London: Thomas Telford, 1990

Stability and recession of the chalk cliffs at Compton Down, Isle of Wight : Barton, M E Proc International Chalk Symposium, Brighton, 4–7 September 1989P541–544. Publ London: Thomas Telford, 1990