Cliff Erosion Research Articles

Lake Waves, Coarse Clastic Beach Variability and Management Implications, Loch Lomond, Scotland, UK

Abstract The variability of two lake gravel beaches (Loch Lomond, Scotland) is described in the context of changing environmental conditions. Waves, water levels and wind orientation and velocity were recorded for 1 year. The wave climate comprises small amplitude, high frequency, short-period waves and periods of calm (mean frequency = 0.92 secs; mean significant wave height = 0.08 m). Incident wind-wave direction was an important influence on beach morphology. Water levels fluctuate and there is a general increase in level. Wave activity combined with high water levels affects the upper beach and backshore although here, the highest waves were recorded at low water levels which minimised wave damage. Cliff erosion rates were recorded. Beach morphological changes showed highly variable profile types which were closely related to beach elevation, exposure and sediment supply. Sections of beach represented by individual profile types showed re-occurring profile types and different sections of beach respond...

Coastal chalk cliff erosion: experimental investigation on the role of marine factors

Abstract In this paper the marine factors of erosion contributing to the chalk cliffs located on either side of the English Channel are examined. From an analysis of the literature, the main physical phenomena determining the marine erosion of the shore platform and the foot of the cliff are considered. Field observations of the coastal chalk cliff show that the vertical erosion of the shore platform does not appear to be the main cause of cliff erosion, which is mainly governed by cliff collapse processes. To estimate the impact of waves on the base of the cliff, experiments were carried out in a wave flume. The pressure due to the waves and the dissipation of waves were measured for three simple configurations of the boundary conditions between the cliff and the sea. The pressure never exceeded the compressive strength of chalk rock. Nevertheless, pressure fluctuations due to periodic waves can induce a fatigue process within the fracture structures. The experimental results showed that the shingle by itself has a low effect on wave energy dissipation. The main effect of shingle is to reduce the water depth at the toe of the cliff. Furthermore, it is demonstrated that a lower water depth leads to a lower impact of the waves on the cliff.

Using geomorphological rules to classify photogrammetrically-derived digital elevation models

An object-orientated expert system is used to identify beach and cliff landforms from Digital Elevation Models (DEMs) on the basis of topological and morphometric rules. The ord landform of the Holderness coast, north-east England, is interpreted as an indicator of enhanced cliff erosion and consists of various beach, till shore platform and associated steep/stable cliff constituents. Each of these are characterised by expert rules through their topological relationship with other constituents and typical values of height, slope, aspect and convexity. Two DEMs (1996 and 1997) are derived from the application of digital photogrammetry to stereo aerial photography provided from the LOIS (Land-Ocean Interaction Study) project. A rule-based classification of landforms is performed using COAMES (COAstal Management Expert System), producing results that conform to historical ground estimations and which identify zones of intense erosion and their commensurate movement with the ord landform over time. The result is achieved through the intelligent storage and operation of classification techniques, which should facilitate non-specialist usage.

Influence of coastal structures on the beaches of southern Karnataka, India

Eight beaches of Dakshina Kannada and Udupi districts were regularly surveyed and monitored between 1985 and 1999 to understand morphological changes. During SW monsoon the wide summer beaches of this coast experience erosion. Eroded beaches start growing during post-monsoon period and are fully developed by April/May. These erosional and accretional trends are cyclic and annual in nature. Minimum sediment is stored on the beaches during July/August and maximum during April/May. Sediment budget estimates reveal a net gain and hence, there is an accretional trend along this coast. Wherever erosion becomes severe, construction of seawalls is taken up as a preventive measure. In fact, these structures enhance erosion or shift erosional sites towards adjacent areas or they undergo destruction. Occupation of protected beaches is an added problem. Material from cliff erosion of northern coast and that contributed by rivers of these districts are the major sources of littoral drift and beach sediments. Net littoral drift is towards south and any construction as barrier to this results in erosion on downdrift side. Three case studies conducted at Old Mangalore Port, New Mangalore Port and Kapu-Mulur areas exemplify this trend. Significant morphological changes have taken place at Old Mangalore Port area after the recent construction of breakwaters. The shoreline has prograded by about 225 m on updrift side and retreated by 165 m on downdrift side between December 1993 and July 1995.

Sea-cliff erosion as a function of beach changes and extreme wave runup during the 1997–1998 El Niño

Over time scales of hundreds to thousands of years, the net longshore sand transport direction along the central California coast has been driven to the south by North Pacific winter swell. In contrast, during the El Niño winter of 1997–1998, comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches. This resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends. Coincident with the south-to-north redistribution of sand, shoreline morphology became prominently cuspate with longshore wavelengths of 400–700 m. The width and elevation of beaches were least where maximum shoreline erosion occurred, preferentially exposing cliffs to wave attack. The resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches. The observed magnitude of sea cliff retreat, which reached 14 m, varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the El Niño winter. A threshold representing the width of the beach performed better than a threshold representing the elevation of the beach. The magnitude of cliff erosion can be scaled using a simple model based on the cross-shore distance that extreme wave runup exceeded the pre-winter cliff position. Cliff erosion appears to be a balance between terrestrial mass wasting processes, which tend to decrease the cliff slope, and wave attack, which removes debris and erodes the cliff base increasing the cliff slope.

Dune, Bluff and Beach Erosion due to Exhaustive Sand Mining – the Case of Santa Barbara Beach, São Miguel (Azores, Portugal).

Coastal dunes are relatively rare features in the Azores islands and contribute to less then 1% to the total length of the archipelago's littoral zone, circa 844 km. Localised indications of aeolian activity, contemporaneous to the arrival of the first colonists in the 15th century have been found, but at present most of the coastal dunes are vegetated and stabilised. Dune sand has been exploited during the 20th century for industrial use, leading to severe damage or complete removal of a significant proportion of these features. In the 1950's the Santa Barbara area contained a rare and well-preserved example of an undisturbed active beach-foredune system, free of anthropogenic activities. It displayed a well-nourished beach profile margined by a coastal foredune and a climbing dune, which covered the adjacent bluff and extended landwards through an aeolian sand-sheet. Persistent sand mining between the early sixties and the late eighties, lead to volumetric depletion of the dune cover, lowering of the surface of the berm and triggering cliff erosion. In total, some 950,000 m3 of sand has been removed, the dunes making up half of this figure. Although this activity was stopped in 1995 by legal enforcement, the erosive process still currently persists indicating a surpassing of the natural resilience and maximum vulnerability of the coastal dune system. At present the bluff retreats at very high rates (0.6 m/yr), the dune features were totally obliterated and the sandy beach has been reduced in width to a single swash ramp which floods during half of the tidal cycle.

ASTER measurement of supraglacial lakes in the Mount Everest region of the Himalaya

AbstractWe demonstrate an application of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images to detect and monitor supraglacial lakes on glaciers in the Mount Everest region in Tibet (Xizang) and Nepal. ASTER offers powerful capabilities to monitor supraglacial lakes in terms of (1) surface area, growth and disappearance (spatial resolution =15m), (2) turbidity (15m resolution), and (3) temperature (90m resolution). Preliminary results show an overall similarity of supraglacial lakes on three glaciers. Lakes have widely varying turbidity as indicated by color in visible/near-infrared bands 1–3, the largest lakes being bright blue (highly turbid), cold (near 0°C) and hydraulically connected with other lakes and supraglacial streams, while small lakes are mostly darkblue (relatively clear water), warmer (>4°C), and appear hydraulically isolated. High levels of turbidity in supraglacial lakes indicate high rates of meltwater input from streams or erosion of ice cliffs, and thus are an indirect measure relating to the activity and hydraulic integration of the lake with respect to other lakes and streams in the glacier.

Towards a sediment budget for the Santa Cruz shelf

A conceptual model is presented for the northern Monterey Bay continental shelf in which coarse sediment moves southward along the coast in the littoral zone while fine sediment moves to the north by advection and diffusion along the midshelf. Data from measurements and estimates of various sediment sources and sinks show that the midshelf mudbelt is the dominant sink for fine-grained sediment introduced into Monterey Bay. The principal sources of the fine sediment are the three rivers that enter Monterey Bay: the San Lorenzo, Pajaro and Salinas rivers. Accumulation rates in the midshelf mudbelt are high relative to documented yields of rivers and cliff erosion, and also are high relative to other documented mud accumulations of the west coast continental shelves.

Suspended sediment transport on the continental shelf near Davenport, California

Suspended sediment transport on the shelves off Santa Cruz and Davenport, California is studied using field measurements and bottom boundary layer modeling. Strong transport events mostly occur during storms in winter; the volume of winter sediment transport is at least one order of magnitude greater than that of summer/spring transport. Rock outcrops on the inner shelf (<40 m of water) indicates an erosional environment, but an elongated mid-shelf mud deposit evidently suggests a depositional environment on the mid-shelf. The seafloor geology appears to correlate to the poleward and offshore sediment transport pattern. This study also suggests that suspended sediment moves out of Monterey Bay, roughly along the isobaths of the northern bay. This fine material, originally from river sources, and the material from the coastal cliff erosion that is subsequently introduced to the transport system through cross-shelf sediment transport, are believed to be the sources of the mid-shelf mud deposit.

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.

A methodology for the study of the relation between coastal cliff erosion and the mechanical strength of soils and rock masses

A methodology is proposed to make approximate estimates of the destructive force of waves at the bottoms of cliffs where no accurate bathymetric data are available, by means of correlation between the erosion rate of rocky coasts and the mechanical strength of soils and rock masses. The correlation used makes it possible to obtain a linear semi-logarithmic expression between the long-term average erosion rate (from an engineering standpoint) of coasts consisting of different lithologies, wave energy, and the uniaxial compressive strength of soils and rock masses forming the cliffs. The uniaxial compressive strength of soils consisting of landslide debris was measured using a pocket penetrometer and the Rock Mass index (RMi) method was used for rock masses. These methods were chosen after critical analysis of the methodologies currently available. The proposed approach was tested in the Cilento area of southern Italy, and in particular along a 6 km stretch of coast typified by rock masses and landslide debris that are particularly susceptible to erosion. This coastline is exposed to south-westerly waves which in deep water reach significant heights (between 1 and 3 m) and significant wave periods (between 4 and 7 s). Estimates of the coastal erosion rates were made by studying the variations, especially in restricted headland areas, occurring over two time spans, 30 and 45 years, respectively by comparing topographic maps and aerial photographs taken at different times. These comparisons give approximate indications of retreats of 15 m over the time span of 30 years (average erosion rate of 0.5 m year −1) and of 35 m over the time span of 45 years (average erosion rate of ca 0.8 m year −1). These data do have a local significance but clearly show how quick these processes sometimes are. Lastly, the study of a notch incised by wave action on a concrete sea wall built to protect a terrace made it possible to quantify the impact of erosion on concrete. It was possible to obtain RMi-values through field observations. Furthermore, it was possible to obtain the constants of the Hoek and Brown failure criterion using RMi. On the basis of RMi-values, the rock masses studied were defined as ‘moderately strong’ to ‘strong’ and, according to the Hoek and Brown criterion, as ‘poor’ to ‘fair’. A semilogarithmic linear relation was found between the strength of landslide debris, rock masses and concrete, as well as their respective long-term erosion. Consequently, a rough estimate of the destructive force of waves (ca 24 MPa) was calculated. This value is given by the product of the mean value of their hydraulic pressure for a non-dimensional constant which, in turn, takes into account the sandy-pebbly beach sediment at the foot of the cliffs that acts as an abrasive on the rock mass.

FIEID OBSERVATION OF SEACLIFF AROUND POINT LOMA AND DEL MAR IN SAN DIEGO IN CALIFORNIA

Cliff erosion was investigated at the coasts around Point Loma in San Diego and Del Mar areas in California. On these coasts, installation of countermeasures against cliff erosion is rare in contrast to the cliff coasts in Japan. On Japanese coasts, concrete armor units are usually installed to protect coastal cliff and this causes decrease in sediment supply from the cliff, which induces beach erosion on the down coast. This gives one of the reasons for extension of artificial coastline in Japan. Overall stability of the sandy beach including cliffy coast as a sand supply source should be deeply considered.

POPULARIZATION OF COASTAL SCIENCES AT LOCAL COMMUNITY

In the preservation of sound coastal environment, public understanding of the state of the coasts and various phenomena occurring on the coasts is important. In order to realize this, scientific knowledge of the coast should be popularized as much as possible. Santa Barbara, California, where is the famous marine resort town of high society in West Coast, was investigated in March and August 1999. Santa Barbara is considered as a field museum to exhibit coastal sciences. People can see various natural phenomena with many explanation panels on the coasts. In Santa Barbara, cliff erosion is severe for much personal property above the cliff to be endangered. A wooden pier was built in the central part of the sandy beach to show shore dynamics. Museums also are useful for the understanding of the local coast.

The generation and degradation of marine terraces

Marine terraces are ephemeral planar landforms. While tectonic and climatic forcings responsible for the generation of existing marine terraces have operated for at least 1 Myr, terraces have been completely removed by erosion above a given altitude (and hence above a given age). Above this altitude, the landscape has forgotten that it was once terraced. We ask what controls this characteristic time‐scale, which we term the ‘forget time’, in a landscape. We approach the problem with simple scaling arguments, and 1‐D numerical models of landscape evolution.Using a simple cliff erosion model with a realistic sea‐level history, rock uplift and a cliff retreat rule, we find that the most important means of terrace removal is through the deeper transgression of a subsequent sea cliff into the landmass. The sequence of preserved terraces depends upon the history of sea cliff incursion into the landmass. The extent of sea cliff incursion depends on the duration of the sea‐level highstand, the far‐field wave energy input and the degree to which bathymetric drag dissipates wave energy. This portion of the marine terrace survival problem is an example of a common problem in geomorphology, in which the record of past tectonic or climatic events is rendered incomplete by the potential for younger events to wipe the topographic slate clean.While sea cliffs decay through time, their form can still be recognized many hundreds of thousands of years after formation. This reflects the diffusive nature of their decay: early rapid evolution and lowering of maximum slopes yields to slower rates through time. Incision by streams, on the other hand, is rapid, as the streams respond to base‐level history driven by sea‐level changes. The rate of incision reflects the local climate conditions, and is limited by the rate of base‐level fall.The principal means of vanquishing a marine terrace is by backwearing of slopes adjacent to these incising streams. The forget time should be proportional to the spacing between major incising streams and to the angle of hillslope stability, and should be inversely proportional to the rate of channel incision. This yields an overestimate of the forget time, as the terraced interfluves are reduced as well by the headward incision of tributary streams.The resulting landscape may be viewed as a terraced fringe separating the sea from the fully channellized landscape. Over time‐scales corresponding to many glacial–interglacial sea‐level oscillations, this fringe can achieve a nearly steady width. The rate of generation of new terraced landscape, reflecting the uplift rate pattern, is then balanced by the rate at which the terraces are erased beyond recognition by channel and hillslope processes. The width of this fringe should depend upon the precipitation, and upon the distance to the nearest drainage divide, both of which limit the maximum power available to drive channel incision.

Balancing the Aims of Geological Conservation with Coastal‐Defence Requirements

ABSTRACTThere are many examples, both nationally and internationally, where coastal‐defence structures have impeded the natural erosion of cliffs and have thereby reduced the geological importance of a particular site. These problems have arisen where piecemeal defence schemes have been adopted as remedial measures to protect property or infrastructure from erosion. The recent onset of ‘shore‐line management plans’ in the UK have attempted to redress this issue by reducing ‘myopic’ planning and, instead, seeking to promote more strategic thinking towards the impact of carrying out such work on the natural environment.This paper has been written to make coastal engineers aware of the importance of this topic within the ‘shoreline management plan’.

Mathematical Modeling of Basal Coastal Cliff Erosion in Uniform Strata: A Theoretical Approach

This article utilizes the general assumption that cliff erosion is dependent on the strength of wave assailing forces and the resistance of the cliff material. It considers the possibility of understanding and describing coastal cliff erosion processes, particularly basal erosion, through a mathematical analysis of one of the clearest manifestations of its action, i.e., the development of the basal cliff notch through mechanical wave action. It analyzes profile change through time, assuming a cliff composed of uniform strata. Deterioration of the cliff is expressed by means of the erosion function, which in this study is related to the cliff erosion rate. An equation, termed the Belov, Davies, Williams (BDW) equation, has been formulated for a moving surface, and this is proposed as a mathematical model of cliff profile change. Explicit solutions of the BDW equation are found for both steady state and time‐dependent erosion rates. In both cases, it is assumed that wave erosion intensity decreases exponentially with height. Solutions obtained showed that cliff retreat, related to basal notching, depends upon the erosion intensity and magnitude of the geophysical parameters. The model predicted the occurrence of cliff basal notching, the depth of which is comparable to field observations and can be applied to other locations. It is believed the approach and model has the potential to be developed further for other structural contexts such as locations with a variable lithology.

海岸崖侵食に対するジオシンセティックスの適用に関する模型実験

海岸崖侵食に対するジオシンセティックスの適用に関する模型実験

Coastal dynamics and impact of coastal protection works on the Spurn Head spit (UK)

The erosion of the glacial tills along the Holderness Coast (eastern England) has released material which has led to the formation of a 4.5 km sand and gravel spit, Spurn Head, across the mouth of the Humber estuary. This paper examines the sedimentology and geomorphology of the spit and of the tidal flat behind it (Spurn Bight), and assesses the effects of coastal defences on the nearshore dynamics. A study of the coastal dynamics was carried out by analysing wind data and modelling wave shoaling and refraction at the estuary mouth, and on the tidal flat. The geomorphology and sedimentology of the beaches and the tidal flat were studied to assess the response of the spit system to different weather conditions. The results show that only 6% of the longshore drift produced by cliff erosion in Holderness is transported along Spurn Head, mainly by waves from the north and the north-east. This drift is stored in an area of sand and gravel banks at the tip. Medium-size sand is carried around the tip by south-easterly waves, leading to the formation of a small area of tidal sand waves. Waves from the southwest, which originate within the estuary, spread the sand over the tidal flat, but are not able to carry it towards the most northern inner part of the spit. Coastal defences built along the spit have slowed its rate of landward migration and prevented overwash processes. The defences have not been maintained for the last 30 years so that the spit is now likely to be breached in the winter months whenever surge conditions exist.

Erosion and sediment supply of sea cliffs of Todos Santos Bay, Baja California, from 1970 to 1991

Aerial photographs from INEGI for October 1970, October 1985, July 1989 and September 1991 were analyzed to calculate the cliff retreat rate and sediment volume supplied to the coastal system in four coastal sectors of Todos Santos Bay: San Miguel, El Sauzal, Punta Morro/El Vigía and Punta Banda. Results indicate that all four sectors are under erosion, with cliff retreat rates of 0.93, 0.97. 0.70 and 0.89 m/yr, and sediment volumes of 14.097.71, 13,996.16, 3,919.14 and 16,194.43 m3/yr, respectively. The cliffs are important for maintaining the sediment budget of the coastal zone in Todos Santos Bay.

Sea cliff erosion caused by a storm drain failure : R. W. Day & D. M. Poland, Environmental & Engineering Geoscience, 1(4), 1995, pp 524–529

Sea cliff erosion caused by a storm drain failure : R. W. Day & D. M. Poland, Environmental & Engineering Geoscience, 1(4), 1995, pp 524–529