Complex relationships exist among offshore conditions, beach sediment transport and morphology, and till cliff erosion. Modelled and measured sediment transport rates established for the Holderness coast are similar to those on comparable coasts elsewhere. The direction of sediment drift depends on wave approach, and determining sediment transport rates, cliff composition and cliff retreat rates allows a sediment budget to be prepared. The beach response predicted by the sediment budget was confirmed by field observations, with budget surpluses and deficits coinciding with full and depleted beach profiles respectively. The area of deficit in the north of the study area was associated with the reduced sheltering effect of Flamborough Head on sediment drift. At most profiles, especially those with a sediment deficit, high energy waves may remove the sand veneer completely, leaving the till platform exposed. These bare till patches which elsewhere have been called ords and have been regarded as unique, were thought, in the present study,to represent a normal beach response to limited sediment supply and prevailing offshore conditions. Beach evolution was also modelled formally, the range of beach profiles exhibited on the Holderness coast being grouped into a number of distinct types, and evolution among them described and predicted by a first-order Markov model. This can be refined to provide different models for "winter" and "summer". Different modal types occur at different locations, and certain types of transitions between classes can be associated with particular ranges of wave conditions. Beach Development, Sediment Budget and Coastal Erosion at Holderness Susan J. Mason. Till cliff retreat at Holderness is extremely variable, both spatially and temporally, being influenced by beach level, energy conditions, cliff moisture content and the actions of man. The sediment transport rates, cliff retreat data, sediment budget and beach behaviour model are all essential elements of a research programme currently being undertaken to find a cheap method of protecting this coast.

Processes, mechanisms and parameters significant to instability have been identified from an investigation which has included 1) Geomorphological mapping and appraisal. 2) Field Monitoring. 3) Quantitative assessement of rock mass geometry, mineralogy, engineering properties and physical/physico-chemical behaviour. The north coast of the Bristol Channel is exposed to severe marine attack. Weak lithologies are exploited and the cliffs undermined. Principal failure modes recognised were toppling and vertical translation. Thermal gravimetry indicated allotropy of sulphide minerals. The least stable forms were identified in the more calcareous mudrocks, and a laboratory leaching experiment demonstrated that weatherability was greatest in such mudrocks. Pyrite oxidation was shown not only to enhance carbonate leaching, but to degrade the clay minerals and induce rehydration of the double layer. Uniaxial compressive strengths of representative mudrocks were determined for a range of moisture contents. Mean values varied between 5 and 64 MPa. An investigation into deformation anisotropy of a clay shale is also recorded. Meso and micro scale carbonate filled discontinuities are apparent in the limestones. Hoek & Brown's criterion was used to characterise results of a programme of strength testing. Average uniaxial compressive strength of the intact limestone was 234 MPa. In the field, many major discontinuities were identified as tensile in origin. Results from shear tests along limestone tension fractures could not be adequately represented by Barton's equation. A power relationship between shear strength and normal stress gave good correlation. Leaching, moisture and temperature movements, freeze-thaw and pressure release all act to impair stability. Extreme weather was shown to trigger failure. Limiting equilibrium analyses of toppling showed that torsional shear strength mobilized along the failure surface in the plane of toppling contributed significantly to forces resisting toppling. Both local masonry protection and pre-split blasting are recommended as viable expedients in protection and stabilization works.

The soft sedimentary deposits of the Waitemata Group which outcrop on the eastern coastline of the Auckland region are a coastal cliff erosion hazard. The determination of the rate that these cliffs erode for hazard zonation purposes still requires research. A database has been collated of a range of structural, geological, geomorphic and climate parameters from 16 representative cliff sites in order to statistically assess what parameters influence cliff erosion and why erosion rates vary within the relatively uniform geology. Four different lithological units have been defined: sandstone beds of turbidites; sandstone beds of densites (contain rip-up clasts); sand to gravel beds of debrites; and siltstone beds. Cliff rock has very weak to weak intact rock strength; apertures of 0.1 to 15 mm; infill types are soft clay and grit, and hard calcite and iron; spacing of discontinuities are smaller in siltstone beds (≥ 5 mm), and up to 5 m in sandstone and debrite beds; bedding and fault planes are continuous, joints are non-continuous; block size is dictated by bed thickness and non-continuous joints. Shore platform widths were used to determine long-term erosion rates which range from 1.2 to 53.0 mm y-1. Platform morphologies are either sloping or horizontal or are a combination of both. Higher platform benches found at some sites are considered to be the result of a higher period of sea-level or are high-tide benches. Intact and rock mass strength increases northwards. Cliff heights are 8 to 38 m; cliff angles are 51 to 79 . Conditions for sporadic planar and wedge failure were determined at some sites; frittered siltstone and low durability sandstone allow smaller-scale, continual erosion. Castor Bay, Army Bay, Waiwera Beach and Leigh Marine Reserve have the lowest rock mass quality. Musick Point, Narrowneck Beach and Waiake Bay have good rock mass quality. A conceptual model for coastal cliff erosion has been developed for Waitemata Group coastal cliffs, based on the dominant processes that act on the cliffs determined from statistical analysis (student t-test, correlation and regression) and field observations. The primary factor for cliff erosion is bed dip, whereby seaward dipping beds have higher erosion rates than landward dipping beds. The secondary factors for cliff erosion include: the intact and rock mass strength of the rock; the rock mass quality; strength of the siltstone beds; strength and structure of the sandstone beds; and orientation of the bedding planes with respect to the cliff face. Shear stresses are enhanced when beds dip seaward and thus shear failure along continuous surfaces is achievable. When beds dip landward the influence of shear stresses along bedding planes, and their contribution to the removal of individual blocks of rock, is severely inhibited resulting in reduced rates of erosion. There is no relationship between cliff height and erosion rates and cliff heights are mainly controlled by the pre-existing landscape. Cliff angle is controlled by the proportion of sandstone and siltstone (whereby lower cliff angles are more siltstone-dominated), rock mass strength and weathering. Erosion rates do vary in Waitemata Group rock of the Auckland region because of the variation in structural and geomorphic conditions of the cliff, most strongly controlled by the dip angle of bedding planes.

Coastal cliff erosion is a widespread problem that threatens property and infrastructure along many of the world’s coastlines. The management of this risk calls for robust quantification of cliff erosion rates, which are often difficult to obtain along rocky coasts. Quantification of sea-cliff rates of retreat on annual to decadal time scales has typically been limited to rapidly eroding soft rock coastlines. Rates of erosion used for shoreline management in the UK are generally based on analysis of historic maps and aerial photographs which, in rocky coast environments, does not wholly capture the detail and timing at which the processes operate and the failures occur across the cliff face. The first stage of this study uses airborne LiDAR (Light Detection and Ranging) data at nine sites around a rocky coastline (Cornwall, UK) to gain a quantitative understanding of cliff erosion where average recession rates are relatively low (c. 0.1 m yr-1). It was found that three-dimensional volumetric changes on the cliff face and linear rates of retreat can be reliably calculated from consecutive digital elevation models (DEMs) several years apart. Rates of erosion ranged between 0.03–0.3 m yr-1. The spatial variability in recession rates was considered in terms of the relationship with the varying boundary conditions (rock mass characteristics, cliff geometries, beach morphology) and forcing parameters (wave climate and wave exposure). Recession rates were statistically correlated with significant wave height (Hs), rock mass characteristics (GSI) and the ratio between the two (GSI/Hs). Although the rates derived using airborne LiDAR are comparable to the longer term rates of retreat, the detail of erosion to the cliff-face provides additional insight into the processes occurring in slowly eroding environments, which are vital for understanding the failure of harder rock coastlines. In addition to this, the importance of the wave climate and rainfall needs further attention on a more localised scale. Monthly cliff face volume changes, at two particularly vulnerable sites (Porthleven and Godrevy, Cornwall, UK), were detected using a Terrestrial Laser Scanner (TLS). Using these volumes alongside information on beach profile, beach- cliff junction elevation changes and nearshore hydrodynamics have allowed an insight into how the cliffs respond to seasonal fluctuations in wave climate and beach morphology. Monthly variability in beach morphology between the two sites over a one-year survey period i  indicated the influence that beach slope and the elevation of the beach-cliff junction have on the frequency of inundation and the power of wave-cliff impacts. Failure mechanisms between the two sites ranged from rotational sliding of superficial material to quarrying and block removal over the entire cliff elevation, according to the extent of wave-cliff interaction. This particular survey period highlighted the sensitivity of cliff erosion to the variability in wave climate and beach morphology at two different locations in the south-west of the UK, where the vast majority (over 85% of the annual value) of cliff face erosion occurs during the winter when extreme storm waves prevail. Coastal cliff erosion from storm waves is observed worldwide but the processes are notoriously difficult to measure during extreme storm wave conditions when most erosion normally occurs, limiting our understanding of cliff processes. Over January-March 2014, during the largest Atlantic storms in at least 60 years with deep water significant wave heights of 6 – 8 m, cliff-top ground motions of a rocky cliff in the south-west of the UK (Porthleven, Cornwall) showed vertical ground displacements in excess of 50–100 μm; an order of magnitude larger than observations made previously. Repeat terrestrial laser scanner surveys, over a 2-week period encompassing the extreme storms, gave a cliff face volume loss 2 orders of magnitude larger than the long-term erosion rate. Cliff-top ground motions and erosion volumes were compared at two different locations, one a reflective beach with steeply shelving bathymetry (Porthleven, Cornwall) and the other an intermediate, low tide bar-rip beach with a wide coastal slope (Godrevy, Cornwall). Under similar wave conditions (6–8 m Hs and 15–20 s. Tp) the vertical ground motions were an order of magnitude greater at the cliffs fronted by steeply shelving bathymetry, where the breaking waves plunge right at the shoreline, with little prior dissipation, leading to large energetic runup impacting the cliff. These storm results imply that erosion of coastal cliffs exposed to extreme storm waves is highly episodic and that long-term rates of cliff erosion will depend on the frequency and severity of extreme storm wave impacts as well as the wave dissipation that occurs as a function of the nearshore bathymetry. Having recorded microseismic cliff-top motion on this scale for the first time and determined an effective method of monitoring the energetic wave impacts, this study emphasises how investigations of cliff behaviour during storms is not only obtainable, but paramount to understanding coastal evolution under extreme conditions.