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A mathematical model was used to predict the effect of climate change on soft and hard rock coasts in a 2 m tidal environment. Erosional equations represented the effect of wave impact and bottom generated shear stresses in the intertidal and subtidal zones. Model runs were made for: 2900 years with constant sea level; a further 100 years, representing the last century, with either constant or slow sea level rise (0.2 m per century); and another 100 years, representing the present century, with either slow or fast (1 m per century) sea level rise, and with either no change in storm frequency or with a 10% increase in the frequency of the highest waves. The results suggest that rising sea level will trigger faster rates of cliff recession, whereas increased storm wave frequency may have only a fairly minor effect on erosional efficacy. Model runs were used to derive a series of predictive equations relating cliff recession during the present and last centuries. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the pattern surface downwearing on shore platforms in Eastern Canada. It states that downwearing rates were measured on shore platforms about 200 transverse micro-erosion meter (TMEM) stations over 2 to 6 years. An overview of the rock-samples experiment process is also presented.

Abstract: Laboratory and field work was conducted to determine rates of surface downwearing on shore platforms at two sites in the Bay of Fundy, Canada; these data are needed to assess and model the effect of downwearing mechanisms on platform evolution. Sandstone and basalt samples (900) were exposed to semidiurnal tidal cycles over 3years, using de-ionized water or artificial sea water. They were immersed for 1, 6, or 11h over each 12h tidal cycle, representing the lowest high (LHT), mid-, and highest low (HLT) tidal levels, respectively. A further 600 samples were immersed in de-ionized water or artificial sea water for 90min every 1, 2, or 3weeks, representing increasingly higher elevations above the LHT level, or exposed for 90min every 1, 2, or 3weeks, representing increasingly lower elevations below the HLT level; these experiments ran for 12months. In the field, surface downwearing was measured at 108 transverse micro-erosion meter (TMEM) stations over 2 to 6year periods. In the laboratory, mean downwearing rates between the LHT and HLT levels were 0.61–1.80mmyr−1 in sandstones and 0.01–0.18mmyr−1 in basalts; rates were highest at the LHT level. Rates decreased with elevation above the LHT level and were uniformly low below the HLT level. Salt weathering was dominant above the LHT level. Salt weathering and wetting and drying were important in sandstones between the LHT and HLT levels, but salts inhibited rock breakdown in basalts. In the field, the mean downwearing rate was 1.254mmyr−1 in sandstones, which was similar to the experimental data, and 0.722mmyr−1 in basalts, which was much higher than in the experiments with artificial sea water but similar to the experiments with de-ionized water. There was no relationship in the field between downwearing rate and rock hardness or TMEM station elevation. [Copyright &y& Elsevier]

Abstract: Work has been conducted, in the laboratory and field, on a micro-tidal, subhorizontal shore platform in argillaceous rocks at Mont Louis, in Gaspé, Québec. Surface downwearing rates for 450 rock samples were measured over 3years in the laboratory at the neap low, mid-, and high tidal levels, under semi-diurnal tidal conditions. De-ionized water was used to determine the role of wetting and drying, and artificial sea water for the additional effect of salt and possibly chemical weathering. Another 300 samples were immersed in de-ionized water or artificial sea water for 90min every 1, 2, or 3weeks, representing conditions between the neap and spring high tidal levels, and exposed in air for 90min every 1, 2, or 3weeks to represent conditions between the neap and spring low tidal levels. Surface downwearing was recorded in the field at 34 transverse micro-erosion meter (TMEM) stations, most of which were installed along 4 shore-normal profiles in 2004 and 2005. Mean downwearing rates in the laboratory ranged from 1.25mmyr−1 at the neap high tidal level to 0.63mmyr−1 at the neap low tidal level. Downwearing was much slower between the neap and spring tidal levels and it was uniformly slow below the neap low tidal level. The presence of salts inhibited downwearing within the neap tidal range, where wetting and drying was dominant, and promoted it between the neap and spring high and low tidal levels. Surface swelling was fairly common in the field, and the mean downwearing rate (0.242mmyr−1) was much lower than in the laboratory, possibly because the TMEM stations were installed in harder rocks. Modeling supports the contention that the Mont Louis platform was cut initially by waves at a higher elevation, and then lowered by weathering in the last few thousand years as relative sea level fell to its present elevation. [Copyright &y& Elsevier]

Abstract: A model was developed to study the erosion of cohesive clay coasts in macro- to non-tidal environments. The model shares some of the characteristics of previous models, including the erosion of bare clay surfaces by wave generated bottom shear stresses, and of mobile, sediment-covered surfaces by abrasion. It differs from previous models, however, in several important ways. The morphodynamics of beaches with clay foundations, under different wave conditions, are based on a previously developed model for beaches on rocky shore platforms. Sediment thickness along a beach profile is calculated at regular intervals and compared with the maximum thickness that could be moved at that location under prevailing wave conditions. Wave friction factors are determined, where necessary, according to the occurrence and morphology of ripples on the bottom. In addition to abrasion and the effect of wave induced shear stresses on the clay bottom, erosion by stresses generated by wave impact at the bluff foot and on the intertidal platform is calculated using an expression derived from hard rock coastal models. Tides are represented by their computed tidal duration values, the amount of time each year that the water level falls within each 0.1 m vertical interval. Water depths are modified by wave setup and set-down conditions. Several preliminary model runs were made. The profiles were concave in the submarine zone and roughly linear in the intertidal zone. Equilibrium profiles developed which were maintained as they migrated landwards. [Copyright &y& Elsevier]

Abstract: Laboratory experiments have been conducted to measure rock expansion and contraction induced by wetting and drying on intertidal shore platforms in eastern Canada. Almost 800 rock cores and cubes were subjected to between 800 and 1000 tidal cycles. The rocks were put into tidal simulators and inundated in de-ionized water for 1, 6, or 11 h of each 12 h cycle, replicating conditions at the high, mid-, and low tidal levels, respectively. Micro-erosion meter (MEM) stations were also installed in slabs of argillite, sandstone, and basalt. The slabs were subjected to conditions at the high, mid-, and low tidal levels, and a traversing MEM was used to measure rock expansion and contraction as the slabs dried in air with variable temperature and humidity during low tide. The slabs were also exposed for long periods to air with variable humidity. Cores and cubes often gained in weight when they absorbed or adsorbed water and retained it for periods ranging from 1 month to 1 year or more, although this did not appear to be a prelude to rock breakdown. Tidal wetting and drying and exposure to humid air caused the argillite and basalt slabs to expand and contract by up to 0.14 and 0.04 mm, respectively. Wetting and drying did not induce expansion or contraction of the sandstone, but the sandstone did respond slightly to changes in air humidity. The greatest amount of expansion and contraction was at the high tidal level in the argillite and at the mid-tidal level in the basalt, which is consistent with previously measured rates of downwearing. [Copyright &y& Elsevier]

Abstract: Rocks were subjected to wetting and drying cycles with de-ionized water under real time conditions. Using tidal simulators, one-third of the samples experienced 11 h of exposure and 1 h of inundation over a 12-h tidal cycle (representing high tidal conditions), one-third experienced 6 h of exposure and 6 h of inundation (representing mid-tidal conditions), and one-third experienced 1 h of exposure and 11 h of inundation (representing low tidal conditions). We obtained 324 cores from igneous, metamorphic, and sedimentary rocks from Ontario, which were exposed to more than 930 wetting and drying cycles over 16 months. We obtained 675 cores and cubes from basalts, sandstones, and argillites from shore platforms in eastern Canada, which were exposed to about 700 cycles over 12 months. Many of the cores and cubes experienced very little to no breakdown, particularly those from the igneous and metamorphic rocks of Ontario. Sandstones from a sloping platform in the macrotidal Bay of Fundy and argillites from a horizontal, mesotidal platform in Gaspé, Québec, were the most susceptible rock types, with equivalent surface downwearing rates ranging from 0 to 4 mm year− 1. The results suggest that downwearing rates decrease with elevation within the intertidal zone, probably because rocks require much longer to desorb than to absorb water. The experiments demonstrated that wetting and drying can be an important process on shore platforms in some types of rock, helping to lower the height and reduce the gradient of sloping macrotidal platforms and to reduce the height of horizontal micro- and mesotidal platforms. [Copyright &y& Elsevier]