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Modeling the development of wave-cut shore platforms

Modeling the development of wave-cut shore platforms,10.1016/S0025-3227(00)00013-X,Marine Geology,A. S. Trenhaile

Modeling the development of wave-cut shore platforms   (Citations: 41)
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A mathematical model was used to investigate the development of wave-cut shore platforms with constant sea level. The model considered the effects of deep water wave height spectra, period and wavelength, breaker height and depth, breaker type, the width and bottom roughness of the surf zone, the gradient of the submarine slope, an erosional threshold related to the strength of the rocks, the number of hours each year in which the water level is at each intertidal elevation and the amount and persistence of the debris at the cliff foot. Intertidal erosion rates were calculated according to the force of the surf reaching the shoreline, whereas submarine erosion rates were determined using a depth decay variable. Each of the two hundred and fifty model runs consisted of 300,000 iterations. Platform width increased and gradient progressively decreased through model runs, and states of static equilibrium were attained by the end of one-hundred and nine runs when the wave induced force at each point in the intertidal zone had became too weak to continue eroding the rock. Runs with mesotidal spring tidal range (3m) generally produced subhorizontal platforms with cliff-platform junctions at the mean low water neap tidal level. A greater variety of profiles was produced in runs with macrotidal spring tidal ranges (9m). Although almost 30% of these runs produced gently sloping platforms, with average gradients of only 0.3°, about two-thirds of the simulated profiles had average gradients ranging from about 1 to 3°. Simulated platform width increased with tidal range and decreased with the rate of submarine erosion, rock resistance, the roughness or irregularity of the platform surface, the amount and persistence of the cliff foot debris and wave period. Because higher waves break in deeper water than lower waves, there was no consistent relationship between simulated platform width and wave height.
Journal: Marine Geology - MAR GEOLOGY , vol. 166, no. 1, pp. 163-178, 2000
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    • ...coast. As the beach is wide at Papanasam (*200 m), wave forces are diminished due to dissipation as platforms widen over time (Trenhaile 2000, 2002); only low-energy waves reaching the cliff base and narrow fissures are developed...

    Avinash Kumaret al. Distribution of coastal cliffs in Kerala, India: their mechanisms of f...

    • ... to changes in rock structure, exposure, and other factors, there is a moderately strong relationship between mean regional platform gradient and tidal range (Trenhaile, 1987, 1999, 2004a )( Fig. 1). Modelling suggests that this relationship may reflect the way that tides, through the tidal duration distribution, determine the amount of wave energy expended at different elevations within the intertidal zone (Trenhaile and Layzell, 1981; ...
    • ...The inability of the exclusively weathering model to produce realistic platform profiles in different tidal range environments is in strong contrast to mechanical wave-erosional models, which generate platform profiles with gradients and other morphological characteristics that are broadly similar to platforms in the same tidal environments in the field (Trenhaile and Layzell, 1981; Trenhaile, 2000, 2001, 2003; Walkden and Hall, 2005)...

    A. S. Trenhaileet al. Can shore platforms be produced solely by weathering processes?

    • ...The formation of wave-cut bedrock platforms along rocky coasts has been extensively modeled for terrestrial conditions [see Trenhaile, 1987, pp. 225–231; Sunamura, 1992, pp. 180– 182; Zheng and Dean, 1997; Trenhaile, 2000, 2001]...
    • ...Energy from the wave field is transferred to the shore area, where surf force against the coast is a function of incoming wave energy, shore slope, and surf zone roughness [Trenhaile, 2000, 2001]...
    • ...The total equilibrium tidal range of the Sun on Mars is 5.2 cm. [29] Trenhaile [2000, 2001] modeled the formation of wave cut terraces on rocky coasts and we follow this method closely with consideration for Martian conditions...
    • ...M is a scaling coefficient of 6.5 � 10 � 10 (m 3 kg � 1 ) used to convert wave energy to erosion in meters per year; this value generates annual erosion rates that are consistent with field measurements of terrestrial horizontal rock erosion rates [Sunamura, 1992, pp. 86–106; Trenhaile, 2000]...
    • ...Trenhaile [2000] represented the total erosion (ET )i n the system (at and below water level) by...
    • ...Time is reported in Martian model years; Trenhaile [2000, 2001] notes that model years are not actual years and cautions them to be used as references rather than absolutes...
    • ...Second, the Trenhaile [2000, 2001] model (explained above) assumes constant yearly conditions...
    • ...Altimeter (MOLA) topographic results [Aharonson et al., 2001] and topographic profiles of basins identified as possible crater lake basins (Figure 1). The erosion threshold (Smin) represents a range of terrestrial bedrock resistance values; the surf attenuation represents the roughness of the surf zone and is also based on terrestrial field data [Trenhaile, 2000]...

    Erin R. Kraalet al. Quantitative geomorphic modeling of Martian bedrock shorelines

    • ...This work was undertaken as a necessary precursor to a larger project which is concerned with extending the wave erosional model of Trenhaile (2000, 2001) through the inclusion of several new factors, including the protection afforded to rock surfaces by thick accumulations of sediment, and the abrasive effects of thinner accumulations...
    • ...Field evidence and mathematical modeling suggest that mean regional platform gradient increases with tidal range, although many other local factors can obscure this relationship (Trenhaile, 1987, 2000, 2001)...

    A. S. Trenhaile. Modeling the accumulation and dynamics of beaches on shore platforms

    • ...Mathematical models have provided further support for the equilibrium concept (Sunamura, 1978b; Trenhaile, 1983, 2000, 2001a, 2001b; Trenhaile and Layzell, 1981), and it has been suggested that submerged platforms on the consolidated clay coasts of the lower Great Lakes also maintain their shape as they shift landwards (Bishop et al., 1992)...
    • ...Other models have incorporated the tidal duration concept into models that examine intertidal erosion and the evolution of shore platforms under constant and changing sea level conditions (Trenhaile, 1983, 2000, 2001b, 2001c; Trenhaile and Layzell, 1981)...
    • ...Trenhaile (2000) used a mechanical wave erosional model derived from basic wave equations to explore the interaction among wave dynamics, tides, coastal morphology, and the evolution of wave-cut shore platforms under constant mean sea level conditions...
    • ...Modelling has demonstrated that wave-and-surf zone energy is increasingly dissipated in crossing shore platforms as they become more gently inclined and trend towards an equilibrium state (Trenhaile, 2000, 2001a, 2001b)...
    • ...The model indicated that whether an ancient surface is inherited, modified, or completely replaced by a contemporary platform depends upon the multitude of factors that determine the erosive efficacy of the waves, including wave size and period, tidal range, the strength of the rock, cliff height and the size and mobility of the cliff-foot debris, and the morphology of the platform (Trenhaile, 2000, 2001b, 2001c)...

    Alan S. Trenhaile. Rock coasts, with particular emphasis on shore platforms

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