Analysis of a beach as a time-invariant linear input/output system of marine litter

Kataoka, Tomoya; Hinata, Hirofumi; Kato, Shigeru

Analysis of a beach as a time-invariant linear input/output system of marine litter

2013

Kataoka, Tomoya | Hinata, Hirofumi | Kato, Shigeru

The exponential decay of the amount of new litter on Wadahama Beach, Nii-jima Island, Japan revealed by 20-month mark-recapture experiments demonstrates a linear response of the beach to the input of target items. Here we show the amplitude and phase characteristics of the beach as a time-invariant linear input/output system and discuss the hydrodynamic and geomorphological factors that would determine the characteristics with the aid of a diffusion equation. The characteristics are fully determined by the residence time of the items (τr=209days) and can be described as functions of the ratio of τr to the period of input variability. The decay is reproduced well by the analytical solution of the equation with a constant diffusion coefficient (D), whose order was estimated by τr and the backshore width. Generally, D would depend on hydrodynamical statistics and beach geomorphology as well as the dimensions and density of the items.

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