A simple model of wind-blown tidal strandlines: How marine litter is deposited on a mid-latitude, macro-tidal shelf sea beach

A simple hypothesis-driven model of how floating marine plastic litter is blown onto a beach, and then moved on and off the beach by winds and rising and falling water levels is implemented in a computer simulation. The simulation applied to Aberdeen beach, Scotland, suggests that the interaction between varying winds and water levels alone, coupled to an assumed constant offshore floating litter density, can account for 1) the order of magnitude of the long term average (2000−2010) beach plastic litter loading (observed = 127 np/100 m, simulated = 114 np/100 m); 2) the observed frequency spectrum of low water beach plastic litter loadings; 3) the magnitude of the ratio between offshore floating plastic litter densities and onshore beach plastic litter loadings; 4) zero overall net beach plastic litter accumulation. Results are relevant to beach survey design, designing methods to estimate litter accumulation rates and the setting of MSFD beach litter targets.