Beach Sediment Alteration by Natural Processes and Human Actions: Elba Island, Italy

Abstract

The surface characteristics and dimensions of many beaches reflect past inputs of sediment due to human activity in tributary drainage basins. Subsequent control of erosion in drainage basins, changes in flow regimes of streams, and construction of shorefront structures have reduced sediment input and eliminated beach area in many coastal segments, leading to calls for artificial beach nourishment. This study evaluates the compatibility of sediments delivered as a result of human activity in terms of the appearance and utility of beaches by comparing sites on Elba Island, Italy. Beach morphology, mineralogy, grain size, and roundness of sediments were determined for five sites where sediments were introduced by artificial nourishment, by erosion of spoils from iron mines, and by stream flow through agricultural or mining lands. Size, sorting, angularity, and color of sediments determine their acceptability by beach users. These characteristics were determined by evaluating the mineralogy and method of delivery of sediment (rivers, bluff erosion, and artificial replenishment) and subsequent modification by wave and human action. Wave energy and time are critical to the reworking of sediments to achieve more natural characteristics, but these constraints can be overcome by more careful selection of the mineral characteristics of fill sediments, prewashing fill sediments to remove silts and clays to reduce turbidity, grading nourished beaches to cycle sediments into the wave and swash zones to cause better rounding of sediments, or raking the beach to create the sandy backbeach that is favored by beach users.