Dune, Bluff and Beach Erosion due to Exhaustive Sand Mining – the Case of Santa Barbara Beach, São Miguel (Azores, Portugal).

Abstract

Coastal dunes are relatively rare features in the Azores islands and contribute to less then 1% to the total length of the archipelago's littoral zone, circa 844 km. Localised indications of aeolian activity, contemporaneous to the arrival of the first colonists in the 15th century have been found, but at present most of the coastal dunes are vegetated and stabilised. Dune sand has been exploited during the 20th century for industrial use, leading to severe damage or complete removal of a significant proportion of these features. In the 1950's the Santa Barbara area contained a rare and well-preserved example of an undisturbed active beach-foredune system, free of anthropogenic activities. It displayed a well-nourished beach profile margined by a coastal foredune and a climbing dune, which covered the adjacent bluff and extended landwards through an aeolian sand-sheet. Persistent sand mining between the early sixties and the late eighties, lead to volumetric depletion of the dune cover, lowering of the surface of the berm and triggering cliff erosion. In total, some 950,000 m3 of sand has been removed, the dunes making up half of this figure. Although this activity was stopped in 1995 by legal enforcement, the erosive process still currently persists indicating a surpassing of the natural resilience and maximum vulnerability of the coastal dune system. At present the bluff retreats at very high rates (0.6 m/yr), the dune features were totally obliterated and the sandy beach has been reduced in width to a single swash ramp which floods during half of the tidal cycle.