The future of insular beaches: Insights from a past-to-future sediment budget approach

Sustainable management of insular beaches, that are critical to tourism-based economies, depends on sound understanding of coastal evolution drivers. However, interconnections among geological, oceanographical, biological and human key-drivers of coastal change, operating at relevant spatial and temporal scales, remains poorly understood. This work aims at understanding and quantifying the main drivers of insular beaches evolution using a past-to-future sediment budget approach, and to address future coastal impacts raised by anthropogenic interventions and climate change. This approach was developed in Porto Santo's beach from the early 20th century to the middle 21st century. Results show that anthropic activities undertaken during the late 20th century perturbed the existing long-term (natural) coastal stability. They caused significant reduction of the main sediment source (river sediment yield) and increased sediment sinks (e.g. sediment extraction from beach, harbour sedimentation). Altogether, this resulted in the onset of an erosive trend that persists until present. Projecting patterns of coastal change into the forthcoming decades strongly depends on sediment management strategies. We show that the adoption of a neutral strategy (i.e. compensating for anthropogenic-induced losses with beach nourishment) will not be enough to cease beach erosion, given the negative impacts related to acceleration of future sea level rise. Still, maintenance of the socioeconomic values of Porto Santo's beach can be achieved by triggering positive anthropic influences on its sediment budget. The past-to-future sediment budget approach proposed herein provided a unified perspective on the evolution of the main drivers of coastal change and simultaneously offers foundations for adaptations strategies aiming at increasing sustainability of insular beaches.