Development of an incipient foredune field along a prograding macrotidal shoreline, northern France

Abstract

In this paper, we examine the development of an extensive hummocky incipient foredune field of approximately 100,000 m² that developed along a short stretch of coastline on the macrotidal coast of northern France. Analysis of historical maps and documents, of a series of aerial photographs as well as recent LiDAR and topographic data allowed us to depict the formation and evolution of this incipient foredune field. Our results show that this coastline stretch is prograding seaward since at least the 16th century, this shoreline advance being related to the onshore welding of subtidal sand banks. During the early 20th century, isolated sand islets, surrounded by the sea at high tide, formed at the landward edge of a wide convex-shape sand flat. They progressively merged to the main shoreline during the mid-20th century, inducing a shoreline advance of up to 300 m between 1938 and 2012. Once merged to the main shoreline in the 1960s, a field of incipient foredunes, facing the dominant winds began to develop, inducing a shoreline progradation at a rate of 5 m.y-¹ that resulted in a seaward widening of the hummocky dunefield. Although the field of incipient foredunes continued to expand since its initiation, the morphology of individual mounds, colonized by a sparse vegetation cover, tended to remain remarkably stable through time. In this area of high sediment supply, the formation of a hummocky dunefield is probably due to the fact that the incipient foredune do not have enough time to coalesce and to merge into a continuous foredune ridge as they rapidly become disconnected from their main sediment source.