Anthony Edward

CEREGE, Aix-en-Provence, France

Harbours and adjacent coastal (in)stability: an uneasy and costly relationship, with examples from the Mediterranean

Harbours probably express the oldest and, in ancient times the closest, relationship Humans have had with the coast, especially in the Mediterranean. This relationship originated with the shelter function, on coasts more or less considered as ‘hostile’, provided by harbours for fishing, maritime trade and military operations. Several modern ports in the Mediterranean originated as harbours that developed at various stages over the last 2-5000 years under successive civilizations, from Phoenician times, and notably the Roman Empire. Many ancient harbours were situated in small sheltered bays that are part of the highly intricate rock-dominated ‘capes-and-bays’ coast of the Mediterranean, whereas others were built on deltas that have more or less strongly prograded, resulting in their abandonment or successive seaward relocations. Examples include the ancient harbours of Ostia (Rome, on the Tiber delta), Luni north of Forte dei Marmi (Magra delta), and Ilium (Troy, Scamander delta). Today, some of these ancient harbours are no longer discernible in the landscape.

Progressively, and especially over the last two centuries, the relationship between harbours and Humans has moved from one of subordination of the latter to the conditions fixed by Nature, to one of increasing engineering mastery of the coast in the quest to build increasingly larger harbours, notably commercial, but also a plethora of leisure harbours, thus moving out of the strict limits of sheltered bays. This development has entailed a commonly uneasy and costly relationship between harbours and their adjacent coastal setting. Harbours, both ancient and modern, are well known as agents of perturbation of the continuity of alongshore sediment transport on coasts. Harbour breakwaters trap bedload, resulting in accumulation updrift of these structures and downdrift erosion generated by the negative sediment budget ensuing from updrift trapping. Several harbours in the Mediterranean generate problems of coastal instability that commonly call for costly structural adjustments, notably through the deployment of groynes and breakwaters, sometimes complemented by nourishment, to counter erosion. Fine examples are those of Marina di Carrara harbour near Forte dei Marmi and several on the Occitania coast of France west of the Rhône delta. While these structures, especially when supported by nourishment, may be successful in containing erosion, they generally engender further sediment budget deficits downdrift, and this may entail a wave of alongshore multiplication of counter-erosion engineering structures. The logic of constructing beach stabilization structures downdrift of harbours is not often consistent with that of maintaining a balanced alongshore sediment budget. Apart from perturbation of alongshore sand transport continuity, harbours in the Mediterranean can also have other serious environmental implications such as coastal pollution. On the French Riviera, the construction of numerous small high-value yachting harbours has occurred to the detriment of pocket beaches because of the paucity of suitable accommodation space for such harbours on the dominantly rocky but increasingly more populated Riviera coast.

The impact of harbours in the Mediterranean needs to be reconsidered in terms of coastal sediment budgets and cells, a perspective that should be embedded in overall coastal management and identification of the stakes of the future, including those related to the impacts of climate change, sea-level rise, and urbanisation and infrastructure development.