Part 1 of this article was originally published in edition 34 of Port Technology International and is available for download at https://18.104.22.168 under journal archives.
Part 1 of this article introduced us to the reasons behind the environmental restoration of the Seine Estuary and detailed the restoration of the mudflats. Part 2 will focus on the creation of a resting islet in the Seine River, for sea birds, south of the Estuary, and then conclude with the port works and follow-up studies, carried out during the works.
Creation of a rest place in the River Seine: M€ 9
Ornithologists wished to produce two or three sites with a minimum surface of about 1,000m2 so that differentiated management types of the areas could be carried out according to the species and to avoid a particularly dominating species colonising the others, which would be contrary to the development purpose of the bio-diversity.
In order to more precisely define this development, a working session was held in 2000, grouping together a representative of the Groupe Ornithologique Normand (Normandy Ornithological Society), a member of the Maison de l’Estuaire (Estuary House), the manager of the Nature Reserve of the Seine Estuary, the Directions Régionales de l’Environnement de Haute et Basse Normandie, DIREN (Environmental Regional Divisions of Lower and Upper-Normandy) and engineers from the Port Autonome de Rouen and Port Autonome du Havre.
Each participant explained their objectives and obligations, and the design progression followed the stages. In order to meet the ornithological objectives, the initial basic scheme was made up of three islets, which were totally independent from one another.
Given the severe hydrodynamic conditions (waves and currents) which can happen at the entry to the Seine Estuary and in order to reduce the costs of the islet protection systems, it appeared to be adequate to consider the idea that the largest islet, that is the westernmost, could serve as a protection structure for the other two. This principle led us to think of a design schematically representing two V-shapes and one circle, in which the biggest islet was sheltering that of an average size and the latter serving as a protection for the smaller one.
As things progressed, it rapidly appeared that it would be shrewder to make the two smaller islets head to foot so that:
• On the one hand, the average distance between the two be increased, which reduces the trouble between species.
• And, on the other hand, a relatively sheltered surface be created between them, thus favouring the deposit of fine materials, such as silt and mud, likely to contain organisms which could contribute to feeding birds.