Île artificielle | EPFL Graph Search

Une île artificielle est une île formée grâce à une intervention humaine, et non de façon naturelle. Elle est généralement construite sur un récif existant, ou peut être l'extension d'un îlot existant. Les îles artificielles sont traditionnellement créées par remblaiement. Quelques exemples récents suivent le modèle des plates-formes pétrolières, mais la désignation d'« île » pour ces structures reste soumise à controverse. Une forme moins discutée d'île artificielle consiste en l'isolation d'une bande de terres par le creusement d'un canal sur le côté opposé à celui bordé par les eaux d'une étendue d'eau ou d'un cours d'eau. Les plus grandes îles artificielles gagnées sur les mers, selon leur superficie Les plus grandes îles artificielles gagnées sur des eaux lacustres, selon leur superficie Construction Les îles artificielles sont construites par remblayage ou par construction de digues. Elles utilisent parfois un ou plusieurs îlots déjà exista

Energy Island, Mumbaï, India

Florian Chazeau, Lucie Murisier

Etendue de terre bordée d'eau, l'île est souvent source d'un imaginaire qui peut osciller entre paradis et enfer. Par ses propriétés d'éloignement et d'isolement, elle a depuis longtemps contribué au rejet de certains programmes hors des limites de la ville avec des exemples concrets comme: les îles écologiques à Amsterdam, les îles industrielles de Tôkyô, l'île aéroportuaire d'Incheon et enfin les îles pénitentiaires de New York. Pour toutes ces villes, l'île artificielle se matérialise comme réceptacle de ces programmes rejetés, et apparaît comme une solution potentielle de développement face à certains problèmes urbains. Depuis plusieurs années, Mumbai, la ville la plus peuplée d'Inde, connaît une forte croissance économique due à l'hyper développement de son pays. Mais ce développement exponentiel, accompagné d'une population croissante, amène sa part de problèmes dans de nombreux secteurs: le réseau de transport est saturé, le secteur énergétique n'arrive plus à satisfaire la demande, la pénurie de logements est importante, la gestion des déchets reste un gros problème sanitaire pour la ville... A l'étroit sur sa presqu'île, la mégapole implose. Elle exige aujourd'hui l'aménagement de son territoire municipal et régional pour son essor comme future capitale internationale. Née de l'artificialisation de 7 îles, et de remblais marécageux, Mumbai se tourne depuis toujours vers la mer. Aujourd'hui, à l'image de nombreux projets off shore (autoroutes, artificialisation, ...) dans la mégapole, l'île artificielle semble être une alternative à ces problèmes qui sclérosent la ville. «The construction of artificial islands would not only create new opprtunities for the futur but help resolve some of today's social and environmental problem». [Gerhart Muller Supervisor Ocean Technologies, Ports ; Artificials islands: development of a new relationship, 1987.]

2008

Hydraulic-morphological habitat assessment in rivers considering residual flow, sediment replenishment and artificial flood events

Severin Stähly

Dams store water and trap sediment in their reservoirs. Downstream river segments, hence, are affected by a limited sediment dynamics. This becomes obvious by river bed incision, limited geomorphological variability and depletion of hydraulic habitats for in-stream ecological organisms. Replenishment is a measure to counteract the lack of sediment. In segments dams such a sediment replenishment can be combined with the release of an artificial flood, by activating spillways and bottom outlets. Recent laboratory studies revealed the potential of multi-deposit replenishment configuration towards an increase of geomorphological richness in the river. However, this has not yet been tested in the field. The hydro-morphological index of diversity (HMID), is based on the spatial variability flow depth and velocity in a river segment, allowing the quantification of the change in morphology such a measure. Its ease in computation and its objectivity makes the index a useful tool for a large variety of users. However, knowledge concerning data sufficiency and a standardized sampling procedure does not exist. Further, the HMID does not account for temporal variability. This research aims at closing these gaps of knowledge for a sustainable management of complex floodplains downstream of dams. Flow depth and velocity data from 19 river segments were analyzed with the HMID. Structured sub-sampling and analysis of the data revealed different data sufficiency depending on the complexity of the river geomorphology. A representative HMID value is computed from at least 100 datapoints distributed over eight cross-sections, in braided rivers more datapoints are required. The geomorphological changes by an artificial flood event in the Sarine were analyzed with the HMID. In the impact perimeter of the multi-deposit sediment replenishment, the HMID increased by 36 % in the Sarine, in the rest of the river 18 %. A similar study was investigated at the Spöl, pointing out that sediment availability is crucial for the hydraulic habitat diversity. With the help of 489 tracer stones, the movement of the replenished sediment was investigated in detail. The deposition pattern results in repeating sediment clusters on the riverbed, as it was observed in the laboratory experiments. For the two characteristic diameters, the tracers allowed the estimation of transport velocities of 19 cm/min (dm = 57 mm) and 28 cm/min (d90 = 113 mm) during the flood event and consequently the erosion efficiency of the different parts of the flood hydrograph. Macroinvertebrates were less affected by the artificial flood event in the hydropeaking river segment of the Sarine compared with the residual flow segment. The species diversity indices decreased significantly due to the artificial flood event. A direct link between flow regime and EPT richness was observed. A river with a natural flow regime hosts the highest richness of macroinvertebrates followed the residual and finally the hydropeaking flow regime. For other ecological indicators, additional physical river parameters for example the frequency duration curve or the grain size distribution need to be considered as well.

EPFL2019

Artificial floods in residual flow reaches – How do they affect hydraulic habitats

Severin Stähly

Floodplains in hydropower-controlled rivers, where a constant residual flow discharge is imposed, often lack sediment supply and periodic inundation due to the absence of natural flood events. In this study we compare two residual flow systems. The first river is the Spöl, located in the Swiss National Park close to the boarder with Italy. Since the year 2000, artificial floods are released from the Ova Spin Dam on a yearly bases, with the aim to restore river dynamics and habitats. The second river, is the Sarine in Western Switzerland where an artificial flood was released from the Rossens Dam for the first time. At one location this flood event was combined with sediment replenishment. In this study, an analysis of the two different systems before and after the event using the Hydro-Morphological Index of Diversity (HMID) is presented. The index is based on the variability of flow depth and flow velocity and represents the habitat diversity on a reach scale. Results reveal that a flood pulse can significantly increase hydraulic habitat diversity in a river reach and that sediment availability is crucial. Nevertheless, the change in habitats of a single flood event has a minor effect if artificial floods are periodically released. Under such conditions, the river has already reached an equilibrium condition considering habitat diversity.

2019

Hydraulic-morphological habitat assessment in rivers considering residual flow, sediment replenishment and artificial flood events

Severin Stähly

EPFL2019

Energy Island, Mumbaï, India

Florian Chazeau, Lucie Murisier

2008