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A three-dimensional coupled hydrodynamic and morphodynamic numerical model was developed to analyze sediment dynamics in the Rance estuary, in response to the tidal power station (TPS) built near the mouth in the 1960s. The Rance estuary is a relatively small low-discharge steep-sided ria , located along the Brittany coast in northern France, with a maximum spring tidal range of 13.5m. Taking advantage of this significant tidal regime, the first and currently the second largest operational tidal power station in the world was built at the estuary's mouth, with peak output capacity of 240MW. After calibration and validation of the model for present-day conditions, suspended sediment concentration (SSC) and bed level evolution were evaluated at tidal and fortnightly scales for different scenarios, with and without TPS. Peak SSC are reached during spring tides and specifically during the estuary's infilling (flood) stage where both turbines and sluice gates are open. Unbalanced with sediment transport during ebb, sediments are accumulated in the main channel of the upper estuary. Under natural tidal forcing (i.e., without TPS), simulations show that an estuarine turbidity maximum forms in the upper estuary, and sediment deposition is significant. However, sedimentation rates are two times lower than those observed in the presence of the TPS. A possible alternative for reducing sediment accumulation in the upper estuary would be the opening of sluice gates simultaneously with the turbines during falling tide, to enhance ebb currents that would allow particles transport towards the estuary's downstream. [ABSTRACT FROM AUTHOR]

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The Rance estuary is a relatively small low-discharge steep-sided ria , located along the Brittany coast in northern France, with a maximum spring tidal range of 13.5 m. Taking advantage of this hyper-tidal regime, the first and currently the second largest operational tidal power station in the world was built at the estuary's mouth and has been in operation since the 1960s. Despite the well-known effect of damping of estuarine water levels, little attention has been given to quantifying the influence of the plant on the propagation and asymmetry of the tidal wave inside the estuary. In this study, hydrodynamics and tidal wave patterns were analyzed in this anthropogenically influenced estuarine system. A two-dimensional depth-averaged numerical model of the Rance estuary was developed. Two scenarios without the tidal power plant involving the dam's pre- and post-construction bathymetry (1957 and 2018 respectively) and present-day conditions scenarios were designed, to highlight the impact of bed evolution and the tidal power station on hydrodynamics and tidal asymmetry. Numerical results showed that, without the structure, bathymetric evolution did not substantially influence estuarine hydrodynamics. Nevertheless, on the estuary-side of the dam, the presence of the tidal power plant induced (i) a decrease in both tidal range and tidal prism, (ii) an increase of low water levels, and (iii) a decrease in both flood and ebb currents. Contrastingly, the region close to the structure reacted differently to plant operating modes, with an increase in flood currents (ebb currents) upstream of the sluice gates (downstream of the turbines). For both the natural condition and the artificially-induced hydrodynamic forcing due to the presence of the plant, numerical results showed that the Rance estuary mainly exhibits flood-dominant behavior, with a longer duration of falling than rising water and stronger peak flood currents than ebb currents. Spanning a period of approximately 60 years, this study presents a quantitative analysis of the influence of the tidal power station on the hydrodynamics in the Rance estuary, and its possible consequences for sediment dynamics. This approach is novel for this particular enclosed water body, characterized by the presence of a dam at its mouth and a lock at its uppermost limit. • Quantitative analysis of hydrodynamics and tidal patterns of Rance estuary, influenced by a tidal power station. • In the absence of the plant, changes in bathymetry does not have significant influence on the estuarine hydrodynamics. • The plant decreases tidal range, currents and tidal prism inside the estuary. • The tidal power station increases the estuarine low-water level and elongates period of slack water and residence time. • Tidal patterns analysis suggest that the tidal power plant does not impact the origin of sediments present inside the basin. [ABSTRACT FROM AUTHOR]

Rtimi, R.; Sottolichio, A. and Tassi, P., 2020. Tidal patterns and sediment dynamics in a hypertidal estuary influenced by a tidal power station. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1520–1524. Coconut Creek (Florida), ISSN 0749-0208. The Rance estuary is a relatively small low-inflow steep-sided ria, located in the Brittany coast of northern France, with a maximum spring tidal range of 13.5 m at the mouth. Taking advantage of this hypertidal regime, the first and largest operational tidal power station in the world was built at the estuary mouth and is in operation since the 1960s. Despite a well-known effect of the plant on the damping of estuarine water levels, little attention has been given to the propagation of the tidal wave along the estuary. Moreover, net siltation has been reported by several observations, but there is no specific knowledge on the role of the plant on sedimentation. In this study, tidal wave patterns and sediment dynamics are analyzed in this particular man-engineered system. A numerical model, based on a two-dimensional depth-averaged approach is implemented to predict the tide propagation and tidal currents along the estuary. Numerical results are analyzed and discussed to highlight the role of the plant on the transformation of the tidal wave in the estuary and its possible consequences on sediment dynamics and morphological evolution. [ABSTRACT FROM AUTHOR]