Effect of large-scale kinetic power extraction on time-dependent estuaries

An open and important question in tidal in-stream energy conversion is the level of kinetic power extraction that is possible without unacceptable environmental degradation. In general, the effects of large-scale kinetic power extraction on estuary-scale fluid mechanics are not well understood. In this paper, these effects are quantified for an idealized estuary using a one-dimensional, time-dependent numerical model. The numerical domain consists of a long, wide inlet and basin connected by a constricted channel. Kinetic power densities within this constriction are suitable for in-stream energy conversion. Modelling shows that the extraction of kinetic power has a number of effects, including: (a) reduction of the volume of water exchanged through the estuary over the tidal cycle; (b) reduction of the tidal range landward of the array; and (c) reduction of the kinetic power density in the tidal channel. These impacts are strongly dependent on the magnitude of kinetic power extraction, estuary geometry, tidal regime, and non-linear turbine dynamics. It is shown that it may be misleading to relate these impacts to the fraction of kinetic energy extracted from the system. Results highlight the importance of time-dependent modelling and the incorporation of non-linear turbine dynamics.