Estuaries are ideal locations for extracting tidal energy and yet the global resource appears poorly mapped. Estuaries typically have high tidal ranges and strong tidal currents, due to amplification processes; and this resource is juxtaposed to industrial/residential areas with electricity demand . For example, 22 of the 32 largest cities in the world are adjacent to estuaries , and UK estuaries collectively worth over £5.5b to UK economy with >1/6th of the population and ~1b tonnes of cargo traded at their ports .
Mapping the tidal energy resource is challenging due to the sensitivity of ocean-model simulated currents to the model resolution . Both tidal amplitude and currents are heavily modified in estuaries . Whilst many estuary-specific resource modelling studies have been achieved (e.g. ), no large-scale future tidal energy resource mapping project has been undertaken – likely due to computational cost (e.g. ). It is therefore unrealistic to hydrodynamically model all global estuarine systems, to resolve current and future changes to the tidal energy resource; instead we aim to apply a simplified analytical technique that could be calibrated and validated by the new NASA SWOT satellite mission (https://swot.jpl.nasa.gov/), as well as citizen science. Estuarine tidal dynamics have been observed to change rapidly due to changes in river-flow climatology and bathymetry (e,g. dredging); see . Indeed, climate change driven impacts to tidal dynamics (sea-level rise and altered riverine climatology), alongside anthropogenic driven morphodynamical changes and interactions with future tidal dynamics, could increase the future estuary tidal resource .
Three physical processes drive mean tidal amplification excluding over-tides): (1) Funnelling - concentration of the tidal energy flux with reducing width; (2) Resonance - when estuary length-scales are close to the natural period of the basin; and (3) Shoaling (reduction in the propagation speed of the tidal wave resulting in an increase in amplitude). Each of these three processes are analytical solved, and a 1D analytical model applied to demonstrate the resource. Sea-Level Rise (SLR) scenarios are included to show SLR can modify estuarine tidal dynamics through both estuarine geometry (e.g. increasing resonance) and boundary conditions (global mean sea-level rise increasing boundary conditions). A normalised result of the analytical approach is shown in Figure 1, which demonstrates a computationally efficient analytical solution that includes future changes to tidal dynamics.
Our research will apply this analytical solution to the Bristol Channel, a region soon-to-be heavily instrumented as part of the “Cal-Val phase of the NASA SWOT project (https://projects.noc.ac.uk/swot-uk/swot-uk-bristol-channel). Finally, we will develop a technique to bring together digital observations from citizens and sensor networks (see https://digitalenvironment.org/), to validate our simplified approach and resolve the tidal energy resource.