IELTS Reading 93: Rethinking the Tide

Adapted from Imperial College London / Ecological Solutions and Evidence (October 2025). IELTS Reading Section 3 difficulty, approximately 1,050 words. Source: https://www.imperial.ac.uk/news/270053/new-study-challenges-ecological-fears-around/

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Reading Passage

A. Among all the renewable sources available to a coastal nation, tidal power has always occupied an awkward position. It is clean, it is long-lasting, and — unlike the wind that turns a turbine or the sun that falls on a panel — it can be forecast centuries in advance with remarkable precision. The gravitational pull of the Moon and Sun on the oceans follows rhythms that astronomers can calculate generations ahead, so a tidal generator never suffers the inconvenience of a calm week or a cloudy month. Yet for decades this apparent gift has been held back, not by engineering failure, but by a single, persistent fear: that harnessing the motion of the sea must mean damaging the sea itself. Developers, investors and regulators have repeatedly paused, persuaded that underwater power stations would scar estuaries, choke fish and fragment the habitats on which marine food webs depend. That reputation has proved remarkably difficult to shake, even as the technology itself changed almost beyond recognition. High upfront costs, a tangled regulatory system and the sheer difficulty of building in a storm-lashed sea have compounded the problem, so that a resource some estimates place at a fifth of the nation's electricity has lingered at the margins. Where wind and solar have matured into multinational industries, the sea's energy has remained a cottage industry of prototypes and trials — promising, but perpetually on the verge of something it never quite reaches.

B. Two quite different families of machine extract this energy, and confusing them is at the root of much public anxiety. The older design is the tidal barrage, a wall built across an estuary that traps water behind it as the tide rises and releases it through turbines as the tide falls — a dam whose cycles run twice a day. The newer approach dispenses with the wall entirely. Tidal flow installations, often described as underwater windmills, sit on the seabed and spin in the powerful currents that race through narrow channels, turning kinetic motion directly into electricity. Scotland's MeyGen array, in the fast-moving Pentland Firth where currents can exceed five metres a second, has become the proving ground for this second method: its early turbines, totalling around six megawatts, were producing enough to supply thousands of homes by the middle of the decade, and cumulative generation passed eighty gigawatt-hours in 2025. Because water is roughly eight hundred times denser than air, even a modest, slow-spinning rotor can deliver striking amounts of power, and a single machine can harness a force far larger than any wind turbine of comparable size. It was this combination — strength and predictability — that persuaded Canada in 2025 to approve its first tidal array, three small turbines staged off the Atlantic coast, a step that regulators justified precisely because it could be scaled up slowly while marine life was watched.

C. It is precisely this tangle of barrages and rotors that a 2025 review from Imperial College London set out to untangle. Its authors, drawing on more than fifty scientific studies from Europe, Asia and North America, concluded that much of the dread surrounding tidal schemes rests on evidence that no longer describes the technology. Many of the alarming findings from the 1960s to the 1980s traced not to the principle of tidal generation but to crude construction practices of the era — in particular, the habit of sealing estuaries off completely during building, which poisoned water quality and wrecked habitats. The same review found that the enclosed basins behind celebrated stations, such as France's la Rance, generating power since the nineteen-sixties, and South Korea's Sihwa Lake, have over the decades settled into stable, even enriched ecosystems, supporting a greater variety and abundance of species than the engineers who built them dared to hope. Kislaya Guba in Russia added yet another long-running case study, demonstrating that a carefully managed basin can mature into a productive marine environment rather than a stagnant pond.

D. The most deeply held anxiety concerns the underwater rotors themselves: surely fish, seals and dolphins must drift into the blades and perish. The monitoring evidence, however, tells a calmer story. Rather than colliding, creatures appear to steer clear of the spinning machinery, altering their paths to keep a safe distance; long-term surveys have found no sign of population decline or broken-up habitats near operating arrays. The reviewers acknowledge that real changes occur — sediment shifts, altered tidal ranges, rearrangements of where species choose to live — but emphasise that these are not uniformly harmful. In several instances the foundations of the structures doubled as artificial reefs, offering hard surfaces on which kelp, shellfish and corals could colonise, and some degraded coastal waters actually saw their circulation improve and their water quality rise. Keeping the tidal regime as close as possible to its natural rhythm, rather than dominating it, emerged as the single most important design rule for minimising any harm. Well sited, a rotor farm is therefore more like an artificial reef than an industrial plant — a structure that the surrounding sea gradually adopts as its own.

E. Beyond supplying low-carbon electricity, the review argues that tidal infrastructure may earn its keep a second time, as sea levels rise and storm surges grow fiercer. A well-designed barrage is simultaneously a power station and a flood barrier, a piece of equipment that can hold back a swollen tide while it harvests one. Modern designs aim to keep the tidal regime as close to its natural rhythm as possible rather than dominate it, combining renewable generation, habitat restoration and coastal defence in a single structure built to operate for well over a century. The researchers estimate that a country with an extensive coastline such as Britain could in theory derive a fifth of its electricity from tides, while contributing billions to the economy. Their closing argument is blunt: the obstacles holding back the technology are no longer scientific. What has been missing, they suggest, is the policy will to fund it, the long-term monitoring that protects local ecosystems, and the confidence to build it at last. A technology that can light a coast while holding back the very sea it harvests, they argue, deserves to be judged on its modern evidence rather than on the worst accidents of its grandparents' age.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. How the two families of machine actually extract the energy ii. Why tidal barrages have now been abandoned worldwide iii. What a fifty-study review revealed about old ecological scares iv. How offshore wind finally overtook marine generation v. Evidence that underwater rotors rarely harm the animals nearby vi. A second use for sea walls as the climate changes vii. The invention of the National Grid in the 1930s

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. According to the writer, tidal power has been held back chiefly because of A. its inability to generate electricity predictably. B. public and official concern over marine ecosystems. C. the sheer cost of seabed cables. D. a shortage of suitable turbine blades.

6. What does the review say about the alarming findings from the 1960s to the 1980s? A. They were based on entirely fabricated data. B. They reflected crude construction methods rather than the principle itself. C. They proved that no estuary could ever be dammed. D. They accurately predicted modern outcomes.

7. What do monitoring studies suggest about fish and the underwater rotors? A. They regularly collide with the spinning blades. B. They tend to avoid the machinery and alter their paths. C. They are unable to detect the rotors at all. D. They migrate away permanently from the whole channel.

8. According to the final paragraph, a modern barrage can double as A. a fish farm and a desalination plant. B. a power source and a coastal flood defence. C. a port and a shipping canal. D. a research laboratory and a visitor centre.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Tidal energy is harder to predict far in advance than solar or wind power.
10. Long-term surveys have found no clear sign of declining populations near operating arrays.
11. Modern tidal projects routinely seal estuaries off completely during construction.
12. The researchers believe a country like Britain could in principle get about a fifth of its electricity from tides.
13. The world's largest tidal barrage is currently operating in the United States.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

The Imperial College review drew on more than (14) __________ scientific studies and concluded that modern tidal structures can serve a dual role, acting both as generators and as protective (15) __________ against rising seas.

Answers & Explanations

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