Take a walk under the river, where treasure awaits
This marvel of modern engineering yields the largest mined resource on the planet
Earlier this year I walked under one of the country’s most powerful rivers.
Not over it, not through it, but right underneath it – and emerged unscathed at the other side to tell the tale.
Though it was flowing faster than a minibus taxi in the Durban rush hour, I was neither soaked nor swept away while walking beneath KwaZulu-Natal’s mighty Thukela River.Because of heavy rains the previous day, the Thukela was in flood. While crossing the river via a narrow steel bridge a few hours earlier, I had seen the frothing brown river tearing away at tree roots and ripping up sand and boulders from the riverbed.
Now I was underneath it.Yet I felt entirely safe as the Thukela River roiled over my head, just a few kilometres from the point where it crashes into the Indian Ocean.
Such are the marvels of modern engineering.
Luckily, vast quantities of reinforced concrete were protecting me as I strolled casually through a 500m service tunnel that has been built deep beneath the river as part of the R1.6bn Lower Thukela Bulk Water Supply Scheme.
When the final phase is completed the new weir and treatment scheme will process up to 110 million litres of water every day to supply commerce and industry and thousands of homes in the rapidly expanding Ilembe district, north of Durban.This is not a conventional dam that arrests the flow of mighty rivers, but rather a massive weir structure that slows down the speed of the river and allows Umgeni Water to suck up “surplus water” before it enters the sea.
It has also been designed to allow significant volumes of river sand and sediments to reach the adjoining beaches and the rich Thukela Banks fishing grounds.
Nonetheless, rivers across the world continue to be obstructed by a multitude of dams, weirs and reservoirs to generate hydroelectricity or to allow the abstraction of increasing volumes of water to bathe, feed and sustain the planet’s burgeoning human population.
A new report published this week to coincide with World Water Week (August 27-31), cautions that in some parts of the world only one-third of large rivers remain free-flowing.
“In some river basins up to 98% of sand is trapped in engineered river reservoirs. Globally, nearly a quarter of annual sediment flux is now captured by them,” according to Valuing Rivers, a report published by the conservation group WWF.So why should it matter whether sand or sediment is trapped by dams?
Lead author Jeff Opperman said river sand was now the largest mined resource on the planet, contributing to the sinking of river deltas and severe coastal erosion as beaches run of out sand.
Vietnam’s Mekong River delta, for example, is being starved of sediments and nutrients even though this delta is home to 17 million people and helps to produce nearly half the nation’s staple crops and 90% of its rice exports.
Opperman said unregulated sand mining and a proliferation of hydropower dams had reduced the Mekong’s total sediment supply by more than half from 160 million tons in 1990 to 75 million tons in 2014.
Dozens more hydropower dams are planned, which would reduce sediment supply to less than 10% of the natural rate.
Closer to home, a 2008 report by the Council for Scientific and Industrial Research found that 12 large dams on major rivers around Durban trap at least one-third of normal river sand flow.
Sand supply had been reduced by a further 33% by more than 30 sand-mining operations on eThekwini’s rivers.
“The implications are far-reaching ... in total, the present remaining sand yield is only a third of what it should be,” said CSIR researcher Andre Theron, raising concern that some beaches south of Durban had been retreating at a rate of almost one million a year since the early 1970s.The new WWF report says the construction of dams and other water impoundments also have other largely unseen effects.
Artificial barriers disrupt or completely block the migration of freshwater fish and other river organisms. As a result of dramatic changes to riverine habitats, some populations of freshwater vertebrate species had declined by 81% since 1970.
There are an estimated 15,000 species of freshwater fish across the world. Of the 5,685 species that have been formally assessed by the International Union for Conservation of Nature (IUCN), 36% are now classified as threatened.
Opperman and his colleagues said naturally functioning rivers were not understood or valued, so they did not become a priority for decision makers – until they were lost.
“Rivers are not just pipes for delivering water, and we don’t have to accept the loss of rivers’ diverse benefits as the unavoidable collateral damage of development,” he concluded.