Salmon Do U-Turn in River Thames Until Sewers Fixed
Oct. 14 (Bloomberg) -- Twenty thousand juvenile salmon were released in a River Thames tributary outside London last year to see if they would migrate to sea and return home to breed. Only three came back.
Sewage spilling into the river that bisects Europe’s financial capital may be the reason, said Darryl Clifton-Dey, head of a program to reintroduce the migratory fish to the Thames after a 176-year absence. Sewer owner Thames Water Ltd.estimates 32 million cubic meters of waste flow into the river a year, enough to fill 12,800 Olympic-sized swimming pools.
“Sewage could be the straw that’s breaking the camel’s back” said Clifton-Dey, a scientist at the Environment Agency, the government watchdog for water quality. “Because they need lots of clean water all the way along, salmon are a very good indicator species of the general health of the whole river.”
With Victorian-era sewers failing to control overflows that occur about once a week, Thames Water plans a 2 billion-pound ($3.2 billion) upgrade. Final bidders for the first 400-million pound contract include Vinci SA, the world’s largest builder, and Hochtief AG, Germany’s biggest, with work to begin in 2010.
Like New York’s efforts to clean up the Hudson River, whose bass were contaminated by mercury, and attempts to revive the Huangpu River where Shanghai gets most of its drinking water, London is trying to restore an historic waterway whose health has suffered from population pressures and industrialization.
Deeper Than Subways
Thames Water is owned by Kemble Water Holdings Ltd., itself owned by an investor group led by Australia’s largest investment bank, Macquarie Group Ltd. The utility is planning two tunnels to collect overflow from the capital’s original sewers. Builders will dig as far as 75 meters (250 feet) under London, deeper than any of the city’s subway lines.
The first tunnel will stretch for 7 kilometers (4.4 miles), passing under the River Lee, a tributary of the Thames, to channel overflow to the utility’s Beckton sewage treatment plant in East London. The Lee winds through the site of the 2012 Olympic Games and into the Thames east of Canary Wharf, home to the city’s second financial district and skyscrapers housing offices for banks including Barclays Plc and HSBC Holdings Plc.
Further east at Woolwich, the city’s main flood defense, the Thames Barrier, stretches a third of a mile across the river with 10 steel gates that can be raised to protect London from tidal surges such as the 1953 floods, when water lapped the top of the walls defending Parliament and about 300 people were killed along England’s east coast.
Rod Kirwan, a London lawyer, rowed on the Lee, also called the Lea, for four years and said its course through fields in east London meant it could be “quite leafy and lovely.” It could also be an unpleasant experience on certain days.
Gas ‘Bubbling Up’
“After heavy rainfall, there were stretches of the river that stank and gas was bubbling up,” said Kirwan, a partner at the London law firm Denton Wilde Sapte. “If you closed your eyes, you had no idea you were in central London. Yet in the water it was definitely urban reality.”
Thames Water, formerly owned by Germany’s RWE AG, aims to pick a builder for the Lee tunnel as early as November, said Nick Tennant, a spokesman for the Tideway Tunnels unit. “It’s a massive project, set to be the biggest contract that Thames Water has ever let.”
Overflows into the Thames and its tributaries happen about once weekly. Officials say they’re triggered by as little as 2 millimeters (1/13th inch) of rain that washes down drains to the sewers, which spill over into the river because they were designed when London had less sewage and more unpaved areas to absorb rainwater. In the Thames, bacteria break down excrement, using up the water’s oxygen and stifling fish.
Floating Condoms
Plastic bags, prophylactics, sanitary napkins, tampons and Q-tips blight the waterway and river shores, said Chris Coode, river programs manager for the litter-cleanup charity Thames 21.
“If tourists and local residents look off a bridge after an overspill and they see condoms floating past, what does that say about the Thames?” Coode said. “It’s still an open dirty sewer.”
The 215-mile river, the U.K.’s second-longest, though far from pristine, has come a long way since the “Great Stink” of 1858. The river’s smell then disrupted work in Parliament and lawmakers considered adjourning to Oxford.
The following year, the capital’s chief engineer, Joseph Bazalgette, began plans for the sewers that remain in use today. It’s the 57 outlets from that system that allow sewage into the Thames when it rains and which the new tunnels must intercept.
Fish life has recovered since the early 1960s, when stretches of the Thames were classed as biologically dead, said Tom Cousins, an Environment Agency biologist. Now, 125 species including flounder and gobies populate the river even as sewage discharges can kill thousands of fish, he said.
‘Wildlife Superhighway’
“It’s quite a unique environment having a tidal river through such an urban environment, and it’s a real wildlife superhighway,” Cousins said. “The tunnels will be a major further step in its recovery.”
Local salmon, which migrate as far as Greenland and the Faeroe Islands before returning to their native river, were once found in such numbers in the Thames before industrialization that thousands were caught and sold yearly in London’s Billingsgate fish market, according to Clifton-Dey.
Salmon were absent from the Thames from 1833 until 1974, when a stray was observed, he said.
The reintroduction program, in the Thames tributary the Kennett about 60 miles upstream from tidal limits in west London, began five years later. It currently costs 50,000 pounds to 60,000 pounds a year, Clifton-Dey said.
River of Provenance
In 2008, tagging showed nine adult salmon returned. Just three have come back this year, Clifton-Dey said. Returning fish are captured in traps that catch about 60 percent of them, he said. Fish that don’t come back may remain in the estuary and die without breeding, he said.
Internal metal tags that can be scanned are used to identify the river of provenance while external tags enable fishermen who catch the salmon to call the Environment Agency.
Challenges faced by the salmon aren’t limited to sewage. The 1-year-old smolt released in the river must avoid predators including birds and other fish as they swim from their release point through London, past Big Ben and Tower Bridge. Others are caught in the estuary and at sea by seals and fishermen.
After one or two years at sea, returning salmon must jump up 37 weirs, and fish ladders have been built to help them. If the fish bred in the river naturally, about 1,000 out of 20,000 could be expected to return, he said.
Once the sewage problem has been sorted, Clifton-Dey said he hopes to see 200-300 of the farmed salmon return to the Thames a year, enough to establish a viable breeding population.
Sewage Overflows
Left unaddressed, sewage overflows will increase due to population growth, more downpours amid global warming and loss of green spaces to absorb rain, said Tennant, of Thames Water.
“The sewer outflows seem to occur right when we’ve got adults ready to come into fresh water,” Clifton-Dey said of the arriving fish. The outflows “have stopped salmon coming in in quite large numbers over the last five or 10 years.”
The Lee tunnel will accommodate half of the excess sewage and the Thames tunnel the rest. Hochtief has joined with the London-based Murphy Group. They’re vying for the Lee deal with a group including Vinci, based near Paris, Soletanche Bachy, another French company, and Rugby, England-based Morgan Est Plc.
Thames Water won’t apply for the second tunnel’s planning approval until 2011 and aims to build it by 2020. That project is more complicated than the Lee sewer because it passes through 13 local authorities and requires about 10 access entrances.
The whole project, which Tennant said will add about 40 pounds to a typical London household’s annual water bill, is a “very necessary” addition to the sewage network, said Murad Qureshi, who chairs the London Assembly’s environment committee.
“In recent times Londoners have rediscovered the main artery of the city, which is the Thames,” Qureshi said. “The more we improve it, the more it becomes a feature of the London landscape.”
To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.
