MARINE CIVILS
WILDLIFE HAVEN CREATED BY MAJOR SEWAGE WORKS The largest infrastructure project ever undertaken by the UK water industry is helping to create new habitats for wildlife Nearly 1.5 million tonnes of underground material have been removed by waterway from central London and deposited on a site that could be the largest habitat-creation scheme inside the metropolis. It’s been possible because of a huge project to build a new sewer for London, whose current system was built for a population less than half its current size. The project is being run by Tideway, a consortium of investors, which has contracted civil engineering firm Land and Water to carry out a lot of the heavy lifting. It’s a massive operation. Tunnel boring machines working underground loosen material which is then removed from the tunnel on a series of conveyors to bring it to ground level. From there it is loaded on to barges usinng MHL360 material handlers and shipped to the various sites for re-use - 1.4 million tonnes to the habitat restoration scheme in Rainham; almost half a tonne to cap landfill; and 2.2 million tonnes to cap ash fields in Ingrebourne valley. Contractors AC Bennetts and Walsh Marine operated a range of barges to transport material by river, ranging from a small 500t barge running material between cofferdams at Albert Embankment to 1,800t barges removing the main tunnel spoil from Kirtling Street and Chambers Wharf. Eight new barges were commissioned for the Tideway West Project and Land & Water unloaded, transported and received it, and in the East, Walsh Contracting managed the offloading and haulage at L & W’s coldharbour jetty. “Due to the nature of the projects - significant volumes of material for a sustained period of time - the Tideway contracts (East and West) have formed the majority of Land and Water Remediation’s business over the last four years,” said Merryn Rodwell, senior account executive with Land and Water. The contractors also used pontoons to assist in delivering the ‘more by river’ strategy by transporting steel reinforcement, precast panels, and main tunnel segments. Habitat creation The Rainham wildlife area lies between a landfill site and a site belonging to the Royal Society for the Protection of Birds, and is 1 million square metres in area. It is already becoming home to a number of bird species. Clay is being used to line pits and create wetlands on Rainham Marshes and chalk laid on top as part of the import of six million tonnes of wet and dry material from the excavation works digging out the new Super Sewer. ”We have a target to beneficially reuse at least 85% of our spoil,” says media relations manager Taylor Geall. ”To date, we have beneficially reused 97.7%. ”Our use of the river has kept 650,000 HGVs off the road network and led to a 90% reduction in CO2, 86% reduction in NO2, and a 54% reduction in NOx emissions (compared to the HGV equivalent).” Dredged material will form the landform, with restoration soils over laid to act as a ‘rainwater harvesting blanket’ that will feed the low-land wetlands.
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”The final landform consists of a patchwork of habitats,” says Land and Water. ”These include upland/dry/sandy areas ideal for some ground-nesting species, with shallow valleys and damp swales, and collecting ditches that eventually channel surface waters to the permanent wetlands.” Sewer history In the grand scheme of things it’s not that long since London’s sewage was simply dumped in the Thames. As the river also served as the city’s drinking water, it wasn’t really surprising that cholera was rife, and thousands died as a result. Eventually, 85 miles of sewers running parallel to the river were built by Joseph Bazalgette, who was later knighted, as well as street sewers dug throughout London. But nothing has been done to the sewage system since, and with London’s population now around nine million, Bazalgette’s designs to cope with the waste from four million people clearly need updating. Raw sewage, in fact, regularly spills over into the river even when there is low rainfall because the system is so clogged up. Thames Tideway is promising the new £4.2 billion (€5 billion) sewer will reduce the amount of raw sewage finding its way into the iconic river by 95%. 8 London Super Sewer engineering
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