Few pieces of UK civil engineering infrastructure are critical to as many households as London’s flood defence system, so when the Environment Agency sought to make improvements to the operation of the Dartford Creek Barrier, it needed a highly reliable motor drives system to get the job done.
Situated at the mouth of the Dartford Creek on the South Bank of the River Thames, the Dartford Creek barrier is a crucial part of London’s flood defence system, preventing tidal floodwaters from reaching the densely populated communities of Dartford and Crayford.
Erected in 1981, the barrier is a highly imposing structure, comprising two 30 metre high towers sitting aside two 160 tonne gates. These gates are driven by a highly robust chain system, which is over 90 metres in length, weighs 13 tonnes and can handle a huge maximum load of just short of 300 tonnes.
The all-important gates are balanced by two water-filled counterweights housed within the two towers, which can regulate between 54 and 105 tonnes of water pressure to allow for gravity lowering in emergencies. This system allows the gates to be positioned sequentially on top of one another to form a 10.4 metre defensive wall against high tides.
Having been subjected to the rigorous tidal flows of the UK’s longest river for almost three decades, in 2009 the Environment Agency took the decision to refurbish the barrier amid concerns about its age and escalating maintenance costs.
Following a competitive tender, consulting engineers, KGAL and Qualter Hall, were awarded the contract to undertake extensive refurbishment works across the site, to include the design and supply of new hydraulic drive and braking systems, new electrical and control systems and refurbishment of the hydraulic latch system including new hydraulic cylinders.
Given its extensive expertise in this field, Bosch Rexroth was immediately consulted to fulfill the replacement of the main gate hydraulic drive machinery through its Hagglunds motor drives offer.
Rexroth hydraulic drive systems have a reputation for performing under severe conditions and provide reliable power internationally to many marine applications above or below water. They are also known to be particularly well suited to chain or winch driven flood gates such as those already in operation at Dartford Creek.
In a £200,000 contract, the company acted decisively to specify and provide two Hagglunds motor drives for each gate, complete with motion control manifolds to provide increased security and precise control.
It also supplied bespoke hydraulic power units for the two towers, with the west tower receiving an 800 litre HPU complete with four 30kw main drives and the east tower, a 250 litre HPU and two 22kw maintenance-free chain tension and locking bolt drives.
Work commenced on the project in October 2009 with on-site operations starting in April 2010. Extensive testing and commissioning took place during August 2010, with the project finally completing later that year.
Given the critical public safety factors involved, balancing priorities was the key to achieving success on the project, explains Steve Smith, UK industry sector manager at Bosch Rexroth.
“On paper, the remit to provide a highly reliable, modern and robust drives solution that could be easily maintained and controlled seemed relatively straightforward. However, even though the works took place during the summer period when river flows are traditionally lower, the engineers still needed to keep one gate fully operational throughout the entire process to maintain flood protection. This called for precision planning during the design and installation process with a extremely close working relationship with the other contractors involved.”
“Given our considerable expertise in the marine sector and the suitability of our direct hydraulic drive offer, which allows for particularly reliable and precision control of large moving structures, we were able to deliver on brief and budget.”