Tom Turner gave us a lecture that covered flooding from the epic of Gilgamesh and Noah's Flood to modern day solutions to the problem. In an entertaining and thought provoking presentation enlivened by video clips he outlined the problems and covered attempts to alleviate flooding ancient and modern.
London gets only 885mm of rain in an average year he told us, less than the world's average of 990mm, so why do we have floods? The three suggested reasons for flooding are: too few drains, (water can't flow away), too many drains, (which accelerate water runoff), or too many impermeable surfaces, (so that water can't seep into the ground.
After speaking about our fear of floods — God's punishment for bad behaviour, according to both the Gilgamesh flood myth and the Bible — and citing the 1953 north sea flood which killed 307 people in the UK and caused a huge amount of damage — Tom went on to cover engineering solutions. One of these is the Thames Barrier, which does a good job, but cost as much as the 1953 flood.
Playing devil's advocate, Tom showed images of Richmond, Strand-on-the-Green and Greenwich, with local residents paddling through the Thames at high tide. Greenwich's waterfront took shape in the eighteenth-century and while Hawksmoor and Wren may have been great architects they had, he argued, poor understanding of flood defence. In sharp contrast, Thamesmead is the epitome of neobrutalist flood control engineering. He also showed heavy-handed flood control on the River Westbourne and a remarkable example from Seoul where a river was covered by an expressway that subsequently had to be demolished and the river reborn as a parkway.
From then on, he dropped the pose of celebrating large scale, mostly concrete, flood control engineering and began to discuss alternative control measures. He pointed out the value of green roofs for both absorbing rainfall and slowing its flow to drainage, using examples from the University of Greenwich and a private house where rainfall takes an hour to leave the roof and then infiltrates through the garden, no water reaching the drains. Rewarding property owners for preventing rainwater entering the sewage system would promote green roofs and other aids to soil infiltration.
Green roofs of this kind would protect against flooding from runoff but cannot help with storm surges from the sea. This was why the Thames Barrier was built though, somewhat ironically, half of its closures are to store water running off the land, due to increased runoff as development creates more impermeable surfaces.
He also advocated the use of public green spaces for occasional flood water storage, citing Sutcliffe Park in Greenwich, an idea initially opposed by Greenwich Council because the benefit would accrue to residents of Lewisham, not Greenwich. It demanded compensation from Lewisham for the loss of football pitches. However, Tom suggested, Greenwich should have asked for payment for the flood mitigation. He sees a great role for public parks in this way and a source of income for park authorities. While this approach has obvious value, he did not mention the deleterious effects this can have on historic park design, as in Dulwich Park and neighbouring Belair.
River restoration is another way of ameliorating runoff. Tom gave the example of the River Ravensbourne. Part of the river, previously covered over, was exposed in Brookmill Park and now helps in flood water storage upstream of the Thames barrier at Woolwich.
Tom then contrasted the approach of dealing with London's flood water by building the Thames Tideway Tunnel, (costing London householders £25 each per year indefinitely), with the Sustainable Urban Drainage (SUD) approach. He pointed out that the Thames Tideway Tunnel is only necessary because of the design of London's Victorian drainage system that does not separate surface water runoff from sewage water. If surface water runoff was carried in a separate system or prevented from entering the sewage drainage system there would be no need for the tunnel. By reducing the flow of surface water runoff by means of Sustainable Urban Drainage we would all have benefited, except for the international investors who funded the Tunnel! The chairman of the committee that proposed the Thames Tideway Tunnel now thinks that it was a waste of money.
There followed examples of flood amelioration measures from different areas — the first was from Pickering, north Yorkshire of Integrated Catchment Management. Here the standard engineering approach of building massive concrete flood walls along the banks of the river through the historic town was rejected in favour of upstream flood detention. It was noted that the engineering solution had been based on standard off-the-shelf data and software rather than actual site-specific observation. The catchment management solution was bespoke and in line with what landscape architects had been recommending for a hundred years.
Explaining why Integrated Catchment Management was necessary, Tom pointed to the runoff created by forest clearance on hills and plains, the alteration of river channels and the greater impermeability in large urban areas due to the use of paving and roofing. The capacity of floodplains to accommodate peak flows was decreased by building on them.
His preferred solution for London is a massive increase in green roofs, which by detaining much of the rainfall at roof top level and allowing it to evaporate would reduce the load on the drainage system to levels it could cope with. This Skyscape policy is in line with one of the principles of landscape architecture, a multi-objective proposal: it would improve biodiversity, lessen air pollution by catching particulates, save energy by insulating buildings, create attractive green areas for the building's inhabitants, capture carbon by absorbing carbon dioxide and generally be good for the urban environment. He didn't mention it but transpiration from vegetation creates considerable cooling on hot days like the one on which Tom's lecture was delivered.
Tom was lecturing to an audience of landscape architects, garden historians, gardeners and green advocates who could be expected to be sympathetic to his message and who gave him an enthusiastic response. How this lecture would have gone down with an audience of civil engineers is difficult to say, but that is the audience that needs to be convinced of this style of flood control.
Tom Turner is a landscape architect and garden historian, and formerly a lecturer at the University of Greenwich. Tom has written a number of books, including Landscape planning and environmental impact design UCL Press, 1998,and helps edit two websites: www.gardenvisit.com and www.landscapearchitecture.org.uk .