I do love a dam. When I was a child, we used to dam the stream that split Duncannon strand, once to triumph effect. If I'd known even one engineer when I was growing up, I might have something concrete to show for 40 years in the work-place. It wasn't really until I started teaching environmental chemistry a couple of years ago, that I started to appreciate of just how devastating dams can be. Holding back the water on a river in some wilderness can have a huge effect on the dissolved oxygen, on the accumulation of sediment, and on the number and sorts of species that inhabit the valley. Dams are created to generate hydro-electric power, to allow the abstraction of water for irrigation and/or to 'tame' the river, so that its flow can be controlled and wild fluctuations in flow-rate damped. If you're not careful, artificially raising the water-level can create a greater catastrophe than any imaginable natural fluctuations. And if the dam fails you can kill people and destroy millions of €€ worth of property: the Baldwin Hills Dam failed on this day 14th December 1963. On a vastly greater scale, work damming the Yangtze River in China started exactly 20 years ago today but some are asking Is the Three Gorges Dam a Ticking Time Bomb?
Today it's dam movie time in the Pacific North West!
Over the last 200 years, dammers have been active along hundreds of rivers across the USA. There are as many as 75,000 dams in the country - about one for every day since 4th July 1776. A lot of these structures were built before the concept of environmental impact had been articulated, and the older structures are either coming to the end of their insurable life-span or have been superseded by other structures or more efficient modern methodologies. The last 10 years have seen a number of dam-removal projects that have been not without interest to environmental scientists . . . like myself. Richard Lovett, a freelancer from Oregon, has written a nicely explanatory and discursive piece in Nature, Rivers on the Run, about the issues and practicalities of returning rivers in his neighbourhood to their wild selves. The problem is that, while the construction of the dam had an enormous effect on the local ecology (drowning millions of trees and their attendant flora and fauna is only the most obvious part of this), the deconstruction is also bound to change things utterly and probably not to the status quo ante because extinction is forever and ecosystems move on.
Lovett contrasts three undammings to illustrate how differences in size scale up, but differences in sediment quality turn out to be a more significant variable. In all cases, Salmonid fish, like steelhead trout Oncorhynchus mykiss, of the rivers were endangered by decades of inhibited access to upstream spawning grounds. Installing a fish-ladder to by-pass the dams was very much a hit and miss affair, with the fish preferring to nose up the spillways rather than taking a detour in the wrong direction up the artificial ladders. They looked good on paper and satisfied the lads from the Environmental Protection Agency, but just had the wrong smell.
First down was the 18m high Marmot Dam on Oregon's Sandy River in 2007. Its chief purpose of early rural electrification which could be replaced by a helluva lot of wind-turbines and so the dam was seen as superfluous. They blew a hole in the bottom of the dam and the river ran through it leaving much of the sediment behind. That sand and grit eroded gradually over the next 8 months and steelhead was soon seen nosing directly upstream past the dam site. The film of the changes is kind of hokey and complacent, and it grated to hear the whole project being monetised in a profit and loss way: each adult steelhead is worth $500 to the local economy; no dam means that some guy's kayaking business can expand. If Oregon tree-huggers are like Irish tree-huggers, you may be sure that wind-turbines don't get a 10/10 score in the local community.
In 2009, the Forest Service targetted the elderly 8m tall Hemlock Dam on the Trout River. Here it was deemed expedient to build a huge sluice pipe to drain the lake and then cart away 42,000 cu.m for sediment in 20 ton loads and then dismantle the dam. The film claims that 2000 truck-loads were required and that they loaded every six minutes for 40 consecutive days which suggests that it was a 5 hour working day. A lot of aerobic bacteria presumably got trucked away; and nobody says where the stuff [which would cover a soccer pitch to a depth of 4m] was dumped. This all cost somewhere North of $1million, and didn't seem to be manifestly a better solution ecologically when compared to the blow-and-go that had been implemented on the Sandy River two years earlier.
Soooo, in 2011 on the White Salmon River in neighbouring Washington state, the Forest Service went back to the Marmot Protocol. The Condit Dam on that river was 38m tall and had pro-rata accumulated about 1.5 million cu.m of sediment - about 40x more than Hemlock. Crucially the quality of the sediment was very different from that that behind the Marmot Dam: instead of it being half-n-half sand and gravel, Condit was bunkering about a third mud, and half sand and a mere leaven of gravel. When the klaxon went and a hole was blown in the bottom of the Condit Dam, an explosive black cloud of aerosolled sludge burst out and travelled downsteam in an emulsion with up to 28% particulate matter. You can see the waterlogged mud slump down in 1000 ton gouts as the sedimented lake drains away through the plug-hole. It was all over in 3 hours! I'm not in a position to say which of these three protocols is 'better' for the environment but clearly blow-and-go is cheaper for the tax-payer.
If you don't spend the next half hour surfing youtube for further "dam removal" videos, then I don't think you are a normal boy - try Elwha or Glines for different protocols again.
Footnotes: "The devil damn thee black, thou cream-faced loon!" is part of a great endgame rant from Macbeth.