These days dam removal is a hot subject. Even Wired News talks about it.
First, some data: about 800000 dams in the world, and 45000 higher than 15m; a majority of them has been built after world war II, i.e. in other words, they are quite old, in average. Let’s add the well-known fact that energy is a key point in actual economical and geo-political problems, even if in this post we won’t consider too much these issues; just remember that hydroelectric energy is 20% of worldwide energy production.
It’s a serious stuff, this river revitalization practice, because one has to envision all the civil and hydraulic engineering problems involved in the demolition, but most of all, the project manager should not forget that such operations imply secondary effects which are not negligible in our environment-sensitive society. The Wired article is focused on the application on models for hydraulic security purposes after a dam removal, which is not so noteworthy for those among us who already know an hydraulic model, while the interesting stuff is maybe elsewhere. In two words: sediments and ecosystem.
- Sediments accumulation is one of the most known side-effects of dam existence. Sometimes it is a problem, because the sediment flow shortages has coast erosion as a possible conclusion. Vive versa, dismantling a dam can lead to excessive, excessively rapid sediment input in rivers, while augmented discharges in the reborn natural river will also probably re-activate all the “sleeping” sediments along the river itself.
- Ecosystems are no more “natural”, according to somebody, which means that ecological communities are no more the “good-old” ones because of exotic species pressure and because, of course, of human artificial structures like dams. Well, removing such structures will not bring back things, au contraire, dismantling tout-court a dam which is the last barrier against exotic fish propagation may even lead to extinction of endangered species. By the way, the still water of an artificial reservoir could host many frog communities and that may naturally make us asking ourselves: are these frogs “natural”, even if they weren’t in place before the dam, or not?
I will add later some comments about some economic aspects of sediment accumulation and about the perverted conservativeness of some Italian environmentalists; meanwhile I’ll conclude this post with some links, as usual:
For first, Fossil creek restoration as an interesting case study;
then Le scienze, an Italian scientific magazine that inspired me and is the main source for this post;
then this report for a deeper reading;
and finally, but just for interested modellers (your comments will be appreciated very much), a free sediment model from the USA.