johnw at mac.com
Fri Mar 24 21:38:07 UTC 2017
> On Mar 25, 2017, at 12:54 AM, Richard <ricoz.osm at gmail.com> wrote:
> This would include most
> levees even if we usualy don't map them explicitly.
We have a dyke tag because the levees do not block the flow of the river. They prevent it from flooding out of the path the river is already flowing.
In this system, except for two-three gates (about 50m total), nothing explicitly is built "across" the river. They contain it.
They built this weird thing out of levees, rather than putting a big gravity dam across the river and making a traditional big reservoir.
This whole thing is built like a radiator's overflow reservoir. It only takes in water when the river flows over the weirs in the sides of the levees. The river always continues, without hinderance, without passing through a weir or a gate, to meet the larger river. There is no dam.
Only the surge that overflows at the narrowing part is captured and slowed down.
I admit, this is weird, and the gates at the bottom of the reservoir could be considered a dam, but it is actually a whole lot of levees.
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