Tuesday, 17 September 2013

Turbulence Precipitator?

Thinking about that new structure at the back of Tseng-wen reservoir... it simply cannot be part of a weir and entrapment pen system. The chief reason for this is that it only spans less than half of the river's breadth when full and therefore the water (and the sediment and debris carried by the water) will just continue past it. There's also the fact that the structure appears to only have two concrete elements separated by a large gap, so water will flow between them anyway. Here it is three months ago...

A full Tseng-wen river is also going to flow past the structure on the eastern side too, so the idea that it is part of an as yet unfinished design to trap water and sediment to be flushed out via an underground tunnel seems untenable. If we zoom in on that shot above, we can see that there are a series of holes on each of the structure's two elements that would seem to be sockets for a set of rods connecting the two...

I wonder what this is. I was talking to a civil engineering graduate last night who thought it might be a structure designed to increase water turbulence rather than reduce it, with the idea being that a more turbulent water flow might prevent sediment from settling at the back and middle of the reservoir and instead carry the sediment further toward the front of the reservoir where it can be more easily flushed by the new tunnel under construction.

If that interpretation is correct, then I wonder whether this structure is just the first of several each of which may be designed to increase turbulence. That would make sense from a budgetary point of view as there is no way several of these structures would cost anything like the massive by-pass tunnel from back to front that I had been shown earlier in the year. On the other hand, the calculations required to specify the design measurements of the structure(s) must be very difficult; Tseng-wen reservoir is twelve kilometers long in a straight line and the challenge is to shift enough sediment to a particular area when it can then be flushed.

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