Tuesday, 27 November 2012

"Looking For Water"

Yesterday morning (Monday morning), I was at Nanhua reservoir just after 7am and then on down to the weir at Yueh Mei just north of Cishan in Kaohsiung County's Shanlin district. This old weir allegedly diverts water to an underground channel that feeds into the back end of Agongdian reservoir.

Problem: The channel was completed in 2006, and the condition of the concrete at its exit point is consistent with a recent construction. However, the weir at Yueh Mei is obviously much older than this, showing signs of erosion and long years of relative neglect. The feeder channel for Agongdian reservoir must therefore have been attached to the existing irrigation canal issuing from the Yueh Mei weir, but... where?

I cannot find it.

The satellite views available from Google Earth show one point toward the end of the old channel where the water seems to disappear under ground and remerge a short distance afterward into a natural tributary stream to the Cishan river, and there doesn't seem to be any further weirs to lead into a new section of the diversion channel from that stream (although perhaps the satellite views are out of date). So that's probably a dead end.

On the other side, where the diversion channel first appears at a control gate in Neimen district (near "Wild Boar Lake"), Google Earth shows nothing - the water simply disappears underground at either end of the gate.

And then there is the problem of altitude.

If the Yueh Mei weir is, as I was led to believe, the actual source of water for the Agongdian reservoir diversion channel, then either the water from the irrigation canal is miraculously climbing the mountain un-pumped to reach the control gate in Neimen or it arrives at the control gate from some source other than the Yueh Mei weir, one which is set at a higher altitude than either the Yueh Mei weir or the Neimen control gate. Along that last line of thought my immediate conjecture would be the Nanhua reservoir trans-basin pipeline; could it be that some water from the Yueh Mei weir is somehow delivered into that pipeline? I don't know. However, the conjecture that the water diversion is provided by the Nanhua pipeline is supported by the brute fact that the Nanhua pipeline's second pressure control station is sited in Neimen just a few hundred meters in front of the Neimen control gate.

I don't think I'm going to be able to get up early enough tommorow morning to go looking for water again, so I'll leave this line of enquiry for now.


The only other thing I can think of is that I am wrong about altitude. To get from the Cishan river and the nearby irrigation works (including the Yueh Mei canal) to the Neimen control gate, I need to drive uphill. However, to get from the back of the Neimen pressure tank to the control gate, I did need to descend somewhat. What these two values are, I don't know. Assuming they are even, or that the Cishan side is in fact slightly higher than the Neimen side, then I still need to find the outlet point where the channel leaves the irrigation canal and proceeds to the control gate.

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