Monday 25 November 2013

Attempting To Locate The Spillover Exit Point From The Yanchao Control Gate For The Cishan Diversion Channel

This morning (Sunday morning) I drove down to Yanchao again, this time to look for the location at which spillover water from the second of the Yanchao control gates is directed to. My guess was that this location was somewhere along the course of the "Zhuo-shui" river, one of Agongdian reservoir's two original feeder streams. Here is my hypothetical straight line (just over 2.4 K) from the Yanchao control gates to the first signs of a reinforced channel prior to the Zhuo-shui river...


Both yesterday and today have been relative scorchers for this time of year; I should have left the air-conditioning on while I was out. Bright sunshine and almost cloudless blue skies all day today. Here is the irrigation control gate at the front of Agongdian reservoir when I arrived there just after 10.30am this morning...


Conscious of the time, I drove straight to the little district town to the south-east where I turned left onto Jinshan road that runs up to the "muddy volcano" tourist attraction. The "Zhuo-shui" river that feeds Agongdian reservoir is actually formed from a confluence of streams emanating outward from under this volcanic mound of mud; since these streams tend to contain large amounts of mud, this is what caused the deposit problem in the reservoir (hence the need for fresh, clean water from the Cishan valley on the other side of the mountains). At one point soon after I left the Yanchao district town behind, Jinshan road gave me something I certainly had not been expecting...


That is the first crested serpent eagle I can recall seeing in this area before. I had pulled over to the side of the road in disbelief that I would get another such opportunity, which is why my first shot was with the 18mm still attached to the camera. I murmured prayers to the bird to stay there whilst I changed lenses with my fingers - eyes stuck on the bird. Luckily enough, the bird agreed to wait for me...


Looking straight at me, perhaps trying to remember where he's seen me before. Given that I've photographed so many of these birds at all of the reservoirs in Tainan, there's probably a good chance that this particular bird and I have eyeballed each other before. I wonder whether, like dogs, they notice the phenotypical differences between foreigners like me and the rest of the local population...


The particular stretch of Jinshan road on which I encountered the eagle can be seen in the shot below; to the right of that image is one of the feeder streams from the volcanic area that coalesce to form the "Zhuo-shui" river for Agongdian reservoir.


Below is the same feeder stream entering the main channel...


In the next shot below, there appears to be a channel bending around a corner off to the right. Yet what is somewhat less apparent in that shot (and I had no way to render this more obvious) is that there is another stream entering the channel from the left - notice the cleft in the rushes along the banks. The stream entering the channel from the right is the feeder stream pictured above, whilst the stream entering the channel from the left is, I believe, the same watercourse that carries the floodwater spillover from the Yanchao control gate.


Further back upstream from that point, I continued my search of the channel looking for a tunnel or large and conspicuous culvert on the northern bank indicating the exit point for spillover waters from the Yanchao control gate. Unfortunately, I didn't find it; none of the leads I had guessed at through map-based inferences gave me anything - all I found was the completed infrastructure that was under construction at the time the google street-view shots were taken (about five or six years ago). The image below was taken from one of the small bridges across the channel and is, I believe, the highest upstream point at which concrete encased banks appear...


From the same bridge looking downstream into the sunshine...


Although I searched extensively further upstream, following almost every single little farmer's road there was, very few of them led back to the channel, and of those that did there was no sign of an exit point for spillover water. Jinshan road cannot be followed upstream indefinitely without eventually approaching the same lattitude as the Yanchao control gates themselves, so the journey became self-defeating. I turned back downstream to take more photographs of the channel and wonder where the exit point must be. In this shot below, a small group of people speaking Hoklo were wading in the channel, at times up to their necks; they could not possibly have been fishing due to the noise they were making and the relatively stagnant condition of the channel waters, so my guess is that they had been looking for snails or other, easy-to-catch, fresh water creatures...


After 12pm, I gave up entirely and went to the 7-11 for something to eat and drink before heading back north to Tainan. Although I didn't succeed in finding the exit-point infrastructure, I was pleased I made that trip because the weather began to turn cold again earlier tonight; I might not have such nice weather next time. So for now, this point remains unresolved.

Here is a path I drew on google earth to connect all the main infrastructure points in the complete trans-basin diversion channel. It begins to the north-east at the Yueh Mei weir on the Cishan river where water enters an irrigation canal; that irrigation canal splits into two at a point further to the south, after which one canal continues to feed Cishan whilst the other is diverted underground; the diverted canal passes under the Taishan camp, flows in a large pipe disguised by a bridge (I believe) and enters a tunnel through the side of a mountain; on the other side of the mountain, the water exits briefly at the Neimen control gate before being directed underground once again; the water passes completely under Tianliao district before finally emerging at the Yanchao control gate and then flowing westward toward its entry point into the back end of Agongdian reservoir...


The total approximate length of the whole thing is, according to my google earth plot, 24.64 km. I would love to find the exit point for the spillover water from the Yanchao control gate, but other than that point, I think I've just about solved the problem of tracking the geography of the trans-basin diversion channel now. There are some papers to read about the construction of the tunnel and other details but those are adjunctive to my main purpose, and can be left for another time.

2 comments:

  1. looks amazing! are there any similar channels in taiwan?

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