Another Visit To The Yanchao Control Gate & The Irrigation Canal Split In Cishan

This afternoon I drove back down to the Yanchao control gates, and, to my surprise (and good fortune), I found that the barbed wire security gate was wide open!

I walked straight in to take pictures, and gestured reassurance to the site supervisor when one of the excavator drivers alerted him to my presence. He was very open and I immediately plied him with questions; first off was whether I was right that the second control gate was for flood control - I was right, but I was wrong about which gate: the one to the left in the image below is the primary gate, and the one to the right is for flood control (I had guessed the other way around - the information is useful because it saves me looking for another channel in the wrong area). However, when questioned as to where the flood control tunnel led to, he replied that he was not allowed to say. So that point remains unresolved.

I asked if I could walk around and take pictures and he said yes; I also asked him what was going on with the "half-cut" trees and he replied (assuming I understood this correctly - he used one or two unfamiliar words) that they were going to be transplanted elsewhere.

Below is a shot of the small dam checking the natural course of the stream at the end of the patch of "half-cut" trees. The flood control tunnel must logically run beneath the bed of this stream to somewhere further westward rather than empty out into this stream - else what would be the point of having two control gates? The dam itself is about five meters high and about thirty to thirty five meters across. The locals fishing at the end of it gave me a beer and when I asked them how they had came here (because usually the gate will be locked) one of them told me he had noticed the Water Bureau people arriving and decided to ask them if they could fish at the end of the dam. I got the impression they were quite familiar with the stream.

The diversion channel exits into the course of the stream from a tunnel with a diameter of about three or four meters.

There was a depth gauge attached to one side of the tunnel's mouth in what seemed to be a scale of decimeters up to the one meter mark; at the time, the water was just below the third decimeter mark...

Immediately upon flowing out from the tunnel's mouth, the water enters a rectangular pen before spilling out over the north-western corner and through some large baffling blocks before entering the natural course of the original stream...

And here is a view of that original stream, looking upstream from the dam...

I thanked the local fishermen and the site supervisor and left; I decided to check out the other roads I had marked out from Tianliao into Neimen. To get there I had to take highway 28 over the mountains into the Cishan valley first; just after the apex of the pass, I came across this strange sign at the entrance of some sort of park - "Flora Lakes"... I didn't have time to explore because I wanted to take new pictures of the Cishan irrigation canal while there was still some late afternoon light.

I arrived there in time, crossed the rickety little bridge over the lower canal by crawling (as I had last time) and was pleasantly surprised by the massive difference in water volume since the last time I was here (an early winter morning in 2012): the water at this point in the channel must be well over two meters deep. For some reason the debris line was disconnected and floating in a disused and useless state off to the right...

And I found that I had made a mistake! Previously, I had observed the water flowing into a rectangular course in the centre of the channel and inferred that that channel must take the water underground to the Neimen control gate. From that inference, I had then concluded that the substantially larger tunnel to the left was for flood control. Yet given the volume of water both at the Neimen control gate and at the Yanchao control gate (and at the channel's entry point into Agongdian's eastern feeder stream), I now suspect that the left hand tunnel is either exclusively for the Agongdian diversion channel, or that both the smaller central tunnel and the larger left hand tunnel feed the Agongdian diversion channel...

The blue grill behind the left hand tunnel is presumably there to filter out large elements of debris such as dead tree branches and the like...

A view from behind the three gates guarding the left hand tunnel...

I still haven't figured out what the third aperture off to the right is for, and how it functions...

After getting photos of the diversion channel entry point before it begins its journey underground and overground to the Neimen control gate, I drove the short distance upstream to photo the split in the original irrigation canal...

Here is the original (1978) irrigation canal before being split in two...

And here is a view of the upper canal (which now functions as the feeder to the Agongdian diversion channel) and the control gate letting water out below into the secondary canal that continues through the Cishan valley...

At no point driving between Tianliao, Neimen and Cishan did I find any further surface signs of the diversion channel. I am therefore inclined to the conclusion that it passes underground all the way from the Neimen control gate to the Yanchao control gate. This would also make a lot of sense given the geography of Tianliao. Given that the Water Bureau's aim in constructing the channel in the mid-2000s was to provide clean supplemental water to Agongdian reservoir, they wouldn't want the diversion channel receiving pollutants from the mudstone ridges of Tianliao - that would defeat their purpose.