Friday, 7 February 2014

An Old Problem Solved With New Information

A year and a half ago, over the course of several trips to Miaoli County, I discovered the water channel entry point for Yongheshan reservoir. On one trip I had heard the distinct sound of large volumes of rushing water falling over a weir whilst cycling around the back of the reservoir, and in my subsequent trip I returned to the same spot and pared my way through the horrendously wild and overgrown plants covering a now long-forgotten causeway to photograph the channel and weir. That underground channel enters Yongheshan reservoir in its northeastern corner...

Directly behind the reservoir to the east lies the Nanzhuang river, only one kilometer away. However, the river bed rests at a lower altitude with the difference being of the order of maybe thirty to fifty feet. I knew that Yongheshan reservoir was built at about the same time as Renyitan reservoir down south in Chiayi and that since both reservoirs are sited off-stream, they must have a similar design, i.e. with an underground feeder channel proceeding from a sedimentation tank. Yet when I followed the Nanzhuang river on google earth, I had not spotted anything that looked even remotely like a viable candidate and I was stumped. My error was simple: as I followed the river further and further upstream and found nothing, I started to think I was looking in the wrong place. If only I had kept following the river even further upstream I would have found it...

The straight line drawn on that google earth image above measures seven and a half kilometers (or just over four and a half miles), yet for obvious geographical reasons the actual route taken by the underground diversion channel must keep to the south and then the west of the river and so is likely to feature two right angles or curves in order to avoid crossing the two bends in the river subsequent to the weir intake and sedimentation tank. Here is what it looks like in a close up on google earth...

The large weir is called "Tianmei" (田美) Weir, after the little village on the Nanzhuang river - the village has an elementary school across on the eastern side of the river. Here is somebody's streetview image of what the sedimentation tank looks like from the south end facing toward the north end (where the water will disappear into the underground diversion channel)...

Needless to say I am quite pleased to have solved this old problem, and look forward to going back up to Miaoli to take my own photographs. As yet however, I am still wondering whether the route of this diversion channel is punctuated by one or more control gates, as is the case with the diversion channel from the Cishan river to Agongdian reservoir in Kaohsiung. If so, I haven't been able to find them yet. There is also the further question of why the diversion channel enters Yongheshan reservoir at its' northeastern corner rather than to the south or south-east given that the channel must approach the reservoir from the south-east.

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