Saturday, 26 March 2016

Short Trip To Nanhua Reservoir (南化水庫): The New Sluiceway Construction

Myself at the public viewing platform at the southwest of Nanhua reservoir at about 3 p.m. this afternoon.
Weather is obviously important to me because it constrains my choices as to which tasks I try to complete in my reservoir work. Last weekend I cancelled my trip to Nantou due to a forecast for electrical storms. During the following week the weather has been miserably cold with rain and overcast skies every day. Although the forecast for this weekend was bright with clouds, I couldn't quite bring myself to believe it. I thought it more sensible to begin the Nantou trip on Sunday rather than Saturday, to give the bad weather more time to clear out.

Yet this morning amazed me. Brilliant sunshine, as if spring really had arrived already. So after having a decent lie in this morning, I did all my necessaries and then got my kit together to drive out to Nanhua reservoir. I wanted to have a look at the new sluiceway tunnel under construction, and hopefully get back to Tainan before the afternoon was over. I was last here on the "Double Ten" weekend in October last year.

The new sluiceway tunnel is needed to relieve a build up of sediment which has occurred behind a mountain spur which slopes down into the water from the western shoreline to hide the dam further to the south. The curve of the spur is such that the drift of sediments loops back upon itself to accumulate and cannot therefore flow further south to be flushed out by the two original sluiceways built when the dam and reservoir were completed in the mid '90s.

The new sluiceway tunnel exit mouth to the west of and downstream from Nanhua reservoir. When completed, sediment rich water from a blocked corner of Nanhua reservoir will be flushed out here and into a channel to join a post-spillway water concourse.
A short wall has been constructed in front of the bridge which crosses the original sluiceway exit channel.
New item: a large concrete mouth for an access tunnel; this tunnel is not the sluiceway itself, but merely provides access to the underground tunneling and construction site for the sluiceway.
The scene of construction downstream from the dam in context. 
The mouth of the access tunnel. The elevated pipes are for ventilation I think.
I remember when all this was green slope; note the old Fairchild Boxcar cargo aircraft in the top left.
The old bird on display could do with having its' windows wiped down with a damp cloth to remove the dirt and grime.
Putting the scene into context from above; looking down over the spillway toward the construction site; the exit mouth is to the left with the bridge over the original sluiceway exit channel in the middle, and the access tunnel mouth to the right. Further behind in the top right of the image, you can see an additional construction site for work on the new sluiceway tunnel.
A 300mm shot of that further-off construction site. There is what appears to be either another access mouth and/or an adit point for the new sluiceway tunnel, with two yellow excavators parked on top of it.
Makeshift road leading down to the water's edge on the western shoreline. This is the particular mountain spur in question; the sediment build-up is occurring on the other side of this spur (and further back to the left).
A recent concrete latticework jacket applied to the south side of the mountain spur to avert possible landslides - the building of the sluiceway entrance is taking place on the other side.
The late afternoon sun was in front of me, which meant hazy air; this was the best I could do with the 300mm lens. This is the upstream construction site for the sluiceway tunnel mouth.
A newly added series of public information displays goes to some length to explain the engineering plan for the new sluiceway tunnel.
This side of the first display is a diagram of how the excavation into the the mountainside and gradual construction of the tunnel is achieved.
The second display begins with both plan and profile views of the new sluiceway tunnel.
The second half of the second display is a 3D rendering of how the sluiceway tunnel will look, including its' control station on the upstream side, and its' baffled exit point on the downstream side.
The first half of the third display gives overall project information including start date and (expected) completion date (February 8th 2018).
The second half of the third display gives further information about how the new sluiceway is designed and expected to perform.
The fourth display goes into the history of the problem and the consequent necessity of the new sluiceway.
More information on the history of sediment build-up and what appears to be a recursive flow, similar to that produced by a weir.
Parting shot of Nanhua reservoir looking toward the troublesome mountain spur and the upstream construction site. 

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