The aqueduct carries the canal in an iron trough over a valley, and the trough is watched by sensors because a crack in a trough is a canal in a field. Every night at one they read a boat going across. And behind the boat the level drops, a foot, along the trough, the way it would if the trough were losing water, and the sensors alarm, and the trough is full, and in the morning the field a hundred feet below has a wet line across it from one side of the valley to the other where a lockful of water has fallen, and the trough has not lost a drop.
I am the aqueduct's inspecting engineer and the trough sensors are my early warning, and every night they warn me about something that already happened.
The aqueduct.
An iron trough, a boat's width, carried on stone piers across a valley, a hundred feet up, and the canal runs through it, and boats cross it, and the water in it is held by the trough's plates and the bolts between them, and there are sensors on the plates and in the water that read the level and the strain, because a plate that fails is the canal going into the valley, and it has happened, once, elsewhere.
At one every night the sensors read a boat.
The crossing.
A boat's weight comes onto the trough at the north end, the strain gauges on the first plates see it, and it moves along, plate by plate, at the speed a boat crosses an aqueduct, which is slow, because people are nervous. And behind the boat the level drops. The water sensors read a foot down, along the trough, following the boat, as if the trough were emptying from behind it, and the alarm goes, on my phone, trough level critical, every night at ten past one.
The trough is full. I have stood on the towpath at ten past one with the alarm going and looked at the water in the trough at my feet and it is at the line, full, and the sensors say it is a foot down.
In the morning the field below has a wet line across it. From pier to pier, the width of the trough, a strip of grass that is soaked, and the stream at the bottom of the valley is up, for an hour, by about a lockful, and the trough has not lost a drop.
What has been checked.
The sensors, every one, replaced. They read the boat and the drop.
The trough, at one, by me, on the towpath at the middle pier, a hundred feet up, in the dark, which I do not recommend. The boat came. I heard it: the engine, a working boat's, and the hull against the trough side, the iron on iron, which is a sound you never forget, and it came past me, and I could not see it, and I put my hand out over the trough and it touched a cabin side, wood, painted, cold, moving, and then it was past, and behind it the water in the trough went down. I saw it. A foot, in a wave, following the boat, and over the edge of the trough, on the valley side, where the trough is a plate and a rail, the water going over, in a sheet, falling, a hundred feet, into the dark, the sound of it hitting the field, and the trough was full, and the water was going over, and both.
Who.
The aqueduct has never failed. The plaque says so. But the company's records have a night in the eighteen hundreds when a working boat had crossed at night, in ice, and the trough had been low, because the ice had been broken and the water had gone over the end plates, and the boat had grounded on the trough bottom, in the middle, a hundred feet up, and the boatman had got off to push, on the towpath, in the ice, and had gone over the rail.
The trough had been refilled. The boat had been got off. The records have the boatman's name and the cargo and the word, drowned, which is the wrong word for a man who fell a hundred feet, and the company knew it and wrote it anyway.
He is crossing. Every night. And the trough goes low behind him, because that is what it did, and the water goes into the valley, because that is where he went.
What is done about it.
The alarm goes every night and the canal company's control room has had it on their screen for years and has asked me to fix the sensors, and I have replaced the sensors, and they have asked me to fix them again, and I have said that the sensors are reading what the trough is doing, and the control room has asked what the trough is doing, and I have said, remembering.
What I do.
I inspect the aqueduct.
A boat on a low trough grounds, and the boatman gets off to push, and there is no rail on the towpath side worth the name, and that was the night. The rail is there now. It has been there since. But a man who got off to push a boat in the dark a hundred feet up did not have it, and he is getting off every night at the middle pier to push, and the rail does not know him.
So I hold it. At one I am at the middle pier, on the towpath, with my hand on the rail, and when the boat comes past and stops, which it does, the engine idling, the hull on the bottom of the trough, and the boots come off onto the towpath beside me, I say, don't push, I've got her, and I put my shoulder to a cabin side I cannot see, and I push. It moves. I do not know what I am pushing. It moves, off the bottom, and the engine picks up, and the boots get back on, and it goes on across, and the water behind it does not go down.
It has not gone down since. The alarm at ten past one has not gone. The field in the morning is dry. And the sensors read a boat crossing, every night, at one, a boat's weight, plate by plate, at the speed of a boat whose steerer is not nervous, and the level behind it stays at the line, and the control room has written to thank me for fixing the sensors, and I have not written back.