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Comment by luhn | Hacker News Reader

I could think of a few potential reasons:

- Maintenance: It could be very difficult to find and fix a fiber break. AFAIK, there's no easy way to determine where a break in the fiber is, you generally end up replacing the entire broken segment, which in this case could be miles.

- Reliability: If the fiber breaks, all the upstream sensors go down. Especially since a fiber break could also mean a pipeline break, you just handicapped yourself at the most critical time.

- Cost: Hundreds of miles of fiber, properly shielded from the elements, must cost a lot. (Of course, getting wireless signal to thousands of sensor stations would also be pricey, and I can't say how they'd compare.)

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None of those are a problem if you're talking about building a canal. From my previous experience, 80% to 90% of the cost of building a fiber network is construction, especially digging ditches, hanging poles, etc. Materials account for the remaining 10%-20%. RoW costs are not included.

IIRC, the materials cost for building long haul fiber is a couple dollar per meter or less, especially in China.

If you're already building a massive structure like a canal, embedding conduits into the infrastructure is a tiny marginal cost. And Fiber maintenance is very, very low in protected environments (such as the electric-fence protected canal).

Not only that, you could easily build two conduits, one on each side of the canal, creating route diversity.

So for laying hundreds of miles (let's say 1000km) of fiber where construction is already happening, the total cost would be a few million USD.

If you're interested, optical time-domain reflectometers are used to characterize fiber cables, including breaks/bends/faults/etc. Pretty standard and relatively cheap test equipment.

I was curious how accurate those are, found a datasheet for the PRO-OBL-201A ($1600, or effectively nothing compared to an oil pipeline). It's a portable "optical break detector", full blown reflectometers might have more features.

They list the maximum range as 100 Km, with accuracy of +/- (0.8 m + 0.001% x Distance). So measuring to a break at maximum range, you'll be within 1.8 meters.

iirc, tunnels use this to know where exactly fires occur.

You mention maintenance of the fibre, but I think the bigger reason would be maintenance of the pipeline. Pipelines require frequent maintenance and inspection, and expecting the workers doing that maintenance to avoid slicing the fibre is probably optimistic.

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