A colleague works in a closed (no public access) watershed and came across this culvert today. These smooth "tracks" down the center of the culvert are something we have never seen before. Any idea what they may be for?

Some details that may afford clues:

  • Culvert installation date is unknown (so 30+ years).
  • The culvert runs underneath an access road.
  • There are no other utilities or structures anywhere near (within a mile) of this culvert.
  • The channel upstream and downstream of the culvert are still in their natural state.
  • Logging use to occur in the watershed in the past, but there are no known logging zones next to this culvert.
  • The culvert is massively over sized (serves an area of 150 acres which typically does not receive significant snow-pack).
  • This stream empties into a main tributary which is about another 1/3 mile downstream.
  • Surface road was originally used for access to the upper part of the watershed, and for logging vehicles/equipment.
  • This culvert is located near Portland, Oregon

Stream Culvert under Access Road

  • 1
    $\begingroup$ [I'm not in construction industry, so this is only a guess.] These could be stiffeners. Maybe a stiffer tube is easier to handle during installation. $\endgroup$ Oct 24, 2018 at 23:54
  • $\begingroup$ Is this really some mine access or entrance for (inspection) equipment?? $\endgroup$
    – Solar Mike
    Oct 25, 2018 at 4:39
  • $\begingroup$ There is no mine in the area. Logging would be the only possible industry, but why push logs under the road first to then just load onto a truck. It is presumably easier to load logs from the upstream side (less vertical distance to road). $\endgroup$ Oct 25, 2018 at 17:36
  • $\begingroup$ Cleanest culvert I have ever seen. Does somebody vacuum that thing? How steep is it? $\endgroup$
    – Phil Sweet
    Oct 29, 2018 at 1:09

3 Answers 3


The "Smooth Tracks" look like gaurd rails from the highway. Somone probably used old ones to create this in the culvert. As an engineer, I would say that this was not craeted by the state or county but an individual that need to get something from one end to the other with much less effort. Put a trail cam up and monitor it for a few months...you will probably get your answer.

  • $\begingroup$ I noticed the same thing. Those do look a lot like w-beam guardrails. $\endgroup$
    – hazzey
    Oct 25, 2018 at 20:00

Given that there are boulders near the entrance and the exit, I would say this has to do with providing a way for low flows to pass through the culvert easier. If there was a well maintained entrance and exit that showed signs of wheeled traffic, then I would have also thought someone was pushing or pulling a cart through there.


One possibility is that in some circumstances culverts can 'float' upwards due to forces analogous to buoyancy so the 'rails' may just be a simple way to pin it down.

Equally if it was made by back filling a trench this could be away to hold the pipe in place during that process.


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