Had the same problem here and fixed it by connecting another 20 feet of pipe and hasn't been plugged yet. It's been 3 years and counting and the beaver are still around.

^^^ bigger problem waiting to happen unseen.

I will guarantee that there is no flex pipe under that setup. That flex pipe is the key to success for a deceiver.

Very true, but the terrain below the culvert is not always conducive for a beaver to effectively dam it up to flood over the road. Every place is different.
I understand your innate desire to kill all of the beavers. I have had that desire on more than one occasion.
It is difficult to fully explain how this device actually functions without seeing it in person.
PETA got a wild hair out my way and pressured the DOT to install Beaver deceivers at every culvert plugged by beavers. I was adamantly apposed to it for the same reasons as many have expressed on this thread.
They failed miserably in most cases, and in one case, caused a road to wash out which had not ever washed out before.
There were a few places where they worked miraculously. The flatter the terrain, the less effective they were. If there was a moderate slope to the terrain, they worked because it was too much work for the beavers to make a dam down stream of the culvert to ever raise the level high enough to impact the road.

There was,It came out with all the other junk the backhoe pulled out.
Beavers don't need to hear water running,They feel current,same as otters,and will continue to build up mud sticks grass and other debris until there is no more current no matter where it is.
Otters feel current even extremely weak current and use it to navigate between ponds under ice.
The deceivers require too much mtc,If neglected they are worse than nothing.Beaver gates require less mtc,and can be let go for a while and still work,making it easy to open a culvert.Trapping in conjunction with good gates is the ticket.

I just set up some traps today ....for a town ...with a plugged culvert.....game on !

I cannot tell what all is involved with that setup in your picture, nor what is under the water level in terms of an underwater diversion pipe, but I can tell you that it is not a Beaver Deceiver design. You indicated that there was a pipe under the "fence". How far away and how deep was the end of the pipe? What was on the end of the pipe to keep debris from collecting in the end of the pipe?

At that particular spot the water at the end of the fencing is about 8 feet deep,there is a float to keep the 6 inch plastic pipe suspended about 3 feet off the bottom.There is a right angle at the end and a cage around the end of the pipe.
I met the guy from the logging company that was installing a bunch of them.He said they were beaver deceivers and had several different designs that he was working from for different location specifics.One type was kind of a triangular page wire fence set up out from the culvert with similar piping with the opening down at a right angle.
None of them worked on a 26 km stretch of road,some lasted longer than others but all eventually had to be ripped out with a backhoe because after the beavers plugged them it was impossible to open them by hand. Gates were installed that could be used to flush out the culvert periodically.
For a while the B+B crew on the railroad installed beaver deceivers at new culvert installations in beaver country.They all wound up being ripped out and replaced with gates because of the same reason-Beavers would eventually plug them with sticks grass and mud weaved into the fencing making it impossible for the men to lower the water levels.
All the companys that hire our nuisance beaver service have gone to the gates.Much easier to lower the water in emergency's and much better for us when it is time to remove the beavers and return the water to natural flow.
Another problem with the beaver deceivers is that they cause a lot of road washouts. Culverts are sized to take the maximum hydrologic flows in a drainage system indicated on the maps when road building takes place.When dams let go upstream a small 6 or 8 inch pipe cannot handle the flow and water will go over the road and wash it out.

A friend of mine owns some property in back of me and had a beaver issue much like what was mentioned by the OP. They tried every conceivable "beaver deceiver" known to man but I think it was the continual harassment that eventually drove the beaver out. That was late last summer and the beaver haven't returned.

Wondering if you can mount a predator decoy at the culvert. Kinda like a scarecrow out in a field.

All good points, Boco. As I said earlier, these devises don't work most of the time. Most of my experience with successful ones is where there are a seemingly non-stop influx of single 2 year olds getting run out of their home pond by their fed up mother. They swim down the stream until they encounter a culvert, plug it, then continue on, never to return. The frustration is trying to catch the beaver which never returns. Then a month or 2 later, another 2 year old comes along, and then lather, rinse, repeat.
The situations which you seem to be running into with the devices which are failing is due to an insane number of mature beavers in that type of habitat. That leaves one with only one option. You need to Jason Bourne them.
Carl

Dr Kroll taught us this and it works. Get inch works roll of drain tile solid 6 inch works great. Run about 20 feet of drain tile out each side of dam or culvert dam. Weigh them down on the bottom. Beaver will not go back 20 feet at least never have and they don't find it under the water. We have never had them plug this up on our dams. Dig the dam down and run the drain tile through it. They dam over top at the (This word is unacceptable on Trapperman) but not the ends. Going on 5 years with ours now.