Another Damn Dam

(Sorry – couldn’t resist)

As I mentioned last post one of the dams we opened had a culvert in it.  Now theoretically a culvert is used to allow water to pass from one side of the road to the other (or perhaps from one side of a dam to the other) – but of course if the beavers get at it this does not work too well and we are unplugging a culvert instead of opening a dam. 

There is a plugged culvert in a dam at the top of this hill

The plug at the culvert primarily occurs on the upstream side for some reason.  A straight up screening or grating across the pipe does not help as this will also be blocked up.  (These are both diligent and resourceful creatures).

What we have found is that by installing a vastly expanded screened area on the upstream side there is not enough flow through any part of the screening to attract specific attention with a result that it is pretty much left alone.  Beavers follow sound to determine where to build and the water sound in this arrangement is beyond reach.  Theoretically this lets us set a desired level for the ponds and once stable that level does not seem to change much.  The ideal shape of the screening seems to be a trapezoid with the wide end farthest from the culvert.

If it is flowing from being opened it looks like this

This screening arrangement is difficult to keep in place however.  We have been using T shaped metal posts dug into the pond bottom as much as possible – but getting them in place is very tricky.  The bottom of a beaver pond is horrible gooey muck, and often is deep very close to the shoreline.  As well the water in a beaver pond is unhealthy and generally you try to avoid contact with it.  Heading out in chest waders limits one to a certain depth, which might not be as far out as you would like to get the desired screen area.  Occasionally too there is rock at the bottom of the pond (we live in a Canadian Shield area) and pounding in a post is impossible. 

If the screening does not reach the bottom of the pond it is not helpful as the beavers will swim under it and still reach the culvert and plug it off.  The solution we have found is to also make a bottom of screening so that you sort of have an open topped trapezoidal box at the culvert opening.  This still needs some cleaning from time to time, but mostly what is being cleared off is debris that has floated along and is either caught on the screen from natural water flow or is small enough to have gone through the screen and has come to rest farther on.

One complication that we are facing though is the material for the screening.  It needs to be quite rigid as it turns out.  In an effort aimed at both cost effectiveness and ease of manufacture we were trying to use a metal fencing product.  It was fairly flexible and so easier to work with to get the desired shape.  This seemed to work for a while but eventually the critters did figure out that if they try to climb it the fencing will sag enough that they can get over and get at the culvert.

This is what happened here.

They managed to climb over or drag down the fencing

Luckily, opening a plug in a new-ish culvert is fairly straight forward.  The old metal culverts in the area are ribbed and plugs get set in quite solidly.  The new ones are ribbed on the outside but are double walled with a smooth interior.  Initially we do need to clear away some of the muck that gets built up near the entrance.

Clearing some muck away at entrance to culvert

We have built a very basic long straight tool that can be inserted from the unplugged end to snag the grasses and small branches that are plugging the entrance.  Once a certain amount is pulled out the rest kind of comes out in a big splosh.  If done regularly it is an OK task, but we will need to replace our fencing with a more rigid metal screening product. (Darn)

More rigid - probably what we will use

Flexible and easy to use - but apparently climbable