Pond Dredging

I’m traveling back to Seattle after visiting my parents for the last week. Down the hill behind my parents house is a pond. When I was growing up the pond had a good supply of fish, as well as frogs and turtles. As the years have gone on it has become more shallow due, in part, to the surrounding trees filling it with more leaves every year, and that has affected the pond’s health. As far as I can tell now, the remaining fish were wiped out last winter.

My dad and I have been talking about the need to make the pond deeper for a while now, but it’s not really clear how to proceed. At the top level the options are to do nothing, raise the level of the water, or dredge the pond. I don’t really want to do nothing, and while raising the water level seems kind of easy (assuming the dam can support a higher water level), converting more land to pond whenever we need to make make the pond deeper it isn’t a great solution. That leaves dredging.

From looking around, I think there’s three main approaches available: mechanical dredging, wet mechanical dredging, or hydraulic dredging.

In mechanical dredging, the pond is drained, and then the bottom is allowed to dry so that heavy machines can be driven onto it. Then excavators or bulldozers are brought in the dig or scrape material from the bottom of the pond. When that’s over, the pond is allowed to fill again. This approach is obviously fatal to the fish. The frogs and turtles aren’t going to like it, either. This is also going to be expensive, but I think that’s true for all of the options.

Wet mechanical dredging is similar in that heavy machines are used. In this case, however, the pond is not drained; the machines reach into the pond and dig it out with the water in it. This stirs a huge amount of sediment into the water, which, if it isn’t fatal, I imagine is not great for the fish.

That brings us to hydraulic dredging. In this approach, a large hose and a pump are used to remove sediment and silt from the bottom of the pond. It is the least traumatic approach. One company I found that does this uses divers to position the hoses. Hydraulic dredging seems nice, but I would guess it does not work well in situations where there’s a lot of fallen trees in the pond. Still, I find it to be the most promising.

That’s what I know so far. It will take more research to figure out how much something like this would cost and find candidates for actually doing the work.