Keeping Water Features Clean and Dealing With Dredging

Date Published: 
July, 2004
Original Author: 
Tom Smith & Tom Pfeifer
Spring Grove Cemetery & Arboretum, Cincinnati, Ohio
Original Publication: 
ICFM Magazine, July 2004

PART 2 0F 2
Adding fountains and maintaining the proper chemistry in your pond or lake can help put off the day you'll need to tackle the ultimate in maintenance: dredging.

In part 1, in the June issue, we talked about how to design a pond or lake to reduce plant growth problems. We also promoted stocking your lake with triploid amur carp (using the right number for the size of the lake). There are a couple of other things you can do to help keep the water in your pond or lake (we're using the terms interchangeably) cleaner and clearer.

• Add a fountain. Fountains help oxygenate the water, they create a great sound, they create a tremendous visual sense and they even create a little bit of an interesting water smell. We can't say enough good things about including some kind of fountain if you're going to have a pond or lake.

We don't care what kind of jet spray you like—use a low, small one or a great big powerful one. The point is that fountains are really important in maintaining aquatic areas. They improve the oxygen level so the fish are happier—the fish get bigger in aerated ponds.

The past couple of winters we've removed the fountains during the winter so there's no open water for any of our feathered friends to fly in and hang around. In other words, without the fountains going, the ponds freeze over and the geese who are looking for open water have to go elsewhere.

Keep that in mind. Maybe your competitor won't tend this nod will keep his fountains buzzing all winter and end up with a few hundred geese over at his place, spreading manure around his lakes. That will mean more nutrients washing into his lakes and, the following summer, the world's finest algal bloom.

• Make sure the chemistry is right. In addition to fish and fountains, one of the things we love to use is a food-grade type of dye, a bluing agent. All it does is turn the water blue, decreasing the infiltration of light, therefore interfering with photosynthesis. That will cut back on the plant material.

This product has been available for a number of years, yet it's amazing to us the number of people who don't use it, even in small ponds, small fountains. The vendors have made it so easy, with soluble packs that you can toss into the water as you walk around the edge of the bank—you don't even have to get the boat out. The packages dissolve automatically, the dye is released and the darkening occurs within 24 hours.
This is the type of maintenance that needs to be ongoing. You don't want to wait until the hottest day in August when the pond is covered with an algal bloom and say, "Oops, I better go out and darken the water." It's too late then; you've lost the race.

Of course, even if you take all these preventive measures, from time to time you may still have problems with aquatic weeds during hot weather. For algae control, we use a copper compound. The oldest known one, which is the least expensive, is copper sulfate, which is readily available. The copper is very toxic to plants, especially algae, so you have to know how many gallons or cubic feet of water the pond holds and then put the proper amount of copper sulfate in.

It's better to use copper sulfate in low dosages. If you have a lot of algae and attack it with a lot of the chemical, you'll end up with a lot of dead algae settling on the bottom of the pond and robbing the water of oxygen. While the oxygen is at work breaking down the algae, the fish can end up oxygen starved and then you've got dead fish floating on the top of the pond.

Again, a deeper pond will need less chemical treatment to keep the algae under control.

Periodically in the life of any pond you have to consider dredging. If you've only got a few feet of water left in a pond, maintenance is going to be a constant battle. At that point, scraping out all the organic matter that has settled on the bottom over time will extend the life of the pond and will improve its appearance.

There are a number of ways you can go about dredging to remove the material in the bottom and restore the original side slopes. There is no simple fix—it's going to cost dollars no matter how you do it. But eventually you're going to have to do it, though it will be later rather than sooner if you've followed the suggestions above.

If you build a new lake today, you might need to dredge it in 50 to 75 years. If you make the pond an acre or more with very steep sides and do the things we advise, you might be able to go for 100 years before you need to dredge.

Some people try draining rather than dredging. They wait till the hottest time of the year when the pond is at a low point. To get the rest of the water out, you use what we call a trash pump, a big pump that can allow sticks and gravel and everything else to fly through the propellor of the pump without tearing it up. You can rent one.

But the pond rarely ends up completely dried out, and then you have gooey silt to deal with, which is problematic. You then have to use rubberized backhoes or extended-arm booms to scoop the material out and then haul it away using bulldozers or trucks. You can just imagine the expense. And just imagine getting a sudden summer thunderstorm that dumps a couple of inches of water into this pond where you're trying to run heavy machinery.

We have 14 lakes in a cemetery that's been around well over 100 years. We recently budgeted the money to dredge about half of them, the ones that needed it the most, over a three-year period. It was a long and pretty complicated process.
We had contractors come in from out of state. The dredges have a pipe with an impeller on it that loosens up the silt at the bottom of the lake as it goes along. We removed 12 to 14 feet of stuff from the bottom of some of our lakes.

You use a tremendous amount of water stirring up all the stuff on the bottom of the lake and then sucking it up and out through the pipe. That slurry, the water and silt, has to be pumped out to a retention pond so the silt can settle back out of the water. There was a lot of pipe that had to be laid from the lakes to the retention ponds.

To dredge, you actually need to pour more water into the lake. The slurry the dredging machine is pulling up consists of a little silt combined with a lot of water. You may have to run hoses from the fire hydrants in the cemetery into the lake.

You can use the material you dredge out, once it's settled to the bottom of the retention ponds and the excess water has been drained off. This stuff is going to be wet and gooey at first, so you have to put it somewhere where you can allow it time to dry out.

There's no real odor problem with the material at this point. It's during the early stages of decay, under anaerobic conditions, that there's going to be a stench. The further along decomposition has gone, the less odor there's going to be.

This is incredibly nutrient-laden material, very fine material. You could grow the world's biggest pumpkin in it. You'll need to add some peat or perlite to make it a bit lighter, since it's going to be very silty. Then you can top-dress a garden with it. We use it in our backfill process and on grave sites right under the sod.