Pondology
news from the waterfront by Tim Matson

LOW-WATER CURVE BALL

I'm just back from a planning session for a new pond which will be going into a site with porous soil and a deficit of ground water and supplementary water supply. It looks like the pond will need a membrane liner, which will solve soil and supply problems. It also happens that at this time of year a bunch of other ponds I've been visiting have water supply problems which is to be expected in late summer, when ground water supplies are low, stream feeds are down, and evaporation is high. The customary remedy for low water issues is to figure out how to find water to add, or make the basin soil less pervious, or both. Pretty straight forward that. But here's a low-water curve ball that doesn't only show up with late summer weather: faulty piping.

In ponds with piped spillway systems, leaks can occur that will produce low-water ponds of varying degree, depending on the severity of the leak(s) and time of year. If a serious flaw in piping occurs, you'll probably notice the low water pretty
fast. And deduce that it's due to a pipe leak. A small drop in waterlevel might be harder to pin on a faulty pipe without careful checking.

Pipe leaks can occur for several reasons. A break in the pipe; break or separation of pipe couplings; corrosion/rust-caused holes in the pipe (metal); faulty valve usually involved with a drain; and sometimes leaks that develop around the outside of the pipe when water finds its way through the dam alongside the pipe, often due to poor backfilling/compaction, lack of anti-seep collars,or frost heaving.

Tracking down and fixing pipe leaks can be a tricky proposition. Unless it's obvious that there's a hole in the pipe, it can be hard to differentiate between water exiting outside the pipe in the discharge area due to natural ground water seepage or pond water following the exterior of the pipe.

If a standpipe is overflowing, it can be hard to tell if discharge water includes pipe leakage; the pond waterlevel will have to be dropped so the pipe should be dry, unless there is a leak.

Steel or iron pipes that were installed 20 or 30 years ago will be nearing the end of their life span, and corrosion leaks are to be expected.

Plastic pipes don't corrode, but movement due to water or wind action can cause breaks or coupling failure, especially in standpipes in deep water.

Repairing a failed piping system can involve a lot of options. Old metal systems are usually beyond
practical repair, and will have to be replaced; or put out of commission, with a new spillway installed in another location (pipe or natural spillway). Plastic that breaks or decouples may be able to be repaired, but could require dewatering the pond and excavation to do the fix.

 

 

I'd like to conclude with a clever leak repair that one of my clients cooked up. After two years on the property he noticed that the old pond dropped its waterlevel a foot or more in the summer. For a while he assumed it was due to dry weather and the general nature of the pond. Then he took a look at the discharge end of the standpipe system, and saw that even with the waterlevel below the standpipe inlet, water was flowing out of the pipe. He took a look down the standpipe, and could see that there was water flowing at the bottom of the pipe. Although it was an old metal pipe, there were no obvious leaks inside the vertical section of the standpipe. Where was the water at the bottom of the pipe coming from? Turns out the pipe system included a drain coupled to the standpipe at the bottom of the pipe. The coupling was a concrete box with inlets for the drain and the standpipe. It became apparent that there was a leak in the coupling box. (In my experience using concrete boxes for couplings involving either steel or plastic pipe is an invitation to leaks: dissimilar materials even when "glued" (cement, hydraulic cement, etc.) are prone to failure.

The pond owner knew that a fix would involve draining the pond and either replacing the drain and standpipe with a newer, better system, or perhaps pumping the pipe full of concrete to seal it off, and installing a new overflow system, either a new standpipe or a natural earthen spillway. However, the pond owner was reluctant to drain the pond at the height of summer season when pond was used for swimming, etc. Perhaps he could seal up the leak? That was not likely to happen underwater to a concrete coupling box. So he went to the discharge end of the pipe and plugged it. He needed something to stop the flow, but not a permanently glued or welded fitting because it would have to come off when the pond started to rise in the fall. Otherwise a plugged spillway could result in a flooded dam. So he went down to the shopping center and bought a bright red inflatable kids' ball, with a slightly larger diameter than the pipe. Then he pumped it up a bit, inserted it in the pipe, and blew it up until it fit tight inside the pipe. For a while the water stopped flowing as water filled the pipe, and then a small leak appeared and the ball started to push out of the pipe. So he drove a couple of stakes in the ground at the end of the pipe to fence the ball inside, and tied the stakes to the back of the dam. There's a still a small trickle running past the ball, but the pond stopped losing water, and the pond is operational for the rest of the summer.

When he told me about the leak repair, I thought about it a second and said, it's an inflatable ball valve. Brilliant.

September 1, 2015

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