Pond Leaks, Part One: Initial Investigation Techniques

Published on July 1, 2010

Water splashing out of the pond can create a huge loss of water. Inspecting any point where the water is being pumped around the pond are easy investigations for potential leaks. In this case all of the splash that is created has flexible liner under it.
Water splashing out of the pond can create a huge loss of water. Inspecting any point where the water is being pumped around the pond are easy investigations for potential leaks. In this case all of the splash that is created has flexible liner under it.

A very common question that many clients will ask is “how much evaporation can occur in a water garden?” The client suspects that a leak is occurring, or hoping that, just maybe, it is merely evaporating “fast.”

Leaks in any type of water body can be tough to figure out, not only to identify whether there is a leak, but also, how to find it. This is especially true when the leak is relatively slow. Most people fear that it could be a leak, but want desperately to believe that it is evaporation, so that is the question they ask first. Water costs keep rising and a leak, even a slow one, can create a lot of expense that can be avoided. These expenses can also include wasted pond chemicals, bacterial additions and algal blooms. The importance of identifying and finding a leak has to take priority for clients. I will be discussing leaks in flexible lined ponds in two parts. Both parts will be a step-by-step investigation of leaks. In Part I, our investigation will start with the easily examined causes, which are, thankfully, the most likely. In Part II we will then proceed to the more difficult to find causes of leaks. Both parts of the article will deal with techniques for avoiding leaks to start with.

 So how fast is evaporation? Depends – of course, this is always the answer but it is especially true with a pond’s evaporation. It depends on how hot it is, how windy it is, the amount of pond surface area, how high and how fast the water is being pumped and even the number of plants in the pond. An increase in any one of these can increase the evaporation rate. When moisture is evaporated through plant leaves it is called transpiration, but the end result is that water is still being lost from the pond at a faster rate than if there were no plants.

Generally speaking a pond level drop of 1˝ in 24 hours could be a possible very fast evaporation rate. However, I would suspect a pond leak, especially if it was a cool calm spring day without much plant growth in the pond yet. I do like to observe for a few days to make a determination as to whether the drop is consistent over the period. Of course, a rain received during this “test” period could confuse the issue.

Automatic fill valves can really complicate the issue of whether or not a pond is leaking. A pond owner can go for years without noticing a small leak, or even a moderate one, if the automatic fill is always in service. Of course, at the end of the month an exceptionally high water bill can be a clear indication of a leak. In this case, the leak will have to be large enough to show a noticeable change in the amount of water used for a client to suspect one.

It is important to have the option of isolating the automatic fill with an easily accessible valve. Then periodically throughout the season the auto fill is shut off for a week or so to determine if there is a leak. Tell the client that, whenever the pond needs filling, to open the isolation valve and then close it later. This could be the next day or week, whatever is convenient. The auto fill is still a very necessary accessory for a pond for the simple fact that if the pond is filled with a garden hose, a person will eventually forget and leave the hose running. If left long enough it can be lethal to the fish and to the ecosystem because of chlorinated water. This is a catastrophe to anyone that owns a pond. Eventually this will happen to almost everybody that fills with a simple garden hose. Recognizing this, a lot of smart ponders without an auto fill are utilizing a water timer attached to their garden hose.

Okay, once a leak is strongly suspected, there is a step-by-step locating process to go through next. Some leaks are more obvious than others so we look for the obvious ones first. Leaks are a relatively easy find in flexible liner ponds compared to earth and concrete lined ponds. This is one of the reasons we like to use the flexible stuff.

Always suspect water splashing out of the pond, especially if there is a fountain in the pond or a high waterfall. The water could be wind-blown or is being splashed outside the edge of the pond. So, inspect the entire perimeter of the pond looking for wet areas outside of the pond. Look closely – it does not take much of a splash to create a loss of water. Where there are wet rocks or wet leaves there needs to be liner under them to make sure the water is contained.

Fountains of various types can create conditions where some of the water shooting out into the air is blown out of the pond or water collection area. Not all of the water is returning to the pond, so you have a loss of water. A vertical fountain should be pumped at a maximum height of 1/2 of the width of the pond or water collection area. For a 10´ wide pond, the fountain height should be no higher than 5´. Even this is too high in very windy areas, so a fountain will need to be adjusted for local conditions. Just make sure all the water is returning back to the collection area of the pond or feature, even when the client is not around.

Continuing the investigation, go around the entire perimeter of the pond and stream looking for a leak where three common mistakes could have been made in the construction phase. The liner may have sagged due to settling of the grade. Enough drop may have not been provided along the edge grade to the eventual water level. Finally, the liner could have been cut too short when being trimmed, or simply, the liner was not large enough to begin with.

In the construction phase of streams and ponds where backfill is used to bring the grade up, a huge mistake is commonly made. The soil backfill under the filter falls box, skimmer box and around the edge of the pond or streambed may not be properly packed. This is vital to the proper construction of a pond. In areas of greater than 6˝ to 12˝ of backfill a jumping jack packer or heavy piece of equipment should be used to pack the soil in the fill areas. Most do-it-yourselfers and inexperienced installers do not know the importance of this step. It is common for these areas to then settle causing the liner to sag, which often results in a leak. This can occur over a several year period. The freeze/thaw cycle enhances this settling during winters where the ground freezes.

The perimeter leaks can also be caused by not providing enough drop between the water level of the stream or pond and the actual grade of the surrounding soil. To aggravate the situation, a stream can be partially blocked with debris or ice, thereby causing water to back up and overflow the sides of the stream.

Cutting the liner too short or not having enough liner to bring up to the surrounding grade are mistakes that happen with inexperience. A foot or two of excess liner should be left along the edge of the entire water feature and be folded back under itself. This is a very inexpensive technique to insure there is enough liner, even if areas settle or enough drop is not provided. With extra liner available, a fix can easily be made by pulling up the excess and bringing in some fill soil.

Initially, an “investigative cruise” of the edge is done without a lot of moving of rocks to make a quick determination if one of the construction mistakes could be the cause of a leak. In the cruise a lot of poking and some moving of rocks is done where the water is close to the edge. Look for high moisture areas. However, the mulch may not be wet on top but a little digging with a finger may reveal a suspect area. In finding an area like this, do more dismantling of the spot to make a better determination. It is not necessary to dismantle an entire pond’s edge to eventually find a relatively easily found edge overflow.

So far, all investigative techniques have been easy and can be done quickly without many tools using simple observations. We have discussed and eliminated the relatively simple leaks, like wind blown water and edge settling.

In Part II of this article, we will graduate to the next level of leak detection. We will look in detail at all possible leak points in a flexible lined pond, and talk about ways to avoid them.

5 thoughts on “Pond Leaks, Part One: Initial Investigation Techniques”

  1. Jeffrey S Miller

    I have a problem with brown field rats burrowing around my pond and in and around my waterfall. I have been told that rats must have water and this is a main reason why they will set up camp near water areas. We also have bird feeders within 60 feet of the pond. We have stopped using these feeders but still have 2 within 150 feet of pond we still fill. They have chewed holes in the liner behind waterfalls quite a few times causing hard to find and usually slow leaks. I have 6 snap traps around pond and have got 16 rats so far within 2 months. I also have a poison bait box and 4 spinner traps and have used gas bombs. Yet they still keep coming. Our house is surrounded by corn fields. Also have 2 ultra sound solar devices in the ground by pond. We are at our wits ends trying to rid our pond of these destructive critters. Any suggestions would be greatly appreciated as I am sure we are not the first ones that you folks have heard from with this sort of problem. Thank you and we love reading your articles they have been very helpfull

    1. Kimberly

      Please refer to my articles on pond leaks. There are hundreds of reasons that your pond liner developed a leak. It could be very simple or it could be difficult to find. Good luck and have fun water gardening. Jamie

  2. Investigation of pond leaks is very important. Any leaks can be dangerous for the pond living being as well as the soil and earth around the pond. Thank you very much for telling everyone about this. I would like to see more investigation techniques regarding pond leaks.

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