When asked to write about the "structural integrity" of ponds, I first want to post a disclaimer: I am a landscape architect not a structural engineer. This is my usual admission: I only know enough to be dangerous, thus, I have a healthy respect for structural engineers. This article is not going to be the Holy Grail on pond construction but rather a general discussion on how water feature contractors and pond builders can relate to the concept of structural integrity. Hopefully this article will at least stir some thought and conversation.
One definition for "structural integrity" is: "Structural integrity is a measure of the quality of construction and the ability of the structure to function as required." Basically: Number One – Does it perform as it was intended to perform? Number Two – Does it hold up against the forces it was intended to? Number Three – Will it work for as long as it is supposed to work?
Every component has a structural integrity requirement and the combined effectiveness of these components also has a structural integrity requirement. A chain is only as strong as its weakest link. Obviously we are glad there are professionals who have the big picture when it comes to buildings, cars, bridges, and airplanes, to name a few. But for the little parts, we need to really appreciate and hope that the guy that picked the bolt for the brake pedal in our car knew structurally what he was doing. Or was he guessing? Or did he randomly just pick a bolt that had a manufacturer’s quip on the box that it was “the one bolt for all your needs?” Yikes. The point is that for a water feature or pond to have structural integrity, each component has to be evaluated in regards to how it is going to be used.
There are organizations that help with this information. ASTM International, originally known as the American Society for Testing and Materials (ASTM), was formed over a century ago, when engineers and scientists got together to address frequent rail breaks in the growing railroad business. Their work led to standardization on the steel used in rail construction. This organization has gone from giving guidelines on steel to more complicated scenarios like—what should be the standard of preparation for a hospital to function in different disasters. I bet the folks at the ASTM could help with establishing the standards for fishpond construction.
Once on a landscape project I hired a structural engineer to help me with some post and beam wood construction issues. The structure was going to be open and was going to have wind loads. He looked at his charts and sized the footings, the spacing of the post and the size of the post the project would need. I asked him who came up with a chart calculating how wind would affect a structure like this. He replied that most of the research was carried out at the direction of an outdoor advertising association. Then he showed me a picture of a large wood roller coaster he had designed using the same data. It is a little spooky to know that the data the outdoor advertising association came up with is also being used for designing roller coasters. But someone had to do the legwork! I think what always impressed me was that the statistics for that type of construction was not originated by a college professor looking for a math challenge. Rather the post and wind load standards were instigated by a business concern that had real needs for the information because they wanted to reduce the chance for failure thus promoting structural integrity. Why? Because structural integrity is good for every business in the industry.
The pond industry, in my opinion, is just getting underway in getting sophisticated enough to organize and/or research the metrics which will allow for more ponds being built with successful structural integrity. Ponds can fail in many methods, such as failure of waterproofing, failure of filter system, pump failure, failure of rock structure, etc. This is to be expected from an industry that not too long ago was not an industry. It did not have any real manufacturing, but was rather a collection of hobbyists using home made solutions.
Often times we resort to testimonials from others, manufacturers’ suggestions (bless their hearts but they can be optimistic), or data generated by other industries. While these are all valuable, the pond industry is certainly ready to compile more accurate specifications. While most associations in the pond industry seemed caught up in giving certificates in construction, there is little being done to standardize the information regarding components that make up a pond.
One should also understand what constitutes structural integrity can and should change from pond to pond. This does make things a little more confusing. What works for one scenario may not have integrity for another. Let’s go over the definition again: "Structural integrity is a measure of the quality of construction and the ability of the structure to function as required." The first responsibility of building with structural integrity rests with the designer. This person must define: what is required, how is it supposed to perform, and what forces will be working against it. If you cannot define these issues up front in the design stage, you cannot aim towards structural integrity. In a koi pond this could be: The pond has to keep this many pounds of koi fish alive, be outside in the Maine winter, and last 10 years without any repair other than pump, light and media replacement. Because of high water table, the criteria includes the pond never being completely drained. The owner has 30 Labrador dogs. Now you can define the forces that are working against a successful pond. There will certainly be fish waste, there will be severe freezing, and there will be the dogs and the need to have a bottom that is cleanable while under water. So right off the bat, it is easy to tell that the pond construction standard that worked for a goldfish pond in a sunroom in Florida may not be sufficient and could lead to failure for this pond in Maine. Yet both ponds could have appropriate structural integrity if they met their original design criteria.
The standards for the components we use may be available. But our businesses need them in terms that we like to use. For instance, for a paint to say that it meets the minimum level of inter gelatinous anti carbons established by the USDA or whatever high brow lingo a chemist may use, is not as important to me as a comment that says “fish safe.’ And by definition you cannot build a fishpond that qualifies as having good structural integrity if its components kill fish.
Water proofing failure is one of the big visible structural integrity failures on which people focus. Today’s flexible membrane liners have made many pond builders think that structural integrity is a non-issue… I am a big fan of flexible liners when my company first started building water features in the mid 1980s. We used concrete reinforced with rebar waterproofed with plaster, the standard practice of the day. When we first were exposed to PVC liners we felt sure that they were shabby construction and probably the work of the devil. Ultimately, we had a client that demanded we use PVC liner covered with concrete as the method of construction. We eventually used this method a lot over the next 15 years. Many of the ponds we built with this technique have needed minimum service while the pools we had built at the same time using concrete/steel/plaster construction have had to undergo major renovation. So we have a lot of good testimonial and first hand experience with flexible liners. But is liner always the best way to build a water feature? No. Can you say that the swimming pools have less structural integrity? No. The swimming pools had different performance requirements: We wanted a surface that was barefoot friendly, yet was not slick, thus plaster was chosen. And since the plaster on the pools lasted as long as the client expected, the pools had appropriate structural integrity.
To this day we rely on different types of construction. The latest liners are ultraviolet resistant, so now you don't even have to protect them from the sun. However, if you have forces around your pond like Labradors, kids with sharp sticks or a probability of public vandalism, protecting the liner would be adding structural integrity to the predictable forces. By overestimating the forces your pond may need to deal with, you are increasing your margin for structural integrity and success.
Every component and every mechanical system associated with ponds have its own structural integrity value. For us that also includes the structural integrity value of installing the component. We once worked with a pond product that was fine once it was installed, but it was subject to failure during installation. We gave this low marks on the structural integrity scale because part of how it was supposed to perform included the actual performance of installation.
Finally you cannot talk about structural integrity without talking about safety. Ponds are built typically with a design requirement of helping people or delighting people. Recently, I have read about individuals that have died from consuming too many bottles of water in a short period of time. Everything can be dangerous if used incorrectly. However, we should always strive for making sure our structures and components are especially strong relative to the safety of the public..
In conclusion, structural integrity is a very important condition for a pond or water feature to have. It starts with identifying what is the goal of the structure, what forces will be working against it, and what is the desired life of the structure. It applies to the components individually, how they are installed and how they work together as a system. As an industry we need to continue to share common definitions, deficiencies and solutions. We should promote the need for independent testing. Only by working together to provide the consumer with successful projects, accurate descriptions and appropriate solutions can we stay competitive with the other industries that are competing for the consumers' smiles and hard earned dollars.
About the Author
Cla Allgood and Janet Allgood own Wakoola Water Gardens (Wakoola.com.), a founding member of the National Association of Pond Professionals (NAPP). Cla is also a practicing landscape architect (Allgoodoutdoors.com) and a member of the American Society of Landscape Architects.