Concrete Ponds and Freezing Climates

The pond liner advocates have maligned concrete constructed ponds and waterfalls for years by making spurious claims that concrete will crack and not hold up over time or in cold freezing climates. Here are the facts about the differences between the rubber liners versus concrete and rebar construction.

My first case in point would have to be the most obvious illustration of the practical application of concrete in relation to rubber liners as a worthy, reliable construction material with structural sustainability. Let’s use dams for my example and illustration.

There are four main types of dams: arch, buttress, gravity, and embankment dams. The type of constructionfor each dam is determined by the structure’s proposed use and/or application, the characteristics of the proposed location, volume of water to be retained by the structure, local construction materials available and last but not least, the budget limitations.

Arch dams are constructed in a horizontal arch facing upstream to most effectively resist the retained water’s force. Arch dams are most commonly utilized in narrow canyons and are almost always constructed of concrete.  

Buttress dams are characterized by a set of angled supports on the downstream side that help to support the structure against the water’s force. The buttress dams are more suited for wide canyons that lack the availability of bedrock. This type of steel framework structure and the associated labor involved makes then unfeasible economically in the current financial market.

Gravity dams withstand the force of water by virtue of its own weight. This type of dam is constructed of cement or masonry, normally utilizing solid rock for its foundation.  But can also be situated over unconsolidated material as long as water can be prevented from flowing under the structure.  

Embankment dams use locally available material (rocks, gravel, sand, clay, etc.) in their construction. For this reason alone, embankment dams or levees are the most economical to build. Similar to the gravity dams, these also use their own weight to retain the water’s force. The major drawback is that the materials are permeable, allowing water to seep into and through the structure. An impervious membrane of clay or rubber liner (the same as used in pond liner construction) must be built into them to lessen or minimize the flow through the dam which can weaken the integrity of the structure. Since all the construction materials are purchased locally, the construction of these dams is extremely less expensive, making embankment dams very desirable and popular.

Are you starting to see the connection between dams and their construction material with that of koi ponds and waterfalls? If not, let me help you.

Pond liner advocates promote their product by maligning the use of concrete as an effective, ­­term construction material for pond construction as opposed to rubber liners with plastic accessories. Straight to the point, of the four types of dam construction, the Hoover Dam is an Arch dam, straddling the mighty Colorado River, which forms the border between the states of Nevada and Arizona. Considered to be the world’s largest dam and an engineering marvel at the time of its construction in the 1930’s, Hoover Dam brings much-needed water and power to the Southwest. Was it constructed using a rubber pond liner or concrete and steel?

Now let’s look at the cheapest form of dam design, Embankment dams or levees. Many are constructed using rubber liners and loose earthen materials. In many cases, these type dams are compromised by burrowing animals such as ground squirrels, gophers, chipmunks, groundhogs, rats, or mice. Once any number of these animals chews through the liner, the water follows the burrows, washing away the soil until eventually, without the necessary support, the force and pressure against the liner causes it to burst. This is the same scenario for pond liners, but in these cases it is very difficult to find the hole, depending on its location.

Another ploy to discredit the use of concrete versus pond liners is to claim concrete cracks in frigid climates either from frost heaving or the hydraulic pressure of expanding ice pushing against the pond’s walls. This can be true depending on the engineering and shape of the pond’s shell. If the sides of the pond are slanted outward slightly as the surface water freezes, the ice is allowed to rise up the sides with the pressure being exerted in the upward rather than sideways directions. Also, depending on the local climate and how thick the ice gets on bodies of water, the pond can be designed deep enough to prevent it from freezing solid.

In this case, as long as the water level is deeper than the thickness of the annual freeze, the temperature of the water prevents frost, which will cause the concrete to heave, move or crack off. Another assurance against this situation is placing a horse tank heater in shallower ponds to keep them from freezing solid. If you drain your concrete pond for the winter, you are removing the very source of protection against frost and its damaging forces. You are now enabling the earth to freeze under the concrete pond shell which in turn, will expand the soil due to the freezing moisture contained within it.

In conclusion, proper engineering and construction methods and material can make all the difference in the performance and longevity of a project related to concrete pond construction. I would say that “You get what you have paid for” applies to the type of materials used and the construction methods applied -- and last but not least, the choice of pond equipment installed.