Unlike the northern part of the country, if you live in Georgia and have a lake or pond on your property it was probably built by someone or something. The “something” could either be a result of beaver activity or it could have been built by the river itself as in the case of an oxbow lake. (https://www.nationalgeographic.org/encyclopedia/oxbow-lake/) Yes, there are some natural lakes in the very southern part of Georgia which are formed as a result of geologic depressions. These lakes are referred to as Carolina Bays. Enough of the geology lesson for now.
In most cases, building a lake or pond involves building a dam to hold back the water and includes a drainage structure in order to allow the excess water to pass down gradient. This drainage structure (DS) is the critical element in the life of the lake or pond. There are thousands of lakes and ponds that have been built in Georgia over the last 50 years.
Generally, the design of the DS included a vertical riser pipe in the pond that drains the water off the top of the lake or pond and the connecting lateral pipe which conveys the water through the dam down gradient. Generally, as part of this system, a valve was installed within the pipe system to allow for manipulation of the water level. The piping system installed primarily consisted of CMP or corrugated metal pipe, since that was the cheapest alternative at the time. Well herein lies the problem. CMP under the best of conditions has a “useful” life of 20 to 30 years, which means it will begin to fail at some point. If it is not addressed this means that you will likely end up with a mud pit instead of a lake.
So, when removing and replacing the DS of a lake or pond there are really only two options to consider. The first option is to dig up and remove the existing CMP structure, which means draining the lake entirely and also involves cutting a big hole through the dam to install the new lateral piping system. Both of these factors are not very desirable for obvious reasons. The second option does not necessitate draining the lake and/or removing a section of the dam and is referred to as a siphon system. The siphon system is generally very easy to install and easy to maintain due to its inherent design. And the plastic pipe that is utilized does not have the lifespan issues as does CMP. The diagram shown below outlines the general schematic of the components and installation of a siphon system.
The basic design of a siphon system is that under “normal” water flow conditions, excess water within the impoundment will be conveyed through the siphon system due to gravity. However, when the lake or pond begins to fill up due to a storm event, the design of the system will charge the piping system and initiate the siphon to engage, which actually sucks the water out of the lake. To see a siphon in action, check out this video:
When the water level in the impoundment drops to a predetermined elevation, the siphon will lose the charge and return to normal flow conditions. One of the positive aspects of a siphon system is that the water is drained off the bottom of the lake and as result, you generally do not have an issue of clearing accumulated debris of the DS which is often the case in most of those systems.
One of the key elements in replacing an aging DS system is to seal off the existing metal pipe system. This involves utilizing pressurized grout that is injected on the back side of the dam up gradient through the existing system. This process ensures that the old metal pipe will not continue to convey water and cause future leaking problems. The photograph below shows the injection point on the end of an old CMP to facilitate the grouting process.
As indicated earlier, the installation of a siphon system is a fairly simple process, and Aquascape Environmental has installed many types of siphon systems. One note for consideration: If you are having to replace a DS for a larger sized lake, the services of a civil engineer may be necessary to ensure the proper design of the system to match the flow requirements that are needed. Also, you may need to check with your local government authorities on whether there are any special permitting requirements that need to be satisfied in conjunction with this project. And just remember that Siphons Suck—and that is a good thing!
