Pond dams are the retaining systems constructed as a means of building and maintaining an artificial pond. The ponds these dams create can be built for a number of different purposes. They are often used for fish farming, irrigation, flood control, recreation and to serve as a water reserve for livestock and people. The typical pond dam is used to create a body of water much larger than most backyard ponds, but it can also apply to small household. Building a dam is necessary for the creation of a pond.
Locate or create a flowing source of water. If the property you are building on already has a free flowing stream or water drain, use that. However, if it doesn't then go ahead and pipe water in from a remote source such as your own property's water supply or from municipal plumbing. Make sure you have regulatory permission to do the latter.
Select a stable pond site that will allow for easy construction. The ideal terrain for your pond will be flat or gently inclined. Also, you should try to excavate and build your pond in clay rich soil that retains water well.
Excavate a hole for your pond that is the appropriate size for your needs. If you have control over the source of water which is going to flow into the pond, shut it off while digging. If you don't, create a diversion channel to run the stream flow around your pond and dam construction area.
Clear away any vegetation, including grass from the area in which the dam is going to be built. You want to do this in order to let the dam solidly bond with the ground. If it doesn't, leaks could form underneath, and later undermine and wash away the whole structure.
Dig out a core trench that spans the length of the dam's eventual span. Dig this trench to a depth of at least 3 or 4 feet, but ideally to a depth that reaches subsurface layers of clay or clay rich soil. Your trench should be about one third of the dam's eventual cross section width. Fill this trench back in with fill soil that contains a very high concentration of clay. Fill in 6-inch deep layers, tamping each one as you lay it down. Build up a large mound of this fill that spans the dam's entire length and is just a foot under the dam's eventual height.
Lay down a sloping drainage pipe (or spillway), which leads through the mass of fill, from your desired waterline mark near the top of the clay core of the dam down to the drainage channel on the outside bottom of the structure. Use a wide plastic pipe with rubber joints to prevent eventual corrosion. Make sure the pipes intake on the inner top of the dam is covered by a steel or plastic grate to keep loose floating material out.
Fill in the rest of the dam's structure with high quality clay-rich fill that is also evenly tamped down for every 6 inches of depth you add. Build the dam with a sloping structure that has a 3:1 ratio to it. This means that for every foot of height which your dam has, it extends outward by three feet to each side. Doing this creates a gently sloping wide dam that is highly resistant to collapse or erosion.
Cover the dam's whole top and outer slope with a layer of good top soil, and seed or turf the entire surface with grass. You want to do this as soon as the dam has been built so that the grass takes firm root early and reinforces the structure's strength.