Things You Will Need
- Sand bags
- 6-inch hex bolts with nuts
- Crescent wrench
- 4-inch hex bolts with nuts (optional)
You can construct a dam using sand bags and wood as a prevention against flooding, or to create a drained portion of an existing body of water. Unlike many other types of dams, the sand bag method is affordable and does not require rental of heavy machinery.
For simple dams for small bodies of water (a creek or shallow pond) or in the path of a potential flood overwash, this method is quick and easy to learn but requires a considerable amount of physical exertion.
- Decide where you are going to place your dam. Keep in mind that you should maintain as straight a line between the two end points of the dam (where the dam meets the shore) as possible. This will create an even pressure over the entire structure of the dam rather than focusing all of the water pressure on one point.
- Place the bottom course of sand bags so that it is two sand bags wide, with the bottom seams of the bags touching. Think of the sand bags as being two pages in a book that is open and the spine is the short seam on the bottom of each bag. For this example, the dam described will fit a 4-foot deep, 8-foot wide creek. If the creek only runs when flooding, lay your sand bags directly on the dry creek bed. If the creek has water in it, place them in the water and guide them as they sink until they are lined up correctly.
- Lay the next course on top of the first, with the sand bags laying across the two below as if laying a brick pattern. The sand bags will touch bottom to top as they are laid down.
- Continue laying three more courses of double bags, alternating the direction the bags are going. The bottom 1/3 of any depth of water should contain this doubled layer and alternating course of sand bags.
- Stack single sandbags one on top of another, aligned in the center of your double width bags until you have reached one foot past the height of the expected or existing water.
- Measure and cut your 2x4s so that you can place one every three feet, at an angle, from the top of the sand bag wall extending down three feet into the ground at the base of the dam. Think of it as creating the frame for a lean-to; you want that angle but the boards placed so that they lay against the bags. Bury or drive the wood into the earth with a sledgehammer and shovel. If the ground is sandy, place a board beneath the end in the ground at an opposite angle to make an anchor kicker then bury both boards.
- Lay boards across the frame every three feet, drill and attach them together with your hex bolts. Tighten well. Attach the ends of the board to trees or stakes made of 2x4s and driven well into the ground to provide further anchoring support for your dam.
To make your dam even stronger, drive 2x4s straight down along the front of the dam (water side) and as you lay your courses, every third one, lay a piece of 2x4 between the bags. Drill and attach them to the straight posts with 4-inch carriage bolts then attach the other end to the angled frame boards.
Water is much heavier and more powerful than most people think–always check with a local engineer to make sure that the dam you plan to construct out of sand bags and wood is safe for the water you expect to control in order to prevent serious accidents or death.