Basic Elements of a Pond Dam (Drawings and Text Version)
NOTICE
Below are some key elements that are part of a properly planned and well constructed dam. Print page for better understanding and future reference.
- The information on this page is not a construction design. It is provided to increase your knowledge of some of the basic components of a COMMON POND DAM. Each component of a well-constructed and maintained dam has an essential function. Omitting a component or a component that is made part of your specific pond design can lead to failure of the dam. It is recommended that the Natural Resources Conservation Service or a private engineer be consulted to obtain a site specific pond design before construction begins.
Below are some key elements that are part of a properly planned and well constructed dam. Print page for better understanding and future reference.
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Key Element
1. CLEAR VEGETATION Clear all vegetation where the dam will be built. This will help insure the soil in the new dam will bond with the base. Failure to do so may cause the dam to leak or slip leading to failure.
2. STOCKPILE TOPSOIL Topsoil should be stockpiled to be used in the final stages of building the dam. Cover the dam and spillway with this topsoil in order to provide the best possible situation to grow a good grass cover. If soil is excavated from above the waterline in the planned reservoir area it should also be topsoiled and reseeded.
3. CORE TRENCH A core is another essential element of a pond dam. It is constructed by digging a trench the length of the dam. The trench is dug down through the top soil, rock, sand or any material that would let water pass until a good clay soil layer is reached. The minimum depth of the core trench is a least 4 feet. Clay soil material is then packed back into the trench. The lack of a core trench is ONE OF THE MAJOR REASONS PONDS LEAK and go dry during the summer.
4. COMPACTED FILL As the dam is built, including filling back the core trench, the soil should be added in no more than 6 inch layers and compacted by driving back and forth over fill. Then another 6 inches can be added and then compacted. The top of the dam is generally no less than 10 foot wide. The side slopes of the dam should be no steeper than 3:1. That means, for every foot in height one must go out 3 foot to the side. If the side slopes are too steep the embankment can slip leading to failure.
5. PRINCIPAL SPILLWAY The principal spillway or draw down pipe, is used to handle most rainfall events so that the emergency spillway is rarely used. This will reduce the chances of gullies forming in the emergency spillway. Heavy weight PVC pipe is normally used over steel because it will not rust. Lack of a pipe or an improperly installed pipe is one of the leading causes of dam failures. Only through a proper design analysis can the correct size for the site be determined. Replacing a rusted out pipe.
6. RUBBER GASKETED JOINTS Provides a water tight, flexible joint. Pipe is installed with the bell end up for added security.
7. ANTI-SEEP COLLARS Prevent water from seeping down the outside of the pipe which could wash out the pipe.
8. CANOPY INLET This special inlet design allows the pipe to flow more water during times of high water. It allows smaller pipe sizes to be used which reduces cost. A solid cap is first glued to end of the pipe. Then saw the end at an angle leaving about one forth of the cap to create a lip at top. This lip will then prevent air from being drawn into the pipe allowing it to flow to capacity with water.
9. TRASH RACK Needed if area above pond is heavily wooded to prevent pipe from plugging.
10. EMERGENCY SPILLWAY As named, this spillway should only be used for emergencies, during heavy down pours. It gives an area for the water to safety flow without going over the dam. Both an emergency spillway and a principal spillway (draw down pipe) is needed for proper construction. Be sure the emergency spillway gets at least a 6 inch layer of topsoil during new construction. Maintain a good vegetative cover.
11. DETENTION POOL The water level from the principal spillway (draw down pipe) inlet to the emergency spillway. This area is important because it allows the draw down pipe time to safety get rid of storm water before using the emergency spillway. Only through a proper design analysis can the correct amount for the site be determined.
12. PERMANENT POOL This is the planned area where the water is impounded. The consistancy of the water level will depend on rainfall, proper sizing of pond for the drainage and how well the core trench and other features of the pond were built. The quality of the water will depend on the management of the land above the pond. This will includes items such as the proper use of fertilizer and pesticides, livestock above or in the pond and maybe even domestic septic systems.
13. CLAY BOTTOM At least a 1 foot thick layer of heavy clay should line the entire reservoir area for every 10 foot of planned water depth. Watch closely for rock, sand or other pourous layers and be sure those areas are well covered with clay.
14. VEGETATION Seed construction area as soon after completion of dam as possible, preferably before the first rain. Be sure emergency spillway area and dam is topsoiled to promote good grass growth. Maintain a good vegetative cover at all times. Do not allow the dam to be over grazed. A fenced out pond with a pipe to a tank below may be a better option than letting livestock have access to pond.
1. CLEAR VEGETATION Clear all vegetation where the dam will be built. This will help insure the soil in the new dam will bond with the base. Failure to do so may cause the dam to leak or slip leading to failure.
2. STOCKPILE TOPSOIL Topsoil should be stockpiled to be used in the final stages of building the dam. Cover the dam and spillway with this topsoil in order to provide the best possible situation to grow a good grass cover. If soil is excavated from above the waterline in the planned reservoir area it should also be topsoiled and reseeded.
3. CORE TRENCH A core is another essential element of a pond dam. It is constructed by digging a trench the length of the dam. The trench is dug down through the top soil, rock, sand or any material that would let water pass until a good clay soil layer is reached. The minimum depth of the core trench is a least 4 feet. Clay soil material is then packed back into the trench. The lack of a core trench is ONE OF THE MAJOR REASONS PONDS LEAK and go dry during the summer.
4. COMPACTED FILL As the dam is built, including filling back the core trench, the soil should be added in no more than 6 inch layers and compacted by driving back and forth over fill. Then another 6 inches can be added and then compacted. The top of the dam is generally no less than 10 foot wide. The side slopes of the dam should be no steeper than 3:1. That means, for every foot in height one must go out 3 foot to the side. If the side slopes are too steep the embankment can slip leading to failure.
5. PRINCIPAL SPILLWAY The principal spillway or draw down pipe, is used to handle most rainfall events so that the emergency spillway is rarely used. This will reduce the chances of gullies forming in the emergency spillway. Heavy weight PVC pipe is normally used over steel because it will not rust. Lack of a pipe or an improperly installed pipe is one of the leading causes of dam failures. Only through a proper design analysis can the correct size for the site be determined. Replacing a rusted out pipe.
6. RUBBER GASKETED JOINTS Provides a water tight, flexible joint. Pipe is installed with the bell end up for added security.
7. ANTI-SEEP COLLARS Prevent water from seeping down the outside of the pipe which could wash out the pipe.
8. CANOPY INLET This special inlet design allows the pipe to flow more water during times of high water. It allows smaller pipe sizes to be used which reduces cost. A solid cap is first glued to end of the pipe. Then saw the end at an angle leaving about one forth of the cap to create a lip at top. This lip will then prevent air from being drawn into the pipe allowing it to flow to capacity with water.
9. TRASH RACK Needed if area above pond is heavily wooded to prevent pipe from plugging.
10. EMERGENCY SPILLWAY As named, this spillway should only be used for emergencies, during heavy down pours. It gives an area for the water to safety flow without going over the dam. Both an emergency spillway and a principal spillway (draw down pipe) is needed for proper construction. Be sure the emergency spillway gets at least a 6 inch layer of topsoil during new construction. Maintain a good vegetative cover.
11. DETENTION POOL The water level from the principal spillway (draw down pipe) inlet to the emergency spillway. This area is important because it allows the draw down pipe time to safety get rid of storm water before using the emergency spillway. Only through a proper design analysis can the correct amount for the site be determined.
12. PERMANENT POOL This is the planned area where the water is impounded. The consistancy of the water level will depend on rainfall, proper sizing of pond for the drainage and how well the core trench and other features of the pond were built. The quality of the water will depend on the management of the land above the pond. This will includes items such as the proper use of fertilizer and pesticides, livestock above or in the pond and maybe even domestic septic systems.
13. CLAY BOTTOM At least a 1 foot thick layer of heavy clay should line the entire reservoir area for every 10 foot of planned water depth. Watch closely for rock, sand or other pourous layers and be sure those areas are well covered with clay.
14. VEGETATION Seed construction area as soon after completion of dam as possible, preferably before the first rain. Be sure emergency spillway area and dam is topsoiled to promote good grass growth. Maintain a good vegetative cover at all times. Do not allow the dam to be over grazed. A fenced out pond with a pipe to a tank below may be a better option than letting livestock have access to pond.
OTHER ITEMS TO BE CONSIDERED:
- Ponds are kept in better condition by fencing livestock from the entire pond including the reservoir. Water is provided to the livestock by installing a water supply line during construction of the pond which leads to a water tank below the dam.
- A permit may be required before pond is built.
- Do not create a hazardous situation for people downstream by building an inadequate structure.
- Do not back water onto another landowner without an easement.
- Make sure that the dam is far enough back from your property line so that water coming around the emergency spillway will return back to the natural drain before leaving your property.
- To reduce the chance of drowning use good common sense around water all year round.
- You cannot cut a landowner down stream from water. Proper sizing of the pond or a drawdown pipe may be required to assure some water will pass through.
- Don't destroy a wetland by building a pond that will cover it up with deep water.