FIGURE 37
Farm ponds can be used for irrigation and watering livestock.
Large-scale Ponds
Large ponds are very similar to smaller backyard ponds, but they do require some special consideration. Most of the topics in this book apply to large ponds, but this chapter will focus on topics that are specific to large ponds.
Various names have been used for large ponds, including earth-lined ponds, earthen ponds, recreational ponds, fish ponds, and irrigation ponds. Design and construction for all are the same. For brevity, these will all be called ponds.
Large ponds can be used strictly for pleasure and aesthetics just like smaller backyard ones. But many times they are created to meet a special functional need. In that case, special design considerations might apply. The following are some typical pond applications. More than one of these may apply to your situation.
An irrigation pond is a great asset for farms of all types and sizes. It provides a ready source of water for crops and livestock. Most irrigation ponds are designed with steeper sides that don’t have planting shelves. Because algae growth is not really a concern, plants don’t play a critical role. Floating planktonic algae is not as big a problem since it will pump easily and add extra nutrients for plants. Filamentous algae tend to be less problematic since the water level is usually dropping during the season.
The main requirement for an irrigation pond is to hold lots of water, and the best way to do this is to make it as deep as possible. A deep pond loses relatively less water than a shallow pond since water only evaporates from the surface. A smaller surface means less water loss.
The location of an irrigation pond is usually determined by how it will be used. When the water is as close as possible to where it is needed, pumping is easier. Having electricity nearby can also be a big advantage.
Having your own fish farm can be a great addition to a small farm. Smaller ponds provide food for your own use, and larger ponds will produce enough fish for sale. Aquaculture ponds should be at least one-quarter of an acre if you will be selling the fish.
The pond shown in figure 38 has a natural clay soil liner. It is built on top of a spring, which provides a steady source of cold fresh water. A shallow warmer end of the pond is used for swimming, and the deeper end near the spring provides the cold water needed for raising a small number of trout.
Ponds for raising fish are not very different from natural ponds. Plants are still important for keeping water clean and providing food for some types of fish.
A shallow pond heats up in summer, which can be very detrimental to some fish like trout. Therefore, most fish ponds are between 6 and 100 feet deep and may have several areas of different depths for various species. Research which ones you want to grow and then plan the depth to provide the right temperature conditions.
Many people try to grow a lot of fish in the pond to maximize productivity; this causes problems in a natural pond. To compensate, you may need pumps to aerate the water and keep oxygen levels high.
Think about how you will catch the fish. Will you go fishing with line and hook for the occasional meal, or do you want to harvest a large catch at the end of the season? To accomplish the latter, you will need to draw down the water and then have some type of net system to catch them.
The inflow and outflow systems should be constructed so that fish can’t escape the pond; maybe include a net or grill system in these areas.
The key to maintaining a natural pond and raising fish is to keep fish levels reasonable. If these get too high, algae will become a problem.
Ponds can be convenient ways to water livestock, both animals and waterfowl. If animals will be entering them to get a drink, provide a beach area for easier access.
Ponds can also be used to raise waterfowl for food or down. They prefer water between one-half foot and three feet deep and like to eat plants, so plan for larger planting areas. Good choices for geese and ducks include sago pondweed, wild celery, coontail, elodea, muskgrass, arrowhead, wild Japanese millet, and wild rice.
Wild animals such as coyotes like to eat large birds, so the pond may need protective fencing. An island for nesting ducks is another way to provide protection. In a larger pond, an island might even attract wild ducks or geese.
If animals or birds will use the water in winter, some of the surface should be kept open all winter long. Use solar-powered aerators for this.
Ponds can be used to provide a very economical way to heat and cool a home. Geothermal systems extract heat from the water in winter when the water temperature is 32°F. In summer, the cool water is used to extract heat from the home.
Pipes run from the home to the pond, where loops run under the water. A heat exchange fluid is pumped through the pipes from the home to the pond and back again. Heat exchangers inside the home transfer heat as needed and in turn warm or cool the air in the house. Such a geothermal system requires a pond that can maintain a depth of at least six feet.
Recreational ponds for swimming have always been popular. They are very similar to most of the ponds described above, which can also be used for swimming.
How will swimmers enter and exit the water? One way would be by a dock, which could overcome steep slopes found in most ponds. Another is to add a large beach area, which should have a slope of no more than 4:1; less is better.
Locate beaches at the north end so bathers face south to make the best use of sunlight. It is best to keep it away from the inflow area, which tends to be murky and colder. Dig out the beach area six inches deep, line it with plastic, and then cover it with a layer of sand. Extend the beach above the high waterline to make it easy to enter the water.
Ponds made in natural streams are highly regulated and may not be allowed in some areas. Be very careful about changing natural water flows.
Many rural landowners don’t realize that they don’t own the water that flows across their property. In the US, most lakes, wetlands, rivers, and streams belong to the government. Doing anything that impacts these waters requires permission from the EPA under the Clean Water Act. Any water that is not covered under federal jurisdiction is often covered under state laws.
A project that involves the building of a dam or embankment may increase your liability for any damage that happens downstream of your location. Contact your insurance provider to see if building a pond changes your policy.
Here are some agencies you should contact.
In the US:
• Natural Resources Conservation Service (NRCS): is part of the Department of Agriculture.
• County Conservation District (CCD): provides information about soil erosion and earth-moving activities.
• United States Army Corps of Engineers (USACE): is responsible for permits influenced by the Clean Water Act dealing with wetlands.
• State Department of Environmental Protection: is the state agency charged with water quality and quantity regulations.
• Local Fish and Boat Commission: regulates chemicals used in ponds and controls fish movement and addition to ponds.
• Local government (county, township, municipal): may have regulations and codes that affect the building of a pond.
In Canada:
• Ministry of Natural Resources: regulates natural creeks, streams, and wetlands.
• Local Conservation Authority: regulates local waterways.
• Ministry of Environment and Energy: requires permits when water comes from a natural watercourse at a rate exceeding 10,000 gallons a day, and for the use of herbicides to control aquatic vegetation.
• Local government (city, county, township, municipal): may have regulations and codes that affect the building of a pond.
Adding water to a large pond becomes an important consideration for its location. The best site may be where nature fills the pond for you and where you have to move the least amount of soil to get water. There are several possible water sources, and a combination of may be the best option, including the following.
A special well can be dug near the pond location and equipped with a solar pump so that no electrical supply is required. Small pumps are also available for windmills. They require a wind of at least five miles per hour, which is less than what windmills require to generate electricity.
Well water is a good source but is generally only practical for smaller ponds or for topping up ponds that have another water source. Water witching, the process of using a forked stick to find water, is very popular, but this method does not work.
A good option is to position the pond where nature will supply most of the water. The base of a sloped hill can collect significant runoff. This hill should not be heavily fertilized, so that runoff does not add excess nutrients to the pond. Runoff from crop lands can add pesticides to the pond, and amphibians, in particular, are very sensitive to such chemicals.
A spring can be an excellent source of water. Most people try to locate the pond on top of it, but downstream from the spring is better because the rock around a spring can have high seepage rates. This will give you better control over the water flowing into the pond.
A pond liner can’t be used on top of a spring since the water pressure from the spring will force it off the bottom of the pond.
Tapping into an existing stream or river is also possible, but this is highly regulated since it might affect living organisms in the stream. It is unlikely you will get a permit to build the pond right in the stream, but you might be able to divert a portion of it into your pond.
Large ponds can be made with the same rubber liner that is suggested for small ponds by joining pieces together to form the right size. There are other options that are worth considering.
The soil may hold water well enough to use it as a natural liner. A high water table will also help. Soil can be used if it contains at least 20 percent clay. Such earth-lined ponds always lose some water, which is called seepage. Soil with higher clay amounts seep less. A newly created pond seeps more in the first few years and becomes better sealed over time.
To find out how much clay is in your soil, dig some pilot holes to one foot below the planned depth of the pond. Collect the soil below the pond and determine the clay content. You can do this by sending samples to a soil lab, or using some DIY techniques to get a good approximation. The References section contains some links to YouTube videos on this process.
It is best to dig the pilot holes in summer or fall before fall rains start, so that you can see the natural low water level at that time of year. When digging, watch for horizontal rock ledges that can run long distances through soil and are a major cause of seepage, as the water runs along the rock. While you are testing the soil, you can also fill the pilot holes with water and monitor how quickly you lose water.
If the clay content is too low, bring in some good clay soil and line the pond to a depth of one foot, spread evenly and compacted to make a good seal. It should contain enough moisture so that it compacts well. Once it is laid, fill with water before the clay dries out and cracks. If you choose this option, it is probably best to hire an expert to do this work properly.
Instead of natural clay, you can also line the pond with a commercial product called bentonite, a colloidal clay that is applied to a dry pond bed. It works best on coarse-grained soil with low clay content. The bentonite is mixed into the native soil to a depth of four inches and then compacted. As water is added, it expands and forms a seal on the bottom of the pond. This is also a job best left to professionals who are familiar with the product and process.
Bentonite can also be used to fix holes in a natural soil pond if only a small section of the pond needs to be treated.
Cheaper plastic or PVC liners can also be used for large ponds. Since the plastic is easily damaged, it is usually covered with soil to protect it.
There are two basic designs for large ponds: excavated and embankment. Figure 15 (page 57) shows the difference between these two types.
Excavated ponds, made by removing the soil, can be made on level or sloped ground. Their advantage is that there is no worry about edges of the pond collapsing. The downside of excavated ponds is that you need to dispose of a lot of soil.
Embankment ponds use the soil that is dug out to form part of the edge. They are usually built on sloped land where one end of the pond butts up against the hill. The removed soil is placed at the low end of the pond to raise up the edge. If it is sited well, this type requires less digging and there is no soil to remove. The downside of embankment ponds is that the dam needs to be constructed properly or it will collapse, sending all of the water flowing downhill. Build embankment ponds in an area where a breach of the dam will not flood homes or livestock.
Important notice: Always consult with a qualified professional engineer when designing and building an embankment pond or dammed pond. The author of this book is not an engineer and is not qualified to provide such consulting services.
The slope of the pond depends on both its type and use. An excavated pond that is used mostly for recreation or as a water source should have an inside slope of at least 2:1 (horizontal:vertical). An embankment pond should have a slope of 3:1 on the dam side. Beach areas where swimmers or livestock will be entering the water should be at least 4:1. Flatter slopes are more stable and will encourage algae and plant growth along the edge.
The volume of large ponds is usually expressed in terms of acre-feet, where 1 acre-foot is equal to 325,851 US gallons. The acre-foot of a pond is calculated as: Acre-foot = surface area (in acres) x average depth (in feet)
Except in beach areas, do not to put sand on the bottom. It discourages weeds for a while, but soon it will be covered with silt and you lose any benefits the sand gives.
The depth of the pond depends on its purpose. A deep pond loses less water to evaporation, which is good if you use it for irrigation. Increasing the depth is even more beneficial in warm dry locations with high evaporation rates. Deep water also stays cooler, which may be a requirement for raising some fish species. Less light gets to the bottom of a deep pond, making it harder for algae to grow. Shallower water is better when the pond is a wildlife refuge, since it can accommodate more plants.
Aerobic decomposition (decomposition in the presence of oxygen) is favored in ponds because it is usually faster and free from offensive odors that characterize anaerobic decomposition. Pond aeration is used to increase the dissolved oxygen level so that aerobic decomposition can take place more efficiently. This is especially critical at the bottom of the pond where organic matter settles. An increased oxygen level can also be beneficial to fish.
Pond water will naturally separate into layers, or strata, through a process called stratification. This is mainly caused by temperature differences: warm water stays at the top, and cold water stays at the bottom. You have probably noticed this while swimming in a calm lake. Each layer of water also contains different amounts of oxygen: the top has the most oxygen, the bottom the least.
Aeration systems, designed to mix up these strata and increase the oxygen levels throughout the pond, do this by producing bubbles at the bottom that then rise to the surface. These bubbles only add a small amount of oxygen. Their main purpose is to lift cold water from the bottom to the surface, mixing up the strata. Oxygen from the air can then dissolve in the top water layer.
Fountains, often added for aesthetic reasons, can also be used to add oxygen to the water. As water from the spray hits the surface of the pond, it has the same effect as wind. It increases the rate at which gases exchange at the surface, thereby increasing oxygen levels. If the fountain gets its water from the bottom of the pond, it also helps to destratify the water layers.
Fountains are less expensive than aeration systems, but they are also less efficient at moving water. The inlet side of the pump also tends to clog, adding more maintenance work. They are better at moving duckweed to the edge of the pond than aeration systems.
Aeration systems and fountains can be solar-powered using commercial products or by making your own. The References section has some links to videos for making these systems.
To retain water, embankment ponds use a dam, which must be constructed with care and meet all regulations. This is not a beginner sport, and if you have never built a dam, you should get some expert advice. The recommendations presented in this book are just approximations. Requirements change depending on location, type of soil, and weather conditions. Check with local authorities to get the best dimensions for your situation.
Building a dam requires a lot of soil and could be the most expensive part of the project. The soil should be composed of high-quality clay containing very little organic matter, since that will decompose over time and shrink the soil level.
Add the soil in thin layers of no more than six inches at a time, compacting between layers. When complete, the inside slope should be at least 3:1 (horizontal:vertical) and the outside slope should be 4:1. Figure 40 shows a typical dam design.
The width of the top of the dam depends on its height. If less than 10 feet, then the dam should be 8 feet wide; if more than 10 feet, make the dam 12 feet wide. Wider dams are safer and easier to maintain. Dams that will be used as a road should be at least 16 feet wide.
The center of the dam in figure 40 has a clay core, which can be added to large dams for extra stability. Speak to a dam specialist about adding this.
Plant the slopes of the dam as soon as possible to reduce erosion.
You will need to empty the pond occasionally to collect fish, perform maintenance, or clean it out. Drawing down some of the water can also reduce algae growth. You can add a drain system in the dam for emptying the pond, but these are the single largest cause for leakage. It is much better to empty the pond using pumps when needed. This may be slower and inconvenient, but it is less problematic. Drain systems are also more expensive to add.
The pond should have a properly designed inflow area if it is being fed from a spring or river. It can also be a good way to control the water from surface runoff. An inflow is added to control erosion of soil beside the pond and to reduce the amount of silt entering the pond.
Erosion on the inflow usually occurs in spring as snow melts or in fall with heavy rains. Whenever a significant amount of water enters the pond, the inflow will tend to be eroded and the soil that is moved will flow into the pond. The best way to stop erosion in the inlet is to use rocks that are large enough so that the water cannot move them. Smaller rocks can then be added to fill the spaces between them. Use a rubber liner in the inlet area to further reduce damage to the inlet.
Figure 41 shows an inflow for a new pond that is made entirely out of concrete with a few stones added to slow down the movement of water.
Moving water carries silt, which on entering a pond will not only fill it up over time but also adds excess nutrients which increase algae problems. The recommended course of action is to design the inflow so that silt gets trapped before it enters the pond.
The best way to control silt is to add a small sediment pond ahead of the main pond. As the moving water enters the sediment pond, it slows down and the silt settles out of the water. The cleaner water can then be allowed to gently flow into the main pond. The silt that settles in the sediment pond can be emptied out periodically to keep the system working properly. The size of the sediment pond depends on how much and how fast the water is flowing into the system. Higher flow rates carry more silt than slower rates.
If a natural constant source of water flows into the main pond, consider raising the inflow above the waterline to create a waterfall. This adds an interesting architectural feature and helps aerate the water in the pond.
The inflow needs to be checked routinely, especially in early spring, to make sure the pathway for the water has not been plugged by vegetation or downed trees.
The outflow on a pond is the area where excess water leaves the pond. If the pond is being fed by a stream or other constant flow of water, the outflow will serve this purpose. If the pond has no natural water source, the outflow is still required as an emergency system. If for some reason too much water enters the pond, the outflow provides a controlled method for dealing with the excess water, ensuring that it does not disrupt the dam.
The easiest way to construct the outflow is to create a rock-lined creek bed. The edge at the pond should be at the level needed to maintain its correct high-water level. The creek should then slope very gently away from the pond so that the water moves slowly. Stones added below the water level on the pond side of the outlet will help prevent erosion of the water side of the outflow.
The creek needs to be wide enough to easily handle the worst-case flooding situation. An approximate size can be calculated by adding 15 feet to one-half of the total drainage area (land and water collecting rain), in acres. For example, a 1-acre drainage area should be 16 feet wide, and a 5-acre area requires 17.5 feet.
A more elaborate outflow can be constructed to also help with emptying the pond. This requires the addition of a sluice gate and concrete support structures. It is best to consult a specialist for this project.
Planting a large pond is not much different than planting a smaller one, except that many more plants are needed. Types and quantity depends on the planned use of the pond. A wildlife refuge will normally have many more plants. A pond used to raise fish or for swimming needs to have more open water.
Planting excavated ponds is fairly easy because you can choose anything you want. Combine shrubs and trees with herbaceous plants in any combination that suits your needs. Planting embankment ponds is a bit more challenging.
Trees and large shrubs should not be planted on the dam of an embankment pond. The tree roots will grow toward water sources such as the pond. In time they create weak points on the dam that increase water seepage. Small shrubs and grasses on the dam provide very good erosion control while still offering hiding places for wildlife. On new dams, use seed for annuals or perennials so that the bank is covered with some type of growth quickly to reduce erosion. Once this is established, other types of plants can be added.
A large pond can be designed with very distinct plant communities, and each area can be designed to have the best depth for the plants that will be grown there. The planting shelves in ponds that use a soil or clay liner will consist of the same soil that is used to line the bottom. Plants are then rooted right into this soil. Don’t add stones for plants on the shelf.
I recommend you cover half of the open water with floating plants like water lilies, which shade the water and make it more difficult for algae to grow. With less light in deep ponds, they stay colder, both of which discourages algae growth.
Eutrophication is a term used to describe the aging process of a natural pond. Over time, sediment accumulates and reduces the depth of the pond. The amount of plants increases, which in turn reduces oxygen levels. The pond slowly becomes a swamp or wetland. You will need to decide on how much of this process you will allow.
