Selecting a Pond Location Selecting the location for your pond or lake is one of the most important steps in its construction. A good pond site will consist of a level topography for economical reasons, a soil with sufficient clay to hold water and an adequate water supply. You need also to consider liability, since a pond owner is normally held liable for any downstream flooding or related damages should an accident occur such as dam breakage. Level topography will decrease your expenses since there will be less costly soil removal. When building your dam, in most instances the maximum height should be 20 to 25 feet, higher dams can be expensive to build. Since a pond or land is simply a depression used for holding water, the dam and bottom must be composed of soil which minimizes seepage. Clay is the best type of soil. Gravel and sandy soils are unsuitable for ponds and lakes, limestone and shale are also unsuitable as they can crack which creates leaks.
The water supply must be efficient enough for quickly filling the pond and also maintain a relative constant water level that will not fluctuate greatly during the year. If you are using a stream as a source of water then you should build the pond adjacent to the stream with an inlet, not dam the stream. Springs, wells and ground water will provide the best sources of pond water. Ground water being the best for supporting aquatic life, however any source of water should first be analyzed before pond construction to ensure it will not harm fish and aquatic life.
Once a decision is made to construct the pond, the site should be cleared of all trees and brush. The dam-site area should be marked with toe and grade stakes, all topsoil removed and a core trench excavated. Once the core trench has been filled with high quality clay soil, a drain pipe with anti-seep collars should be installed. Many types of drains are available. The one you choose depends on the costs, availability and suitability. The drain should be of sufficient size to drain the pond in a 3 to 7 day period. Filling the exposed portion of the dam is the most expensive operation in pond construction. All fill should be composed of high quality clay soil applied in thin, well-packed layers. When completed the dam should have a 2:1 slope on the pond side and 3:1 slope on the downward side of the dam. The top of the dam should be 12 feet in width to allow vehicle traffic and prevent muskrats from burrowing through the dam.
Spillways and Inlets
Inadequate spillway capacity is the main cause of earthen dam failure. All dams require this protection which can be provided by one or several emergency spillways of sufficient size. The spillway should be adequate to release flood waters and minimize flows to less than one foot above the spillway. This reduces loss of valuable sport fish and structural damage.
Spillway size should be related to the drainage area. Recommended spillway size can be calculated by adding 15 feet to one-half of the total drainage area acres. For example, a 50-acre drainage area should have 40 feet of spillway, 100 acres requires 65 feet of spillway, and 200 acres requires 115 feet of spillway. It may be necessary to provide a system which can be used to drain the pond as both a management and maintenance practice. If gravity drainage is not possible, a pumping system will be necessary. In addition, surface drainage may be necessary to properly route excessive water inflows. This may be accomplished through drainage culverts or grassed spillways. Concrete spillways are expensive but may be necessary on larger ponds and where excessive flows may be expected. An emergency spillway is not required on ponds with no runoff discharging into them. If an excavated pond is located on sloping terrain, part of the excavated material can be used to build a small dam on the lower side of the pond to increase the ponds capacity. Care must be taken that failure of this dike does not result in adverse downstream impacts.
An emergency earth spillway is necessary to pass excess storm runoff around the small dam. If the pond is being supplied by surface runoff, the capacity of the emergency spillway should be sufficient to discharge the maximum outflow expected for a rainfall frequency of once in 25 years. For large ponds the design rainfall is 100 years. The emergency spillway may consist of a concrete or vegetated earthen spillway, a conduit (pipe), or a combination of a vegetated spillway and a conduit. If a vegetated spillway is used, the crest of the spillway should be at least .06 m (.2 ft) above the normal reservoir water elevation. A trickle spillway is usually designed to provide flood protection or to reduce the frequency of operation of the emergency spillway.
If the runoff is entering the pond through a confined channel or ditch rather than through a broad shallow waterway or watercourse, the pond inlet must be protected against erosion. A steel or concrete culvert can be placed in the ditch and extended over the side of the excavation. The extended portion of the pipe should be either cantilevered or supported with timbers. Pipe diameters depend on the peak rate of inflow and must be appropriately sized. If the water is carrying significant amounts of silt or suspended particles, a sedimentation area or filtration strip planted with grass should be provided above the pond to remove the sediment before water enters the pond.
Excavation is a pond construction method used in relatively flat topography. The natural slope at the site should not exceed 4 percent. Because all material must be removed to obtain the desired capacity, the size of a pond constructed by excavation will be limited by excavation costs and site conditions.
Excavated ponds can be classified by the way water enters the pond. An excavated pond can be supplied by surface runoff, by water diverted from a stream or a river, by water pumped from a well by surficial aquifer sources (water table), by shallow water table seepage, or by any combination of the above sources. In Florida, shallow natural water tables (surficial aquifer) and heavy rainfalls combine to provide most of the water supply for excavated ponds.
Excavated ponds which are supplied by surface runoff should be located in natural depressions, in broad natural drainage swales or paths, or to one side of the drainage swales where the runoff can be diverted into the pond. If the pond is constructed in or near a natural drainage swale, excess runoff from a full pond may be discharged through natural drainage paths and construction of a spillway may not be necessary.
Excavated ponds supplied by surficial groundwater aquifers (natural high water tables) must be located in flat or nearly flat topography. A prevailing, reliable water table should be within 1 m (3 ft) of the ground surface. The level of the water table indicates the water level in the completed pond. In addition, the shallow aquifer must be sufficiently large and permeable to yield water at a rate that satisfies the maximum expected demand for water. However, in most Florida locations the yield is usually not a limiting factor. When the water table and surface runoff cannot provide a sufficient supply of water, an additional water supply such as a well or a diversion from a nearby stream may be necessary. If the water level in the pond is above the level of the natural water table, significant losses can occur through subsurface flow. These losses can be significant in Florida sandy soils and will depend on the permeability of the bank material and on the difference in height between the pond surface and the surrounding water table.
Planning the Excavation
Design of an excavated pond is based on the required storage capacity, depth to the water table, other available water sources, and the stability of the side-slope materials. The topographic conditions at the site must allow economical construction. Cost is a direct function of the volume of excavated material required to obtain a certain storage capacity in the pond. This method of construction results in the limited practical size of excavated ponds. However, these ponds can be designed to minimize evaporation losses by decreasing pond surface area in proportion to stored volume.
A rectangular shape is usually the most convenient for excavation equipment. The size of the pond is determined by the purpose for which water is needed, the site conditions, and the amount of inflow that can be expected. The required capacity of an excavated pond fed by a shallow water table is difficult to determine since the estimated rate of inflow into the pond can rarely be estimated with reasonable accuracy. Long narrow ponds will yield (or lose) more water from (or to) the surrounding area than square ponds. In some cases it may be necessary to augment the pond volume with water pumped from a nearby well or other water source.
The proposed pond site should be thoroughly investigated prior to design and construction. Core samples of the soil profile should be obtained to provide information on the permeability of the material within all depths and below the bottom of the proposed pond. Permeability requirements for pond construction vary with the type of water supply into the excavated area. For a pond supplied by a surficial aquifer source the permeability of the surrounding soil must be high to assure sufficient inflow into the pond. Conversely, a pond supplied with water from another source as discussed above must be located in an area with low permeability soils in order to avoid seepage losses. Permeability is defined as the readiness with which soil transmits water under standard field conditions. It depends primarily on the size and shape of the soil grains, the porosity of the soil, the shape and arrangement of the pores, and the degree of saturation. There are several laboratory methods to determine permeability for a given soil. Indications of soil permeability can also be obtained at the sites by filling test holes with water and observing the seepage characteristics of the material. Permeability tests performed in the field are frequently more representative of the actual site conditions since the soil is not disturbed as much as when the samples are transferred from the field to the laboratory. The simplest method used in the field in the presence of high water table is to dig an auger hole into the soil below the water table. First determine the elevation of the existing natural water table by allowing the water surface in the hole to reach equilibrium with the surrounding area. Next, the water in the auger hole is pumped out to lower the elevation of the water surface in the hole, and then the rate of rise of water in the hole is measured. From this measurement soil permeability can be calculated.
At sites without natural water tables, other permeability tests must be used. An infiltration test over a large area (13 ft or 4 m in diameter) may be used as a field test. This avoids the soil compression that is inherent in core sampling, which is necessary for the lab samples. The area is diked with a ring of soil and filled with water to form a shallow pond. A circular pond is recommended rather than a rectangular one because the circular pond has less lateral and undesirable seepage loss per unit area than a rectangular one. To perform this test water is added to the pond area as needed to saturate the soil in the surrounding area, and then the falling water level of the pond in the absence of added water is observed and used to determine permeability. This rate should be a measure of the ability of the soil to pass water into and through the observed soil layer.
When excavated ponds are supplied by surface runoff or by water pumped from a well, relatively impervious soils at the site are essential to avoid excess seepage losses. Soil materials must be available to provide a stable, impervious fill where needed. Clay and silty clay are the most desirable; however sandy clay may also be satisfactory. In some regions, the soils contain sufficient clay to allow pond construction without adding soil amendments or artificially lining the pond. Unfortunately, most of the soils in peninsula Florida are very sandy, and additional measures to prevent seepage are necessary for pond construction. In some cases the only solution may be an artificial lining material. An artificial lining is expensive but should be considered at sites where soils are porous or are underlined by sands or gravel.
In addition to permeability tests, the core sample holes may be used to determine the existing level of the water table from the shallow aquifer. The depth to the water table generally varies throughout the year. Therefore, several observations may be necessary to help with design. The performance of other nearby ponds may provide useful information with respect to the suitability of the proposed site and for design purposes.
Larger ponds should be equipped with some drainage facilities. A drain pipe is necessary to facilitate maintenance and fish management. On flat topography a pump may be necessary to drain the pond.
Proper Pond Excavation
Proper construction practices should be followed to ensure safety and to reduce potential problems. After the pond site has been selected, an area or areas for spoil placement (excavated material) should be located. Stake the boundaries of the pond and spoil placement locations with the depth of cut from the ground surface to the pond sides or bottom clearly marked on the stakes. All woody vegetation should be cleared from these areas.
The type of excavating equipment for construction will depend on availability, climate, and physical conditions at the site. During dry periods most types of equipment can be used. The most common are tractor-pulled wheeled scrapers, draglines, and bulldozers. Inefficiency in transporting material limits the use of a bulldozer for excavation to relatively small ponds. Dragline excavators are commonly used for pond construction in the high natural water table areas of Florida. This is the only type of equipment that will operate under saturated soil conditions.
It is desirable to keep topsoil separated from subsoil materials during excavation. Place topsoil material in a location where it can be accessed after excavation has been completed. After excavation, this material should be placed on the surface of the side slopes, berms, spoil banks and spillways. These areas should be seeded or plugged with a grass or other cover material for erosion control. The grass or cover material should require minimal maintenance, be tolerant to local drought or wet conditions, and be relatively easy to establish.
Filter Strip Design
Sediment leaving agricultural land is often a significant source of pond non-point pollution. This sediment delivery can be reduced by grass filter strips near the edge of the field or the disturbed area. Filter strips increase the hydraulic roughness of the flow surface, reducing the flow velocity and thus the transport capacity. Since concentrated flows tend to submerge the grass and decrease the roughness, filter strips are most effective when flow is shallow and enters the strip uniformly along its length. Thus, care in placement and maintenance of filter strips is advised. Assistance in the design of filter strips is available through the Natural Resources Conservation Service.
FREQUENTLY ASKED QUESTIONS
How much does it cost to build a pond or lake?
Here are some numbers you can use for your pond or lake project. To move dirt to dig a pond, you can expect to pay roughly $2.50 per cubic yard of material dug out of the pond. Figure $1.50 – 3.50 per yard of material depending on the difficulty of excavation and costs specific to local market conditions. Very small ponds cost more because smaller equipment is required. Of course the volume of material to be moved will be entirely dictated by the habitat design. Because of this, we can’t estimate without knowledge of the specific project.
If the land needs to be cleared of trees and stumps, expect to pay at least several thousand dollars per acre for clearing plus disposal. If soils and debris have to be removed from the site expect to pay several dollars per cubic yard to truck the soil to another location. It is always best to have a plan to use excavated soils somewhere near the lake or pond. Removing soils from a site can become very expensive.
The most cost effective sites for pond construction often have gently sloping topography. Ideally, this would be in a low area with roughly ten feet of elevation difference between the sides and the bottom. This greatly reduces the volume of material to excavate. For instance, a one acre pond that averages ten feet deep will have a volume of 16,133 cubic yards. If you only need to excavate one-tenth of this to build a low dam, your excavation expense could drop from the $30,000 per acre range to the $8,000 range. Note that building a dam is more expensive per volume than simply excavating a basin. We further reduce excavation expense by designing habitat to perform better with less depth. Most ponds are dug too deep. To create high quality pond and lake habitats, there are significant additional expenses associated in the form of materials and detailed excavation.
Once the site is excavated, the new basin must be sealed unless the site is dug into a tight clay formation. Most sites require at least compacting existing clay soils, or if clay is not present then we need to augment the soil by importing quality clay or other sealants. Compacting a site costs several thousand dollars an acre. The cost of importing and applying sealants may range from $10,000 to $30,000 per acre depending on location and soil conditions. Installing synthetic pond liners cost even more than our estimated range.
Keep in mind these are a very basic examples. There are a number of technical issues that contribute to site selection. Clear water is very attractive, but the addition of a wildflower meadow and a spring creek elevate the financial and emotional value of a project to a higher level.
You will realize the value of professional design when you see how much can be saved during construction, and realize continued savings in maintenance and tremendous increase in life expectancy of the lake or pond. You will move less earth with our assistance. We are very strong in this niche due to our biological experience in combination with construction experience. You can start to plan the budget of a pond or lake with the figures we offer realizing the total cost per acre of water is very dependent on the geology and slope of the site, the price of materials (clay, soil, sand etc.) excavation expense and quality of habitat you desire. Our lake and pond property evaluation service becomes an excellent investment because of these potential costs. The right site is going to cost much less to build on when compared to most sites.
Annual maintenance expenses span a range of nearly zero to an excess of $2,000 per acre, depending on the quality of the design. The projects we design do not use any chemicals, mechanical management, or commercial bacterial products, so our clients enjoy long term savings along with the quality we offer. Poorly designed ponds require a continual investment in order to keep them clean. You may have noticed that we really don’t offer any pond maintenance service. We are too busy building quality projects that have little or no need for ongoing maintenance.
If you do not have a year around spring, stream or reliable clean surface runoff on your property, you will need to put in a well. Well drilling costs are best estimated by your local well drilling contractor. Since property without a stream or spring is generally much less expensive, it may be more cost effective to purchase dry ground and drill a well.
After the pond has been in place a year or two, the vegetation is established and healthy, and the fish are large and healthy, then the pond brings a significantly higher value to the property. You may want to talk to a local Realtor regarding the value a high quality pond brings to property. We mention this under the construction cost heading because improved property value should be considered when evaluating pond construction costs.
It is our experience that water clarity, large fish size, high quality aesthetics and little or no maintenance requirement for a pond, will bring much more value than a larger, poorly built pond with weed problems, high maintenance expense and/or dirty water.
We just dug our pond. Can you make it perfect now?
Creating a high quality lake or pond begins with design. Yes we can improve your pond, but you can expect to have to drain the pond and make major modifications to what you have installed. Much of our business comes from redesigning and rebuilding new ponds that were not efficiently designed. If you are thinking of building a new stream, pond or lake, talk to us before you break ground.
Is my pond leaking?
When evaluating a pond or lake that is reported as leaking, we start by looking at the circumstances of the site. The first thing we do is compare the evaporation rate of the area with the change in water elevation in the pond or lake. During the heat of summer, it is common to see evaporation rates of a half inch per day throughout arid areas of the Southwest United States. Less than a quarter inch of daily evaporation is common in more temperate climates. If your water supply is not contributing to the lake or pond and you are losing on the order of 15-17 inches (arid climate) or 7-9 inches (temperate climate) of water per month during summer, you may not need to even think about resealing the pond. An inch or two of seepage per month is usual even in a tightly sealed pond. This is included in these figures. By the way, we actually want a pond to leak a little since it helps rid the pond of excess nutrients which accumulate in the depths.
To test for leakage vs. evaporation, we suggest setting a bucket full of water next to the pond and protect it from animals by placing a screen over the bucket. Compare the water loss in the bucket with the water loss in the pond. The difference will tell you if you need to consider sealing the pond. Any water flowing into the pond will either need to be shut off or calculated into this comparison.
There is a very important exception to this technique: if your pond has a large area of emergent vegetation, then you need to consider the evapotranspiration rate in the plants. Even in Western Oregon, we can see vegetation use an inch of water per day via evapotranspiration, compared to less than 0.2 inches of daily evaporation during summer. If your pond has extensive shoreline and shallow water vegetation, this may be your “leak”. If a quarter of your pond is covered by emergent vegetation, then figure an additional quarter inch per day of evaporation since one-quarter of the pond may be evapotranspiring an inch per day. We have not researched all species of emergent vegetation so results will vary.
Testing for evapotranspiration in plants may be more involved than you want to get, but it is much less involved than trying to reseal a pond that does not need to be sealed.
Another source of leakage is the moist soil along the shores of the pond which is produced by capillary action. If the clay or synthetic liner does not extend above the capillary zone, the pond is going to continually send water out via its edge. This is usually fixed by extending the liner sufficiently high enough above the water surface elevation. Periodically check for moist soil along the shoreline during dry weather.
If this sounds like clay lined ponds are trickier to build than synthetic lined ponds that may be true. On the other hand, clay is generally much cheaper than synthetics, plus clay produces much higher quality lakes and ponds when designed correctly. Over the life of the pond, quality construction in clay will result in a pond with less expense and maintenance than synthetic lined ponds and lakes, which do not cleanse their own nutrients without further design and/or equipment etc.
With clay, it is important to utilize a contractor who has experience building clay lined ponds. We recently heard of a contractor who quipped that he has made a lot of money off people who had him build clay lined ponds. He says he makes the extra profit when he goes back in to line the pond with a synthetic liner. What this says to us is this particular contractor does not possess the required knowledge to build clay ponds. If he has sufficient knowledge, he wouldn’t need to reseal the ponds. Be sure your pond contractor is qualified for the task before you hire them. We also help clients select the best contractor. Investing a few hundred dollars on a soils lab test is very good insurance for a lake or pond.
A qualified contractor is crucial if you intend to use commercial Bentonite clay. Bentonite is a very effective pond sealant in the right hands. We see way too many people try to use this material who have no concept of its requirements. We urge everyone to seek out a contractor who has been successful with Bentonite instead of trying to seal their own lake. Subtle design requirements exist in order to create an efficient seal with Bentonite.
Testing materials to seal a pond or lake
Historically ponds were usually built within a stream channel due to construction convenience. Those days are over for most situations now. While streams were an inexpensive source of ample water, more projects are now relying upon wells for their water. When water was abundant, few people concerned themselves with a tight seal. A good seal is more important now when considering the cost of pumping additional well water. We outline general methods of ensuring a proper seal in the following discussion.
We are often asked how to evaluate soils used to seal ponds and lakes; our approach is two tiered. The first thing we do is a very simple test, and then if we need further research, we bring in a soils scientist or engineer to utilize techniques that improve the quality of marginal materials. We will outline the simple method here.
To quickly identify the best clay material, grasp a handful of moist earth in your hands and roll it into a ball shape. If the ball maintains its form when you drop it on the ground, it may contain sufficient clay. Take the ball and roll it between your hands to form a thin pencil shape. If this pencil shape of clay will bend before breaking, the clay is likely of sufficient quality to seal a pond. There are always exceptions, so move onto the next test.
Using something like a five-gallon bucket, drill several holes along the vertical edge near the bottom of the bucket. Holes of around 3/8th inch work well. Next, fill the bottom of the bucket with four inches of crushed gravel, such as 3/4 minus. On top of the gravel, place about six inches of whatever soil/clay type material you plan to use for the pond. Thoroughly compact this clay layer throughout the bucket, paying particular attention to the edge. Make sure the clay is somewhat moist. Moist enough to make a ball out of the material is about optimum. Now fill the bucket to the rim with water. Cover the bucket with an impervious surface such as plastic. Wait a couple days, and then refill the bucket. The soil needs time to saturate with water. Cover the bucket once again. Now wait up to a week to see if the soil will hold water. Obviously you can check after the first day to see if the material failed. Our experience has been that if you lose less than an inch of water after a week in the bucket, you have good material. We don’t seem to get as good of compaction in a bucket as we do out in the lakes and ponds themselves. This is why we relax our expectations within the bucket.
If you are really interested in an acid test, create a small pond out of the materials you plant to use. Fill the pond and compare water elevation decline with a bucket of water placed in the shallows of the pond. Again, be sure to screen the top of the bucket to keep animals from drinking etc.
Having a professional soils scientist or engineer test the quality of the clay is always a good idea before investing in pond and lake construction.
Excessive algae growth often occurs within ponds and can result in many problems. The algae can be effectively treated with copper sulfate (CuSO4). Applications of 1 to 2 ppm (1.4 to 2.7 pounds per acre foot) CuSO4 are sufficient and safe to treat algae growth and should be applied when the pond water temperature is above 60° F. Treatments may be repeated at 2- to 4-week intervals, depending on the nutrient load in the pond. Copper sulfate should be thoroughly mixed into the pond (i.e., sprinkled into the wake of a boat). As with other biocides, distribution into surface water must be in compliance with EPA regulations.
Copper sulfate can be harmful to fish if alkalinity, a measure of the waters capacity to neutralize acid, is low. Alkalinity is measured volumetrically by titration with sulfuric acid (H2SO4) and is reported in terms of equivalent calcium carbonate (CaCO3). Table 2 provides a reference for determining the amount of copper sulfate to add given different alkalinity levels. Repeated use of copper sulfate can result in a toxic accumulation of copper for aquatic plants.
Copper Sulfate (CuSO) Levels Safe for fish
|Alkalinity Value (CaCO3,mg/l||Addition of Copper Sulfate|
|Below 40||Do Not Use|
|40-60||1.0 lb per acre-ft of water|
|60-100||1.3 lb per acre-ft of water|
|Over 100||2.7 lb per acre-ft of water|
|1 ppm = 2.7 lb per acre-ft (Dupress and Hunter, 1984)|
Additional Construction Tips
1. The pond dam should be grassed immediately after construction to prevent erosion. A permanent species of grass, suitable for your local area, should be used. A quality grass, properly fertilized, will quickly cover to prevent erosion and weed growth and will be easy to maintain.
2. The pond bank should have a 2:1 slope to prevent excessive growth of rooted aquatic weeds. Irregular shaped ponds (non-circular) increase angler access. All pond edges and piers should be sodden with a suitable permanent species of grass.
3. The pond side face of the dam can be protected from wind and wave action by rip rapping the face of the dam with rock. Riprap should extend several feet below the low anticipated water level.
4. Livestock should be excluded from ponds by fencing; A gravity-flow watering trough can be installed below the dam for livestock water.
5. Pond inlets should be constructed so that inflows can be controlled and filtered. The filter prevents unwanted fish species from entering the pond, and a good outlet design prevents fish loss.
6. In drainage areas that contain silt or heavy loads of toxic chemicals, the surface runoff waters should be diverted via a ditch around the pond. Diversion ditches prevent excess turbidity, siltation, fertility and fish kills.
7. Inspect and repair your pond periodically. Fill gullies, replant grass, and riprap as needed. Mow pond edges to prevent woody plant growth and promote easy access.
- Dupress H.K. and J.V. Huner. 1984. Third Report of the Fish Farmer. United States Department of Interior, Fish and Wildlife Service. Washington, D.C. 202 pp.
- Flanagan D.C., G.R. Foster, W.H. Neibling, and J.P. Burt. 1990. Simplified Equations for Filter Strip Design. Transactions of the ASAE 32(6):2001- 2007.
- Haman D.Z., A.G. Smajstrla, F.S. Zazueta, G.A. Clark. 1990. Selecting a Method for Sealing Ponds in Florida. Institute of Food and Agricultural Sciences, University of Florida. Gainesville FL.
- Extension Circular 870. Available online: http://edis.ifas.ufl.edu/WI012
- Ogrosky H.O. and V. Mockus. 1964. Hydrology of Agricultural Land. In: Handbook of Applied Hydrology, Ed. V.T. Chow. McGraw-Hill, New York.
- Soil Conservation Service. 1984. Ponds and Reservoirs, Chapter 11. In: Engineering Field Manual. United States Department of Agriculture, Soil Conservation Service, Washington, D.C.
- U.S. Army Corps of Engineer Service. 1970. Laboratory Soils Testing. Manual EM 1110-2-1906 Department of the Army, Office of the Chief of Engineers, Washington, D.C.
- U.S. Department of Agriculture, Soil Conservation Service. 1982. Ponds – Planning, Design, Construction. Agricultural Handbook Number 590.2.