Planning the pond
A. Reasons for constructing a pond
Landscape appeal
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A local river, the Maskinonge River in |
Henry David Thoreau, in his famous book, Walden, describes a lake (or pond) thus: "a lake is the landscape's most beautiful and expressive feature. It is earth's eye: looking into which the beholder measures the depth of his own nature. The fluviatile trees next to the shore are the slender eyelashes which fringe it, and the wooded hills and cliffs around are its overhanging brows." (1) Advertisement
Throughout Walden, Henry refers to the advantages of a pond as a psychological medium adding an extra dimension to one's life: "it is well to have some water in your neighborhood, to give buoyancy to, and float the earth" (1). I suspect the "buoyancy" he refers to also applies to the enhancement of human spirit. Selecting a pond site that is aesthetically pleasing and is visible from your home will improve your overall landscape. Your chosen location should also be compatible with the surrounding landscape. For example, a pond perched on a high piece of ground, in the open, never looks as if it occurred naturally, and is impossible to sustain without a liner or other artificial means. A pond serving as a transitional feature between a wet meadow and a wetland forest edge will look more like natural forces created it. Backed by a forest, or even a hedgerow provides an indication of linkage to another natural feature, improving its natural setting. The treatment of the excavated materials resulting from a dugout or embankment pond is also of utmost importance. Nothing looks more unfinished and unnatural than a mounded perimeter that was never graded out. Nature rarely, if ever, creates mini-drumlins scattered every which way around a body of water. The area ultimately becomes unmanageable, usually ending up as a weed-infested perimeter because it cannot be cut effectively. So many ponds I visited seem to end up that way, almost unfinished-looking, the owner having no aesthetic sense, nor an appreciation of natural landforms. Also, the selection of a site that allows for the spreadout of excavated soils is an expense saved, since trucking them elsewhere will be an added cost. |
Once constructed, and graded out, the pond can benefit from plantings, preferably natural plants (indigenous to the area) to draw attention to it as part of a "landscape feature," or focal point on the property. Beyond its aesthetic appeal, a pond also serves as a natural greenhouse where a variety of wetland plants can be introduced, expanding the diversity of plant life on your land.
Many relaxing hours can be spent sitting by your pond, reading or writing, immersed in a serene, private ecosystem. A pond on your landscape can also serve as a "memorial garden" created as a contemplative memorial to those who have passed away. Carefully planted, with the addition of natural perch stones or a bench, the pond can offer a place to retreat to when you are in need of privacy and reflection. A fountain operating on a pump system, adds the sound of falling water which induces relaxation in such a setting. Such was the fate of our own pond, complete with small monument, tiger lilies, and sun dial. The memorial garden by the pond, quite reserved from the rest of the managed areas of our landscape, offered a peaceful escape from reality.
It is unfortunate that of all the reasons for constructing a pond, the aesthetic benefit is rarely talked about, for it ranks as the most immediate and also most lasting benefit.
Waterfowl and wildlife habitat
Ponds are major attractors of wildlife. Migrating waterfowl use them as nesting sites in annual flights south and again on the way back north. You will find that many of the species that nest in the pond will return year after year, which is a pleasant surprise every spring. Upland game species also find ponds essential as watering places, and in early morning or evening will visit your pond on a regular basis, often creating pathways which emerge from a nearby forest or farm woodlot. Pond shorelines and connecting buffer areas can be planted to create a more diverse habitat around the pond which also provide some cover for interested animals.
Many landowners and golf course managers fail to manage their pond for wildlife even though the natural habitat around many ponds is already initiated, and a good starting point for enhancement. The key to attracting a variety of wildlife is to create a great variety of habitats, in areas of groundcover, intermediate, and canopy levels around the pond.
The new pond owner should first consider his/her primary goals, i.e. nature appreciation, fishing, swimming, golf course hazard, etc., which may conflict with maintaining a wildlife pond.
Ponds designed for waterfowl, for instance, are usually no more than 1.2 – 1.5 metres deep with low, sloping banks, and mucky bottoms which are not satisfactory for wading or swimming use. They do, however, provide the landowner with wildlife viewing and photographic opportunities. Wildlife nesting structures for species such as mallard ducks, wood ducks, purple martins, bluebirds, etc., can be added to the pond, aiding in insect removal, and to some extent-aquatic weed control.
The shallow near-shore area around wildlife ponds, called the littoral zone, contains the diverse habitats preferred by many species. These near-shore zones can also be easily degraded by human activities such as grass-cutting, dumping of fill, or removal of emergent vegetation (such as cattail). Also dependent on the nutrient level, the wildlife-type pond will tend to have moderate to dense aquatic weed growth, making it quite unsatisfactory for swimming if that is the primary objective of the pond owner. Wildlife ponds should also have a somewhat irregular shoreline which creates shallow slopes and depths around the margin of the pond. All these factors create a pond which is essentially only a wildlife pond and, coupled with its shallowness, also a poor fish pond.
Irrigation
Domestic
For my own situation, the irrigation of gardens, lawns, and other domestic uses was accomplished effectively by pumping water from my wildlife pond. The pond water was also an indispensable aid in cleaning my lawn tractor deck which soon became clogged with grass clippings from trimming the meadows. Using precious well water would have been out of the question. The added nutrients from the pond provided any fertilization the landscape needed without the addition of commercial product. I have never needed to fertilize the lawns.
When the long roadway into the site was under construction, I buried both outdoor electric wire and hose lines (separately) underneath the road fill in a suitable location to hook up to the future house site. A small pump house was constructed on the pond deck, which was built large enough to accommodate a pump and aerator. A ½ horse power electric centrifugal pump was installed with no tank, the idea being to supply water directly from the pump pressure only when needed. The pump supplied only enough pressure to lift the pond water about 10 feet over a 200-foot distance. I regretted later that I had not installed a heavier-duty outdoor wire over the distance, which would have allowed a higher horse-power pump with more pressure.
I suggest a minimum of No. 10 gauge buried wire as a minimum, since you never know just what your future needs will be. The water intake held a screened foot valve placed on the end of the two-inch intake line, held about two feet underwater. The foot valve prevented any water from seeping back into the pond, maintaining a constant "head" of water in the lines above the pump. This assured an easy startup with no requirement to prime the pump. An instant flow of water was always available with the flick of a switch. Make sure that all switches and junction boxes on the line are ground-fault protected.
The system was engineered to be switched over to a fountain in the pond centre by means of a "Siamese valve" on the hose line, which provided many hours of enjoyment when sitting by the pond, also delivering a small measure of aeration and circulation. Additional to providing the irrigation the landscape needed, the return flow off the lawns leached back down through the naturalized pond perimeter, cleaning the water re-entering it. A miniature water cycle was operating which aided both pond and landscaping.
Commercial
Water quantity requirements for commercial irrigation are greater than those of any of the uses discussed so far. The area to be irrigated from a pond is limited by the amount of water available throughout the growing season. The capacity of the pond must be pre-calculated in the design stage, in order to avoid excessive water loss due to over-application or too extensive an application. As an example, a three-inch depth of water applied over an acre will require approximately 80,000 gallons. Because of such large water requirements, irrigation from ponds is usually only realistic for high-value crops on small acres (usually less than 50 acres). The calculated storage capacity of a pond used for irrigation depends upon several factors which are inter-related: (4)
• the water requirements for the crop to be irrigated
• the effective precipitation expected during the growing season
• the efficiency of the irrigation method
• the losses due to evaporation, evapotranspiration and seepage
• the predicted flow rate into the pond
The importance of estimating water requirements can be illustrated by growers who practise continuous water-taking from a nearby stream or river. In some locales, growers irrigating large crop acreages next to low-flow rivers have dried up the sources completely. Disregarding the effect of a severe drought, they constantly pump acre-feet of water during daylight hours when the evaporation rate is highest. The river beds eventually become dry and cracked, losing all their aquatic life. Had they constructed large dugout ponds adjacent to their croplands, water could have been collected from spring runoff and flooding. Stored separately and monitored, with occasional input from the river, the ponds would have signaled a low-water warning before the river was pumped empty. Any authority controlling water-taking would thus have an indication of a future disaster through the draw-down of the ponds alone, and avert major losses through direct pumping from the river.
Fire protection
In some remote rural areas, a good water supply is needed for fire protection. If the pond is not too distant from your home and other out buildings, a gasoline pump with a flexible fabric hose will suffice in warmer seasons. Make sure it is long enough (with enough sections) to reach all sides of the buildings. In winter, a dry hydrant will be required since not only the surface of the pond will be frozen, but also any permanent intake pipes left in the pond. Because of the height of the vertical standpipe extending below the frost line, the suction capability of the pump must be high. Attempting to prime such an arrangement during the course of a fire is out of the question. Make sure you match the pump's suction capability with the lift required. In the case of an excessive vertical standpipe height due to a deep shoreline, a foot valve can be installed in the horizontal section close to the inlet screen. This will retain water in the system, providing there are no air leaks throughout, from pump to screen. Although the water storage requirements for fire protection alone are not great, the consumption rate per unit time is high for firefighting pumps.
Make sure you test your ability to unroll and lay out hose sections over the distance required if you plan on fighting a fire yourself to judge its practicality. For my own situation, the distance from pond to my forest was excessive, the pine plantation being my prime concern to protect beyond the residence. Rolling out the eight-foot by 50-foot hose sections (400 feet needed) along with coupling them together, starting the pump, and running back to the nozzle required 20 minutes to accomplish. By that time, a fire in the pines would be raging through the under story of 3,000 trees and likely crowning with any wind at all. Self-extinguishing such a fire was impossible.
A typical fire hose composed of polyester yarn with rubber lining four inches inches in diameter couples together in 50-foot sections which can be managed one at a time. The weight limitation (62 pounds per 50 foot roll) (5) requires carrying one coil of hose at a time, connecting it, and running back to get another. The operation really requires two people to be efficient.
A typical centrifugal fire pump operating at 83 psi, utilizing a three-inch diameter hose will deliver a stream of water at 265 gpm with a nozzle pressure of 50 psi. Sustained pumping for five hours requires a foot of water per quarter acre of pond (i.e. a quarter-acre foot of water) (4). On the other hand, if you are within reach of a municipal or town firefighting service, make sure to provide enough water storage capacity for four streams of water.
In this case, an acre-foot of water will be sufficient for most firefighting needs. Consult with your local agricultural official, your fire department, and a fire pump dealer to help you in the design and capacity requirements of your pond for both irrigation and fire protection.
End notes
(1) Henry David Thoreau, 1854, Walden,
(2) Ohio Department of Natural Resources, 2008 Ohio Pond Management – Wildlife Habitat Enhancement Around the Pond
(3) Slemming Brian, June 2006, "A Dip in the Pond," Landscape Trades, Volume 28, No. 5
(4) Soil Conservation Service, U.S. Department of Agriculture, 1971 Ponds For water Supply and Recreation, U.S. Government Printing Office, Washington, D.C.
(5) Rawhide Brand, Dry Hydrant System Fire Hose, Orrville, Ohio
B. Site selection and suitability
A successful pond is not simply a hole dug out in a wet area filled with water. The resulting body of water, if permanent, will become a complex biological and zoological system that ultimately becomes part of a surrounding watershed. Ponds are normally supplied with water from surface streams, sub-surface springs or general runoff sources, in order of priority for continuity of supply. Drainage areas that feed the proposed pond can possess a highly variable degree of runoff. Soil types and land management practices will affect runoff and influence water storage potential. In general, surface run-off is the poorest source of water for constructed ponds in that water quality is often unreliable, containing silt and excessive nutrients. If considering a dug pond ("an offline pond"), the chosen site should be above a floodplain and there should be some indication of the existing water table nearby (wet ground, sloughs, etc. If a bypass type pond ("an online pond"), there should be good indication of a suitable stream flow. Nearby forest cover along with additional trees and shrubs planted adjacent to the pond site will reduce siltation, helping to filter run-off. Surface water flowing through agricultural lands, golf courses, and other heavy-fertilized areas will carry dissolved fertilizer into a proposed pond.
Be careful not to dig a pond in a wetland thereby destroying a threatened part of our natural heritage. A wetland marsh is subject to periodic flooding, particularly if located near a river or lake, and its water level may be quite variable. In late summer it may dry out completely. Similarly, a swamp or wooded marsh will be unsuitable for a dug pond with excessive leaf fall adding to bottom sediments. Eventually such a pond will progress toward eutrofication and return to a swamp environment. Peatbogs and fens also should be avoided as they act as sponges, soaking up rainwater and snowmelt to slowly release water in drier seasons. Since these natural mechanisms filter water so efficiently and reduce downstream siltation, they should never be converted to ponds. In certain watersheds on small streams, constructed ponds can damage stream ecology by raising water temperatures downstream, affecting the sustainability of fish populations.
Good site conditions along with proper design and construction provide a successful, manageable pond. If fish are to be a consideration, the pond should be at least eight feet deep with banks at 3-to-1 slope. It is also advisable to create a pond one acre or larger in size for suitable habitat, oxygen, and spawning opportunities. Locations to avoid include those where runoff from barns or sewage systems could enter or influence the pond through ground water. The potential indicators for a good "offline pond" site include downslope wet corners of fields and areas supporting tell tale cattail growth, as long as the cattails are not extensive which would indicate an existing marsh ecosystem. To avoid major aquatic weed infestation, the pond should have a minimum depth of three feet to discourage the growth of most submergent and emergent weeds. If a bypass pond type is to be dug, water flowing into the pond should be pollution and sediment-free. If a pond is to be considered near to forest cover, or abutting a forest wall, leaf fall in autumn will be excessive and ultimately contribute to the accumulation leaf litter on the surface. The leaf litter trapped within the pond will sink to the bottom and contribute to the organic muck accumulation on the pond bottom.
Leave adequate space around the pond perimeter for landscaping and wildlife plantings. Depending on the function of the pond, site furnishings such as a shed to house a water supply system, an aerator, or tool storage should be considered at the site selection stage, since space for these may ultimately be required.
Also, pumps and aerators will most likely require access to electrical hookup, and a light fixture comes in handy inside a tool storage shed. Distance to electrical mains must be carefully considered for potential overload and appropriate gauge wire selected for the run. Typically, more elaborate landscape ponds require more infrastructure, such as gazebos, picnic shelters or a sauna facility as outdoor extensions to the rural home, all requiring suitable space around the pond.
Access
Lastly, access to the pond for future maintenance, enlarging, etc., must be planned for at the earliest stage of design. Failure to provide for, and maintain a route for heavy equipment access to the banks of the pond will likely result in a future restriction on maintenance. Drag-line dredges weigh in at more than 20 tons and carry up to 60-foot booms (some units have telescoping booms). The majority of the older units move on steel tracks, which will chew up an asphalt road, or sink well into boggy marshland. Many contractors have steel mats, which they lay down for the machine to run over in wet or soggy ground, or supply-used auto tires for the machine to run over on normal residential asphalted roads. It is much better to provide for and maintain a crude road on stable ground for this purpose. In most cases, the owner has landscaped the area accessing the pond, with a nice layer of managed turf. A drag line will chew it up beyond imagination, destroying years of growth and possibly plantings around the access. Plan for this carefully, as it is essential. Keep the right-of-way relatively clear of vegetation, as once overgrown it will require much effort to clear out again and may contravene your municipal tree bylaw, requiring a variance, or be prohibited entirely.
Liability
Site selection can involve the aspect of liability, since the failure of a structure through excessive storm water overtopping the banks, or a burst dam, could result in flooding an adjacent parcel and properties downstream. Research the utility services on the property both underground and overhead, which might preclude the installation of a pond, or be affected by an excavation. It is always imperative to build in an emergency spillway on any pond, either in the form of pipe system below the top of bank, or as a constructed, reinforced dip in the pond bank. The spillway choice is directed by the inflow rate, size and depth of the pond, but usually the reinforced dip in the pond bank is the most trustworthy avenue if erosion control methods are used to finish the spillway surface.
Topographic and soil type requirements
A suitable pond location should have level topography that will allow for economical construction, and soils with sufficient clay mixture to contain water. For economic reasons, the site should allow for the largest volume of water with the least amount of excavation or landfill (landfill in the case of a dammed pond). If the site is level, it will reduce the cost and effort of soil removal and disposal of excavated materials elsewhere.
A pond's bottom and dam structure must be composed of a soil mix which will minimize seepage. Clay soils are always the best for lining the pond, minimizing leakage. Most sites which contain gravel or sand, being naturally porous, will lose water through seepage. On the other hand, swampy soils become difficult to drain and require costly maintenance, often disrupting the original swampland in the process. Limestone and shale bedrock sites, exhibiting fractures and stratification, will naturally leak. If a dam is required or simple impoundment, the maximum height should be no more than 20 to 25 feet. Any earth structure higher than this will be expensive to build, and exhibit thermal stratification due to its depth, unless a it has a good turnover with fresh water flowing in and out. Installation of a bottom draw structure, aiding in reducing thermal stratification will also be expensive. Dams or impoundments should be high enough, however, to accumulate a depth of six feet of water and maintain that level.
Ponds are frequently located in valleys or depressions, which have the capability to store water during a heavy rainfall or in the spring runoff, but cannot sustain it. These eventually dry up in hot weather months or often shrink to a boggy, smelly, low water level, clogged with weeds. Becoming unsightly, they are discouraging to the landowner who invested his time and money into the venture.
Water supply requirements
A water supply sufficient enough to fill the pond rapidly is important to maintain a relatively constant level over the year. A supply that overflows and flushes nutrients out of the pond is not as desirable as it might seem, also allowing fish to escape. Although prohibited by most stream regulatory authorities, impounded small streams were often satisfactory sources, but due to flooding, silt load, and the blocking of fish migration, they are generally no longer permitted. In addition, their tendency to increase stream temperature downstream quite offsets their advantages. A wiser alternative is the construction of a bypass pond (or "on-line pond") adjacent to the stream with inlet and outlets (screened or closed as necessary) leading to the stream body. This provides some measure of control over silting and flooding, while maintaining fish migration in the stream proper. It still permits a warm water increase to the stream or creek body, which is undesirable, although this can be controlled by closing outlet and inlet pipes, and re-opening the inlet pipe if water levels drop in the pond. The pond then becomes essentially a dugout pond within the flood plain.
The most common water source is surface runoff resulting from rainwater flow or seepage. In Virginia, for instance, pond owners require approximately two to three acres of land for each acre-foot of pond (a pond with a surface of one acre one foot deep). In Kansas the requirement increases from 20 to 50 acres of land for each acre foot. The characteristics determining the adequacy of the drainage area vary according to relief, soil infiltration, vegetative cover and existing surface storage. Storm characteristics must also be considered, relative to the amount, intensity, and duration of rainfall, which also affect water yield. Tables are available for all of these parameters and adjustments must be made for local conditions (rainfall intensity and runoff curves). Soil types such as sandy soil types in the drainage area will reduce the effective pond supply drastically.
Springs, wells, and ground water are the best sources if a landowner is lucky to have them. Aquatic life is usually best sustained in ground water, often containing just enough of the required nutrients. Some well waters contain excessive amounts of carbon dioxide or nitrogen and must be oxygenated before using (through aeration). Many ground water sources contain an over-abundance of harmful minerals dangerous to fish and aquatic animals. It pays to have your water sources analyzed first before construction of a pond to promote a healthy aquatic environment.
Storage capacity estimate for larger ponds
In order to guarantee that the proposed pond will have sufficient capacity for storage events (heavy rainfall, storms), a calculation should be undertaken by a professional (your local conservation authority may offer this service, or you may require the services of an engineer, landscape architect, or hydrogeologist). The calculation will determine the peak discharge (Q) in cubic feet per second (or cubic metres per second) for the watershed containing the pond site. Basically, an air photo and topographic map are combined to define the overall watershed limit, the contours establishing the average slope and the overland flow distance that water takes to travel from the height of land to the proposed pond site. A final check of field conditions should be undertaken to discover any new uncharted avenues for loss of runoff, and also to determine the vegetation type along with management practices in the watershed.
These parameters are used to determine the runoff coefficient (i). Once the watershed boundary is ascertained, the area (A) of the watershed can be calculated.
The rainfall intensity parameter (C) in the calculation is the most difficult to obtain, found from intensity/duration/ frequency curves produced for your geographical region.
The storm frequency must be decided upon but it is usually taken as a 100-year "design" storm event by most watershed authorities as "the largest storm that will occur in 100 years." The following equation, known as the "Rational Equation" or "Mannings formula" can be used to determine the peak discharge (Q) over a specific duration storm:
Q = CiA
Several, more complex formulas which refine the runoff coefficient (i), and the rainfall intensity factor (C), are available, but in general the calculation is best researched by a professional to suit your site conditions, and should preclude the design of dam structures or emergency spillways for larger pond and lake designs. A good web page reference for these formulae is http://www.sewrpc.org/rainfallfrequency.
End notes
1. Ohio Pond Management, Ohio state University, Bulletin 374-99, Extension Services Ohio State University Extension
2. Soil Conservation Service, U.S. Department of Agriculture, 1971, Ponds for Water Supply and Recreation, U.S. Government Printing Office, Washington D.C.
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