A “smart pond” can be defined as a pond with recreational and aesthetic attributes that are balanced against the potential for adverse impacts to a specific ecosystem, watershed, or connected water resource. Every intended purpose of the pond—such as recreation, stormwater management, or wildlife habitat—must be taken into account in establishing a proper balance and must not negatively affect natural habitats or ecosystems, water quality, drainage patterns, or fish passage. Achieving this balance often requires an interdisciplinary approach in design and maintenance that may call on the expertise of limnologists, hydrologists, biologists, engineers, landscape architects, herpetologists, geologists, and land planners.
Ponds serve municipalities in a variety of ways. They are a recreational resource, they enhance the aesthetics of the area, provide habitat for fish and wildlife, furnish flood control measures and stormwater detention, and preserve water quality. Aside from their inherent qualities, they also increase the value of the properties around them and, in areas without municipal water service, they are sometimes maintained specifically for fire protection.
Ponds, however, are often beset by an array of problems that municipalities may find difficult to deal with and costly to remedy. Among the most common problems are: excessive algae growth; invasive plant growth; poor water quality, including temperature variations, clarity issues, odor, and detrimental pH levels; sedimentation and loss of depth; eutrophication; access and safety; water supply and the need for conservation; mosquito control; and costly maintenance.
WHAT DETERMINES A SMART POND?
Using as a reference ponds that are less than 5 acres in surface area, there should be about 1½ to 2 acres of watershed adjacent to the pond for each acre-foot of pond storage. A watershed of woodlands and meadows is ideal with respect to minimizing run-off and erosion and maintaining the health of a pond.
The quality of the buffer area can be critical to the maintenance of a pond. A woodland area, particularly one consisting of evergreens and deciduous trees, is best, since there would be reduced leaf litter and shade at various times of the day and year. Also important are the area and width of the buffer and the topography and bank slopes. If, for example, vegetation is sparse, there is likely to be more erosion, which contributes to the sediment loading of the pond. Easy public access that allows people to walk right up to the edge of the pond may lead to serious erosion around the perimeter of the pond.
A pond should have a minimum depth of 6 to 7 feet, an irregular shape, and rounded edges, which optimize water flow and eliminate the formation of stagnant pockets that can create water quality problems. The source of the water also contributes significantly to the health of a pond. The water supply systems in some regions contain additives to protect pipe systems, which may foster algae growth.
RATE OF FLOW AND CONTAINMENT
The rate of flow and containment can affect not only a pond but other bodies of water as well. Ponds should be designed to turn over 8 to 12 times annually, while the maximum seepage loss should be no more than 3 inches per year. Since containment is essential, it is important to know where the water is going. Is it evaporating, or seeping into the ground? When building or establishing a pond, the aim is to be within a foot or two of groundwater for natural containment.
The ability to regulate inflow and outflow is critical. Downstream flow should be maintained during construction within an existing watercourse, and all sediment and other debris must be contained so that other bodies of water downstream are not affected. Within the pond itself, it is best to allow the vertical transfer of water and to establish main points of inflow and outflow at opposite sides of the pond. If there is runoff into a pond and the pond is designed as a catchment or sedimentation basin, the water should be flowing through at a rate that is low enough to allow the sediment to be retained.
Possible upstream and downstream impacts cannot be ignored. The designer must know the flood storage capacity of the pond and how sediment is being controlled. If a pond is being built in a park or on a golf course where fertilizer may be used, a decision must be made on application rates within the watershed, containment, and what might be done to absorb excess nutrients. For stormwater flows from developed sites, most municipalities have established a goal of 80% as the standard for removing suspended sediments. This practice requires ongoing maintenance to assure that constructed measures are functioning as designed.
MANAGEMENT AND RESTORATION
No matter how well-designed and constructed a small pond is, it must be well-maintained if it is to remain healthy. Numerous management and restoration techniques are available, and each has its advantages and disadvantages. The following were adapted from “Ponds in Connecticut, A Guide to Planning, Design, and Management,” by the State of Connecticut Department of Environmental Protection.
Nutrient removal—This entails the application of alum to remove phosphorus, silt, and suspended particulates. Alum has less toxicity than most algaecides and a longer period of effectiveness, but it is difficult to calculate the proper dose, it has diminished effectiveness on sites with algae, and its benefits are short-lived for shallow ponds that turn over quickly.
Dyes—Dyes limit the light entering the water column and the bottom of the pond. They are organic and are easy to use. However, the use of dyes may be restricted where there is an overflow from the pond, and their effectiveness is limited in shallow ponds.
Cutting/harvesting—The machine removal of plant growth from the bottom of the pond can sometimes be useful for large ponds. There are few restrictions and the potential for algae growth is reduced. Cutting/harvesting, however, is labor-intensive for large areas, and multiple cuttings a year are sometimes required. This practice is also disruptive to wildlife, fragmentation may cause increased growth, and it is ineffective on floating plants and filamentous algae.
Mechanical raking—This operation, which removes vegetation and unconsolidated bottom material, is similar to removing the weeds from a lawn. One raking each year is usually sufficient and has a more long-term benefit than cutting/harvesting but is higher in cost. While raking removes rooted plants and limits disturbance to the pond edge, it disrupts fish and wildlife and has a negative, though short-term, impact on water clarity. It may also cause damage to a pond liner if the liner is not protected.
Herbicides/algaecides—The application of chemicals to control weeds and algae is effective, easy to use, and relatively inexpensive. Controlling the doses may, however, be difficult, it may conflict with other water uses, the release of nutrients may result in increased growth of algae, it is potentially toxic to nontargets species, and applications must be repeated regularly. Environmental regulations may also prohibit the use of some chemicals.
Overwinter drawdown—Lowering and raising water controls vascular plants. Drawdown and winter cold-weather exposure effectively freezes and dries plants. This is easy to implement if elevation control measures are designed properly, it is not costly, and the exposed base allows for annual or biennial cleanup or dry-dredging. On the negative side, this practice is effective only on certain plants, prohibits use of the pond in winter, and has an impact on fish and wildlife.
Benthic weed barriers—Synthetic coverings are used to control rooted plants through compression and light restriction. Barriers are highly effective on submerged rooted plants, and have a long useful life. However, barriers require extensive maintenance, are costly over large areas, and alter habitat for fish and wildlife.
Dredging—Dredging removes accumulated sediment from the bottom and is the only method of adding depth and volume to the pond while controlling vegetation, removing nutrients and pollutants, and restoring habitat. It is effective in the long term, but is often costly to design and implement. Careful planning with regard to dewatering and sediment analysis and disposal is critical to the success of the project. Also, a great deal of sediment is likely to be disturbed with possible effects on water quality downstream.
Aeration—Oxygenation with increased water circulation is one of the few non-chemical techniques for controlling algae while benefiting the fish population. However, operation and maintenance costs may be high, it is not effective on vascular plants, and can often yield unpredictable results.
Biomanipulation—This is a simple technique using plant material to absorb some of the nutrients in the water body. It is a nonchemical treatment that may be effective for many years, but the results are uncertain and other ecosystem components might be adversely affected. The technique requires removal of the plant material that has absorbed excess nutrients in the pond.
Grass carp introduction—The use of sterile carp to consume vascular plants is easy to implement, has a relatively low cost, and may provide several years of benefit. However, the carp may consume desirable plants while having little effect on some nuisance plants. Also, feces may promote algae growth through increased nutrient loading.
KEY STEPS TO A HEALTHY POND
The key to constructing a healthy pond begins with a thorough preconstruction site evaluation. The design must protect existing wetlands, preserve wildlife, provide low-impact dewatering systems, provide for sediment control, balance water source volume and outflow rate, and conserve water. All mechanical needs, such as drainage and aeration should be identified and installed, and measures to sustain optimum depth and temperature must be designed and installed. Finally, all watershed activity should be monitored following construction.
There is no one-model approach to designing, constructing, or maintaining a pond since it is virtually impossible to create a system that will serve all purposes. Achieving a balance in uses, however, is possible providing care is taken at the outset to determine the source of the problem and the restoration techniques best suited to the remedy.
— Gary Sorge, ASLA, is a senior associate with Vollmer Associates, Hamden, Conn.
Too much of a good thing?
Damage to the health of a pond is most often the result of eutrophication, which is an excess of nutrients and a lack of oxygen in the water. Eutrophication is a derivative of human activity that accelerates biological production and sets off a chain of events. The increased biological production results in nutrient loading, which causes accelerated plant growth. As the plants die, they remain in the water and decay, depleting the oxygen and adding to the organic matter at the base of the pond. Fish die for lack of oxygen. As the pond gets shallower, the decreased volume results in warmer water temperature, which also contributes water quality degradation and the ability of the pond to sustain wildlife.
There are, of course, ways to interrupt the cycle or diminish its effects. These include: maintaining a proper balance between wildlife, plant life, and nutrients; designing the pond to make it easy to maintain (controlling elevation, temperature, rate of flow); protecting vegetative buffers; maintaining an adequate depth; and aerating the pond to increase oxygen levels and support aquatic life.