Farm Ponds: Strategies for Multiple Functions
By Ben Falk
Ponds have been a part of the working landscape since agriculture emerged. Since water is the basis of productive biological systems, retaining and distributing this storehouse of fertility and life within a landscape is key to the success of any operation.
The climate, topography, soils, and access to machinery and cheap energy (for now) in the Northeastern U.S. offer us particularly timely opportunities to capture, store and distribute water via ponds on farms.
Ponds in this climate can be cropped for a variety of outputs, most established of which are fish – especially trout. However, many other fish can be cultivated in this climate at least in a modest scale including perch, bluegill, bass and others. Shallow-water systems such as paddies, of course, have their own unique uses including for brown rice and likely a host of other crops that will emerge with continued innovation in the coming decades.
Ponds have many uses beyond what can actually be produced inside of them, however, and it is these uses that make them an especially attractive working landscape feature.
• Microclimate enhancement: water bodies capture and store solar energy and release this heat slowly, especially in the autumn, to the adjacent area. In our testing on the Whole Systems Design Research Farm in Vermont, this affect varies from year to year with the severity of the fall’s first frost. Our three ponds will often not buffer against frost if the first freeze is about 27 degrees F or less, yet will extend the growing season by weeks if the first frost in the fall is a mild one, which is usually the case.
• Wildlife: There’s perhaps nothing we can do to more quickly enhance the biodiversity of species in our landscapes than by creating water bodies. In addition, amphibians are in need of particularly strong support given the decline in health of their populations in recent years. Ponds with large wetland edges are ideal – and often rarely-found habitats – in many areas of the Northeast. Each time we’ve built a pond at least three species of frog and two species of salamander arrive on site within weeks. The values ponds offer for beneficial insects, birds and mammals can also be observed in short order.
• Storage for Distribution: Large water storage is invaluable for fire control and irrigation as well as for drought-proofing a landscape over time. It takes two to three days or less to make a pond that can hold 100,000 gallons or more making it the most economical means of storing large quantities of water. Farms with a need for irrigation often recognize the opportunity to gravity feed such water via a supply located high in the landscape such that its water can be fed to the entire farm. without pumps or electricity. Capturing surface water from as many acres as possible is important for farms wishing to be adaptive to shifting climate conditions and the adverse affects of drought punctuated by intense rain events. A well-sited and properly integrated pond can be the most crucial “shock absorber” farms have to large precipitation fluctuations. Ponds in this capacity serve like batteries, storing excess energy (water) when it is abundant such that it can be distributed slowly over long period of time (drought).
• Other: Recreation, food storage, and increasing radiative light for crops and building interiors are several other important side benefits of well-integrated ponds which demand more space than possible here to discuss but are worth mentioning.
Siting and Connectivity
In my site design and land development work I see poorly located ponds across the Northeast – an all too common, expensive, destructive, but avoidable mistakes. Often ponds are located too high for them to capture enough water or are not properly integrated with surrounding (uphill) landscape via swales and ditches to actually perform the work of capturing water from as many acres as possible in a given location.
Other commons mistakes are ponds built on ledge (that often leak into the bedrock) and pond berms that are too steep to be stable (berms need to be 1:3 or less in slope). The most important step in determining pond site feasibility aside from locating and topographical/grade assessment is the digging of a test pit to at least 7’ of depth, ideally deeper, to determine water table depth and native material composition. A high water table with a high clay-content soil is ideal. While not always possible, it is optimal to observe the test hole for a year to understand the water table fluctuations across the seasons to understand how the pond will behave.
Ponds can be made on well-drained soil locations but they are expensive due to importing clay or a poly-based liner. We have constructed ponds on sandy soil using both liners and clay with success, but this adds 25-40% of cost to the construction. Recommended liner types are EPDM (rubber-based) for small ponds and polyethylene for larger ponds. If using clay to line a pond it must be put down in “runs” of no more than 6” and at a proper moisture content with the cleanup bucket of an excavator, and compacted carefully while building up the clay blanket to a depth of about 12” or more for a pond depth of 10 feet.
Form and Management
A multifunctional pond can only perform as such by providing its inhabitants with the resources they need via the structure of the pond, physically, and the food provided ecologically. In other words, we want to develop an ecosystem that can feed itself, where the highest members (fish, birds and people) of the food chain are naturally fed by the lower trophic levels which are supported by the ponds features, from boulders to its shape below waterline. The most direct ways to do this are by creating significant edge via boulder placements and a scalloped perimeter and by ensuring large areas of shallow water at the edge. These wetland edges and “planting shelves” are the biological engine of a pond and also greatly aid water quality by providing aeration via plants. They are also crucial nursery zones for fish. While making ponds with such features adds time and cost to construction, the values of such design make the pond more economical in the long run, not to mention more beautiful. Avoiding the temptation to push boulders over the nearest bank and instead place them at the waterline and just below, along with avoiding the bathtub/steep walls on all sides approach are the two most oft-made mistakes we address with excavators and landowners before construction.
To become valuable ecological habitats as quickly as possible, ponds need to be seeded with a wide diversity of both deep-water, marginal (wetland) and terrestrial plants immediately after construction and at least once, during the spring, in the years following construction.
We have found it most effective to buy a bulk supply of wetland seed mix (or collect seed from local wetlands and ponds), mix this seed with lime or sand as a carrier and then broadcast as the machines are leaving the site. Often this mix should be raked into the soil and then mulched with hay or straw for protection against rain events and to enhance germination rates.
The area above waterline and especially on the pond berm favor annual rye for quick stabilization in constructions happening after mid June, while earlier projects are preferred in that the soil can be “set” with cool season grasses and legumes such as red, white and alsike clover, all of which are especially valuable soil-builders, for bee-fodder and as slope stabilizers.
Management over time is more involved than the scope of this article permits but the following guidelines are basic ground rules for ecologically-enhancing multipurpose ponds:
• Don’t mow to the water’s edge. That’s the best way to wreck the most abundant wildlife habitat a pond offers. If you must make access via a mower do so in limited areas along its perimeter.
• Seed any bare areas that are not greened up every spring through early summer until there are none left – this can take 2-3 years or more depending on vigilance and weather.
• Keep a watchful eye on overflow spillways (recommended) and drainage fixtures/piped (not recommended) to prevent clogging and waterline rising to a dangerous point.
Ponds are one of the most important features we can install today to ensure a more productive, multifunctional and resilient landscape tomorrow. Well designed and constructed ponds can help farms become more fit for a future that is likely to bring with it adverse conditions including drought, flood, increased pest pressures, increased costs of inputs and other stresses which only highly resilient, low-input farms will handle successfully.
Ben Falk is the Design Director at Whole Systems Design based in Moretown, VT. He may be reached at 802-496-3128 or email@example.com