Farm Pond in Iowa. Photo copyright ©2014 by Iowa Public Radio.
Farm ponds have great potential to improve agricultural water security through the capture, storage, and provision of water for irrigation in all regions of California. Farm ponds can also supply a water source for frost protection, recharge groundwater, and provide a wide range of additional economic and environmental benefits.
Ponds can be filled by rainfall, as is common with farm and ranch ponds that are sited at a low point and serve to collect runoff from higher in the watershed. Alternatively, farm ponds can be filled with tailwater from irrigation, which can then be recycled. Ponds can also be filled by diverting water from streams at peak winter flows, offsetting water withdrawals during the dry season when higher instream flows are needed.
Ponds can recharge groundwater, which keeps more water in the system for longer, providing greater quantities for use in the watershed and allowing seepage into streams later into the summer. Devoting more land to ponds in valleys that are overdrafting groundwater would help minimize impacts and would contribute positively to overall watershed management.
Ponds can also be used to trap, filter, and store tailwater from irrigation. Sediment can be settled and returned to the fields; water can be re-used in subsequent irrigations, reducing the need to divert or pump more irrigation water. Pumping from a pond uses much less energy than pumping groundwater. A common approach is to construct a smaller sediment trap that then flows into a pond.
Ponds are common on farms and ranches, however the vast majority of ponds are currently constructed for fish farming, fire protection, stock watering, or simply landscape beautification. Their usefulness as irrigation and watershed management tools have not been sufficiently appreciated or exploited in the West, probably because farmers have largely been able to rely on organized irrigation districts and their reservoirs to store and deliver irrigation water. As water supplies become more uncertain in California, it will behoove farmers and water regulators to make more concerted efforts to institute on-farm ponds.
The regulatory context for constructing new farm ponds is currently challenging. A significant obstacle to using ponds to manage watersheds is the system of water rights. As the State Water Resources Control Board attempts to permit and regulate farm ponds, they are faced with dilemmas in trying to rearrange water rights to accommodate in-stream flows and fish. The Department of Fish and Game, the Environmental Protection Agency, and county governments also have jurisdiction and their own laws and rules that govern when and how such ponds can be filled. The cost and time involved in such permitting is often discouraging to the farmer.
The cost of constructing the pond can be an issue. A tailwater return pond can easily cost $20,000-$40,000 plus $1,000 a year to maintain, although the federal government (through NRCS) will often share the construction cost, and ponds provide a long-term offset for the cost of purchased water.
Another obstacle to creating more farm ponds in intensively farmed areas is simply the opportunity cost of removing land from production. In the Central Coast, for example, where land can rent for $2,000 per acre per year, and most of the land is not owned by the people farming it, this is a barrier. The recent rise of often irrational food safety concerns in such areas as the Salinas Valley has also slowed or reversed the creation of ponds, as frogs are associated with salmonella bacteria by some in the food industry.
Ponds can attract wildlife and increase populations of endangered species such as red-legged frogs or the San Francisco garter snake. However, the National Fish and Wildlife Service has developed “safe harbor” agreements that allow the development of such ponds and limit any subsequent Endangered Species Act consequences for the farmer.
Farm ponds can significantly offset growers’ and ranchers’ reliance on purchased water. One calculation in Pennsylvania showed that a 2-acre clay-lined pond with an average depth of 7 feet will provide roughly 10 acre-feet of irrigation water, accounting for loss to seepage and evaporation. For a vegetable crop that requires 4 inches of irrigation water, this 2-acre pond will irrigate 30 acres of crop. Click here for more detail on the calculation.
Ponds also present an opportunity to store water in ways that can have other beneficial effects on water supply for growers and ranchers. For example, seepage from ponds can recharge groundwater and help to offset pumping from groundwater basins. In this sense, ponds act to slow the flow of water through the basin, allowing more of it to be retained for use. In a clay soil-lined pond, seepage of only 500 gallons/day is considered excellent and 1,000 gallons/day good, so even in these cases the ponds will augment groundwater supplies throughout the year.
In the case of using ponds to maintain in-stream flow levels for anadromous fish, as in the Pine Gulch Creek case study, removing irrigation water from the stream in the winter provides more water for the environment in the summer. Though more total water would have to be withdrawn for agriculture due to seepage from the ponds (though this would be returned to groundwater flows) and evaporation from the ponds (which reportedly averages 6 inches a month during the summer in this region) than would be the case if the water were pumped as needed for irrigation directly from the stream to the fields, the added water is essentially going to sustain fish (salmonid spawning).
The greatest water savings associated with ponds can be realized by constructing tailwater return flow ponds. By capturing tailwater in a pond and allowing sediment and contaminants to settle out, the pond provides the dual benefit of recycling irrigation water while also recharging groundwater. This approach is carried to an extreme in the Red Rock Ranch case study where on-farm drainage management in the southern San Joaquin Valley by John Diener reuses tailwater again and again through a series of ponds, applying the resulting water to ever more salt tolerant crops.
Ponds do not function well on sandy or other highly porous soils, but the many clay soils around California provide ample opportunity to employ this practice. Irrigation ponds can be effectively applied in both coastal and Central Valley agriculture. The use of ponds to simultaneously supply irrigation water and regulate streamflows for anadromous fish is being explored along the coast from Santa Cruz northwards. Tailwater recovery ponds are being implemented all around the state, especially in the Sacramento and San Joaquin Valleys.
The size of ponds, the water demands of the crop, and the acreage of irrigated land all determine the efficacy of ponds. While ponds can benefit all sizes of farms, they can have the greatest impact on smaller acreages of intensive crops.
Ponds can provide the following benefits in addition to the provision of irrigation water:
Ponds are commonly used on ranches for stock watering. Cattle and horses require 12-15 gallons of water per day. Rather than allow the stock to drink directly from the pond, a more environmentally friendly innovation is to fence the pond and use solar pumps to move water into troughs for the cattle.
Ponds are often used for frost protection, particularly on wine grapes. The use of water for this purpose typically ranges from 0.4-1.6 inches of water in a year.
Ponds can be managed to provide wildlife habitat. Although any pond will attract waterfowl, a number of RCDs, Audubon California, and other organizations have been working with farmers to plant native habitat around farm ponds. Researchers are also exploring the use of such ponds to re-introduce native fish species, for example an effort to raise threatened Sacramento perch in Yolo and Solano counties.
Ponds constructed primarily for fish production, typically at least a half-acre in size and a minimum depth of 8 feet, can yield 100-300 pounds of fish per year for each acre of water surface.
Ponds can assist in flood control by capturing and slowing the flow of water through a watershed. Particularly as climate change leads to greater storm flows, a distributed network of ponds could play an important role in attenuating peak flows and reducing flooding.
Ponds help recharge groundwater. Whether filled with water diverted from a stream or with tailwater from irrigation, clay-lined ponds seep water into the ground at highly variable rates (anywhere from 500-10,000 gallons/day depending on size and construction), but typical seepage loss from a well-sealed pond is estimated at one foot of water per year. Every acre of pond would thus on average recharge groundwater with one acre foot—or 325,000 gallons—of water a year.
Storing water captured from rainfall or from tailwater in on-farm ponds can also reduce energy use by displacing pumped groundwater. Even if ponds are used to store pumped or delivered water, there can be a cost savings associated with energy. During the summer months when energy costs are the highest, having on-farm water storage also allows you to pump groundwater during the off-peak times (like at night) when electricity is cheapest and the electric grid is not constrained, rather than pumping during the most expensive and on-peak periods.
Ponds at least one acre-foot in size can serve as water sources for fire protection if they are sited in proximity to structures.
Ponds can be used to settle and filter farm runoff, capturing soil that can be returned to fields and filtering pollutants and particulates that would otherwise negatively impact the broader ecosystem.
A more localized and distributed water supply can offset water transported from distant reservoirs, reducing the energy needed for water conveyance.
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