It seems like an exercise in frustration to dig an enormous hole when there’s no water to fill it with, right? After all, if there was enough water to do that, the reservoir wouldn’t even be necessary. Today, though, that water can be hard to come by and the reservoir is necessary. Fortunately, there are other sources of water, even in dry areas, and even during drought. Collecting it is mostly an issue of being creative and making your preparations in advance.
When traditional surface and groundwater sources can’t be stretched or are off-limits, water for irrigation reservoirs comes primarily from captured stormwater and recycled irrigation water, supplemented by certain non-traditional sources like reclaimed municipal water.
Stormwater
Precipitation rarely falls exactly when and where we need it. It may come in the winter but completely disappear for the late spring and summer growing seasons. Or when it does come, it may dump several months’ worth of water in a monsoon-like 3-day storm. Neither of those scenarios are particularly helpful to farmers whose crops rely on consistent moisture for an abundant harvest.
Fortunately, significant rain events do occur, even during extended droughts. The problem is that most water tends to be wasted during big storms since parched ground cannot absorb large amounts of water quickly. With nowhere to go, most of the rain simply travels along the surface of the soil, leading to excessive runoff, flooding, damaging erosion, and mudslides. Worse, sediment picked up by fast-moving stormwater is carried into waterways and ponds within the watershed, triggering a catastrophic plunge in water quality downstream. This kind of deluge isn’t ideal, but it can be a welcome blessing for the well-prepared farmer. Whether you’re faced with plentiful rain in the wrong season, or the unpredictable arrival of an atmospheric river, the key is to be prepared so you can capture rainfall quickly and efficiently, minimize any potential damage to your fields, and store it safely until you’re ready to use it. A stormwater management system, consisting of a series of ditches and berms should be installed in any case, to minimize damage from erosion. These ditches can direct accumulated water to one or more retention ponds, where it can drop collected sediment, before being released into the storage reservoir.
Even in areas where rainfall is abundant, intermittent dry periods during summer may push down yields. Capturing and saving precipitation throughout the course of a year can give you enough surplus that you can carry your crop through a few weeks of July heat, making the difference between a good crop and a bumper crop.
Collecting Tailwater
Sedimentation Ponds
Tailwater is irrigation runoff, or water that’s been applied to crops but hasn’t been absorbed by the soil. In this type of system, tailwater is directed to ditches or pipes along the edges as it flows off the field, which typically routes it to a sedimentation pond. In this model, the sedimentation pond may be as simple as an enlarged drainage ditch. The captured runoff remains in the “pond” for a limited period (ideally up to 3 days) where, as it sits, suspended particles like sand, clay, and bits of organic matter slowly settle to the bottom. Once sediment has finished settling, the water can be returned directly to the irrigation system or moved to a longer-term storage reservoir. Deposits in the sedimentation pond are rich in decayed organic matter and plant nutrients, so they’re regularly removed and returned to the fields. With a two-pond setup, it’s a simple matter to periodically allow the small pond to dry so that accumulated sediment can be easily removed.
This simple system offers several important benefits:
More Efficient Use of Water
Use of a tailwater recovery system can significantly improve irrigation efficiency since almost all water that drains off the field is saved to be reapplied. Lower-efficiency irrigation methods such as high-pressure water cannons and impact sprinklers deliver large amounts of water with very little precision and farmers may be forced to apply too much water in order to ensure that all areas get enough. A certain amount of excess water inevitably runs off the field and is lost as waste without a recovery system.
Recaptured Nutrients
Soil loss associated with erosion is an expensive problem for farmers, but the practice of directing irrigation runoff and collecting sediment in a settlement pond allows that soil to be replenished, along with valuable nutrients.
Reducing Nonpoint Source Pollution
Nonpoint source pollution originates from a variety of locations and sources and can’t be traced back to a single point. Irrigation and farm runoff, municipal stormwater, and air pollution are all sources of excess nutrients, chemicals, salts, toxins, and other hazardous substances that can damage the environment. When farmers can prevent irrigation tailwater from escaping into the environment by capturing and reusing it, it protects local waterways and benefits the entire ecosystem.
This same system can be used to capture stormwater from other locations around the farm as well. If this is the intent, it may be wise to construct an additional large sedimentation pond that can handle overflow from the first, since storms may bring considerably more water than the typical small pond (or glorified ditch) is designed to handle.
Tiled Systems
Widely used in some regions of the Midwest, tiled drainage systems are installed where the natural drainage capability of farmland is limited, leaving cultivated fields vulnerable to waterlogging. In these cases, connected lengths of perforated tubing or pipe are buried several feet below ground along a slight grade leading off the field. Excess water in the field drips or flows into the drainage tubes and is removed by force of gravity. Some farmers already use water from their drainage tiles to supplement irrigation, but there’s room for much broader use of this type of system. Since drainage tiles are already in use in those regions, the limiting factor is as simple as constructing a storage reservoir for irrigation.
Non-Traditional Water Sources
In the last few decades, increasing demand from growing urban centers have seen water allowances transferred from agricultural activities to municipal uses. This has already triggered some farmers to consider innovative solutions for a shrinking water supply. One example is reclaimed water, or wastewater that has been filtered and treated, but not to drinking water standards. Desalinated brackish water is another possible source, although desalination techniques are expensive and require a lot of power. Currently, this isn’t a cost-effective solution, but it’s possible that rising water prices combined with improved technology may someday make this a viable option. In the meantime, scientists work on developing salt-resistant crops that can tolerate brackish water.
There are some special considerations to remember as farmers consider using more and more novel water sources. Using reclaimed water to irrigate food crops is one point of concern, since those crops may take up contaminants commonly found in wastewater through their roots, ranging from pharmaceuticals to heavy metals. Nonetheless, these are important options to investigate. As treatment processes and standards are established, these may prove to be important to achieving resiliency in irrigated agriculture.
