Building an irrigation pond isn’t a casual, spur-of-the moment undertaking. Depending on the size of the reservoir, excavation costs alone can range from significant on upwards. Permitting requirements may be expensive in your area as well. So, there are some valuable things to consider before you sign on the dotted line.
- Is a cheaper source of irrigation water available? If you have access to an underground aquifer that’s not severely depleted where you can sink a well at a reasonable depth, that may prove to be a cheaper option. Of course, groundwater depletion is a problem across most of the US now and your most expensive option would be to dig a well only to have it run dry in short order or be forced to re-dig it, and then re-dig it again as the aquifer is depleted.
- Is there an existing farm pond that could be adapted for irrigation? If you have one that’s conveniently located and large enough for your purposes, that’s a great way to save a chunk of money. Even if the pond has dried up, it’s comparatively cheap to clear out and prep the area and line it with an impermeable geomembrane. It can be just that simple.
- Is there a suitable reservoir site close to the field? If you don’t already have a suitable hole in the ground, you’ll need to dig one. Additionally, you still need to make sure it’s a good site. You’ll need level ground, preferably in an area that’s not full of rocks or sharp stones and that’s not close to any trees where root incursion may become a (significant!) problem.
- What is the irrigation method? Irrigation methods that can draw from surface water will draw from an irrigation reservoir just as easily. If you’re using a high energy sprinkler system, you’ll need to use high powered pumps to generate the necessary pressure, but at least you won’t have to pull it up from 400’ underground.
- What is the estimated amount of runoff and subsurface drainage that could be harvested, and how many cropland acres can be irrigated by this amount of water? If your soil type is dense, full of clay, or otherwise tends to runoff fairly quickly, you’re likely able to set up a collection system from a relatively small area of watershed. Soils that are sandy or drain very efficiently could make the concept of an irrigation reservoir impractical.
- What is the value of the land that will be used for water storage? If you’re looking at a 30% yield increase by having a steady supply of irrigation water, it may make it worthwhile to devote some fraction land to storing that water. On the other hand, it doesn’t make sense to take highly valuable land out of service without a clear and substantial return. Make sure that you’re not taking land out that is worth more in production than you’d be paying for an alternative source of water.
Irrigation reservoirs are critical improvements for farmers who operate in areas where water availability is inconsistent or where periodic droughts can damage valuable plants or productive capacity. Reservoirs allow farmers to collect and save water during times of plenty and then to release it when needed.
- To calculate the capacity of your reservoir, it’s useful to plan for a worst-case scenario - how much water would you need to irrigate during an extended drought. It’s probably not realistic to store water for a complete multi-year drought, but it is important to take a fresh look at local climate and weather trends and base your estimates on the most current data. Climate changes mean that trends calculated based on data from 50 years ago simply aren't useful any longer.
- Reservoirs should be designed to manage sediment and contaminants, especially if you’re collecting and reusing tailwater, but even when that’s not the case. Runoff water has plenty of opportunity to pick up contaminants, and one of the best methods for managing that is to design an artificial wetland and settlement pond. Riparian plantings will slow the flow of incoming water, permitting any sediment load to settle out. The natural filtering action of riparian and wetland plants are also effective at removing contaminants like excess nutrients, pesticides and other chemicals.
- It’s important to monitor water in your irrigation reservoir regularly and test for water quality or contaminants. If values are out of the acceptable range, water may need to be treated before use.
There are a variety of state and federal programs that offer technical support and even financial assistance for infrastructure improvements like irrigation reservoirs. These may require time to get set up but could be well worth the effort.
