Traditional irrigation systems that apply wastewater and freshwater are designed to provide supplemental water to a growing crop when it is most opportune for the crop. This is not the purpose of the sprinkler Vegetative Treatment System (VTS).
Design principles between a sprinkler vegetative treatment area (VTA) and a conventional irrigation system are the same (pressures, friction loss, etc.). However, there are a few additional criteria to consider in the design of a sprinkler VTA that would not be applicable to a conventional system. First, the system must have the ability to operate at near-freezing temperatures (in cold climates) and be easy to drain between uses. Second, the distribution system must be able to operate when the soil is at or near field capacity. Solid set and K-line irrigation systems have this capability. While operation under such circumstances is not desirable, extended wet periods can make this necessary. Next, the system must have the ability to distribute the runoff from the production area in a short period of time yet not at a rate that will generate runoff. We try to design our systems so that they can be empty from a 25-year, 24-hour storm in less than 48 hours (this is our self-imposed criteria). In addition, the VTA is sized to uptake the nitrogen generated and to store the liquid in the root zone.
The system must also be able to withstand the corrosive effects of being in contact with manure. Equipment made of galvanized steel, for example, will deteriorate over time from use only with feedlot runoff. A conventional system applying wastewater and freshwater will not deteriorate since components are flushed out with clean water. We make sure the pumps, pipes, and sprinklers can withstand exposure. Our risers are galvanized and will need to be replaced periodically. However, the cost of replacement for those items is far less than a small pivot (one reason a pivot is not used in our systems).
Author: Chris Henry, Biological Systems Engineering, University of Nebraska
