Pipe Type and Performance Summary
Research Published: 2022
Over the years, the agricultural drainage industry has made efforts to analyze, calculate, and compare aspects of tile systems using equations, models, and experiments to better understand what’s going on beneath the ground. Michigan State University published two studies (Ghane 2022, Ghane et al. 2022) that dive into the details of how easy it is for water to get into corrugated pipes with various perforation sizes, patterns, and the use of a sock filter. By integrating the results of the studies into the equations we’ve been using for years, we can better compare performance of various pipe types.
The Takeaway
The seemingly large difference in drainage rate between the pipe types has a fairly minimal impact on system performance in practice. What might be ideal spacing in one soil type could be vastly insufficient in another soil type within the same field, no matter the pipe type. However, more data and details from experiments like this help us improve designs and management of drainage systems. A better understanding of performance also highlights the need to ensure all aspects of a drainage system (soil type, Drainage Coefficient, lateral spacing, perforation style, lateral size & slope, mainline size & slope, and outlet) are in sync with each other so any one of them doesn’t drastically limit the performance of the entire system.
The Site & Testing
The researchers focused in on quantifying how easy it is for water to get into the pipe with various popular perforation patterns – standard perforations (PF), narrow slot (NS), and knit sock. To do this, a short section of each pipe type (from all the major North American pipe manufacturers) was tested in a 43” wide by 40” tall by 20” deep container. The 20” long pipe sections were buried in sand, which water moves through well, so measurements could be taken easily. The container was filled with water and flow measurements were taken from the drain pipe after flow stabilized over 24 hours.
The measured flow from the pipe matched up with what was predicted from theoretical equations. This information was then input into field-scale equations and models that predict ideal lateral spacing, water table movement, and potential crop yield.
The Results
Socked pipe acted as a nearly completely permeable conduit (similar to the outside diameter of the pipe) in the sand; the other perforation types had much lower equivalent completely permeable conduit sizes. This is how ‘ease of water inflow’ is accounted for in the lateral spacing calculations.
The large difference in pipe permeability results in about a 10-20% difference in drainage rate and ideal lateral spacing. For example, if a system had an ideal spacing of 55-ft with NS pipe, socked pipe could be spaced at about 60-ft with similar effectiveness.
Here are some other key points and conclusions from the testing:
- Both sock and NS pipe are effective at keeping sediment out of pipe
- Performance depends more on number of perforations than the size (width) of the perforations
- Pipe with 8 perforations per valley (PPV) had a higher drainage rate than pipe with 4 PPV
- NS and PF performed similarly with the same number of perforations per valley
- Water Inlet Area doesn’t necessarily correlate to a higher drainage rate
Citation(s)
Ghane, E., 2022. Choice of pipe material influences drain spacing and system cost in subsurface drainage
design. Applied Engineering Agriculture, 38, 685–695. https://doi.org/10.13031/aea.15053.
Ghane, E, et al. 2022. Knitted-sock geotextile envelopes increase drain inflow in subsurface drainage systems.
Agricultural Water Management, Volume 274. https://doi.org/10.1016/j.agwat.2022.107939.