News Guest Column
Guest column: Material matters: Water quality performance

When designing a conservation drainage practice, did you know that you can improve its water quality performance by picking a certain pipe material?

Saturated buffers, woodchip denitrifying bioreactors and phosphorus removal structures are conservation drainage practices aimed at reducing nutrient concentration in subsurface drainage discharge. One way to improve the performance of these practices is to treat a higher volume of drainage water by picking a certain pipe material.

To explain which pipe material improves the performance of conservation drainage practices, let us start with an example that resembles water entry into the pipe. Imagine fans entering a football stadium with only one entrance gate. Because there is only one gate, the fans must stand in long lines and enter the stadium very slowly. If that stadium had 10 entrance gates, the fans would be able to enter the stadium much quicker. In this example, the stadium resembles the pipe, the entrance gates resemble the pipe openings, and the fans resemble water entering the pipe. The higher number of stadium gates (that is, the number of pipe openings) allows for faster entry of fans (that is, water) into the stadium (that is, the pipe). The same example applies to when water exits the pipe; the higher number of stadium gates allows for faster exiting of fans out of the stadium.

The message from the above example is that a pipe with a greater subdivision of openings (that is, a higher number of stadium gates) allows for faster water movement into and out of the pipe. Suppose you have two pipes with equal water inlet area per foot. In that case, the pipe with a greater number of smaller openings allows faster water movement into and out of the pipe than the pipe with fewer number of larger openings. Now that we know the importance of greater subdivision of openings, how do we pick a pipe with faster water movement into and out of the pipe?

Tip: The easiest way to choose the pipe with the quickest water movement into and out of a pipe is to go for an eight-row pipe rather than a four-row pipe. An even faster option is a sock-wrapped pipe that allows quicker water movement than an eight-row pipe.

A sock-wrapped pipe resembles a football stadium without any walls, and the entire boundary of the stadium is open for entry or exit. The fans can enter or exit the stadium without delay. This is because the sock-wrapped pipe has the maximum subdivision of openings. Consequently, a knitted-sock envelope maximizes water movement into and out of the pipe because it functions as a completely open conduit without walls, like mole drains. As a result, the sock-wrapped pipe allows faster water movement into and out of the pipe than an eight-row pipe.

In a saturated buffer, woodchip bioreactor, and phosphorus removal structure, drainage water exists the pipe and enters a porous media. Water needs to re-enter the pipe after being treated in the bioreactor and P-structure. If the designer of the conservation drainage practice wants to improve its performance, they should use either an eight-row pipe or a sock-wrapped pipe to treat a higher volume of drainage water.

For more information about pipe materials, visit MSU Drainage Website (https://www.egr.msu.edu/bae/water/drainage/choice-pipe-material).