P2988

Slotted Inlet Pipes

Illustration of section and plan view showing how water enters a slotted inlet pipe, with sediment settling in the pipe while cleaner water flows from the pipe into the adjacent ditch. — Figure 1. A section view and plan view of slotted inlet pipe installation at the edge of a farm field.

Using a slotted inlet pipe (Natural Resources Conservation Service, or NRCS, conservation practice code 410) is a best management practice (BMP) that is implemented as a sunken pipe to enhance field drainage, while reducing gully erosion, soil loss from fields, and decreasing sediment loads in runoff.
Slotted inlet pipes are used on surface-drained acreage to minimize erosion in the primary ditch by preventing head cutting and directing water through a conveyance device with a fixed elevation.
A slotted inlet pipe controls drainage to reduce erosion and allows sediment to accumulate behind pipes and holds it in the field.

A ditch with a horizontal pipe coming out from the ground on the right.

Close-up of a large slotted inlet pipe opening installed at the edge of a crop field. — Figure 2. The top image shows the outflow of a slotted inlet pipe where it exits through an earthen berm or pad and discharges into a drainage ditch. The bottom image shows the slotted pipe intake installed at the edge of a crop field to receive runoff.

A line graph showing how sediment builds up in front of a slotted inlet pipe over time. The graph has a curved line starting near the bottom‑left and rising gently, with many blue data points scattered along it. There is a downturned‑D‑shaped symbol stretching horizontally across the middle of the graph, and a thick double‑headed arrow connects the bottom of this D‑shape down to the main sediment‑curve, highlighting the range of sediment accumulation. — Figure 3. This image plots sediment accumulation (mm) in front of the slotted pipe over time (days). An image of a slotted pipe is visible in the background of the graph to show where sediment accumulates in front of the slot.

The chart above shows that, over time, slotted inlet pipes require maintenance—just like any other sediment-trapping BMP—to maintain maximum effectiveness. As sediment accumulates, slotted inlet pipes become less effective. To ensure their effectiveness, a scheduled clean-out about once a year (396 days) may maintain the maximum amount of sediment accumulation.

The amount of phosphorus held by a slotted pipe structure will depend on three dominate variables:

pipe catchment area
pipe retention area
soil type

Pipes tested by the Mississippi State University Research and Education to Advance Conservation and Habitat (REACH) program retained between 7.3 and 41.6 pounds of phosphorus. It is possible that slotted-board riser pipes could achieve the same benefits as slotted pipes if a board is left in the slot.

Water flows out of a rusted pipe onto large rocks.

For more information, contact your local NRCS office or Beth Baker at beth.baker@msstate.edu, or visit the MSU Extension Mississippi Land Stewards web page.

References

Kröger, R., Prince Czarnecki, J. M., Tank, J. L., Christopher, S. F., & Witter, J. D. (2015). Implementing Innovative Drainage Management Practices in the Mississippi River Basin to Enhance Nutrient Reductions. Journal of the American Water Resources Association, 51(4), 1020–1028.

Kröger, R., Littlejohn, K. A., Pierce, S. C., Henderson, J., Brandt, J., Flora, C., Poganski, B. H., & Prevost, J. D. (2013). Evidence toward sediment accumulation characteristics of slotted inlet pipes as best management practices on agricultural landscapes. Ecological Engineering, 51, 249–255.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

Publication 2988 (POD-03-26)

By Beth Baker, PhD, Associate Professor and Assistant Director, Wildlife, Fisheries, and Aquaculture; Austin Omer, former Extension Associate, Wildlife, Fisheries, and Aquaculture; and Robert Kröger, PhD, Covington Civil and Environmental LLC.

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P2988