Methods are needed to not only locate buried agricultural drainage pipe, but to also determine if the pipes are functioning properly with respect to water delivery. The primary focus of this research project was to confirm the ability of ground penetrating radar (GPR) to locate buried drainage pipe, and then determine if GPR provides insight into drain line water conveyance functionality. Ground penetrating radar surveys using 250 MHz transmitter/receiver antennas were conducted at a specially designed test plot under drained, moderately wet soil conditions (water table below drain lines) and undrained, extremely wet soil conditions (water table above drain lines). The test plot contained four drain lines: one a clay tile to corrugated plastic tubing (CPT) drain line that was completely open to flow; one comprised of CPT with an isolated obstruction near the midpoint, completely preventing through-flow of water; one comprised of CPT but filled with soil; and one comprised of CPT but severed near its midpoint, producing a partial obstruction to water flow. Subsequent GPR computer modeling simulations were employed to assist with interpretation of the GPR field data. Results of the GPR field surveys indicate that given suitable shallow hydrologic conditions, GPR not only finds drainage pipes, but can also determine the position along a drain line where there is an isolated obstruction that completely blocks water flow. However, results show that a partial pipe obstruction is difficult to locate using GPR. Surprisingly, the soil-filled drain line was clearly detectable under both soil hydrologic conditions tested. The GPR computer modeling simulations indicate that soil had likely settled within the pipe, and that the GPR responses obtained at the test plot for the soil-filled pipe were responses representative of a pipe that was in fact only partially filled with soil. Overall, these research results provide valuable information for those contemplating the use of GPR to locate agricultural drainage pipes and then determine their functionality.

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