Assessment of Agricultural Drainage Pipe Conditions Using Ground Penetrating Radar

Abstract

Farmers and land improvement contractors, especially in the Midwest U.S., need methods to not only locate buried agricultural drainage pipe, but also to determine if the pipes are functioning properly with respect to water delivery. Previous investigations have already demonstrated the feasibility of using ground penetrating radar (GPR) to find agricultural drainage pipes, so the primary focus of this research project was to determine if GPR can provide additional insight into the condition of subsurface drainage pipes. Ground penetrating radar surveys using 250 MHz transmitter/receiver antennas were conducted at a specially designed field 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 open to flow and comprised of clay tile along part of its length with the rest constructed of corrugated plastic tubing (CPT); one comprised of CPT with an isolated obstruction near the midpoint, 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 simulations were employed to assist with interpretation of GPR data obtained from the test plot. Results of the GPR field surveys indicate that given suitable shallow hydrologic conditions, GPR can determine the position along a drain line where there is an isolated obstruction that completely blocks the flow of water. However, an obstruction that only partially limits water flow through the drain line will be difficult to locate using GPR. Surprisingly, the soil-filled drain line was clearly detectable under drained, moderately wet and undrained, extremely wet soil conditions. The GPR computer simulations indicate that soil had likely settled within the initially soil-filled 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.