|Redman, David -|
Submitted to: Journal of Environmental & Engineering Geophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2010
Publication Date: September 1, 2010
Repository URL: http://handle.nal.usda.gov/10113/54108
Citation: Allred, B.J., Redman, D.J. 2010. Location of Agricultural Drainage Pipes and Assessment of Agricultural Drainage Pipe Conditions Using Ground Penetrating Radar. Journal of Environmental & Engineering Geophysics. 15/3:119-134. Interpretive Summary: Ground penetrating radar (GPR) surveys using 250 MHz transmitter/receiver antennas were conducted at a specially designed test plot for the purpose of confirming GPR drainage pipe detection capabilities and then determining whether GPR can provide useful insight into drain line water conveyance functionality. 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, 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. Ground penetrating radar data were collected at the test plot under drained, moderately wet soil conditions (water table below drain lines) and undrained, extremely wet soil conditions (water table above drain lines). Ground penetrating radar computer modeling simulations were conducted to assist with the interpretation of the GPR data collected at the field test plot. The major findings of the investigation are listed as follows. 1) Under drained, moderately wet and undrained, extremely wet shallow hydrologic conditions, GPR proved capable of mapping drain lines buried to a depth of 0.6 m in a clay loam soil. 2) Given the proper conditions regarding shallow hydrology, GPR data collected along trend of a drain line can be used to precisely locate an isolated obstruction that completely blocks the flow of water through the drain line. 3) An isolated partial obstruction that does not completely block the flow of water through the drain line will be difficult to locate with GPR. 4) Ground penetrating radar computer modeling indicates that a partially soil-filled drainage pipe produces a response shown on GPR profiles that in most cases will be difficult to distinguish from the GPR profile response of a pipe which contains no soil. However, based on test plot GPR data, relatively weak drain line responses depicted on a GPR amplitude map may be indicative of a drainage pipe that is partially soil-filled. 5) Ground penetrating radar computer modeling can be an important tool for interpreting GPR field data collected for assessing drainage pipe conditions. Consequently, the findings of this research support the feasibility of using GPR to not only locate buried agricultural drainage pipes, but to also, given the right field conditions, determine drain line conditions regarding ability to deliver water. Future research will focus on GPR soil water content mapping as potential method of delineating parts of an agricultural field where the subsurface drainage pipe system is not functioning properly.
Technical Abstract: 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.