Summary: Enhancing the efficiency of soil water removal, and in turn crop productivity, on land already containing an agricultural subsurface drainage system, typically involves installing new drain lines between the old ones. However, before this approach can be attempted, the older drainage pipes need to be located. A research investigation has found that ground penetrating radar (GPR) was successful in locating on average 74% of the total amount of pipe present at fourteen test plots in southwest, central, and northwest Ohio. This method worked well in finding clay tile and corrugated plastic tubing drainage pipe down to depths of around 1 meter (3 feet) within a variety of different soil materials. Additional research has focused on various factors that can be important for achieving success using GPR to find agricultural drainage pipes. Results with respect to equipment parameters indicate that choosing the proper antenna frequency is crucial, and antennas with a center frequency of around 250 MHz seem to work best. Also, data quality is similar over a sampling interval range of 2.5 to 10 cm (1 to 4 inches) between points along a measurement line and for averaging 4 to 32 signal traces at a measurement point. In regard to site conditions, shallow hydrology, soil texture, and drainage pipe orientation all influence the GPR response. Moist soils with pipes at least partially filled with air provide good GPR field conditions, assuming the radar signal penetrates to the drain line depth. Sandy soils allow greater radar signal penetration than do clayey soils. Field operations (spacing distance between measurement lines and bidirectional vs. unidirectional surveys) along with the algorithms used in the computer processing sequence to generate GPR profiles and GPR maps are all very important considerations. Furthermore, GPR has also proven capable of providing information on drainage pipe condition with respect to the presence of flow obstructions. The information obtained in this study can hopefully be used to develop guidelines that will enhance the potential for success of using ground penetrating radar to locate buried agricultural drainage pipe and evaluate their condition.
Contact Information:
USDA/ARS - Soil Drainage Research Unit
590 Woody Hayes Drive, RM. 234
Columbus, Ohio 43210
Phone: 614-292-9806
Fax: 614-292-9448
E-mail: barry.allred@ars.usda.gov