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Application of Near-Surface Geophysics to Agricultural Drainage
Pipe Detection
1. In a 1985 economic survey, the Midwest U.S. was estimated to have 12.5 million hectares containing subsurface drainage systems.
2. Today, this subsurface drainage infrastructure would be worth 30 billion U.S. dollars, and the total does not include the extensive amount of drainage pipe installed since 1985.
The Importance of Subsurface Drainage to Midwest U.S. Agriculture
Types of Drainage PipesClay Tile Corrugated Plastic Tubing
Methods of Drainage Pipe EmplacementClay Tile Corrugated Plastic Tubing
Agricultural Drainage Pipein the Soil Profile
Subsurface Drainage System Patterns
Farm infrastructure assessment is one reason that a better way of finding agricultural drainage pipe is needed.
1. Before modifications on pre-existing subsurface drainage systems can be attempted, the agricultural drainage pipe already in place needs to be located.
2. The methods now typically being used are time consuming, tiresome, and often result in damage to the older drainage pipe.
The Hypoxic Zone in the Gulf of Mexico is another reason that a better way of finding agricultural drainage pipe is needed.
Nitrate from agricultural subsurface drainage in the Midwest U.S. contributes significantly to the Hypoxic Zone in the Gulf of Mexico.
An alternative water table management approach can reduce nitrate discharge.
To aid in the assessment of watershed nitrate discharge, remotesensing technologies that are being tested to map agriculturalsubsurface drainage systems over large areas need to be verified.
Near-Surface Geophysical Methods Initially Tested Without Success
Ground penetrating radar (GPR) may provide the solution to the drainage pipe detection problem.
GPR Equipment Utilizedin the Investigation
Typical GPR Drainage Pipe Detection Results
Note: GPR was successful in locating, on average, 72% of the total drainage pipe present at thirteen test sites in southwest, central, and northwest Ohio. On the whole, GPR appears reasonably capable of finding clay tile and corrugated plastic tubing drainage pipe down to depths of around 1 meter.
Summary of GPR Results from Thirteen Test Plots in Ohio
Test Plot Surface SoilTextural Class
Amount of PipeLocated
(%)
ElectroScience Laboratory silty clay 100
South Waterman Farm #1 clay to silty clay 75
South Waterman Farm #1 clay to silty clay 50
North Waterman Farm #1 silty clay loam 50
North Waterman Farm #2 silty clay 90
Fayette County Airport clay 0
Defiance County WRSIS #1 clay 75
Defiance County WRSIS #2 silty clay 100
Southeast Defiance, Ohio sandy loam 100
Fulton County WRSIS #2 sandy clay loam to sandy loam 100
Fulton County WRSIS #1 clay loam 100
OSU Campus – Lima, Ohio silty clay to silty clay loam 100
OSU Ag Research Station - Hoytville, Ohio clay 0
Items That Can Potentially Affect GPR Drainage Pipe Detection
1. Antenna Frequency
2. Computer Processing
3. Shallow Hydrologic Conditions
4. Field Measurement Equipment Parameters
5. Soil Type
Ohio State UniversityElectroScience Laboratory (ESL) Test Plot
Typical Field Operational Set-Upfor a GPR Grid Survey
GPR Antenna Frequency Effects
GPR Antenna Frequency Effects
Computer Processing of GPR Data
Impact of Shallow Hydrologic Conditionson GPR Drainage Pipe Detection
Impact of Shallow Hydrologic Conditionson GPR Drainage Pipe Detection
Field Measurement Equipment Parameter Effects
Impact of Soil Type on GPR Drainage Pipe Detection
Summary1. GPR can be very successful in finding buried agricultural
drainage pipe.2. The best GPR data was obtained with 250 MHz antennas.3. Computer processing is a critical component of GPR
drainage pipe detection.4. Shallow hydrologic conditions with moist soil and at least
partially air-filled pipes are good for locating subsurface drainage systems.
5. Within limits, increasing the spatial sampling interval and reducing signal trace stacking still produces good quality GPR data.
6. Strong radar reflections off of layers in a sandy soil profile can interfere with the GPR drainage pipe detection response.