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.