Geoscience Reference
In-Depth Information
29
Agricultural Drainage Pipe
Detection Using Ground-
Penetrating Radar
Barry J. Allred and Jeffrey J. Daniels
ContentS
29.1 Introduction ......................................................................................................................... 363
29.2 Materials and Methods........................................................................................................ 364
29.3 Results and Discussion........................................................................................................ 366
29.4 Summary............................................................................................................................. 373
References ...................................................................................................................................... 373
29.1 IntRodUCtIon
A 1985 U.S. Department of Agriculture (USDA) Economic Research Service economic survey
showed that the states in the Midwest United States (Illinois, Indiana, Iowa, Ohio, Minnesota,
Michigan, Missouri, and Wisconsin) had by that year approximately 12.5 million hectares that
contained subsurface drainage systems (USDA Economic Research Service, 1987). Cropland con-
stituted by far the large majority of this acreage. The same economic survey estimated the 1985
on-farm replacement cost for these cropland subsurface drainage systems to be $18 billion. Today,
this subsurface drainage infrastructure would be worth $35 billion based on a 1986 to 2008 average
yearly consumer price index inflation rate of 3 percent, and this total does not include the extensive
amount of drainage pipe that has been installed in the past 20 years. The magnitude of the area
involved along with infrastructure costs indicate how crucial subsurface drainage is to the Midwest
U.S. farm economy, without which, excess soil water could not be removed, in turn making current
levels of crop production impossible to achieve.
Figure 29.1 is a schematic illustrating drainage pipe placement within the soil profile typical of
agricultural fields in Ohio. Prior to the 1960s, agricultural drainage pipe was constructed primarily
of clay tile and was then superseded by corrugated plastic tubing (CPT), which is today the mate-
rial still used in drainage pipe fabrication (Schwab et al., 1981). The drainage pipe diameter is most
commonly 10 cm. The pipe is emplaced at the bottom of a trench, which is then backfilled. The
trench is typically 0.3 to 0.5 m wide with its bottom depth ranging between 0.5 and 1 m. Modern
drain line installation equipment often produces a trench that is wider at the bottom than the top.
The water table can be either above or below the drainage pipe depending on the amount of recent
rainfall and the mode of operation for the subsurface drainage system (uncontrolled drainage, con-
trolled drainage, or subirrigation). The surface tilled zone is commonly less than 0.3 m, assuming a
no-till management strategy has not been adopted.
Increasing the efficiency of soil water removal on farmland that already contains a function-
ing subsurface drainage system often requires reducing the average spacing distance between drain
363
