LOCATING DRAINAGE TILES AT AN OLD FARM FIELD WITHIN OHIO’S OAK OPENINGS REGION USING LAND- AND DRONE-BASED GEOPHYSICAL TECHNIQUES

Drainage tiles have been extensively used in the Oak Openings Region of Ohio to drain what was historically part of the Great Black Swamp and convert them into farmlands. As farmland operations have lasted over decades with different succession of ownership, mantainance, and re-installations, utility maps showing location of these tiles are no longer accurate or simply do not exist. Knowledge of these drainage tiles’ network is needed to effectively implement best farm management practices and restor some of the farmlands to wetlands in efforts to reduce nutrient load in receiving surface water and restore the habitats. With many of the fields spanning several hectares, there is the question of how to efficiently survey the area to locate the drainage tiles. Our goal in this study is to develop an efficient framework for locating drainage tile networks at a large farm scale using both land- and drone-based geophysical techniques. The geophysical survey involved cart-mounted and ATV-pulled ground penetrating radar (GPR) measurements using 100 mHz, 200 mHz, and 250 mHz antennas at a proposed 750 m ´ 1,400 m Sandhill Crane Wetland restoration site in Swanton, Ohio which has been used as a farmland for several decades. We also conducted thermal infrared imaging with a UAV mounted FLIR Vue Pro thermal imager flying on a regular grid at 50’ or 100’ AGL, depending on local airspace restrictions. Given significant thermal contrast between the surrounding ground and the drainage tiles themselves, a flyover with the UAV-mounted thermal camera can identify drainage tiles and their orientation in the field. The GPR data using the 250 mHz antenna reveal the drainage tiles mostly in the East-West direction with an ~15 m spacing network, provide depths estimates of ~1 m and compared well with thermal infrared images in identifying where the tiles are located. By using an ATV to pull the GPR system, we were able to efficiently collect data along long profiles covering the entire site. From our study, we recommend drone-based thermal infrared imaging for quick mapping of drainage tiles at a large farm scale and then use land-based GPR to validate their locations and depths.