Delineation of tile-drain networks using thermal and multispectral imagery – implications for water quantity and quality differences from paired edge-of-field sites

Authors: WILLIAMSON, TANJA - Us Geological Survey (USGS); DOBROWOLSKI, EDWARD - Us Geological Survey (USGS); MEYER, SHAWN - Us Geological Survey (USGS); FREY, JEFFREY - Us Geological Survey (USGS); Allred, Barry

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2018
Publication Date: 1/15/2019
Citation: Williamson, T.N., Dobrowolski, E.G., Meyer, S.M., Frey, J.W., Allred, B.J. 2019. Delineation of tile-drain networks using thermal and multispectral imagery – implications for water quantity and quality differences from paired edge-of-field sites. Journal of Soil and Water Conservation. 74(1):1-11. https://doi.org/10.2489/jswc.74.1.1.
DOI: https://doi.org/10.2489/jswc.74.1.1

Interpretive Summary: As part of the Great Lakes Restoration Initiative, paired edge of field sites were established in high priority sub-watersheds to assess the effectiveness of Best Management Practices. One pairing is in Black Creek, a tributary to the Maumee River and Lake Erie. Following two years of baseline data collection from these fields, consistent differences in water quantity and quality were observed for tile networks draining the fields, despite these fields being proximally adjacent to another and managed together. Consequently, it was hypothesized that differences in sub-surface water management, specifically tile-drain density and connectivity, were the source of the observed differences. One objective was to map the tile-drain network using remote sensing methodology in order to improve the understanding of nutrient and water transport as well as management on these fields. A combination of multispectral and thermal imagery, collected in spring 2017, was incorporated to delineate the tile-drain network within each field. This new information led to a technician locating a cracked tile which provided a direct path for overland flow to enter the tile-drain system and suggested that a tile-drain segment connected the two fields. A ground-penetrating-radar survey verified multiple tile locations and the link between the two fields. The distribution of these tiles helps explain the difference in water quality in the two fields.

Technical Abstract: A combination of thermal and multispectral imagery was used to delineate the tile-drain networks in two adjacent fields. This targeted data collection was a success for two primary reasons. First, while the date of the first flights (April) had been a long-term plan to target general spring conditions after a rain event, it was a smaller rain event. The second data acquisition was planned for a few days after a large rain event combined with sunny and warm weather. Soil moisture around 30% provided a clearer delineation of tiles using multispectral imagery. Second, the thermal imagery successfully showed the tile-drain network and differences between the thermal and multispectral imagery helped identify areas where tile-drain connectivity may be interrupted. Tiles tended to have warmer temperatures than the surrounding soil. For water quality, tiles to the surface have characteristics similar to surface runoff, specifically higher total phosphorous and suspended sediment concentrations. This is in contrast to dissolved forms of nitrogen and phosphorous that are expected from tile-drain discharge. The outcome of this work was that the land owners were given detailed information that they were able to use to find multiple places where the tile-drain network was exposed to the surface and fixing this will improve nutrient and water management on their fields. After further testing, these methods of tile-drain delineation could be extended to coordinated imaging of critical basins in order to decrease nutrient transport to streams and water bodies while better protecting agricultural fields and improving crop yields.