Locating tile drainage outlets and surface flow in riparian lowlands using thermal infrared and RGB-NIR remote sensing

ABSTRACT Artificial drainage of agricultural fields represents a major flow path way of both water and nutrients which may contribute to eutrophication issues in the recipient waters. Several studies have shown that riparian lowlands (alluvial plains, wetlands, meadows), if present, may act as buffer zones with high nutrient retention capacities. To assess the fate of water and nutrient flow in riparian lowlands in tile drained catchments, it is essential to know the locations of tile drainage outlets as sources of nutrient input. Using a thermal infrared (TIR) remote-sensing survey, we identified potential tile drainage outlets in a riparian lowland. We also applied a normalized differentiated vegetation index (NDVI) approach to illustrate how tile drainage outlets can be identified with free broadband RGB-NIR data. The positions of identified outlets were validated in the field by visual observation. Our study finds that TIR remote sensing is a strong tool when assessing the sources of water input. NDVI is also applicable, however the background values are very variable making the outlets difficult to locate. The results can be applied in studies of water movement and solute transport via tile drainage as well as model studies where knowledge of input areas through tile drainage is of great importance.