SWAC Seminar | Sept. 23 | Satish Gupta, PhD

Join us Wednesdays at 3:30 for our fall departmental seminar series. This week will feature a talk by Satish Gupta, PhD, professor emeritus in the Department of Soil, Water and Climate.

"Assessing Tile Drainage Impacts on River Flashiness"

In recent years, several publications have suggested that tile drainage increases river flashiness. However, most analysis in these publications relies on only 10 to 15 years of data and that too from the crop growth period. The primary approach has been statistical comparisons of flows from watersheds with varying degrees of tile drainage, irrespective of their landforms. Over the past 30 to 40 years, soil physicists and soil water engineers have emphasized the concept of
"paired watershed studies," recognizing that no two watersheds are identical and their hydrological processes cannot be fully described by simple parameters. Furthermore, truncating data to the crop period ignores previous-year soil water storage, which directly contributes to current-year streamflow and flashiness. This presentation examines the concept of flashiness and methods for its characterization, followed by a flashiness analysis of several Midwestern rivers across Minnesota, Iowa, Ohio, Indiana, and Michigan. This analysis demonstrates that flashiness is not driven by tile drainage, but rather by precipitation combined with landform characteristics. Long-term river flow analysis shows that flashiness indices, such as the baseflow index, have remained largely unchanged over 100 years. These indices also group by landform, regardless of the extent of tile drainage. During the presentation, I will briefly discuss the history of the Great Black Swamp Area (GBSA) of northwest Ohio, where agricultural drainage is extensive. Rivers from this region flow into Lake Erie and serve as the primary source of nitrogen and soluble phosphorus from agricultural lands, which frequently trigger toxic cyanobacteria blooms that impact Toledo's water supply. Consistent with concepts developed for the Upper Midwest rivers, flow analysis of rivers in the GBSA shows that (1) flows remain nearly the same for a given precipitation level, and (2) differences in baseflow reflect variations in landform conditions resulting from glacial history. The presentation concludes by emphasizing the necessity of incorporating soil physics concepts in river flow analysis when evaluating landscape and crop management effects.