HEADWATER STREAM DISCHARGE CHARACTERIZATION IN THE KONZA PRAIRIE’S MEROKARST ENVIRONMENT USING A PITOT TUBE

Characterization of intermittent, headwater streams is critical for understanding groundwater-surface water interactions, because headwater streams comprise fifty percent of the stream network in the USA. Accurate measurements of low-stream flow rates are important for quantifying numerous stream-discharge related parameters, such as watershed water balance, nutrient export, and CO₂ flux, but are difficult to achieve using common methodologies because these streams are typically very shallow. Here we use an alternative approach, the Pitot tube, to measure stream velocity in a headwater stream in order to calculated stream discharges. Measurements were taken along the lower ~400 meters of a ~2-km long intermittent stream in an upland watershed at the Konza Prairie Biological Station and Long-Term Ecological Research Site (Konza) in northeastern Kansas. The goal was to identify reaches that are gaining or losing water to the subsurface. The Konza is located on merokarst, which is characterized by imperfect limestone karst topography, that is, alternating limestone and mudstone. Because the strata are nearly horizontal, the stream crosses the boundaries of four different units, two limestones and two mudstones, in the study area. Preliminary results from this study indicate a significant amount of groundwater-surface water interaction occurring with both gaining and losing reaches. Overall, the studied stream segment is a losing reach, as approximately 87% of the surface water is lost to the subsurface. Notable gains in discharge, ranging from about 9% to 331%, occur locally at sites that are in contact with modern alluvium and the Permian Morrill Limestone Member of the Beatty Formation. Results from this study are consistent with preliminary findings at this site, and further confirm the presence and complexity of surface and groundwater interactions in merokarst stream systems.