For my PhD research, I investigated the relationship between surface saturated area and groundwater dynamics during rainfall events. Near-stream saturated areas are known to often play a disproportionate role in creating runoff (Hewlett 1961, Hewlett & Hibbert 1967, Dunne & Black 1970 etc). These near-stream areas are often saturated, or close to saturation, and can quickly respond to precipitation with increased water table levels, surface saturation extent, and ultimately increased runoff to the stream. I quantified how incident precipitation, an expanding saturated zone, and elevating groundwater levels relate to one another and help explain the geochemical variability observed at the catchment outlet during rainfall events.
To achieve this, I used small, field-deployable infrared cameras (FLIR b450 and SC325) to intensively monitor a (100 m2) semi-saturated area within the headwater reach of the Weierbach catchment (0.45 km2). I quantifed the temperature within a saturated area in order to estimate the saturation extent, as the temperature of water is different from surrounding vegetation, soil, stone etc. This assumption was not always valid, but is generally true during the rainy winter months when groundwater, which is typically 6-8 °C, exfiltrates into the riparian area, which is commonly 0-4 °C.
In addition to physical measurements of saturation and water table within the studied saturated zone, water samples from surface saturation and channel flow have been collected to geochemically link saturation area dynamics to stream chemistry. The concentrations of a suite of cations/anions as well as water isotopes 2D and 18O were determined in water samples taken throughout the study area and throughout rainfall events.
I continuously monitored the saturation extent, rainfall, discharge, and groundwater levels within this semi-saturated area in order to test three hypotheses: Saturation is rainfall-dependent, groundwater exfiltration lags saturation development, and that groundwater exfiltration drives the movement of stored riparian water into the stream channel.
This work was successfully defended in December, 2015 at Oregon State University and has resulted in 3 publications:
1) “Unraveling hydrological controls on stream water chemistry in a headwater catchment (Weierbach, Luxembourg).”
2) “Application of high-frequency infrared imagery to investigate plot-scale surface saturation dynamics and sources of surface overland flow in response to fluctuating groundwater tables and incident precipitation”
3) “The role of near-stream groundwater exfiltration on headwater stream chemostasis”