Characterization of Diffuse Groundwater Inflows into Streamwater (Part I: Spatial and Temporal Mapping Framework Based on Fiber Optic Distributed Temperature Sensing)

Abstract

Although fiber optic distributed temperature sensing (FO-DTS) has been used in hydrology for the past 10 years to characterize groundwater–streamwater exchanges, it has not been widely applied since the entire annual hydrological cycle has rarely been considered. Properly distinguishing between diffuse and intermittent groundwater inflows requires longer periods (e.g., a few months, 1 year) since punctual changes can be lost over shorter periods. In this study, we collected a large amount of data over a one-year period using a 614 m long cable placed in a stream. We used a framework based on a set of hypotheses approach using thermal contrast between stream temperature and the atmosphere. For each subreach, thermal contrast was normalized using reference points assumed to lie outside of groundwater influence. The concepts and relations developed in this study provide a useful and simple methodology to analyze a large database of stream temperature at high spatial and temporal resolution over a one-year period using FO-DTS. Thus, the study highlighted the importance of streambed topography, since riffles and perched reaches had many fewer inflows than pools. Additionally, the spatial extent of groundwater inflows increased at some locations during high flow. The results were compared to the usual standard deviation of stream temperature calculated over an entire year. The two methods located the same inflows but differed in the mapping of their spatial extent. The temperatures obtained from FO-DTS open perspectives to understand spatial and temporal changes in interactions between groundwater and surface water.

Groundwater–Surface Water Interactions: Recent Advances and Interdisciplinary Challenges

“…This Special Issue consists of 20 original research papers . The majority of the contributions [3,5,[8][9][10][11][15][16][17][19][20][21][22][23] focus on the interactions between rivers or streams and groundwater. Three studies [6,13,14] investigate the interactions between lakes and groundwater, while two studies [4,18] deal with the exchange between groundwater and oceanic water.…”

“…For example, Mojarrad et al [11] used the temperature difference between groundwater and surface water to numerically model up-and downwelling areas in the hyporheic zone. Le Lay et al [9] and Gilmore et al [5] applied fiber-optic distributed temperature sensing (fo-DTS) for pattern identification as a prerequisite for optimized point measurements of groundwater exfiltration into a river. Le Lay et al [10] used the diurnal atmospheric temperature signal propagating vertically through the hyporheic zone with a characteristic attenuation and phase shift to calculate vertical flow velocities.…”

Characterization of Diffuse Groundwater Inflows into Stream Water (Part II: Quantifying Groundwater Inflows by Coupling FO-DTS and Vertical Flow Velocities)

“…Many authors quantified in-stream measurements robustly at multiple times throughout the year [17,37,38]. However, the method is adapted for focused inflows that equal at least 2% of total stream discharge [39], as used in Part I of this study [40]. If groundwater inflows are weak and diffuse, FO-DTS cables must be buried in the sediment to prevent the signal from being displaced by stream flow [41].…”

“…Multi-scale approaches combining multiple measuring methods may considerably constrain estimates of fluxes between groundwater and surface water [44][45][46]. In part I of this two-part study [40], we developed a framework to locate and map groundwater inflow along a reach. Here, we focus on quantifying groundwater inflows, which is essential for investigating resilience of aquatic ecosystems to climate change [47][48][49].…”

“…We discuss the potential and relevance of each method. The present article applied the framework presented in the previous article [40], which was dedicated to automatic mapping of such diffuse inflows with sub-hour resolution using FO-DTS. Our research framework consists of two parts to map and quantify diffuse and intermittent groundwater inflows into the stream.…”