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As the climate warms and dry periods become more extreme, shallow groundwater discharge is generally becoming a less reliable source of streamflow while deep groundwater discharge remains a more resilient source. The implications of shifts in the relative balance of shallow and deep groundwater discharge sources are profound in gaining streams. These different sources exert critical controls on stream temperature and water quality as influenced by legacy groundwater contaminant transport. Groundwater discharge flux rates over time were used for the inference of source groundwater characteristics to prominent riverbank groundwater discharge faces along the mainstem Farmington River, CT USA. To estimate groundwater discharge rates, we deployed sediment temperature loggers (iButton #DS1922L, Maxim Integrated, Inc., San Jose, CA, USA) in vertical profilers installed directly into mapped preferential groundwater discharge points across extensive riverbank discharge face features.Temperature data contained in this release were collected from June 24 to November 5, 2020, at 40 distinct discharge point riverbank locations, similar to those described by Barclay et al. (2022) and Briggs et al. (2022). Saturated sediment thermal conductivity and heat capacity were measured in-situ with a TEMPOS Thermal Property Analyzer (TEMPOS, Meter Group, Inc., Pullman, WA, USA) at multiple points across each riverbank discharge face to aid in estimating groundwater discharge flux rates. Barclay, J. R., Briggs, M. A., Moore, E. M., Starn, J. J., Hanson, A. E. H., & Helton, A. M. (2022). Where groundwater seeps: Evaluating modeled groundwater discharge patterns with thermal infrared surveys at the river-network scale. Advances in Water Resources, 160. https://doi.org/10.1016/j.advwatres.2021.104108 Briggs, M. A., Jackson, K. E., Liu, F., Moore, E. M., Bisson, A., & Helton, A. M. (2022). Exploring Local Riverbank Sediment Controls on the Occurrence of Preferential Groundwater Discharge Points. Water, 14(1). https://doi.org/10.3390/w14010011
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Shallow and local or deep and regional? Inferring source groundwater characteristics across mainstem riverbank discharge faces
Abstract Riverbank groundwater discharge faces are spatially extensive areas of preferential seepage that are exposed to air at low river flow. Some conceptual hydrologic models indicate discharge faces represent the spatial convergence of highly variable age and length groundwater flowpaths, while others indicate greater consistency in source groundwater characteristics. Our detailed field investigation of preferential discharge points nested across mainstem riverbank discharge faces was accomplished by: (1) leveraging new temperature‐based recursive estimation (extended Kalman Filter) modelling methodology to evaluate seasonal, diurnal, and event‐driven groundwater flux patterns, (2) developing a multi‐parameter toolkit based on readily measured attributes to classify the general source groundwater flowpath depth and flowpath length scale, and, (3) assessing whether preferential flow points across discharge faces tend to represent common or convergent groundwater sources. Five major groundwater discharge faces were mapped along the Farmington River, CT, United States using thermal infrared imagery. We then installed vertical temperature profilers directly into 39 preferential discharge points for 4.5 months to track vertical discharge flux patterns. Monthly water chemistry was also collected at the discharge points along with one spatial synoptic of stable isotopes of water and dissolved radon gas. We found pervasive evidence of shallow groundwater sources at the upstream discharge faces along a wide valley section with deep bedrock, as primarily evidenced by pronounced diurnal discharge flux patterns. Discharge flux seasonal trends and bank storage transitions during large river flow events provided further indication of shallow, local sources. In contrast, downstream discharge faces associated with near surface cross cutting bedrock exhibited deep and regional source flowpath characteristics such as more stable discharge patterns and temperatures. However, many neighbouring points across discharge faces had similar discharge flux patterns that differed in chloride and radon concentrations, indicating the additional effects of localized flowpath heterogeneity overprinting on larger scale flowpath characteristics.
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- Award ID(s):
- 1824820
- PAR ID:
- 10478244
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Hydrological Processes
- Volume:
- 37
- Issue:
- 7
- ISSN:
- 0885-6087
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/hyp.14939
