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Assessing Stream-Aquifer Connectivity in a Coastal California Watershed

1
Department of Natural Resources Management & Environmental Sciences, California Polytechnic State University, San Luis Obispo, CA 93407, USA
2
Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407, USA
*
Author to whom correspondence should be addressed.
Current address: DUDEK, San Diego, CA 93407, USA.
Academic Editor: Aldo Fiori
Water 2021, 13(4), 416; https://doi.org/10.3390/w13040416
Received: 28 December 2020 / Revised: 29 January 2021 / Accepted: 29 January 2021 / Published: 5 February 2021
(This article belongs to the Section Hydrology and Hydrogeology)
We report the results of field and laboratory investigations of stream-aquifer interactions in a watershed along the California coast to assess the impact of groundwater pumping for irrigation on stream flows. The methods used include subsurface sediment sampling using direct-push drilling, laboratory permeability and particle size analyses of sediment, piezometer installation and instrumentation, stream discharge and stage monitoring, pumping tests for aquifer characterization, resistivity surveys, and long-term passive monitoring of stream stage and groundwater levels. Spectral analysis of long-term water level data was used to assess correlation between stream and groundwater level time series data. The investigations revealed the presence of a thin low permeability silt-clay aquitard unit between the main aquifer and the stream. This suggested a three layer conceptual model of the subsurface comprising unconfined and confined aquifers separated by an aquitard layer. This was broadly confirmed by resistivity surveys and pumping tests, the latter of which indicated the occurrence of leakage across the aquitard. The aquitard was determined to be 2–3 orders of magnitude less permeable than the aquifer, which is indicative of weak stream-aquifer connectivity and was confirmed by spectral analysis of stream-aquifer water level time series. The results illustrate the importance of site-specific investigations and suggest that even in systems where the stream is not in direct hydraulic contact with the producing aquifer, long-term stream depletion can occur due to leakage across low permeability units. This has implications for management of stream flows, groundwater abstraction, and water resources management during prolonged periods of drought. View Full-Text
Keywords: stream depletion; aquifer; aquitard; leakage; hydraulic conductivity; resistivity; connectivity; spectral analysis stream depletion; aquifer; aquitard; leakage; hydraulic conductivity; resistivity; connectivity; spectral analysis
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MDPI and ACS Style

Malama, B.; Pritchard-Peterson, D.; Jasbinsek, J.J.; Surfleet, C. Assessing Stream-Aquifer Connectivity in a Coastal California Watershed. Water 2021, 13, 416. https://doi.org/10.3390/w13040416

AMA Style

Malama B, Pritchard-Peterson D, Jasbinsek JJ, Surfleet C. Assessing Stream-Aquifer Connectivity in a Coastal California Watershed. Water. 2021; 13(4):416. https://doi.org/10.3390/w13040416

Chicago/Turabian Style

Malama, Bwalya; Pritchard-Peterson, Devin; Jasbinsek, John J.; Surfleet, Christopher. 2021. "Assessing Stream-Aquifer Connectivity in a Coastal California Watershed" Water 13, no. 4: 416. https://doi.org/10.3390/w13040416

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