Pumping-Induced Drawdown of Streams in Proximity to Agricultural Wells

Author

Sara Alina SternbergFollow

Date of Award

9-2023

Degree Name

MS in Environmental Sciences and Management

Department

Natural Resources Management

College

College of Agriculture, Food, and Environmental Sciences

Advisor

Bwalya Malama

Advisor Department

Natural Resources Management

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

In the context of unprecedented drought and aquifer overdraft in California, understanding surface water and groundwater connectivity have become increasingly important. While there is a clear understanding of how wells induce drawdown in aquifers (Theis, 1935; Hantush, 1965), secondary effects on local streams have not fully been considered. Current mathematical models targeting aquifer drawdown do not address stream drawdown response in aquifer-stream systems with strong connectivity; instead, they assume the stream to be a constant head boundary. In the drought-stricken and summer-dry climate of California, streams often run dry for months out of the year, which is currently not reflected in stream depletion models, leading groundwater researchers to refer to this missing information as the “stream depletion paradox” (Malama et al., 2021) where streams undergo depletion while maintaining a fixed stage or constant head. This project aims to expand knowledge of stream-aquifer interactions by collecting field data to use in new, more realistic mathematical models that do not assume streams are constant head boundaries but rather areas of finite storage. To support the accuracy of these improved models, in-situ stage measurements of two production wells and nearby streams were taken in San Luis Obispo, CA for nine months, from October 2022 through June 2023. Standard time-series data on stage and groundwater fluctuations, as well as hydraulic conductivity and stream discharge measurements were taken to classify stream-aquifer interactions. This data was analyzed to determine whether pumping induces stream drawdown and depletion (Malama et al., 2021; Butler, 2001). Depending on the degree of connectivity, recommendations can be made on sustainable pumping practices to local water managers and farm managers who operate the wells and raise scientific understanding of complex surface and groundwater interactions.