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Abstract
Though present in all climatic environments, non-perennial channels are a dominant hydrologic feature of semi-arid regions. At present, projected warming trends are anticipated to shift climate patterns within arid regions, increasing temperatures and decreasing precipitation volume and storm frequency. In combination, these changes have the potential to alter the flow patterns of many presently perennial river systems, decreasing their discharge and resulting in infrequent, seasonal, or cyclic periods of flow cessation. This evolution from perennial to ephemeral systems will likely have significant impacts on regional hydrologic processes and water management. This dissertation explores the varied impact of this transition in semi-arid regions both domestically and in Morocco, applying a combination of statistics, remote sensing, and field work to better characterize shifting flow dynamics and their impact on regional groundwater recharge.
(1) Significant trends in stream drying are observed within semi-arid regions of CONUS. From 1980 to present, the timing of wet season moisture was identified as a primary control on the novel stream intermittency observed as developing across the region. Projected shifts in regional precipitation underscore the expected expansion of non-perennial stream flow into higher elevation, perennial systems.
(2) Characterization of intermittent flow patterns remain a challenge in data-scarce regions, which lack sufficient gaging. Linear Discriminant Function Analysis is demonstrated to effectively predict channel flow in a shallow, turbid, and flashy ephemeral system in central Morocco. From 1984 to 2022, flow frequency was observed to decrease. The spatial and temporal distribution of flow however, which was maintained in the channel upstream and during the wet season, support potential channel infiltration and groundwater recharge despite this reduction.
(3) Infiltration through ephemeral channels is a primary form of aquifer recharge in arid regions. In central Morocco, subsurface temperature probes were deployed to characterize surface flow events and their connection to infiltration. Across two ephemeral channels in disparate recharge zones, infiltration was concentrated within the upstream channel reach, and increased in velocity with greater depth in the subsurface. Improved characterization of channel flow patterns informs our understanding of potential transmission loss, crucial for accurate estimates of groundwater recharge in semi-arid environments.
(1) Significant trends in stream drying are observed within semi-arid regions of CONUS. From 1980 to present, the timing of wet season moisture was identified as a primary control on the novel stream intermittency observed as developing across the region. Projected shifts in regional precipitation underscore the expected expansion of non-perennial stream flow into higher elevation, perennial systems.
(2) Characterization of intermittent flow patterns remain a challenge in data-scarce regions, which lack sufficient gaging. Linear Discriminant Function Analysis is demonstrated to effectively predict channel flow in a shallow, turbid, and flashy ephemeral system in central Morocco. From 1984 to 2022, flow frequency was observed to decrease. The spatial and temporal distribution of flow however, which was maintained in the channel upstream and during the wet season, support potential channel infiltration and groundwater recharge despite this reduction.
(3) Infiltration through ephemeral channels is a primary form of aquifer recharge in arid regions. In central Morocco, subsurface temperature probes were deployed to characterize surface flow events and their connection to infiltration. Across two ephemeral channels in disparate recharge zones, infiltration was concentrated within the upstream channel reach, and increased in velocity with greater depth in the subsurface. Improved characterization of channel flow patterns informs our understanding of potential transmission loss, crucial for accurate estimates of groundwater recharge in semi-arid environments.