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Hydrologic System Response to Environmental Change: Three Case Studies in California


Hydrologic systems are vulnerable to anthropogenic and natural environmentalchanges. When these changes impair a system’s ability to function and serve as aresource, then restoration or mitigation may be needed. Successful management offreshwater resources requires a quantitative understanding of hydrologic processes and dynamics, and an assessment as to how hydrologic systems may respond to futurechanges. Some systems are sufficiently large or complex so as to defy direct control or restoration, but people can still benefit from understanding that will allow more reliable and thoughtful resource use, as part of a comprehensive management approach. The three chapters presented in this thesis examine hydrologic system response to a variety of environmental changes, including: (1) a recovering riparian wetland located downstream of a dam, (2) an overdrafted and seawater intruded coastal groundwater basin, and (3) a region experiencing an increase in the intensity of extreme precipitation events. In Chapter 1, our studies show that riparian wetland conditions can be improved while water is conserved in upstream reservoirs by utilizing surface infiltration to establish wetland saturation conditions, rather than lateral and upward groundwater transport. Results from the second study indicate that ~13% of the study area (29 of 220 km2 in the basin) may be suitable for managed aquifer recharge (MAR). Modeling suggests that MAR projects placed along the coast provide the greatest initial decrease in seawater intrusion, but MAR projects placed in suitable locations throughout the basin provides the greatest reduction in seawater intrusion over subsequent decades. In Chapter 3, we show that there has been a statistically significant increase in extreme precipitation, beyond proportional changes in mean annual precipitation, in the San Francisco Bay Area in the last 120 years. The extent of changes varies on a spatial scale of ~50 km, the scale at which city planning and risk management decisions should be based. The results of each chapter contribute to the fundamental understanding of hydrologic system dynamics, and demonstrate new field and computational methods. Results presented in Chapters 1 and 2 also compare the efficacy of hypothetical restoration and operational scenarios for improving resource conditions.

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