UC Davis

Rivers have a fundamental importance to human civilization and are considered the primary source of renewable freshwater supply for societies worldwide. Human prosperity depends heavily on surface water and the groundwater it replenishes, but this growth often comes with a heavy cost to river health. Rivers worldwide and particularly in arid climates have experienced profound levels of human alterations, particularly through damming, that affect flow patterns, channel form, and species composition. Functional flows theory offers a promising method to characterize ecologically-important aspects of flow and how changes to flow patterns may affect ecosystems. The goal of this dissertation is to quantify and understand hydrologic alteration of rivers and its ecological effects using a functional flows approach. This work validates functional flows as an effective strategy for ecological streamflow analysis with evidence that they can be used to differentiate California’s natural flow regimes, quantify streamflow response to climate change, and reveal the links between flow management and riparian forest health. Chapter 1 describes creation of a novel tool to quantify functional flow metrics for Mediterranean streamflow patterns using time series analysis methods. Chapter 2 characterizes climate-caused changes to streamflow in snowmelt-dependent regions of California, highlighting the importance of both temperature increase on functional flow change and human emissions levels on potential outcomes. Chapter 3 describes an ecohydrologic field study linking riparian cottonwood growth to functional flows and offers promising evidence that environmental flows can lead to measurable improvement in riparian forest productivity. This dissertation advances river science through the creation and implementation of new tools that can be used to balance human and ecological needs of streamflow.