Observed Changes in Stream Morphology Due to Hydromodification in Southern California

We conducted field investigations of over 50 streams in Southern California as part of a project evaluating the impact of hydromodification on channel morphology. An initial step of the project involves developing quantitative tools for evaluating the relative susceptibility of channel types and risk of channel instability in response to watershed urbanization. Field investigations indicate that most Southern California streams naturally transition from single-thread to braided channels in the presence of certain boundary conditions, and that watercourses near the single- to multi-thread threshold are potentially more susceptible to hydromodification. Based on the field investigations, we present a general channel-reach morphology sequence, and a general modeling framework for assessing the risk of various channel response trajectories associated with urbanization in Southern California.