Watershed context and the evolution of urban streams

2014 Fall Cyberseminar Series

Derek Booth / University of California, Santa Barbara

Talk Description:

Over the last 50 years, great advances have been made in the understanding of the nature and the causes of urban stream degradation. Although we haven’t made as much progress in fixing these problems, an unprecedented level of social, economic, scientific, and regulatory attention is now being paid to this problem, and the progress being made on many fronts is noteworthy. This talk will focus on one aspect of our growing appreciation of the fundamental principles, and the countervailing complexities, associated with the development, diagnosis, and restoration of urban stream—namely, the temporal and spatial influences on what we might consider the “watershed context” of urban streams. The temporal context in which stream channels evolve is most commonly expressed through a Channel Evolution Model (CEM), for which a classic framework has been long-accepted but which does not incorporate some of the characteristic disturbances and constraints common to many urban environments. The spatial context embraces the variability imposed by climate, geology, and physiography, variability for which urbanization is a profound homogenizer of channel responses but that nonetheless permits significant differences to be expressed from one place to another. The integration of these perspectives leaves us with some useful guiding principles for urban stream restoration: (1) Not every channel is able to respond to urban-induced flow increases in the manner predicted by the classic CEM; (2) flow increases are not always the primary urban disturbance to streams (but they commonly are); (3) any channel evolution model (and channel evolution trajectory) is context-bound by its location; and (4) despite this talk’s focus on geomorphology, comprehensive urban stream restoration requires consideration of not only channel form but also the myriad other features of an urban stream that probably have also been impacted.

CUAHSI's Fall 2014 Cyberseminar Series on Sustainable Urban Streams— Science to Support Evolving Management Objectives!

The management of urban streams and rivers has historically emphasized two critical ecosystem services: stormwater conveyance (flood protection) and wastewater disposal. Maximizing these services has generally resulted in major alteration of aquatic ecosystem structure and function, and reduced provision of other ecosystem services, such as aesthetics, recreation, food and biodiversity. Recent decades have seen a renewed appreciation of the value of these other services, an improved understanding of the processes by which streams are altered, and the development of engineering and design practices to manage these processes in ways that can provide multiple services.   

Hosted by Seth Wenger, Director of Science of the River Basin Center at the University of Georgia