Research - Category I: Hydrology, Climatology & Hydraulics

Predicting Flow and Sediment Transport in Steep Channels: Field Study and Flume Experiments to Develop and Test Models
(Funded 2002-2003)

Principal Investigator: William E. Dietrich
Department of Earth and Planetary Science
UC, Berkeley
(510) 642-2633
bill@geomorph.berkeley.edu

Executive Summary:
Over the past 150 years, California has experienced widespread land use disturbance that has released large quantities of sediment into the network of rivers that drain the land. Increasingly in the past decades, regulations have been introduced that are intended to reduce sediment loading with the expectation that receiving channels will cleanse themselves of the sediment burden and restore ecosystem functions. At present, we have no ability to predict the time lag between reduced sediment load and the desired morphologic response in channels, hence we can't answer the simplest of questions: If we make improvements, how long must we wait to see the benefit? This is a sediment routing problem and it begins with the steep tributaries that feed the main stem rivers where most habitats, especially for salmon, occur. Most landscape of hilly and mountainous areas drains first into the numerous steep tributaries, channels with small drainage areas and slopes greater than about 3%, that dissect them. Currently, there is no general theory or set of empirical relationships that would permit calculation of the rate of gravel transport down these steep channels. There is also growing understanding that these steep, typically fishless tributaries are important amphibian habitat about which very little is known.

We propose to conduct a two-year field and laboratory flume study to test and develop further a theoretical approach for calculating velocity and sediment transport in steep channels. The fieldwork would be conducted at the University of California Angelo Coast Range reserve north of Fort Bragg, while the experimental study will be conducted in an existing flume in Berkeley. Results of this study will fill a critical void in field observations, as there are virtually no relevant measurements in California (and rarely so elsewhere). The experimental results will provide testing of the model and permit its further development so that it may better succeed in the field. The theory is intentionally simple, such that with a minimum of field measurements, it can be used. It is the expectation that if the theory is supported with the field work it could easily be used in field studies to document whether sediment supply issues are important. The results will help assess how disturbed these small channels are, which are the least protected, but most extensive part of the river network.