A theoretical model for the initiation of large woody debris movement in Caspar Creek, CA

Over the last twenty five years, our understanding of the geomorphic and ecological role of large woody debris (LWD) has altered our view of wood in streams. Where managers were pulling LWD out of the channel in the 1970’s, they are now adding wood to channels to improve their aquatic habitat. The pace of placing the wood in channels, however, is greater than our increases in understanding of LWD dynamics. Therefore, our ability to predict the stability of LWD is somewhat limited. In particular, there are no guidelines that can be used to assess how wood stability differs according to channel type (e.g., small channels versus large channels). Movement of logs can pose several potential problems, particularly if there are structures such as culverts, bridges, or houses downstream that could be affected by moving logs. This is a particularly sensitive issue if the logs have been added to the stream for restoration purposes, rather than entered the stream naturally. Because of this uncertainty, logs added to restore stream habitat are often cabled to the bank, or not added at all where their downstream movement could be potentially harmful. A better understanding of log dynamics will help to make restoration projects more effective in two ways. First, logs could be added that were likely to be stable at a given flow. Also, understanding log dynamics would help make wood budgets more accurate.

There are two components to understanding the LWD added to or naturally occurring in the channel, the first is defining the thresholds for log movement and the second is predicting how far logs will travel once in motion. In this study, we seek to address the thresholds for log movement for wood added to Caspar Creek in the Jackson Demonstration State Forest in Mendocino County, CA. A full understanding of LWD dynamics requires understanding both components.