Process based management of large woody debris at the basin scale

Catastrophic floods occurred five times from 1898 to 2003 in the Soquel Creek basin, Santa Cruz County, California, when logjams at local bridges diverted flow into populated areas. In response, managers removed wood from the basin to prevent clogging and failure of bridges and culverts. Most large woody debris (LWD) management programs are unsuccessful in preventing flood and roadway damage as they fail to consider basin-wide processes of LWD recruitment and transport. In particular, bridges and culverts are installed without knowledge wood sizes that are mobilized during floods. A more ecologically and economically sustainable approach is to design infrastructure to pass wood in order to maintain habitat and reduce management effort.; This research examined the characteristics of LWD in study reaches, developed a model to simulate wood transport and assess the effects of management on wood transport, and compared the economic costs of current wood management to a wood passing approach. I identified two LWD reach types: (1) source reaches that were the source of wood for the basin, (2) transport reaches that receive wood from the source reaches. Wood remained in source reaches until flushed out to transport reaches during large storms, thus the current practice of wood removal from transport reaches had little effect of preventing catastrophic logjams. The model showed that current management techniques, such as piece size reduction and wood removal, increase the pressure of infrastructure to pass LWD by mobilizing greater volumes of wood and increasing travel distance by eliminating natural logjams. The economic comparison estimated that a wood passing approach reduced current management costs by more than 50%.