29 Historical channel modification and floodplain forest decline: implications for conservation and restoration of a large floodplain river – Willamette River, Oregon

Abstract

Abstract Trajectories of change in channel structure and riparian plant communities have been documented for the 273-km mainstem of the Willamette River from Eugene to Portland, OR, USA. We also map current human systems (population density, buildings and roads, public lands, land values, land use) as measures of social opportunities and constraints. We use this channel-change detection and human systems analysis as a basis for spatially explicit prioritization of potential restoration efforts. Priorities for conservation of relatively functional reaches are based on current conditions of the channel and floodplain forest along the river. We also measured the consequences in future alternatives as described by stakeholders in the Willamette River basin. Scenarios of change from 2000 to 2050 were developed for current policies and practices, development alternatives, and conservation options. We compare patterns of recent floods to historical channels to provide estimates of the potential for natural flood processes to restore biophysical structure and function in floodplain rivers. These quantitative evaluations of historical changes and future trajectories of ecological properties of the Willamette River will be used to identify potential strategies for restoration of a large river during a period of rapid population growth.