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THE GAPS BETWEEN AN INTEGRATED UNDERSTANDING OF CHANNELIZATION, HYDROLOGY AND WATER QUALITY VERSUS HOLISTIC FUTURE MANAGEMENT: A CASE STUDY OF THE WILLAMETTE RIVER, OREGON
LANDERS, D. H. THE GAPS BETWEEN AN INTEGRATED UNDERSTANDING OF CHANNELIZATION, HYDROLOGY AND WATER QUALITY VERSUS HOLISTIC FUTURE MANAGEMENT: A CASE STUDY OF THE WILLAMETTE RIVER, OREGON. Presented at Symposium at New Mexico State University, Las Cruces, NM, March 01, 2007.
Over the last 150 years the main channel of the Willamette River has been drastically altered by human activity. It has changed from a generally meandering and anastamosing river with extensive reaches of broad, active and connected flood plain features to a river with 13 major tributary dams, extensive revetments, encroaching urban and agricultural land use and limited riparian forest corridors. These alterations have reduced the amount of off-channel features by over 80% and by changing the magnitude and duration of high flow events in combination with revetments, have limited the ability of the river to maintain and regenerate these features.
We characterized the ecological functions and ecosystem services of the remaining off-channel habitats over a ~70 km reach of the river to distinguish their spatial and temporal characteristics. We used aquatic physico-chemical parameters to examine connections between off-channel habitats and the main channel via hyporheic and river flow. For selected sites, these attributes were tracked daily and seasonally. Hyporheic cooling in some alcoves was as much as 9oC while the diel T range in the main channel was typically about 2oC. Landform maturation processes on a decennial timeframe appeared to affect ecological function by decreasing hyporheic connectivity due to colmation. Finally, we relate these characteristics to the use of off-channel habitats by fish and postulate important considerations for future research and management actions.