Geomorphic Change in Two Historical Flood Events on the Umatilla River, Oregon
Abstract
We mapped geomorphic change in an 80-km length of the active channel and floodplain of the Umatilla River for two flood events, 1965 and 1996/1997, both about 20 to 70-yr events. More artificial bank stabilization structures were in place during the 1996-7 cluster. We scanned and georectified pre- and post-flood aerial photos, achieving RMSE of 1.5 to 3m, and we digitized channel and floodplain features. Sinuosity generally decreased, and the scour zone and active bars increased in each flood. Secondary channels were created or reactivated. Changes were smaller during the 1996-7 flood cluster, due partly to increased bank protection. In both floods, geomorphic change was spatially variable and related to local influences (tributary junctions, human influences) as well as landscape-scale controls (downstream trends in alluvial deposit characteristics and incision). Both flood events increased areas of several types of features important for fish habitat and water quality, such as alcoves and riparian woody vegetation. Where human influences such as bank protection severely limit geomorphic change, floods can no longer renew habitat and ecological health may decline over time.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.H31C0483M
- Keywords:
-
- 1803 Anthropogenic effects;
- 1821 Floods;
- 1824 Geomorphology (1625)