Georectification of historical aerial photos to track meander change in Wood River, Klamath County, Oregon
Abstract
The Wood River in Oregon’s Upper Klamath Basin is a meandering channel draining the southeastern slopes of Crater Lake National Park. Its valley floor is heavily grazed and highly altered by a series of irrigation channels that have substantially affected the river’s spring-fed flow regime and morphology. Despite efforts to restore the river’s hydrology, very little information is available about the river’s geomorphology. Using high-resolution LIDAR data from 2004 and georectified aerial photos from 1940-2009, we analyzed meander changes along the Wood River in the geomorphic context of its valley floor and meander belt. Aerial photos were scanned to produce digital images with sub-meter pixels, then georectified with a second-order polynomial transformation. Nine or fewer ground-control points were used for each photo to achieve an overall root-mean-square error value of 0.6 - 0.7 m. The scarcity of buildings and changes in the road and fence networks over the study period required the partial use of “natural pattern matching” during photo rectification. Semi-permanent patterns of fan erosion on the upper valley floor and hydrogeomorphic wetland patterns in lower valley provided the primary bases for natural pattern matching, further aided by the use of transparency during photo overlaying. Six prototypes of meander change were identified: extension, compression, translation, rotation, compound heading, and cutoff. Of these types, extension of meanders was the most frequently occurring. However, the effects of extension were counteracted by numerous meander cutoffs, which nominally affected sinuosity, but actually shortened the channel by about 1 km, or about 3%. Cutoffs were most frequent in the upper reaches of the river, where valley slope is higher, the meander belt is wider, and accommodation space was adequate to promote relatively high initial sinuosity. In these reaches, some cutoffs appear to have initiated downstream transfers of bedload, triggering serial extension of proximal meanders. In the lower reaches, where valley slope is lower, the meander belt virtually vanishes and the river flows through levees perched over partially drained lake-fringe wetlands. Sinuosity is generally low in these reaches and, in contrast to the upper reaches, increased in several areas. This increase in sinuosity can be partially attributed to a restoration project carried out by the Bureau of Land Management that re-meandering the lower 2 miles of the river channel in 2002. The single largest channel change occurred in the transition between the upper and lower reaches, where a series of meanders where artificially straightened. Fundamental differences in the hydrogeomorphology of the Wood River in the upper (more active), middle (straightened), and lower (narrower, less active, leveed) reaches imply different opportunities and constraints for ecological river restoration. Whereas restoration in the upper river and middle reaches could emphasize promoting natural processes and patterns of river meandering, re-establishing the geohydrologic connection between the channel and adjacent wetland systems appears to be the most urgent need in the lower river.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H43G1332N
- Keywords:
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- 0481 BIOGEOSCIENCES / Restoration;
- 1825 HYDROLOGY / Geomorphology: fluvial;
- 1855 HYDROLOGY / Remote sensing;
- 1856 HYDROLOGY / River channels