Geomorphology of the Sprague River Basin, Oregon

Contact: Jim O'Connor

 Sprague River Valley. (Photograph by Jim O'Connor, USGS)

Background

The Sprague River basin encompasses about 1,610 square miles (4,170 square kilometers) of south central Oregon and is a principle tributary (via the Williamson River) of upper Klamath Lake. The lower reaches of the North Fork and South Fork Sprague River, the Sycan River, and the 86 miles (139 kilometers) of the mainstem Sprague River meander through broad alluvial valleys historically supporting agricultural crops and livestock grazing. National and regional interest in restoring Klamath Basin ecosystem conditions and processes has motivated several restoration strategies and projects in the Sprague River basin to improve aquatic, riparian, and upland habitat conditions, particularly for endangered fish species.

This study, jointly conducted by the U.S. Geological Survey and University of Oregon and in cooperation with the U.S. Fish and Wildlife Service Klamath Basin Ecosystem Restoration Office and the Hatfield Restoration Program, documents historical and current channel and floodplain processes and conditions to assist management and regulatory agencies in evaluating restoration proposals and designing effective restoration and monitoring strategies for the Sprague River and its principle tributaries. The study involves multiple analyses, including assessments of historical channel change, riparian and floodplain vegetation, and surficial geology. To support these analyses, digital floodplain and channel maps were prepared to depict channel and floodplain conditions at different times. The geospatial database of current and historic channel and floodplain conditions will also enable evaluation of long-term trends pertaining to aquatic and riparian habitat conditions.

 Geomorphological features of the Sprague River Valley as depicted in the geomorphic map. (Click to access full-size map.)

Geomorphic Map

Geomorphic mapping establishes the basic context for understanding modern channel conditions by (1) defining major elements of the late Cenozoic geologic history shaping the geomorphology of the study area and (2) outlining the active geomorphic floodplain, which is the domain for assessing channel change and floodplain vegetation conditions. The mapping domain broadly corresponds with the extent of Light Detection and Ranging (LiDAR) topography acquired in November 2004 and includes the broad alluvial valleys of the lower Sycan River, mainstem Sprague River, and lower North Fork of the Sprague River. The mapping encompasses the main floodplains and contiguous alluvial and colluvial landforms. The geomorphic mapping was based on aerial photographs, LiDAR topography acquired in November 2004, U.S. Geological Survey 7.5-minute topographic maps, existing soil mapping, prior geologic mapping, reconnaissance field observations, and stratigraphic sections, primarily along bank exposures but supplemented by augering.

Geomorphic Map Data

Floodplain Feature Mapping

From rectified and mosaicked aerial photograph sets, we mapped channel position, bars, vegetation classes, and cultural (built) features (levees, buildings, and roads) within the floodplain boundary shown in the geomorphic map. All features for the entire study area were mapped for the 1940, 1968, and 2000 aerial photographs. The 1940s aerial photographs, however, did not completely cover the upstream parts of the South Fork Sprague River (upstream of FKM 95.2), North Fork Sprague River (upstream of FKM [floodplain kilometer] 5.8), and Sycan River (upstream of FKM 13.6). Supplemental measurements on the channel centerline position were mapped from 1975 imagery forming the basis of a 1977 soil survey, 2004 LIDAR, and 2005 USGS digital orthophotoquadrangles.

Sprague River Basin Floodplain Features Data

Publications

Geomorphology and Flood-Plain Vegetation of the Sprague and Lower Sycan Rivers, Klamath Basin, Oregon

Banner photo credits: 1,2,4,6,7 Tim Wilson, Chiloquin, Oregon; rest, USGS