Beyond Cross Sections; LiDAR in Support of Sprague River geomorphology Studies, Klamath Basin, Oregon

LiDAR terrain data was collected in November 2004 for 750 square kilometers of the Sprague River valley, Oregon, by Watershed Sciences, Inc., under contract with the Klamath Tribes. This coverage, obtained to support multiple ecologic analysis and restoration activities in the Klamath Basin, encompasses about 90 km of valley- bottom corridor for the main Sprague River as well as downstream alluvial sections of principal tributaries, including 15 km of the Sycan River, 15 km of the South Fork Sprague River, and 10 km of the North Fork Sprague River. Acquisition conditions were leaf-off at normal fall low flow. Assessment of the vertical divergence between 967 surveyed points and the laser points gave a RMSE of 0.052 m with a standard deviation of 0.051 m. The resulting bare-earth 1-m grid has been used for geomorphic mapping, paleo- and historical-channel mapping, qualitative and quantitative analysis of floodplain morphology, and assessment of channel incision over various timescales.4 Using the high resolution topography in combination with floodplain stratigraphy, we delineated the late Holocene (post 7.7 ka Mazama eruption) active floodplain. The morphology of this floodplain reveals processes locally important in forming the Sprague and Sycan river floodplains, including avulsion, meander abandonment and filling, lateral bar building, deposition by crevasses, and lateral migration. Mapping present and paleo-channel positions determined from historic photos and maps onto the LiDAR digital terrain model, coupled with augering to determine channel gravel depths, has allowed local assessment of long term channel incision and aggradation over the last several thousand years. Reaches of possible historic incision have also been delineated by comparing floodplain elevation to channel elevation in an essentially continuous manner along the valley corridor. This analysis reveals multiple reaches where the 1940 channel, as depicted on aerial photographs, is apparently higher than the 2004 channel, and these incised reaches generally correspond to reaches of lower sinuosity (locally imposed by channelization) and rates of channel migration. The continuous and high-resolution elevation data provided by LiDAR terrain models provides a means for continuous mapping of floodplain and channel features at scales relevant to geomorphic and ecologic processes on many river systems, thus providing a means to obtain significantly more information on state and process than can typically be accomplished by the sparse sampling of river systems afforded by a cross-section based approach.