Sacramento River Geomorphic Atlas, Red Bluff to Colusa, California (1896–2012)

The Sacramento River Geomorphic Atlas (1896–2012) (SRGA) documents the geomorphology of the middle reach of the Sacramento River from Red Bluff to Colusa, California, shown in Figure 1. The SRGA was created using a combination of geologic maps, U.S. Geological Survey (USGS) topographic maps, U.S. Department of Agriculture (USDA) and National Agriculture Imagery Program (NAIP) imagery, light detection and ranging (LiDAR) data, other aerial imagery, historical data, and fieldwork performed by California Department of Water Resources (DWR) staff. The SRGA illustrates channel movement of the Sacramento River from 1896 to 2012. Pre- and post-Shasta Dam meander channels show waterway migration patterns and geomorphologic changes that occurred during each time period. (Construction on Shasta Dam began in 1938 and ended in 1945.) Geologic units mapped along the river indicate areas of geologic control (sedimentary rock units that resist erosion), as well as areas where sedimentary deposits display a greater potential for erosion. The meander patterns of the historical meander belt (pre-1896) and the modern meander belt (1896–2012) are apparent within the sedimentary deposits of the river’s floodplain. LiDAR data was used to create a hillshade mosaic to improve the geologic control boundary by enhancing visual signatures of terraces, meander scrolls, and abandoned channels covered by heavy vegetation. In addition, total station topographic survey data collected in the field over a 27-year period, from 1985 to 2012, indicate erosion patterns at 16 sites along the Sacramento River where there is the highest potential for bank erosion. For each of the 16 sites, geographic information system tools were used to determine the area of erosion for both the pre- and post-Shasta Dam time periods. The data are presented in a series of maps and imagery showing Pre-Shasta Dam Meanders (Series A), Post-Shasta Dam Meanders (Series B), All Meanders (Series C), Geology (Series D), DEM/LiDAR (Series E), Bank Erosion Characterization (Series F), and Pre- and Post-Shasta Dam Bank Erosion survey sites (Series G). Channel locations are approximate and subject to cumulative errors in the original mapping, scanning, georectification, and digitization process. Depending on the series of maps, other data are also shown, such as bank protection, levees, river mile markers, meander scrolls, paleo channels, and the modern and historical meander belts. Figure 2 shows the general legend and the geologic legend for the map series. For reference, Figures 1 and 2 are also shown at the beginning of each map series. Additional data presented in the SRGA include meander avulsion identification, bank protection identification, river sinuosity, and centerline length.