Water Resources Collections and Archives

With the populations of anadromous salmonids in steep decline throughout California, many river restoration projects attempt to bring fish back to tributaries by enabling fish passage and creating spawning habitat. Carneros Creek, a tributary of the Napa River, is an incised and sinuous stream which poses a challenge for restoration planning land use management, as the watershed supports steelhead runs and valuable agricultural land. We documented the physical channel morphology of a 150 meter long reach in the Upper Carneros Creek using ground based Light Detection and Ranging (LiDAR) scans and assessed grain size using pebble counts in order to gain insight into restoration and management opportunities. These data provide a baseline geomorphic assessment for future restoration projects and allowed us to compare velocities predicted by 1-dimensional (1D) and 2-dimensional (2D) models. For the 1D model, we simulated flows by pulling out cross-sectional points from the LiDAR scans. Using a Manning’s n value of 0.033 for clean, sinuous channels with some pools and riffles, we found 1D velocities at four cross-sections corresponded to 3.3 m/s, 2.3 m/s, 2.5 m/s, and 2.8 m/s with a mean velocity of 2.73 m/s. For the 2D model, we used FaSTMECH in U.S. Geological Survey’s (USGS) Multi-Dimensional Surface Water Modeling System (MD_SWMS) based on LiDAR data. Our 2D velocity results decreased to an average of 0.85 m/s and ranged from 0 to 4.53 m/s based on local slope changes from the detailed channel morphology measurements. By adding grain size variable roughness to the 2D model, we saw a range of velocities from 0 to 1.98 m/s with an average of 0.65 m/s. We found that because 1D modeling of cross-sectional data using Manning’s equation does not simulate flow curvature in bends, our 2D model can provide betterdefined velocities than a 1D model. Because Carneros Creek is listed as a viable migration passage for steelhead, restoration managers concerned about the level of incision and the ‘flashy’ nature of the stream should consider how the variability in channel morphology and geomorphology models influence velocity predictions that are important drivers of habitat quality for migrating fish and juveniles.