Surveys of channel bed topography from two restored reaches of the lower Merced River, California

Surveys of channel and floodplain topography were used to characterize the morphology of two reaches of the lower Merced River in California's Central Valley and to parameterize a hydraulic model. These data were collected to support research intended to evaluate the extent to which large-scale restoration projects provided improved salmon spawning habitat. A related goal of this study was to improve our understanding of the geomorphic factors influencing spawning site selection by salmon. At the Merced River Ranch field site, river channel and floodplain topography was measured using a combination of real-time kinematic (RTK) GPS for wadable parts of the channel, an echo sounder for deep pools, and photogrammetry on dry land [CFS, 2013]. The raw point data were used to generate a triangular irregular network (TIN) and the TIN was converted to a 1 m raster using natural neighbor interpolation. For the 2.5 km long Robinson Reach field site, bed topography was surveyed during the summer of 2012 using real-time kinematic (RTK) GPS, with a mean cross-section spacing of 7 m. The original survey points were interpolated to form a continuous surface using kriging methods developed for curved river channels [Legleiter and Kyriakidis, 2008]. The result of the kriging was a digital elevation model (DEM) of the river channel and 10 m of the floodplain adjacent to each bank, with a spatial resolution of 1 m.