Floodplain sedimentation on the Feather River, California: Combined use of remote sensing and numerical modeling to analyze contemporary deposition patterns in a historically mined basin.

摘要

Floodplain sedimentation prolongs basin recovery to anthropogenic sediment loading, such as through hydraulic mining. The Feather-Yuba River system offers a unique case study because of the longevity of research related to channel accommodation. Two record floods---1986, 1997---were modeled on these rivers using a finite element, hydrodynamic (Telemac-2D) and sediment transport system (Sisyphe) to compare inundation and floodplain sedimentation patterns. Rating curves developed for the system predicted greater sediment influx in 1997 compared to 1986; however more deposition occurred from the 1986 event. Suspended fine sediment was deposited primarily in association with distributary channels, and secondarily on the inside of bends in reaches with narrow levees. As a consequence, there is no clear trend in sedimentation with distance from these rivers.;Remote sensing provided topography (LiDAR), friction, and model validation via synoptic maps of suspended sediment concentration (SSC) and inundation extent generated from a spectral mixture analysis of two Landsat, and four SPOT images. A two-endmember model was used, with synthetic endmembers derived from optical and radiative transfer modeling and inversion of field spectra to infer absorption from color dissolved organic matter. Closure errors were at most about +/-10 mg/L. Agreement between model and image-derived patterns suggests that image interpretation could prove to be a viable approach for verifying spatially-distributed models of floodplain sediment transport.;Four unknown variables are required in Telemac---elevation, friction, settling velocity, and the critical velocity for deposition. Model runs were compared for two roughness conditions, and with three different settling velocities in order to examine model sensitivity. Incorporating spatially variable resistance on the floodplain increased peak flow depths, reduced peak velocities, and increased the accumulated sediment by 16%. A comparable change was measured by increasing the median grain-size. These particular results contribute by quantifying properties of the flood other than the peak magnitude which influence the patterns and total amount of fine sediment deposited overbank onto floodplains. In particular, this work quantifies the impacts of expanding the amount of spatial and temporal information included in the modeling, demonstrating that these impacts can outweigh other, integrated measures typically correlated with accretion rates.