Authors: Allan James*, University Of South Carolina, Carrie Monohan, California State University, Chico, Brandon Ertis, California State University, Chico
Topics: Geomorphology, Anthropocene, Spatial Analysis & Modeling
Keywords: Fluvial geomorphology, sediment budget, river channel change, LiDAR DEM
Session Type: Paper
Start / End Time: 10:00 AM / 11:40 AM
Room: Balcony K, Marriott, River Tower Elevators, 4th Floor
Presentation File: No File Uploaded
Recent realizations that hydraulic mining sediment (HMS) in California is toxic due to high concentrations of elemental mercury have led to efforts to locate, map, and estimate volumes of HMS. This study employed geomorphometrics to measure volumes of HMS and to construct sediment budgets in selected mountain watersheds for two time periods: under 19th century and modern conditions. Volumes of HMS produced during the late 19th century were estimated by interpolating pre-mining surfaces of mine pits on LiDAR DEMs and using those surfaces to compute DEMs of difference (DoDs). These volumes were compared to estimates derived by plane-table mapping of select mines by G.K. Gilbert before 1917. Volumes of HMS now stored below the mines were estimated by geomorphometric measurements of sediment in terraces and behind debris-control dams. This involved developing models of pre-mining valley cross-section at-a-station hydraulic geometry, projecting these profiles beneath the modern terraces, and subtracting the corresponding cross-section areas from modern cross sections. Volumes of HMS stored below the mines during the 19th century mining period were computed by interpolations of terrace threads across valleys and adding the volume of sediment excavated to the modern volumes of HMS. Large volumes of HMS storage remain in relatively low-gradient small and intermediate-sized streams long after deposition, whereas little storage remains in the steep, large master canyons.