HR: 0830h
AN: H51D-1111    [PDF]
TI: Dramatic Changes in Sediment Discharge and Runoff From a Rapidly Urbanizing Coastal Watershed
AU: * Warrick, J A
EM: jwarrick@usgs.gov
AF: Coastal and Marine Geology, USGS, 345 Middlefield Rd., MS 999, Menlo Park, CA 94025 United States
AU: Orzech, K M
EM: korzech@usgs.gov
AF: Coastal and Marine Geology, USGS, 345 Middlefield Rd., MS 999, Menlo Park, CA 94025 United States
AB: The southern California landscape has undergone dramatic urbanization and population growth during the past 60 years and currently supports almost 20 million inhabitants. Here we show that these landscape changes have imparted significant decreases in suspended sediment concentrations for the region's largest river, the Santa Ana (over 10 fold decreases in sediment rating curves between 1967 and 2001). These decreases do not, however, represent alteration of the total sediment flux to the ocean (a common interpretation of sediment rating curves), but rather a dilution of sediment by increases in runoff from the urban impervious surfaces. We hypothesize that the observed decreases in sediment concentrations have changed the buoyancy of river discharge into the ocean from negative (i.e. hyperpycnal) to positive (i.e. hypopycnal). Thus, not only is landscape urbanization responsible for altering runoff patterns, but it may have also been responsible for changing the dispersal mechanisms and fate of sediment on the continental shelf.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2003 Fall Meeting