HR: 09:20h
AN: H51F-05    [Abstracts]
TI: The Effects of Urbanization and Flood Control on Sediment Discharge of a Southern California River, Evidence of a Dilution Effect
AU: * Warrick, J A
EM: jwarrick@usgs.gov
AF: Coastal and Marine Geology, USGS, Pacific Science Center 400 Natural Bridges Drive, Santa Cruz, CA 95060 United States
AU: Orzech, K M
EM: korzech@usgs.gov
AF: Coastal and Marine Geology, USGS, Pacific Science Center 400 Natural Bridges Drive, Santa Cruz, CA 95060 United States
AU: Rubin, D M
EM: drubin@usgs.gov
AF: Coastal and Marine Geology, USGS, Pacific Science Center 400 Natural Bridges Drive, Santa Cruz, CA 95060 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. During this time, rivers of the region have been altered with damming, channel straightening and hardening, and water transfer engineering. These changes have drastically altered water and sediment discharge from most of the region's drainage basins. Here we focus on changes in sediment discharge from the largest watershed of southern California, the Santa Ana River. Order-of-magnitude drops in the suspended sediment rating curves (the relationship between suspended sediment concentration and instantaneous river discharge) are observed between 1967 and 2001, long after the construction of a major flood control dam in 1941. These sediment concentration decreases do not, however, represent alteration of the total sediment flux from the basin (a common interpretation of sediment rating curves), but rather a dilution of suspended sediment by increases (approx. 4x) in stormwater discharge associated with urbanization. Increases in peak and total stormwater discharge are consistent with runoff patterns from urbanizing landscapes, supporting our hypothesis that the diluting water originated from stormwater runoff generated in urban areas both up- and downstream of dams. Our dilution hypothesis is further supported with water and sediment budgets, dilution calculations, and suspended and bed grain size information.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting