HR: 1340h
AN: H33H-1712    [Abstracts]
TI: Stratigraphic Controls on Seawater Intrusion, and Implications for Ground-Water Management, Dominguez Gap Area of Los Angeles, California
AU: * Siade, A J
EM: siade@seas.ucla.edu
AF: U.S. Geological Survey, 4165 Spruance Rd., Suite 200, San Diego, CA 92101, United States
AU: Nishikawa, T
EM: tnish@usgs.gov
AF: U.S. Geological Survey, 4165 Spruance Rd., Suite 200, San Diego, CA 92101, United States
AU: Reichard, E G
EM: egreich@usgs.gov
AF: U.S. Geological Survey, 4165 Spruance Rd., Suite 200, San Diego, CA 92101, United States
AB: Development of ground water in coastal Los Angeles in the 20th century led to extensive water-level declines and associated seawater intrusion. The U.S. Geological Survey (USGS) has developed a solute-transport model to quantitatively test the hydraulic implications of a sequence-stratigraphic model and to assess the possible effects of alternative management strategies. The transport modeling was conducted using SUTRA, a finite-element, density-dependent, ground-water flow and solute-transport model. The SUTRA configuration for this case is two dimensional and considers flow and transport along an approximate flow line extending from the Pacific Ocean through the Dominguez Gap area of coastal Los Angeles. The lithologic representation is based on a stratigraphic cross section developed by Ponti and others (2007) http://pubs.usgs.gov/of/2007/1013/. The transient-state simulation period is from 1850 to 2004. Trial-and-error model calibration was conducted using the measured water levels and chloride (Cl) concentrations at nine wells along the cross section. The results from the calibrated model indicate that faulting can provide the main pathway for downward transport of seawater by juxtaposing low permeability layers with high permeability layers; prior stratigraphic models for the region did not recognize this fault system. Three 20- year management scenarios were considered: (1) status quo, that is, no change in water-management strategies; (2) installation of a slurry wall; and (3) raising inland water levels through increased injection or decreased pumpage. Scenario 1 resulted in increasing Cl concentrations. Scenario 2 slowed Cl migration; however, this did not reverse seawater intrusion. Scenario 3 reversed seawater intrusion, but there remained Cl in the deeper regions that will be removed only by dilution over time.
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1847 Modeling
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: 2007 Fall Meeting