HR: 13:30h
AN: H13C-01    [Abstracts]
TI: Application of a Density-Dependent Numerical Model (MODHMS) to Assess Salinity Intrusion in the Biscayne Aquifer, North Miami-Dade County, Florida
AU: * Guha, H
EM: guhah@miamidade.gov
AF: Miami-Dade County, Department of Environmental Resources Management, 33 SW 2nd Avenue, Miami, FL 33130 United States
AU: Panday, S
EM: spanday@hgl.com
AF: Hydrogeologic, Inc., 1155 Herndon Pkwy, Suite 900, Herndon, VA 20170 United States
AB: Miami-Dade County is located at the Southeastern part of the State of Florida adjoining the Atlantic coast. The sole drinking water source is the Biscayne Aquifer, which is an unconfined freshwater aquifer, composed of marine limestone with intermediate sand lenses. The aquifer is highly conductive with hydraulic conductivity values ranging from 1,000 ft/day to over 100,000 ft/day in some areas. Saltwater intrusion from the coast is an immediate threat to the freshwater resources of the County. Therefore, a multilayer density-dependent transient groundwater model was developed to evaluate the saltwater intrusion characteristics of the system. The model was developed using MODHMS, a finite difference, fully coupled groundwater and surface water flow and transport model. The buoyancy term is included in the equation for unconfined flow and the flow and transport equations are coupled using an iterative scheme. The transport equation was solved using an adaptive implicit total variation diminishing (TVD) scheme and anisotropy of dispersivity was included for longitudinal, transverse, vertical transverse, and vertical longitudinal directions. The model eastern boundaries extended approximately 3.5 miles into the Atlantic Ocean while the western boundary extended approximately 27 miles inland from the coast. The northern and southern boundaries extend 6 miles into Broward County and up to the C-100 canal in Miami-Dade County respectively. Close to 2 million active nodes were simulated, with horizontal discretization of 500 feet. A total of nine different statistical analyses were conducted with observed and simulated hydraulic heads. The analysis indicates that the model simulated hydraulic heads matched closely with the observed heads across the model domain. In general, the model reasonably simulated the inland extent of saltwater intrusion within the aquifer, and matched relatively well with limited observed chloride data from monitoring wells along the coast. Saltwater intrusion in the Biscayne aquifer is the result of a combination of natural variations in recharge, evapotranspiration, ground-water withdrawals from the aquifer, and relative canal stages in comparison to tidal stages in the Biscayne Bay. Pre- and post wellfield pumpage scenarios were conducted to determine the effect of wellfield pumpage on saltwater intrusion. The model is being used for future water supply management scenarios and for evaluating the best placement of saltwater intrusion monitoring wells along the coast.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2005 Joint Assembly