Caribbean-Florida Water Science Center
Simulation of Transient Groundwater Flow in the Surficial and Floridan Aquifer Systems in East-Central Florida
Project Chief: Nick Sepulveda
Figure 1. Areal extent of the east-central Florida study area, Central Florida Coordination Area, and model area, including lakes, streams, and springs.
As part of an ongoing water resources planning process, the St. Johns River Water Management District (SJRWMD) has undertaken efforts to evaluate the environmental impacts of proposed surface-water withdrawals from the St. Johns River. The planning process has progressed in phases. The primary goal of the Phase I groundwater modeling was to predict changes in discharges of groundwater into the St. Johns River resulting from increased surface-water withdrawals. In Phase II, the model was updated to simulate transient groundwater flow in the Surficial Aquifer System (SAS) and the Floridan Aquifer System (FAS) in east-central Florida (fig. 1). This update was necessary to assess the effects of projected increases in groundwater withdrawals from the FAS. The model will be used to evaluate future impacts on wetlands, streams, lakes, springs, and groundwater levels in the FAS caused by projected increases in groundwater use.
The objective of the project was to develop a 3-dimensional transient groundwater flow model for east-central Florida.
Figure 2. Correlation chart showing the relation between lithostratigraphic and hydrostratigraphic units in the East-Central Florida Transient (ECFT) model area
The East-Central Florida Transient (ECFT) model used MODFLOW-2005 to simulate 7 layers that span the thickness of the surficial aquifer system (layer 1), the intermediate confining unit or intermediate aquifer system (layer 2), the Ocala permeable zone (layer 3), the Ocala low permeable zone (layer 4), the Avon Park permeable zone (layer 5), the middle confining units I and II (layer 6), and the Lower Floridan aquifer (layer 7) (fig. 2).
(1) simulates 3-dimensional flow
(2) uses general-head boundary conditions to simulate flow through the lateral boundaries of the model domain as well as springs contributions
(3) uses the Green-Ampt infiltration (GAI) algorithm to partition rainfall into infiltration and runoff
(4) calculates Hortonian runoff from GAI
(5) calculates Dunnian runoff by using the UZF1 package
(6) routes runoff to lakes and streams
(7) routes streamflow using the SFR2 package
(8) simulates water-surface elevation at the lakes using the LAK7 package
(9) calculates the temporal distribution of recharge rates to the SAS by routing infiltration through the unsaturated zone,
(10) simulates only the freshwater section of the ECFT model area shown in figure 1, and
(11) allows for the simulation of the impact of land-use changes by adjusting the hydraulic conductivity of the top soils, which results in the calculation of updated infiltration and runoff rates from the GAI algorithm.
Sepulveda, Nicasio, “Hydrogeology and Transient Simulation of the Groundwater Flow System in East-Central Florida”, U.S. Geological Survey Scientific Investigations Report, (in review).