Simulation of ground-water flow in the Intermediate and Floridan aquifer systems in Peninsular Florida

Abstract

A numerical model of the intermediate and Floridan aquifer systems in peninsular Florida was used to (1) test and refine the conceptual understanding of the regional groundwater flow system; (2) develop a data base to support subregional groundwater flow modeling; and (3) evaluate effects of projected 2020 groundwater withdrawals on groundwater levels. The four-layer model was based on the computer code MODFLOW-96, developed by the U.S. Geological Survey. The top layer consists of specified-head cells simulating the surficial aquifer system as a source-sink layer. The second layer simulates the intermediate aquifer system in southwest Florida and the intermediate confining unit where it is present. The third and fourth layers simulate the Upper and Lower Floridan aquifers, respectively. Steady-state groundwater flow conditions were approximated for time-averaged hydrologic conditions from August 1993 through July 1994 (1993-94). This period was selected based on data from Upper Floridan aquifer wells equipped with continuous waterlevel recorders. The grid used for the groundwater flow model was uniform and composed of square 5,000-foot cells, with 210 columns and 300 rows. The active model area, which encompasses about 40,800 square miles in peninsular Florida, includes areas of various physiographic regions classified according to natural features. Hydrogeologic conditions vary among physiographic regions, requiring different approaches to Hydrologic conditions reflected by the time average from August 1993 to July 1994 (1993-94) potentiometric-surface maps, groundwater withdrawals, and water-level and spring flow measurements constitute the steady-state approximation referenced in this report. The rationale for selecting the 1993-94 period is explained later in the report.

Evaluation of actual evapotranspiration rates from the Operational Simplified Surface Energy Balance (SSEBop) model in Florida and parts of Alabama and Georgia, 2000–17

“…Leakage rates between the surficial aquifer and the Upper Floridan aquifer for basins in Northwest Florida Water Management District (NWFWMD), SWFWMD, Tampa Bay Water (TBW), and basins 6 and 9 in South Florida Water Management District (SFWMD) (fig. 2) were estimated from the product of vertical leakance obtained from Sepúlveda (2002) and annual differences in water-level data from each pair of wells (tables 7, 8, and 9) that are near each other and tap these aquifers. Leakage rates for basins 7, 8, and 10 in SFWMD were calculated from simulated vertical flows that were calculated from SFWMD groundwater-flow models (Y. Assegid, South Florida Water Management District, written commun., 2019).…”

“…2), where the control volume included the Upper Floridan aquifer, the water-level difference between the ending and the beginning of the year for these seven basins was calculated from Upper Floridan aquifer wells (tables 7 and 11). An average specific yield value of 0.15 was applied to areas where the Upper Floridan aquifer is unconfined (Sepúlveda, 2002).…”