PROBLEM
A number of ground-water flow models exist for regions within central
Florida, but the more areally extensive of these models are of a relatively low
resolution. Additionally, the fragmentation of Florida into several Water
Management Districts has resulted in ground-water modeling efforts that are
bounded by an individual District, resulting in a reduced ability to estimate
inter-District ground-water flow under current and projected stresses. This
problem is predominant in the common boundaries of St. Johns River Water
Management District, Southwest Florida Water Management District, South Florida
Water Management District, and Suwannee River Water Management District because
of the present and projected developement of the ground-water resources in these
districts. To address these problems, a high-resolution, areally-extensive
ground-water flow model of the Floridan aquifer system in central Florida is
needed. This model can act as a consistent framework from which more
smaller-scale ground-water flow models can be constructed and reconciled among
each other.
BACKGROUND
Ground-water flow modeling has been a tool of the hydrologist since the
1970's. However, the only areally-extensive model of the Floridan aquifer system
in central Florida was completed by Bush (1982). Unfortunately, this effort was
of relatively low resolution (8 miles by 8 miles). Later models (Ryder, 1985;
Tibbals, 1990) completed as part of the USGS Regional Aquifer-System Analysis
(RASA) investigation were of improved, but still coarse, resolution (4 miles by
4 miles).
The generalized hydrogeologic profile in central Florida is shown in figure
1. The Floridan aquifer system consists of a thick sequence of carbonate strata
and occurs throughout central Florida. The high permeability Upper Floridan and
Lower Floridan aquifers are separated by a lower permeability Middle
semi-confining unit. This prolific aquifer system supplies most of the potable
water for central Florida. Throughout most of Florida the Floridan aquifer
system lies below the Surficial aquifer system or the Intermediate aquifer
system or confining unit, although the Upper Floridan outcrops in areas of
northwest-central Florida where the Surficial aquifer system and the
Intermediate confining unit are thin or absent. The Intermediate confining unit
between the Surficial aquifer system and the Floridan aquifer system serves as a
confining unit in central and east-central Florida. The Intermediate aquifer
system serves as a modestly productive aquifer in southwest Florida. The
surficial aquifer is likewise only a modestly productive aquifer, however, they
are more areally extensive than the Intermediate aquifer system.
Figure 1
The predevelopment flow system within the Floridan aquifer system can be
generally described as from potentiometric surface highs to potentiometric
surface lows. Multiple circulation scales exist within this flow system.
Recharge along the central Florida ridge and subsequent discharge to coastal
areas is the dominant large-scale circulation process. Recharge/discharge
relations can also be quite localized, particularly in the vicinity of springs.
Pumpage imposed on the flow system following development has resulted in
significant modification of the flow system in parts of central Florida,
including water level decline, spring discharge reduction, and movement of low
quality water into the fresh water system.
Annual rainfall averages about 52 inches over central Florida.
Evapotranspiration rates average from 30 to 52 inches/year, depending on the
location. Annual runoff averages from 8 to 15 inches over central Florida. The
remainder of the water budget, 0 to 14 inches annual average, serves to recharge
the underlying aquifer systems.
OBJECTIVES
The primary objective of the proposed study is to develop a high resolution
numerical flow model of the Floridan aquifer system in the central Florida area
in order to 1) provide a common framework upon which more localized ground-water
flow investigations can be built, providing current and projected boundary
conditions, heads or fluxes, to models of smaller scale, 2) develop a more
comprehensive understanding of the regional ground-water flow system in central
Florida, and 3) provide a consistent understanding of the nature of ground-water
flow across the common boundaries of the St. Johns River Water Management
District, the Southwest Florida Water Management District, the South Florida
Water Management District, and the Suwannee River Water Management District and
along the boundaries of previous ground-water flow models. The availability of
the proposed megamodel could be of use by the Water Management District's Needs
& Sources evaluations for cumulative impact analysis.
APPROACH
The steps to follow to accomplish the objectives of this study are listed in
the following time table, where each year is divided in 4 quarters.
Time Table:
| No. | Description | 3Q
96 |
4Q
96 |
1Q
97 |
2Q
97 |
3Q
97 |
4Q
97 |
1Q
98 |
2Q
98 |
3Q
98 |
4Q
98 |
1Q
99 |
2Q
99 |
3Q
99 |
4Q
99 |
| 1. | Literature review | X | X | X | |||||||||||
| 2. | Determination of time period to be simulated | X | X | ||||||||||||
| 3. | Water use , aquifer test, and aquifer thickness data compilation | X | X | X | |||||||||||
| 4. | Water-quality data compilation | X | X | X | X | ||||||||||
| 5. | Preliminary delineation of rainfall recharge distribution for areas where the Floridan Aquifer outcrops | X | |||||||||||||
| 6. | Grid generation and determination of areal extent of active cell in each layer | X | |||||||||||||
| 7. | Generations of watertable contours and compilation of water levels for the Surficial aquifer system at the beginning of the calibration period | X | X | ||||||||||||
| 8. | Generation of potentiometric contours and compilation of water levels for the Floridan aquifer at the beginning of the calibration period | X | X | ||||||||||||
| 9. | Analysis, selection, and application of boundary conditions | X | X | ||||||||||||
| 10. | Estimation of trans missivity distribution, vertical leakance, storage coefficient, and specific yield in simulation area | X | X | ||||||||||||
| 11. | Generation of 3-D GW flow model input files - first approximation before calibration | X | X | ||||||||||||
| 12. | Calibration of GW flow model - changes to input files | X | X | X | X | ||||||||||
| 13. | Generation of attribute table of ARC grid coverage using INFO files generated from calibrated parameters | X | |||||||||||||
| 14. | Text writing, generation of tables and figures, colleague reviews, approval, and publication of final report | X | X | X | X | X | |||||||||
| 15. | Archive and document MODFLOW input files and ARC/ INFO coverages | X |
CONTACT