A predictive computer model of the Lower Cretaceous aquifer, Franklin area, southeastern Virginia
Links
- Document: Report (pdf)
- Superseded Publications:
- Download citation as: RIS | Dublin Core
Abstract
The Lower Cretaceous aquifer of Southeastern Virginia is simulated in this study. The aquifer is only a few feet thick along the Fall Line, where it is near or at the surface, but it thickens and dips to the east. At Franklin where the top of the aquifer is 220 feet (67 metres) below sea level, it is about 600 feet (180 metres) thick. Thirty five miles (56 kilometres) east of Franklin, along the eastern boundary of the model area, the top is about 900 feet (270 metres) below sea level, and the thickness is estimated to be 2,000 feet (610 metres). The aquifer consists of an alternating series of permeable and semipermeable beds, which contain various mixtures of sand, gravel, silt and clay. The sediments are continental stream deposits in the western and central parts of the area, but grade to marine deposits in the eastern part. Transmissivity is zero at or near the Fall Line, and increases eastward to 19,000 cubic feet per day per foot (1,800 cubic metres per day per metre) at Franklin. Further eastward, trans-missivity probably increases slightly, but then decreases as the marine phase is reached. The aquifer is.overlain by a semiper-meable'confining layer and is underlain by relatively impermeable rocks of the pre-Cretaceous basement.
The model used is the finite-difference digital type described by Pinder (1970). Historical water levels of the aquifer were simulated from 1891 to December 1, 1972. The 1891 water-level surface was developed by running a steady-state version of the Pinder model. Simulation runs from 1891 to 1941, 1970, and 1972 are in good agreement with historical water levels. A modeling factor was used as a multiplier for varying the coefficients of transmissivity and vertical permeability of the confining layer without altering the initial (1891) surface used to start the modeling runs. This technique should be helpful in the development of other models of artesian aquifers.
Predicitive runs show that, if pumpage continues to increase as it has in the past, serious dewatering of the aquifer will occur at Franklin and possibly at other centers of increased pumpage. However, a predictive run to the year 2022 shows that if pumpage does not increase, additional drawdown would be small. Other predictive runs show the effects caused by hypothetical withdrawals at other locations.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | A predictive computer model of the Lower Cretaceous aquifer, Franklin area, southeastern Virginia |
| Series title | Water-Resources Investigations Report |
| Series number | 51-74 |
| DOI | 10.3133/wri7451 |
| Year Published | 1975 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Contributing office(s) | Water Resources Program |
| Description | ix, 62 p. |
| Country | United States |
| State | Virginia |
| Google Analytic Metrics | Metrics page |