publications > paper > summary of the hydrology of the floridan aquifer system... > hydraulic properties > leakage coefficient
Summary of the Hydrology of the Floridan Aquifer System In Florida and In Parts of Georgia, South Carolina, and Alabama
By Richard H. Johnson and Peter W. Bush
Professional Paper 1403-A
The leakage coefficient of the upper confining unit is highly variable, especially in the semiconfined areas where the confining beds may be either sandy or clayey. Leakage coefficient values of the upper confining unit derived from simulation range from less than 0.01 (in./yr)/ft in tightly confined areas to more than 1.00 (in./yr)/ft in semiconfined areas. The leakage coefficients calculated from aquifer-test data are in general very much larger than those obtained from simulation, ranging from 0.44 to 88 (in./yr)/ft.
In the majority of locations, leakage coefficients from aquifer-test data are too large to realistically represent the exchange of water between the surficial aquifer and the Upper Floridan. The values obtained from aquifer-test data can reflect not only downward leakage from the surficial aquifer, but upward leakage from permeable rocks beneath the pumped interval, as well as leakage from beds of relatively low permeability that might exist within the pumped interval. Upper confining unit leakage coefficients derived from Floridan aquifer-test data are composite, or lumped, properties that include leakage from all available sources. Wells in the Floridan aquifer system are usually partially penetrating and often intersect local low-permeability units. Thus in most Floridan test situations it is probable that leakage coefficients obtained from the test data will characterize leakage from all sources, not just downward leakage from the upper confining unit or the surficial aquifer. A map portraying the values of leakage coefficient required to deliver vertical flow between the surficial aquifer and the Upper Floridan aquifer during simulations is presented in Professional Paper 1403-C.
No quantitative field data on the water-transmitting characteristics of the middle confining unit exist. Miller (1986) used lithology and thickness to qualitatively assess the degree of confinement offered by each of seven low-permeability units of subregional extent that together form the middle confining unit. Leakage coefficient values of the middle confining unit used in simulation were arbitrarily assigned based on Miller's geologic assessment of the confinement. However, due to the insensitivity of Upper and Lower Floridan heads to changes in middle-confining-unit leakage coefficients, simulation was unsuccessful in developing better estimates of the leakage coefficients.
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sofia.usgs.gov/publications/papers/pp1403a/lcoef.html
Comments and suggestions? Contact: Heather Henkel - Webmaster
Last updated: 04 September, 2013 @ 02:04 PM(TJE)