Identification of a hydrodynamic threshold in karst rocks from the Biscayne Aquifer, south Florida, USA

• Published in: Hydrogeology journal Vol. 16; no. 1; pp. 31 - 42
• Main Authors: DiFrenna, Vincent J., Price, René M., Savabi, M. Reza
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.02.2008; Springer Nature B.V
• Subjects: Anisotropy; Aquatic Pollution; Aquifers; Earth and Environmental Science; Earth Sciences; Effective porosity; Geology; Geophysics/Geodesy; Hydrogeology; Hydrology; Hydrology/Water Resources; Karst; Laminar flow; Limestone; Porosity; Rocks; Studies; Vertical flow; Waste Water Technology; Water Management; Water Pollution Control; Water Quality/Water Pollution; Florida; United States > US; USA, Florida, Biscayne Aquifer; USA, Florida, Florida Keys, Key Largo; USA, Florida; USA; Karst; Porosity; Reynolds number; Hydraulic properties
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-007-0219-4

A hydrodynamic threshold between Darcian and non-Darcian flow conditions was found to occur in cubes of Key Largo Limestone from Florida, USA (one cube measuring 0.2 m on each side, the other 0.3 m) at an effective porosity of 33% and a hydraulic conductivity of 10 m/day. Below these values, flow was laminar and could be described as Darcian. Above these values, hydraulic conductivity increased greatly and flow was non-laminar. Reynolds numbers (Re) for these experiments ranged from <0.1 to 7. Non-laminar flow conditions observed in the hydraulic conductivity tests were observed at Re close to 1. Hydraulic conductivity was measured on all three axes in a permeameter designed specifically for samples of these sizes. Positive identification of vertical and horizontal axes as well as 100% recovery for each sample was achieved. Total porosity was determined by a drying and weighing method, while effective porosity was determined by a submersion method. Bulk density, total porosity and effective porosity of the Key Largo Limestone cubes averaged 1.5 g/cm 3 , 40 and 30%, respectively. Two regions of anisotropy were observed, one close to the ground surface, where vertical flow dominated, and the other associated with a dense-laminar layer, below which horizontal flow dominated.