Karst Conduit Networks, Connectivity and Recharge Dynamics of a Sinkhole

Abstract

Management of karst aquifers is often limited by a lack of understanding of recharge and flow dynamics. This article presents the identification of conduit networks and the connectivity, dynamic nature of recharge and inherent uncertainties in recharge assessment in karstic settings. The study was carried out at two large sinkholes located in the Poocher Swamp fresh water lens, south east of South Australia. Point recharge to the sinkholes was calculated using stream flow data at gauging stations and water balance of the swamp. Conduit system and their interconnectivity in the vicinity of sinkholes were characterized by the use of transient electromagnetic survey (TEM) to identify high potential porosity zones of the aquifer. Resistivity data were used to estimate aquifer porosities using Archie's law. Recharge response to the karstic aquifer was monitored using four monitoring wells located at various distances from sinkholes. Measurements were taken during recharge and recession phases. Four dynamic stages of water level rise and fall were observed in response to filling of conduit zones, transmission and possible effects of entrapped air pressure within conduits. Electrical conductivity (EC) profiles were obtained at two stages. These confirmed interconnectivity of conduits, and re-adjustment to ambient groundwater quality following the recharge event. The lower EC water was found in the monitoring well furthest from the sinkholes indicating the complexity of conduit connection and the nature of mixing with ambient groundwater.

Geophysical Input to Improve the Conceptual Model of the Hydrogeological Framework of a Coastal Karstic Aquifer: Uley South Basin, South Australia

“…The ULE208 well ( Figure 15) was drilled in 2003. At 24−42 m (6.5 m AHD to −11.5 m AHD) depth interval, "lost circulation, no returns, no samples, hard bar at 38 m" was reported in the drillers log and lithological descriptions [16]. Depth to water of ULE208 is about 28 m and drilling logs show 'lost circulation' begins in the unsaturated zone indicating the presence of conduit porosity in both saturated and unsaturated zones [23].…”

“…The interpretation of TEM lines are described in previous work of Somaratne and Mann [15] and Somaratne [16] with the following limitations. The variation in resistivity of particular minerals can be enormous, for example limestone: 50-10 7 Ωm; Marls 3-70 Ωm; Clays: 1-100 Ωm [28].…”

“…They include conductivity mapping with the EM-31 and EM-34 methods [12] and electrical resistivity tomography using multi-array electrodes [13][14][15][16]. A study by Wedekind et al [17] shows that surface geophysical data can be combined with downhole measurements to locate sinkholes more accurately.…”

Limnological characteristics, community metabolism and management strategies of a coastal sinkhole in Cuba (Cenote Jennifer)

“…Around the world, sinkholes have been well studied, particularly in the Yucatan Peninsula (México) (Suárez Morales and Rivera Arriaga, 1998;Schmitter-Soto et al, 2002;Beddows et al, 2007;Sánchez y Pinto et al, 2015;Cervantes-Martínez et al, 2018;Enseñat-Soberanis et al, 2019), Australia (Humphreys, 1999Somaratne, 2017), USA (Brinkmann et al, 2008;Emmert 2016;Young et al, 2018) and The Bahamas (Gonzalez et al, 2011;Keeton, 2017;Tamalavage et al, 2018). Brankovits et al (2017) studied the role of coastal karts subterranean estuaries as sink of methane and its contribution of nutrients and carbon to the ocean.…”