Quantifying Potential Recharge in Mantled Sinkholes Using ERT

Abstract

Potential recharge through thick soils in mantled sinkholes was quantified using differential electrical resistivity tomography (ERT). Conversion of time series two-dimensional (2D) ERT profiles into 2D volumetric water content profiles using a numerically optimized form of Archie's law allowed us to monitor temporal changes in water content in soil profiles up to 9 m in depth. Combining Penman-Monteith daily potential evapotranspiration (PET) and daily precipitation data with potential recharge calculations for three sinkhole transects indicates that potential recharge occurred only during brief intervals over the study period and ranged from 19% to 31% of cumulative precipitation. Spatial analysis of ERT-derived water content showed that infiltration occurred both on sinkhole flanks and in sinkhole bottoms. Results also demonstrate that mantled sinkholes can act as regions of both rapid and slow recharge. Rapid recharge is likely the result of flow through macropores (such as root casts and thin gravel layers), while slow recharge is the result of unsaturated flow through fine-grained sediments. In addition to developing a new method for quantifying potential recharge at the field scale in unsaturated conditions, we show that mantled sinkholes are an important component of storage in a karst system.

Characteristics of Point Recharge in Karst Aquifers

“…For shallower water tables, a linear relationship between depth to the water table and water-level response time is evident in granular porosity aquifers [58]. Typically, connected sinkholes add large volumes of water to the aquifer in a relatively short time, while conduit systems in the aquifer may rapidly transport and remove it leading to short residence time [24]. This is evident in recent water level responses to an extreme rain event in the Robinson lens, where 109 mm of rainfall was received on 14 February 2014.…”

“…Sinkholes connected to the watertable bypass the soil zone, directly recharging the aquifer as point recharge. Unconnected sinkholes add runoff deeper into the unsaturated zone, which can then rapidly drain into the watertable via macropores and slow infiltration through the soil profile between the sinkhole bottom and watertable plane [14,24]. Karstic features supply a significant amount of recharge to many carbonate aquifers in temperate and humid regions throughout the world [16], yet the applicability of the assumptions used in recharge estimation methods has not been studied.…”

“…Whilst connected sinkholes transfer surface water to groundwater rapidly through shafts and conduits systems, unconnected sinkholes can act as regions of both rapid and slow recharge [24]. Sinkholes connected to the watertable bypass the soil zone, directly recharging the aquifer as point recharge.…”

Sinkhole evolution in the Apulian Karst of Southern Italy: a case study, with some considerations on Sinkhole Hazards

“…Of course, an air-filled void would generate a high-resistivity anomaly, but this would not constitute a sinkhole, strictly speaking. ERT sections acquired in a karst area outside an urbanized environment should clearly display the types of anomalies routinely encountered in sinkholes (Dobecki and Upchurch, 2006;Schwartz and Schreiber, 2009). …”

Technical Note: Deciphering the Hydrologic Response of Riverbeds across Changes in Recharge with Electrical Resistivity Imaging

“…Hydrogeologic and environmental factors such as the water content, porosity, salinity, clay content, pore geometry, and pore-fluid temperature control the electrical resistivity of a medium (Everett, 2013). ERI surveys can be used to delineate 15 groundwater discharge areas (Nyquist et al, 2008), recharge pathways through mantled sinkholes (Schwartz and Schreiber, 2009), and riverbed sediment architecture (Crook et al, 2008). Daily et al (1992) showed that ERI can effectively map changes in water content within the vadose zone by analyzing the temporal changes in electrical resistivity as a result of an infiltration event.…”