Karst Aquifer Recharge: Comments on Somaratne, N. Characteristics of Point Recharge in Karst Aquifers. Water 2014, 6, 2782–2807

Abstract

Abstract:The article "Characteristics of Point Recharge in Karst Aquifers, Water 6: 2782-2807" by N. Somaratne evaluates various recharge estimation techniques applied to four limestone aquifers in South Australia. Somaratne [1] concludes that methods based on watertable fluctuations, groundwater modelling and water budgets are independent of recharge processes, and are therefore superior to the chloride mass balance (CMB) approach for karst aquifers. The current comment offers alternative interpretations from existing field measurements and previous literature, in particular for the Uley South aquifer, which is the focus of much of the article by Somaratne [1]. Conclusions regarding this system are revised, partly to account for the misrepresentation of previous studies. The aeolianite sediments of Uley South are mostly unconsolidated or poorly consolidated, and dissolution features in the calcrete capping provide point infiltration into a predominantly unconsolidated vadose zone, whereas Somaratne's [1] findings require that the system comprises well-developed conduits in otherwise low-conductivity limestone. Somaratne's [1] assertion that the basic premise of CMB is violated in Uley South is disputable, given strong evidence of relatively well-mixed groundwater arising from mostly diffuse recharge. The characterization of karst aquifer recharge should continue to rely on multiple techniques, including environmental tracers such as chloride.

Karst Aquifer Recharge: A Case History of over Simplification from the Uley South Basin, South Australia

“…The simplistic conceptual model in Werner [2], appears "fit-for-purpose" for demonstrating the general application of the conventional CMB and 1-D unsaturated flow modelling, but is far removed from the reality of the basin. Werner [2] describes the conceptual model and well-mixed groundwater system in the QL aquifer without providing supporting evidence, although substantial lithological, hydrogeological, hydrochemical and salinity profile data are available. For reader convenience, this reply is sub-divided into two sections as in Werner [2]: (1) Uley South Recharge Processes; and (2) Uley South Recharge: Methods and Estimates.…”

“…The article of Werner [2], "Karst Aquifer Recharge: Comments on Characteristics of Point Recharge in Karst Aquifers", contains inappropriate over-simplifications of the hydrogeology and recharge processes in Uley South basin. Werner [2], using the conventional chloride mass balance method (CMB) and one-dimensional unsaturated flow modelling, arrives at distorted characteristics of the Uley South QL aquifer.…”

“…Werner [2], using the conventional chloride mass balance method (CMB) and one-dimensional unsaturated flow modelling, arrives at distorted characteristics of the Uley South QL aquifer. The simplistic conceptual model in Werner [2], appears "fit-for-purpose" for demonstrating the general application of the conventional CMB and 1-D unsaturated flow modelling, but is far removed from the reality of the basin.…”

“…Werner [2], using the conventional chloride mass balance method (CMB) and one-dimensional unsaturated flow modelling, arrives at distorted characteristics of the Uley South QL aquifer. The simplistic conceptual model in Werner [2], appears "fit-for-purpose" for demonstrating the general application of the conventional CMB and 1-D unsaturated flow modelling, but is far removed from the reality of the basin. Werner [2] describes the conceptual model and well-mixed groundwater system in the QL aquifer without providing supporting evidence, although substantial lithological, hydrogeological, hydrochemical and salinity profile data are available.…”

“…The conventional CMB is not suitable for accounting chloride mass balance in groundwater systems displaying extreme range of chloride concentrations and complex mixing [3]. Over simplification of karst aquifer systems to suit application of the conventional CMB or 1-D unsaturated modelling as described in Werner [2], is not suitable use of these recharge estimation methods. …”