An evaluation of semidistributed-pipe-network and distributed-finite-difference models to simulate karst systems
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PAPER
An evaluation of semidistributed-pipe-network and distributed-finite-difference models to simulate karst systems L. W. Gill 1 & P. Schuler 1 & L. Duran 1 & P. Morrissey 1 & P. M. Johnston 1 Received: 5 June 2020 / Accepted: 8 September 2020 # The Author(s) 2020
Abstract Several different approaches have been developed to model the specific characteristics of karst aquifers, taking account of their inherent complex spatial and temporal heterogeneities. This paper sets out the development of a semidistributed modelling approach for applications in an Irish karst context using urban drainage software. The models have proven to be very useful for different studies, with examples given for the ecohydrology of ephemeral karst lakes, extreme groundwater-flood alleviation, karst network investigation, submarine groundwater discharge, and quantification of different recharge and flow components. The limitations of the approach are also highlighted, in particular not being able to simulate diffuse infiltration and flow paths explicitly across the groundwater catchment. Hence, a more distributed, finite-difference modelling approach using MODFLOW Unstructured Grid (USG) with the newly developed Connected Linear Network (CLN) process is then compared against the semidistributed approach on the same karst catchment. Whilst it has proven difficult to achieve the same levels of model performance in simulating the spring flows in the distributed model compared to the semidistributed model, the ability to interrogate the flow paths at any point on the three-dimensional aquifer is demonstrated, which can give new insights into flows (and potential contaminant transport) through such complex systems. The influence of the proximity of highly transmissive conduits on the flow dynamics through the much-lower transmissive matrix cells in which the network is embedded has been particularly investigated. Keywords Karst . Numerical modelling . Groundwater/surface-water relations . Submarine groundwater discharge . Ireland
Introduction Karst aquifers host some of the most important drinking water resources across the world with roughly one quarter of the global population estimated to be relying on the supply of freshwater from these aquifer types (Ford and Williams 2007). In Europe, approximately 22% of the land surface of the continent is underlain by (more or less) karstified Published in the special issue “Five decades of advances in karst hydrogeology”. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10040-020-02241-8) contains supplementary material, which is available to authorized users. * L. W. Gill [email protected] 1
Department of Civil, Structural and Environmental Engineering, University of Dublin Trinity College, Dublin 2, Ireland
carbonate rocks (Goldscheider et al. 2020). Karst systems also support many unique ecological habitats such as calcareous fens, ephemeral lakes (poljes and turloughs), cenotes etc., many of which provide habitat for floral and faunal species
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