Applying a modified conduit flow process to understand conduit-matrix exchange of a karst aquifer

Abstract. Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix, resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most mathematical karst models assume quasi-steady-state flow in conduits neglecting conduit-associated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g., large-scale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed-head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this work is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical discrete-continuum model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The effects and the proper functioning of these modifications are demonstrated by simplified model studies. Both enhancements, CADS and FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems, as illustrated by its application to the Cent Fonts karst system.

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Use of the Conduit Flow Process for the simulation of passive mitigation measures against the piezometric damming effect at the new underground High Speed railway station of Florence

Rendiconti online della Società Geologica Italiana ◽

10.3301/rol.2016.92 ◽

2016 ◽

Vol 41 ◽

pp. 57-60

Author(s):

Maria Filippini ◽

Mario Martina ◽

Stefano Menichetti ◽

Francesco Palmiero ◽

Luca Ranfagni ◽

...

Keyword(s):

High Speed ◽

Mitigation Measures ◽

Flow Process ◽

Railway Station ◽

High Speed Railway ◽

Conduit Flow

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Changes in groundwater quality in a conduit-flow-dominated karst aquifer, following BMP implementation

Environmental Geology ◽

10.1007/s00254-001-0515-6 ◽

2002 ◽

Vol 42 (5) ◽

pp. 525-531 ◽

Cited By ~ 8

Author(s):

James Currens

Keyword(s):

Groundwater Quality ◽

Karst Aquifer ◽

Conduit Flow

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Representation of water abstraction from a karst conduit with numerical discrete-continuum models

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-10-4463-2013 ◽

2013 ◽

Vol 10 (4) ◽

pp. 4463-4487

Author(s):

T. Reimann ◽

M. Giese ◽

T. Geyer ◽

R. Liedl ◽

J. C. Maréchal ◽

...

Keyword(s):

Boundary Condition ◽

Large Scale ◽

Pumping Test ◽

Karst Water ◽

Karst Aquifers ◽

Flow Process ◽

Conduit Flow ◽

Water Abstraction ◽

Model Studies ◽

Karst Conduit

Abstract. Karst aquifers are characterized by highly conductive conduit flow paths embedded in a less conductive fissured and fractured matrix resulting in strong permeability contrasts with structured heterogeneity and anisotropy. Groundwater storage occurs predominantly in the fissured matrix. Hence, most karst models assume quasi steady-state flow in conduits neglecting conduit associated drainable storage (CADS). The concept of CADS considers storage volumes, where karst water is not part of the active flow system but rather hydraulically connected to conduits (for example karstic voids and large fractures). The disregard of conduit storage can be inappropriate when direct water abstraction from karst conduits occurs, e.g. large scale pumping. In such cases, CADS may be relevant. Furthermore, the typical fixed head boundary condition at the karst outlet can be inadequate for water abstraction scenarios because unhampered water inflow is possible. The objective of this paper is to analyze the significance of CADS and flow-limited boundary conditions on the hydraulic behavior of karst aquifers in water abstraction scenarios. To this end, the numerical hybrid model MODFLOW-2005 Conduit Flow Process Mode 1 (CFPM1) is enhanced to account for CADS. Additionally, a fixed-head limited-flow (FHLQ) boundary condition is added that limits inflow from constant head boundaries to a user-defined threshold. The affect and proper functioning of these modifications is demonstrated by simplified model studies. Both enhancements, CAD storage and the FHLQ boundary, are shown to be useful for water abstraction scenarios within karst aquifers. An idealized representation of a large-scale pumping test in a karst conduit is used to demonstrate that the enhanced CFPM1 is potentially able to adequately represent water abstraction processes in both the conduits and the matrix of real karst systems.

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