Publication Date:
2021-03-29
Description:
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 conduitassociated
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., largescale
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.
Keywords:
water abstraction; karst;
;
551
Language:
English
Type:
article
,
publishedVersion
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