Representation of water abstraction from a karst conduit with numerical discrete-continuum models
Representation of water abstraction from a karst conduit with numerical discrete-continuum models
复制标题
DOI：
10.5194/hess-18-227-2014
复制
发表时间：
2013-11
影响因子：
6.3
通讯作者：
T. Reimann;M. Giese;T. Geyer;R. Liedl;J. Maréchal;W. B. Shoemaker
中科院分区：
文献类型：
--
作者：
T. Reimann;M. Giese;T. Geyer;R. Liedl;J. Maréchal;W. B. Shoemaker
岩溶含水层的特点是嵌入在导电性较差的裂隙和断裂基质中的高导电性管道流动路径，导致渗透性与结构异质性和各向异性形成强烈对比。地下水储存主要发生在裂隙基质中。因此，大多数数学岩溶模型都假设管道中的准稳态流动，忽略了与管道相关的可排水储存（CADS）。 CADS 的概念考虑了存储量，其中岩溶水不是主动流系统的一部分，而是通过水力连接到管道（例如岩溶空隙和大裂缝）。当直接从岩溶管道中取水时，例如，忽视管道储存可能是不合适的。例如，大规模抽水。在这种情况下，CADS 可能是相关的。此外，岩溶出口处的典型固定水头边界条件可能不足以满足取水场景，因为可以实现不受阻碍的水流入。这项工作的目的是分析 CADS 和限流边界条件对取水场景中岩溶含水层水力行为的重要性。为此，数值离散连续模型 MODFLOW-2005 导管流动过程模式 1 (CFPM1) 得到增强，以考虑 CADS。此外，还添加了固定水头限流 (FHLQ) 边界条件，将来自恒定水头边界的流入量限制到用户定义的阈值。这些修改的效果和正常功能通过简化模型研究得到了证明。事实证明，CADS 和 FHLQ 边界这两种增强功能对于岩溶含水层内的取水场景非常有用。使用岩溶管道中大规模抽水测试的理想化表示来证明增强型 CFPM1 能够充分表示管道和真实岩溶系统矩阵中的抽水过程，如其在 Cent Fonts 岩溶系统中的应用所示。
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.