The Importance of Capturing Topographic Features for Modeling Groundwater Flow and Transport in Mountainous Watersheds
The Importance of Capturing Topographic Features for Modeling Groundwater Flow and Transport in Mountainous Watersheds
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DOI：
10.1029/2018wr023863
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发表时间：
2017-12
影响因子：
5.4
通讯作者：
Chao Wang;J. Gomez‐Velez;John L. Wilson
中科院分区：
文献类型：
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作者：
Chao Wang;J. Gomez‐Velez;John L. Wilson
包括地下水在内的基于物理的分布式水文模型被广泛用于理解和预测流域内的物理和生物地球化学过程。通常，由于计算的限制，分水岭建模器在域离散化、平滑甚至忽略关键地形特征时尽量减少使用的元素数量。我们使用一个理想化的模型来研究沿溪流和山脊的网格细化对模拟山地流域三维地下水流动和运输的影响。对于不同程度的地形复杂程度（随网格细化程度的增加而增加）和地质非均质性，我们估计并比较了稳态基流流量、平均年龄和地下风化产物浓度。结果表明，忽略低阶流或脊减少了局部流道的流量，偏置提高了中间和区域流道的贡献，偏置增加了基流。对于渗透率随深度迅速下降且以浅层流道为主的系统，偏置的幅度会增大。基于简单的地球化学模型，风化产物的浓度对TCL不太敏感，部分原因是化学反应的热力学约束。我们的理想模型还再现了观测到的地下水对径流的贡献与流域面积之间的紧急标度关系，并发现这种标度关系对网格TCL不敏感。偏差效应对水文模型在环境示踪剂数据解释和山区流域水流生物地球化学演化预测中的应用具有重要意义。
Physics‐based distributed hydrological models that include groundwater are widely used to understand and predict physical and biogeochemical processes within watersheds. Typically, due to computational limitations, watershed modelers minimize the number of elements used in domain discretization, smoothing or even ignoring critical topographic features. We use an idealized model to investigate the implications of mesh refinement along streams and ridges for modeling three‐dimensional groundwater flow and transport in mountainous watersheds. For varying degrees of topographic complexity level (TCL), which increases with the level of mesh refinement, and geological heterogeneity, we estimate and compare steady state baseflow discharge, mean age, and concentration of subsurface weathering products. Results show that ignoring lower‐order streams or ridges diminishes flow through local flow paths and biases higher the contribution of intermediate and regional flow paths, and biases baseflow older. The magnitude of the bias increases for systems where permeability rapidly decreases with depth and is dominated by shallow flow paths. Based on a simple geochemical model, the concentration of weathering products is less sensitive to the TCL, partially due to the thermodynamic constraints on chemical reactions. Our idealized model also reproduces the observed emergent scaling relationship between the groundwater contribution to streamflow and drainage area, and finds that this scaling relationship is not sensitive to mesh TCL. The bias effects have important implications for the use of hydrological models in the interpretation of environmental tracer data and the prediction of biogeochemical evolution of stream water in mountainous watersheds.