A methodology for regionalizing 3‐D effective porosity at watershed scale in crystalline aquifers
A methodology for regionalizing 3‐D effective porosity at watershed scale in crystalline aquifers
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结晶含水层流域尺度 3D 有效孔隙度区域化方法
DOI：
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发表时间：
2017
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通讯作者：
J. Maréchal
中科院分区：
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作者：
B. Dewandel;Y. Caballero;J. Perrin;A. Boisson;Fabrice Dazin;S. Ferrant;S. Chandra;J. Maréchal
提出了一种三维有效孔隙度区域划分的创新方法，并将其应用于位于印度南部的两个大型、过度开发和深度风化的结晶含水层。该方法源于早期对地下水位波动部分含水层的二维有效孔隙度区进行区划的工作，现在使用三维方法将其扩展到整个含水层。还开发了一种基于地质和地球物理调查的风化剖面层（腐岩和裂缝层）制图方法。三维有效孔隙度分区方法结合了不同单元大小的地下水位波动和地下水预算技术，并使用了基于卫星的数据（用于抽取地下水）、风化剖面结构和地质统计学技术。详细介绍了该方法在Kudaliar流域（983平方公里）的应用，并在730平方公里的Anantapur流域进行了测试。在流域尺度上，Kudaliar含水层的有效孔隙度为0.5% ~ 2%，Anantapur含水层的有效孔隙度为0.3% ~ 1%，这与早期的研究结果一致。结果表明：(1)不同地质条件和风化剖面结构的不同，有效孔隙度的垂向分布可能有很大差异，结晶含水层裂缝层的有效孔隙度不一定会迅速减小；(2)有效孔隙度的横向变化可能大于垂向变化。这些变化表明，在同一风化剖面内，裂缝带的开放裂缝密度和/或风化程度可能在不同地方有显著差异。所提出的方法提供了有效孔隙度空间分布的信息，有效孔隙度在晶体含水层的通量和污染物输送方面具有重要意义。本文还讨论了绘制地下水储量和稀缺性地图的意义，这将有助于改进地下水资源管理战略。
An innovative approach for regionalizing the 3‐D effective porosity field is presented and applied to two large, overexploited, and deeply weathered crystalline aquifers located in southern India. The method derives from earlier work on regionalizing a 2‐D effective porosity field in that part of an aquifer where the water table fluctuates, which is now extended over the entire aquifer using a 3‐D approach. A method based on geological and geophysical surveys has also been developed for mapping the weathering profile layers (saprolite and fractured layers). The method for regionalizing 3‐D effective porosity combines water table fluctuation and groundwater budget techniques at various cell sizes with the use of satellite‐based data (for groundwater abstraction), the structure of the weathering profile, and geostatistical techniques. The approach is presented in detail for the Kudaliar watershed (983 km2) and tested on the 730 km2 Anantapur watershed. At watershed scale, the effective porosity of the aquifer ranges from 0.5% to 2% in Kudaliar and between 0.3% and 1% in Anantapur, which agrees with earlier works. Results show that (a) depending on the geology and on the structure of the weathering profile, the vertical distribution of effective porosity can be very different and that the fractured layers in crystalline aquifers are not necessarily characterized by a rapid decrease in effective porosity and (b) that the lateral variations in effective porosity can be larger than the vertical ones. These variations suggest that within a same weathering profile, the density of open fractures and/or degree of weathering in the fractured zone may significantly vary from a place to another. The proposed method provides information on the spatial distribution of effective porosity that is of prime interest in terms of flux and contaminant transport in crystalline aquifers. Implications for mapping groundwater storage and scarcity are also discussed, which should help in improving groundwater resource management strategies.