Evidence for extreme variations in the permeability of laterite from a detailed analysis of well behaviour in Nigeria
Evidence for extreme variations in the permeability of laterite from a detailed analysis of well behaviour in Nigeria
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通过对尼日利亚油井行为的详细分析，得出红土渗透率极端变化的证据
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发表时间：
2014
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通讯作者：
J. Davies
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作者：
H. Bonsor;A. M. MacDonald;J. Davies
红土在非洲热带地区分布广泛，对其覆盖地区的水文有很大影响。红土的渗透性有助于确定径流和交汇流的分配，并调节地下水对下伏基岩的补给。红土中的地下水也是一种广泛的饮用水来源，通常来自未经改进的悬挂挖井。尽管它很重要，但关于红土含水层属性的公开信息很少。在这项研究中，分析了尼日利亚一口6 m深的井的数据，以通过反复抽水试验来表征红土的水力传导性。40个试验的导水率测量范围从0.1到1000 m~2/d不等。对数据的进一步解释表明，水平导水率随深度呈强烈的非线性下降，其特征是上层位具有极高的渗透率(400 m/d)，而下层具有低得多的渗透率剖面(<；0.1 m/d)。这些数据与该地区其他油井的观测结果相吻合。这种非线性渗透性结构有几个含义：在雨季，上层红土可以促进快速的横向渗流，使污染物能够被输送到很远的距离(高达1 公里)；天然地下水位在一年中的大部分时间被限制在一个狭窄的范围内；在旱季，较深的红土的低渗透性限制了可以从浅井中抽取的水量，导致油井失灵。这项工作突出表明，有必要进行更广泛的研究，以更好地了解红壤及其在区域水文学中所起的作用。©2013自然环境研究理事会。约翰·威利父子有限公司出版的水文过程。
Laterite soils are widespread in tropical Africa and have a large impact on the hydrology of the areas they cover. The permeability of laterite helps determine the partitioning of runoff and interflow and regulates groundwater recharge to underlying bedrock. Groundwater within laterite also forms a widespread source of drinking water, typically from unimproved hang‐dug‐wells. Despite its importance, there is little published information on laterite aquifer properties. In this study, data from a 6 m deep well in Nigeria have been analysed to characterise the hydraulic conductivity of the laterite from repeated pumping tests. Transmissivity measurements from 40 tests spread out across a hydrological year varied from 0.1 to 1000 m2/d. Further interpretation of the data demonstrate a strong non‐linear decrease in horizontal hydraulic conductivity with depth, characterised by an upper horizon of extreme permeability (400 m/d), and a much lower permeability profile beneath (<0.1 m/d). These data are substantiated with observations from other wells throughout the area. This non‐linear permeability structure has several implications: the upper laterite can facilitate rapid lateral throughflow in the wet season, enabling contaminants to be transported significant distances (up to 1 km); natural groundwater levels are restricted to a narrow range for much of the year; and, in the dry season, the lower permeability of the deeper laterite restricts the amount of water which can be abstracted from shallow wells, leading to well failure. The work highlights the need for a wider study to better understand laterite soils and the role they play in regional hydrology. © 2013 Natural Environment Research Council. Hydrological Processes published by John Wiley & Sons Ltd.