Large‐Scale Aquitard Consolidation Near Mexico City
Large‐Scale Aquitard Consolidation Near Mexico City
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DOI：
10.1111/j.1745-6584.1993.tb00841.x
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发表时间：
1993-09
期刊：
影响因子：
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通讯作者：
A. Ortega-Guerrero;J. Cherry;D. Rudolph
中科院分区：
文献类型：
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作者：
A. Ortega-Guerrero;J. Cherry;D. Rudolph
墨西哥城东南部广阔的湖相Chalco平原下面是一个厚达300 m的弱透水层，由一系列非常多孔（80-90%）的细粒、富含有机物的第四纪沉积物组成，并有火山砂（“卡帕斯杜拉斯”）的水平薄夹层。弱透水层上覆一层厚的冲积-火山碎屑沉积物，形成高产的区域含水层。在20世纪40年代之前，Chalco平原是一个浅水湖，当时它被排干用于农业和人类居住。历史资料表明，在开始大量抽取地下水之前，Chalco平原是一个地下水排泄区。然而，由于含水层抽水，在弱透水层较薄（<100米）的地区，整个弱透水层厚度的水力梯度发生了逆转，现在补给条件占主导地位。在弱透水层较厚的地方，尽管水力梯度仍然表明至少在湖相序列的上部向上流动，但水头数据显示随时间逐渐下降。从20世纪60年代初开始在弱透水层外围以外抽取大量地下水，到1982年开始从弱透水层下面的含水层大量抽水，陆地表面下沉了大约3米。1984年至1989年又发生了2米的沉降，形成了一个浅湖，并逐渐扩大。如果目前从中铝盆地抽取地下水的速度继续下去，平原中部的总地面沉降可能会继续以每年约0.4米的速度持续多年，并最终在中铝平原最厚的部分达到数十米的总沉降。大部分弱透水层的孔隙水是咸水;然而，盐和其他化学成分向下层含水层的释放尚未显着损害含水层的水质。需要更好地了解含水层抽水影响下的弱透水层的行为，以协助长期管理地下水和土地利用在中铝平原。
The extensive lacustrine Chalco Plain in the southeastern part of Mexico City is underlain by an aquitard up to 300 m thick composed of a layered sequence of very porous (80-90%) fine-grained, organic-rich Quaternary deposits, with thin horizontal interbeds of volcanic sand (“Capas Duras”). The aquitard overlies a thick sequence of alluvial-pyroclastic sediments which form a highly productive regional aquifer. The Chalco Plain was a shallow lake until the 1940s when it was drained for agricultural use and human habitation. Historic information indicates that the Chalco Plain was an area of ground-water discharge prior to the onset of heavy ground-water extraction from the semiconfined aquifer. Due to aquifer pumping, however, the hydraulic gradient has reversed throughout the full thickness of the aquitard in areas where the aquitard is thin (< 100m), and recharging conditions now prevail. Where the aquitard is thick, the hydraulic head data show a progressive decline with time even though the hydraulic gradient still indicates upward flow in at least the upper part of the lacustrine sequence. Between the early 1960s, when major ground-water extraction began beyond the periphery of the aquitard, and the onset in 1982 of heavy pumping from aquifers beneath the aquitard, the land surface subsided approximately 3 m. An additional subsidence of 2 m occurred between 1984 and 1989, causing a shallow lake to form and gradually expand. If the present rate of ground-water withdrawal from the Chalco Basin continues, total land subsidence in the middle of the plain will probably continue to a rate of about 0.4 m per year for many years, and could eventually reach a total subsidence of tens of meters in the thickest part of the Chalco Plain. Pore water in much of the aquitard is saline; however, release of salts and other chemical constituents to the underlying aquifer has not yet significantly impaired the aquifer water quality. A better understanding of the behavior of the aquitard under the influence of aquifer pumping is needed to assist in long-term management of ground water and land use in the Chalco Plain.