Water transport through the unsaturated zone of the Middle Chalk: a case study from Fleam Dyke lysimeter
Water transport through the unsaturated zone of the Middle Chalk: a case study from Fleam Dyke lysimeter
复制标题
通过中白垩不饱和区的水输送：Fleam Dyke 蒸渗仪的案例研究
DOI：
--
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
J. D. Cooper
中科院分区：
文献类型：
--
作者：
H. K. Jones;J. D. Cooper
摘要 裂缝在白垩岩非饱和带输水过程中的作用多年来一直存在争议。尽管直接观察很少，但裂缝显然有可能将水和污染物快速输送到饱和区。关于旁路流的重要性，来自井水文、溶质剖面和土壤水测量的证据是不明确的。本文检查了剑桥郡弗莱姆戴克 (Fleam Dyke) 的 5 m 立方体未受干扰的整体式渗漏计几年运行的排水数据，以寻找旁路流的证据，并调查了导致其发生的因素。还提供了现场白垩不饱和水力传导率测量和土壤水原位测量的证据。蒸渗仪和土壤水观测都一致认为，通过裂缝的流量约占该地点总排水量的 30%，明显高于其他 Chalk 地点的推断。观察到旁路流量发生在约 -50 cm H2O 基质势的阈值之上，或在约 1 mm day−1 的流速之上。在土壤不缺水的时期，约 50% 的排水是通过裂缝进行的。一般来说，降雨和渗漏仪底部排水之间有三到四天的延迟。有一次，强烈的夏季降雨满足了现有的土壤水分不足并引发了裂隙流，通过蒸渗仪的排水峰值在 24 小时内出现。在土壤水分亏缺发生后的一段时间内，蒸渗仪的排水量始终高于 MORECS 估计的水文有效降水量。
Abstract The role of fractures in transporting water in the unsaturated zone of the Chalk has been a source of controversy for many years. There is clearly a potential for fractures to transport water and contaminants rapidly to the saturated zone, although direct observations are rare. The evidence from well hydrographs, solute profiles and soil water measurements is ambiguous concerning the importance of by-pass flow. This paper examines drainage data from several years’ operation of a 5 m cube undisturbed monolith lysimeter at Fleam Dyke, Cambridgeshire, for evidence of by-pass flow and investigates the factors responsible for its onset. Evidence from measurements of unsaturated hydraulic conductivity of the Chalk at the site and in situ measurements of soil water are also presented. Both the lysimeter and soil water observations agree that flow through fractures accounts for approximately 30% of the total drainage from this site, significantly higher than has been inferred at other Chalk sites. By-pass flow was observed to occur above a threshold of approximately −50 cm H2O matric potential, or above a flow rate of approximately 1 mm day−1. During periods of no soil water deficit, about 50% of drainage occurred via fractures. In general, there was a delay of three or four days between rainfally and drainage at the base of the lysimeter. On once occasion, intense summer rainfall satisfied the existing soil moisture deficit and initiated fracture flow, the peak in drainage through the lysimeter occurring within 24 hours. Drainage from the lysimeter was consistently higher than MORECS estimates of hydrologically effective precipitation during the period after the onset of soil water deficits.