School of Environment and Technology, University of Brighton, Brighton, Lewes Road, BN2 4GJ, UK.
University of Brighton, Lewes Road, Brighton, BN2 4GJ, UK.
Ground Water. 2021 May;59(3):381-395. doi: 10.1111/gwat.13055. Epub 2020 Nov 24.
The Chalk aquifer is one of the main sources of water in South East England. The unsaturated zone in the aquifer plays an important role controlling the time and magnitude of recharge and is major pathway for contaminant transport to the water table. A range of previous work has addressed flow processes in the Chalk unsaturated zone, but physical understanding is still incomplete. Here we present the results of a study on flow mechanism in the Chalk unsaturated zone using a combination of statistical analysis and novel laboratory methods. The study was undertaken at three sites (North Heath Barn [NHB], Pyecombe East [PE], and Preston Park [PP]) on the Chalk of the Brighton block, South East England. Daily and hourly time series data of groundwater level and rainfall were correlated. The results show that a slower groundwater level response to rainfall occurs during dry seasons (summer and autumn) when the amount of effective rainfall is less than 4 mm/day, with a thicker and drier unsaturated zone. A faster response occurs during wet seasons (winter and spring) when the daily effective rainfall exceeds 4 mm/day with a thinner and wetter unsaturated zone. Periods of very rapid response (within 15 h) were observed during wet seasons at NHB and PE sites, with unsaturated hydraulic conductivity (K ) inferred to reach 839 mm/day. A slower response was observed at an urbanized site (PP) as a result of reduction in direct recharge due to reduced infiltration, due to presences of impermeable infrastructure covering the area around PP borehole. Laboratory measurements of K of the Chalk matrix using a geotechnical centrifuge show variation from 4.27 to 0.07 mm/day, according to the level of saturation. Thus, the rapid responses cannot be linked to matrix flow only but indicate the contribution of fracture and karstic flow processes in conducting water.
白垩含水层是英格兰东南部的主要水源之一。含水层中的非饱和带在控制补给的时间和幅度方面起着重要作用，是污染物运移到地下水位的主要途径。以前有很多研究都涉及到白垩非饱和带中的水流过程，但物理理解仍然不完整。在这里，我们使用统计分析和新的实验室方法相结合，介绍了一项关于白垩非饱和带水流机制的研究结果。该研究在英格兰东南部布莱顿区块白垩地层的三个地点（北希思巴恩[NHB]、皮科姆东[PE]和普雷斯顿公园[PP]）进行。地下水水位和降雨量的日时程数据进行了相关分析。结果表明，在有效降雨量小于 4 毫米/天的干燥季节（夏季和秋季），当非饱和带较厚且干燥时，地下水水位对降雨的响应较慢。在有效降雨量每天超过 4 毫米/天的湿润季节（冬季和春季），当非饱和带较薄且湿润时，响应较快。在 NHB 和 PE 站点的湿润季节，观察到非常快速的响应期（在 15 小时内），推断非饱和水力传导率（K）达到 839 毫米/天。在城市化程度较高的 PP 站点，由于不透水基础设施的存在减少了直接补给，导致渗透减少，观测到较慢的响应。使用岩土离心机对白垩基质的 K 进行实验室测量，结果表明根据饱和度的不同，K 的变化范围从 4.27 毫米/天到 0.07 毫米/天。因此，快速响应不能仅与基质流有关，而是表明裂缝和喀斯特流过程在导水方面的贡献。
