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_u) 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_u 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.

中文翻译：

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英格兰东南部布莱顿的粉笔含水层中的非饱和带流动过程和含水层响应时间

粉笔含水层是英格兰东南部的主要水源之一。含水层中的非饱和区在控制补给时间和幅度方面起着重要作用，并且是污染物向地下水位输送的主要途径。一系列先前的工作已经解决了Chalk非饱和区的流动过程，但是对物理的理解仍然不完整。在这里，我们结合统计分析和新颖的实验室方法，介绍了在粉笔非饱和带流动机理的研究结果。这项研究是在英格兰东南部布莱顿地块的粉笔上的三个地点（北希思谷仓[NHB]，Pyecombe East [PE]和普雷斯顿公园[PP]）进行的。地下水位和降雨的每日和每小时时间序列数据是相关的。结果表明，在干燥季节（夏季和秋季），当有效降雨量小于4 mm / day时，地下水位对降雨的响应变慢，且非饱和区较厚且较干。在雨季（冬季和春季），当每日有效降雨量超过4毫米/天，且较薄且较湿的非饱和区时，响应速度更快。在NHB和PE站点的雨季期间，观察到非常快速的响应期（在15小时内），并且具有不饱和的水力传导性（K _u）推断为达到839毫米/天。在城市化站点（PP）观察到响应较慢，这是由于渗透减少导致的直接补给减少所致，这是由于存在覆盖PP钻孔周围区域的不可渗透基础设施所致。使用岩土离心机对粉笔基质的K _u进行实验室测量，结果表明，根据饱和度水平，其变化范围为4.27至0.07 mm /天。因此，快速响应不能仅与基质流动相关，而可以指示裂缝和岩溶流动过程在导水中的作用。