Abstract The frequent sinkholes along the temporary water streams in Saffré basin can be compared with those occurring in Upper Normandy which are commonly referred to as ‘bétoires’. These collapses are not directly linked to karst cavities. They result from a draw-off effect of fine particles contained in the Plio-Quaternary alluvium lying above the carbonate Oligocene series. The draw-off phenomenon appears through fine cracks (1 to a few millimetres) open in soft palustrine limestones broadly comparable with chalk. Based on the knowledge of backfilling work design undertaken at some ‘bétoires’ in Upper Normandy, a new project was undertaken at four sinkhole funnels, which appeared near the surface in the Saffré basin at the end of the winter in 2017. The works consisted of digging the decompressed surface and filling up the excavation pit with materials of decreasing granulometry from bottom to top in order to ease the surface water infiltration through the identified fractured zones to the bottom of the excavation. This design was also complemented by the implementation of a filtering trench in between the watercourse and the filtering bed, laid above the fractured zones, which were enlarged by the dissolution process, on the one hand, and by the construction of a pipe network on top of the filtering bed to allow for pressurized air exhaust towards the surface, on the other hand. The pressurized air comes up from the aquifer as it recharges as soon as the surface water streamflow resumes and takes part in the mechanism, leading to sinkhole collapse, which should be prevented by this backfilling design.

Abstract Chalk and limestone aquifers contribute one-third of the drinking water supply in Denmark, and one-sixth of that national groundwater resource is assessed as having a ‘Poor’ status in terms of the quantitative Water Framework Directive due to intensive abstraction. This paper describes the national groundwater level monitoring network with regard to the following three applications: (1) when used for the annual surveying and reporting of groundwater resources and impacts from climate and groundwater abstraction; (2) as part of real-time monitoring and modelling for daily and seasonal forecasting; and (3) for tracking long-term climate change impacts on groundwater levels. Groundwater level monitoring provides a particularly important indicator of abstraction pressure and sustainable balance compared with recharge. Many larger chalk and limestone groundwater bodies in Denmark are only monitored by local water companies and not represented in the national groundwater level network. This raises the concern that current national groundwater level monitoring does not fully support integrated modelling and assessment purposes for chalk and limestone groundwater bodies. This also implies that, for tracking long-term climate change and anthropogenic impacts on groundwater levels, the national groundwater monitoring network especially lacks long-term records with complete 30-year time-series for many intensively exploited large chalk and limestone aquifers.

Abstract The implementation of new groundwater tracer tests to the chalky karst plateau of the northwestern end of the Paris Basin, combined with a critical review of previous tracer test investigations, makes it possible to characterize the role of karsts in relation to many structural features. The impact of tectonic structures and lithology on the development and evolution of the karst networks is analysed. The consequences for drinking-water supplies and its protection are examined.

Abstract The small town of Yport in the northern part of the Pays de Caux, Normandy, is located on the shore of the English Channel between Étretat and Fécamp, at the outlet of a long dry valley that incises the chalk plateau. Eight hundred metres to the east, at the base of a cliff, is a cluster of springs, the ‘Fontaines d'Yport’, that emerge on the foreshore. Given their high discharge, measured at between 1 and 2.5 m 3 s −1 , the Le Havre authorities have been interested in these springs since the 1960s, in determining their origin, locating the karst conduit, developing them, and investigating the boundaries and vulnerability of the groundwater basin. Today, one third of the drinking water that supplies the Le Havre conurbation comes from the Yport wells, and investigations into their vulnerability and protection of their resource continues.

Abstract Nitrate concentrations in groundwater abstracted from the Hampshire Chalk have increased over the last 20 years. Concentrations at a public water supply are now close to or above the drinking water standard and additional treatment will be required. Investigations of land use and nitrate source apportionment indicate that the largest contributor of nitrate entering the chalk aquifer comes from arable agriculture. Modelling has shown that, under present land use conditions, nitrate concentrations will continue to rise until the latter half of the twenty-first century. South East Water have successfully engaged with land managers and have trialled the use of cover crops at two sites close to the public water supply. Cover crops retain nutrients in the soil and improve soil condition as an integral part of crop rotation. Trials included different crop mixtures such as a variety of Raphanus sativus (oil radish), Vicia sativa (common vetch) and Trifolium alexandrinum/Trifolium incarnatum (clover). Trials were calibrated using porous pot installations and water extracted from the pots was analysed throughout the cover crop growing season. Results indicate cover crops can reduce nitrate concentration losses to the subsurface by up to 80%. Widespread use of cover crops could reduce nutrient leaching to the aquifer and provide a sustainable solution to current groundwater quality issues.