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 The Great Miami Buried Valley Aquifer system (GMBVAS) is a U.S. EPA–designated sole-source aquifer for most of the ~2.3 million residents of the Great Miami River basin. The aquifer system is similar to many of the glacial outwash–alluvial aquifers found throughout the southern Midwestern United States: a valley deeply incised into bedrock by meltwater from repeated glaciations, subsequently aggraded with glacial outwash, lake clays, tills, and post-glacial alluvium. These aquifers are often immediately adjacent to or below modern streams with which they are hydrologically connected. Because of the exchange of water between the aquifer and surface streams, they must be considered two parts of a single hydrogeologic system; anything impacting one part will impact the other. Because virtually all water is recycled, public water suppliers, agricultural users, and industrial users withdraw water from the GMBVAS, then discharge the used water to the next downstream consumer. For example, agricultural runoff and municipal wastewater enter the Great Miami River. River water recharges the aquifer near well fields through induced infiltration. Municipalities, agriculture, and industry pump groundwater from the aquifer and discharge some of the water back into the river as a return flow. Sound water management requires balancing the needs of these diverse users. Agriculture, particularly in the upper Great Miami basin, is a major source of revenue and jobs but requires heavy application of nutrients and herbicides. Sand and gravel quarrying in the Great Miami basin is critical for construction and infrastructure but also removes vast amounts of aquifer material. Not only is healthy reliable groundwater important for the public water supply, it is also essential to bottling facilities, distilleries, pharmaceutical companies, and other water-dependent industries that have been attracted to the area. This field trip explores the GMBVAS, its uses, its interaction with Great Miami River, and the contrasting needs of the people and businesses that depend on it.

Abstract Open framework gravels (OFGs) are an inherent textural component of alluvial gravel outwash deposited by braided river systems. Being exceptionally permeable, they play an important part in facilitating the transmission of water and contaminants through alluvial gravel aquifers. Understanding how connected OFG facies are is helpful in making informed predictions about groundwater flow and contaminant transport through such aquifer systems. This work examined a section of the Rakaia fan, Canterbury, New Zealand. A 3 × 3 grid of large diameter auger holes was drilled in close proximity to a sea cliff, which provided very good three-dimensional exposure of the fan architecture. A novel smoke tracing experiment and water tracing field tests were conducted to measure the dynamic connectivity of the OFG facies. Smoke proved to be an effective tracer for measuring the interconnectedness of OFGs over set distances of 5 m. The water tracing tests confirmed that OFGs are connected across much longer distances – in excess of 18 m. Results from both tests revealed how rapid, and non-uniform, aqueous transport can be through alluvial outwash materials. The connectivity information will be used to improve realizations of the heterogeneity of the Canterbury Plains aquifer and inform future hydrogeological modelling.

Abstract Afghanistan is a mountainous, arid country with limited surface water supplies. The complex geology in this country includes active tectonics and mountain ranges. Afghanistan is subdivided into three distinct hydrogeological areas: the Central Highlands, the Northern Plain, and the Great Southern Plain. Most groundwater is located in the Central Highlands, where water of sufficient quantity to meet the needs of the population is available primarily by digging wells into unconsolidated alluvial aquifers located in mountain valleys. A lack of sustainable, high-quality water supplies can have a negative impact on the ability to conduct military operations. An understanding of hydrogeological conditions is required in order to minimize exposures to natural and anthropogenic sources of contamination that may pose either acute or chronic health risks to military forces. This same scarcity of potable water can have a negative impact on the local population. Projects that improve the quantity and quality of water available to both military forces and the local population are important to improve the overall stability of Afghanistan.