Cost-effective mini drive-point piezometers and multilevel samplers for monitoring the hyporheic zone

摘要

The development of cost-effective approaches to monitor groundwater-surface-water exchange processes and contaminant fate within the hyporheic zone fundamentally underpins implementation of legislation such as the European Community Water Framework Directive, which requires integrated management of groundwater and surface water. Cost-effective mini drive-point piezometers (MDPs) and multilevel samplers (MLSs) are presented that use cheap construction materials, involve simple fabrication and installation procedures, and have a proven durability with low vulnerability to flood events and vandalism. They have been used across a range of hydro(geo)logical settings in the UK and proven to be effective in discerning flow exchange, geochemical trends, and contaminant transport and attenuation over monitored depths of 0.25 to 2 m at a resolution as low as 0.05 m. Example depth profiles, cross-river transects and river-reach longitudinal profiles from the River Tame catchment (West Midlands, UK) illustrate the value of MDP-MLS approaches in establishing surface-water-groundwater mixing zone depths, contaminant natural attenuation as a result of biotic activity within the hyporheic zone, and estimates of contaminant flux exchanges between groundwater and surface water. The MDP-MLS approaches allow discernment of contaminated groundwater plume discharges that may go undetected, or at best poorly resolved, if reliance was solely placed on conventional riverside monitoring wells and/or surface-water sampling. The MDP-MLS approaches described also have potential to be used in the investigation of shallow sediment aquifers, lake shorelines and wetland features.