Measurement of vertical environmental-head profiles in unconfined sand aquifers using a multi-channel manometer board

The vertical hydraulic gradient in an unconfined sand aquifer frequently exceeds the horizontal gradient when measured close to a surface discharge boundary, around an abstraction bore or close to a saline interface. The vertical gradient can be efficiently investigated using a multi-channel manometer board connected to a bundled piezometer installed using hollow-stem-auger-drilling techniques. The design and construction of a manometer board is described. Manometer board data from a site in a 30-m-deep fresh-water aquifer adjacent to a pumping bore are described. The bore is screened in the lower part of the aquifer and the impacts of partial penetration are evident on the manometer board results. Data are then described from the centre of a coastal sand spit where fresh water overlies saline water. Fluid electrical conductivity measurements from the individual tubes of the bundled piezometer are used to derive fluid density at each of the bundled piezometer ports. The average fluid density of water above the mini-piezometer port at each depth is then calculated using Gaussian quadrature. The environmental-water head profiles are compared to point-water and fresh-water head profiles and the implications of the incorrect use of point-water or fresh-water head vertical profiles are clearly demonstrated.