Spatial variation in salinity of some alluvial aquifers in central Queensland - a steady state analysis

Abstract

This paper reports on the spatial variation of salinity in the alluvial groundwaters of the Callide Valley, central Queensland. The spatial distribution of salinity in this area is very complex with substantial variation occumng over small (< 1 km) and large (> 10 km) distances. This complexity has been attributed to variable leakage of highly saline water into the alluvium from adjacent hard rock aquifers. A simple but elegant steady-state dimensionless analysis is introduced to clearly establish if salt additions or subtractions are occurring in the alluvial groundwaters. By using ions not normally complicated by precipitation reactions (sodium and chloride), our analyses show that solutes are conserved, with excellent agreement between the measured data and theory. This result strongly supports a hypothesis of progressive concentration of a localized source of salt, introduced near the headwaters, with increasing distance down discrete alluvium-stream valleys. We conclude our paper with a caution on the delayed effects of distributed salt import into alluvial aquifers with large solute response times.