Groundwater flow in the transition zone between freshwater and saltwater: a field-based study and analysis of measurement errors

Post, Vincent E. A.; Banks, Eddie; Brunke, Miriam

Groundwater flow in the transition zone between freshwater and saltwater: a field-based study and analysis of measurement errors | Ecoulement des eaux souterraines dans la zone de transition eau douce-eau salée: étude sur le terrain et analyse des erreurs de mesure Flujo de agua subterránea en la zona de transición entre agua dulce y agua salada: un estudio de campo y análisis de errores de medición 淡水和海水之间过渡带中的地下水流:基于野外的研究及测量误差的分析 Fluxo das águas subterrâneas na zona de transição entre agua doce e salgada: um estudo baseado em campo e análise de erros de medição

2018

Post, Vincent E. A. | Banks, Eddie | Brunke, Miriam

The quantification of groundwater flow near the freshwater–saltwater transition zone at the coast is difficult because of variable-density effects and tidal dynamics. Head measurements were collected along a transect perpendicular to the shoreline at a site south of the city of Adelaide, South Australia, to determine the transient flow pattern. This paper presents a detailed overview of the measurement procedure, data post-processing methods and uncertainty analysis in order to assess how measurement errors affect the accuracy of the inferred flow patterns. A particular difficulty encountered was that some of the piezometers were leaky, which necessitated regular measurements of the electrical conductivity and temperature of the water inside the wells to correct for density effects. Other difficulties included failure of pressure transducers, data logger clock drift and operator error. The data obtained were sufficiently accurate to show that there is net seaward horizontal flow of freshwater in the top part of the aquifer, and a net landward flow of saltwater in the lower part. The vertical flow direction alternated with the tide, but due to the large uncertainty of the head gradients and density terms, no net flow could be established with any degree of confidence. While the measurement problems were amplified under the prevailing conditions at the site, similar errors can lead to large uncertainties everywhere. The methodology outlined acknowledges the inherent uncertainty involved in measuring groundwater flow. It can also assist to establish the accuracy requirements of the experimental setup.

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