Hydrogeologists And Geotechnical Engineers – Lost Without Translation

Philip Pells and Steven Pells

Fundamental to structural, geotechnical, hydraulic and groundwater engineering are coherent, functional, mathematical theories that obey the laws of physics and thermodynamics. Whether explicit, or intuitive, and though they be simplifications of a complex reality, it is these theories that set engineers apart from lay persons.

Like all practitioners, hydrogeologists have developed categorisations of common phenomena to make their tasks easier, of which two that are ubiquitous in hydrology are:

  1. The notion of ‘aquifers’, and their inverse; ‘aquicludes’ and ‘aquitards’
  2. The notion of ‘confinement’, and its inverse; ‘connectivity’.

These relate to geology, and mathematics, and are enticing because geology is complex and mathematics can be difficult. While the categorisations have been helpful, where the only consideration is groundwater production, they are deceptions when it comes to assessing depressurisation impacts. In addition they are not scientifically quantifiable with satisfactory precision.

The categorisations form a heuristic, where:
“heuristics are simplified rules of thumb that make things simple and easy to implement Their main advantage is that the user knows they are not perfect, just expedient, and is therefore less fooled by their powers. They become dangerous when we forget that.” (Taleb, 2012)

In this paper, we trace the etymology of the classification of ‘aquifers’ and ‘confinement’, and the development of the current hydrogeologist’s heuristic. We show how this leads to a contagion of error when considering depressurisation impacts. We also deal with other words and concepts that are particular to hydrogeology, being Specific Storage, Hydraulic Diffusivity, Specific Yield, Specific Retention and Transmissivity, and which often mystify civil engineers with conventional training in soil mechanics. By translating these hydrogeology terms to those understood by engineers we hope to help communications between these closely aligned professionals.