Glossary of Karst and Cave Terms
Based on "A Lexicon of Cave and Karst Terminology with Special to Environmental Karst Hydrology" EPA/600/R-02/003, 2002, EPA: Washington, DC., Speleogenesis Glossary includes 2699 cave & karst terms
A simplifying assumption for the solution of a free surface well flow problem  (e.g. a water-table aquifer.) It is based on the assumption that the slope of the phreatic surface is negligibly small so that the equipotential lines are vertical and flow is essentially horizontal.