UIS Commission on Karst Hydrogeology and Speleogenesis
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Glossary of Karst and Cave Terms

Hagen-Poiseuille equation
The equation used to define the laminar flow of water in either fractures or tubes and is given as for laminar flow in fractures and for laminar flow in tubes which states that the average volumetric discharge of flow through either type of opening is directly proportional to the type, shape, and dimensions of a particular pore and the hydraulic gradient [5]. Note: Q=discharge, w=width of the fissure, b=open portion of the long dimension of the fissure, r=radius of the tube, (?and ç are the specific weight and dynamic viscosity of water respectively, dh/dL=gradient, and a minus sign is attached to the equations to indicate that flow occurs in the direction of deceasing hydraulic head.