Flow nets consist of two sets of lines. One set, referred to as equipotential lines, connect points of equal head. The second set, referred to as flow lines depict the idealised paths followed by water particles.
Flow nets consist of two sets of lines that are perpendicular to each other. The first set (equipotential lines) represents the height of the water table or potentiometric surface of a confined aquifer, above a datum. The second set (flow lines) indicates that route a particle will follow through an aquifer.
Why are flow nets important?
Flow nets not only show the direction of groundwater movement but can also, if they are drawn with care, be used to estimate the quantity of water in transmitted through the aquifer.
Source: PMWIN Training Manual (Chaing and Kinzelbach, 1998)