Dunkirk: Where History Happened. We visit 10 places connected with the remarkable evacuation of the British Expeditionary Force from northern France in 1940. This feature was first published in the April 2010 edition of BBC History Magazine. Tuesday 25th May 2010.
The seepage velocity is less than the actual flow rate of the liquid or gas in the pores because the fluid moves only through the portion of the cross-sectional area S that is occupied by the pores.
1 Seepage or filtration spring. The term seep refers to springs with small flow rates in which the source water has filtered through permeable earth.  Fracture springs, discharge from faults, joints, or fissures in the earth, in which springs have followed a natural course of voids or weaknesses in the bedrock.