= Buckley-Leverett equation
{c}
{title2=$\phi s_t+Q\partial_xF(s)=0$}
The one-dimensional <mass conservation> equation for saturation when total <Darcy flux> is constant and capillary pressure and gravity are neglected. It is a <scalar conservation law> with dimensional characteristic speed $(Q/\phi)F'(s)$. Shock speeds obey a <Rankine-Hugoniot condition>; physically admissible solutions satisfy an entropy selection. <Capillary diffusion> regularizes the saturation transition.
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