Draining gravity current
= Draining gravity current
A draining gravity current loses fluid through its substrate while spreading horizontally. For a two-dimensional viscous current of thickness $H(x,t)$ that loses fluid according to <pressure-dependent Darcy drainage>,
$$
H_t=A(H^3H_x)_x-DH^{1-\beta},
\qquad A=\frac{\rho g}{3\mu},
$$
when the <hydrostatic pressure> is $p=\rho gH$ and $k/h\propto p^{-\beta}$.