= Square-root drainage boundary
{title2=$h\sim\sqrt{2Jx},\quad hh_x\to J$}
A zero-height outlet can carry finite nonzero <volume flux per unit width> in a nonlinear <Darcy flow> model with $q=-Khh_x$. If $hh_x\to J>0$ as $x\downarrow0$, then $(h^2)'\to2J$, and <integration> gives $h\sim\sqrt{2Jx}$ and $h_x\sim\sqrt{J/(2x)}$. Thus the height vanishes while its slope diverges; the flux must be evaluated as a limit of the product. The divergent slope also identifies a region where the outer <Dupuit approximation> eventually needs a local correction.
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