= Channel-cavity drainage instability
{title2=$N_R'(Q_R)>|N_K'(Q_K)|$}
At fixed total discharge $Q_R+Q_K$, remove a small amount $\varepsilon$ from a channel and send it through connected cavities. The equilibrium channel effective <pressure> drops by $N_R'\varepsilon$, while the cavity <pressure> difference drops by $|N_K'|\varepsilon$. Under the displayed inequality the cavity system leaves a common effective <pressure> higher than the reduced-flux channel can sustain. Excess creep closure then decreases channel discharge further, amplifying the perturbation.
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