Electrical Analogy

If you imagine the porous media part of the pipe as a resistor in an electric circuit, it may help to understand the process.

In an electric circuit the current through a resistor is;

I = V/R,

and R can be defined in terms of resistivity;

R = ρL/A,

so you end up with;

I = VA/ρL = Aσ V/L. (where σ is the conductivity)

You can compare this to Darcy's Law;

q = Ak dh/dx.

You can compare the coefficient of permeability to the conductivity and the height (which is like gravitational potential) to voltage (the electrical potential). The current is comparable to the flow rate for obvious reasons. Thinking about Darcy's law like this may help you recall it in the exam.

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I = Current ρ=resistivity

V = Voltage σ= conductivity = k

R = Resistance dh/dx = hydraulic gradient (no units)

A = Area