Darcy Flow

Water flows through a saturated soil from high total head to low. The head at a point is the height water rises to in a standpipe there, measured above a common datum. Darcy's law says the flow is proportional to the hydraulic gradient i = Δh/L, the head lost per length of flow path: the Darcy flux is q = k i, and the discharge through the area A is Q = qA = kAΔh/L.

What you are seeing

• The schematic. A horizontal soil-filled pipe between two standpipes. The water level in each standpipe is the head, h₁ upstream and h₂ downstream, measured from the dashed datum. The dashed blue line is the hydraulic head line, falling from h₁ to h₂ through the soil. The drawing is not to scale: the pipe gets longer and thicker as L and A grow, and h₂ is chosen only to draw the picture, since only Δh matters.
• Key results. The gradient, flux and discharge from Darcy's law for the values you set.