Theory and Method
Discharge capacity describes the volume of water a drain carries along its own length per unit time under a stated hydraulic gradient. The test applies a head difference across the two ends of the specimen, holds it constant, and collects the water leaving the downstream end over a timed interval. Dividing that flow rate by the applied gradient yields qw, the discharge capacity value a designer feeds into well resistance calculations. Darcy's law underpins the relationship, so the method keeps gradients low enough that flow stays laminar.
The horizontal frame lays the drain flat along its full 450 mm test length, which keeps the flow path straight and the head difference acting purely along the drain axis. Water enters the core channels through the filter membrane and travels down the grooves in the plastic core rather than through the surrounding fabric. Holding the specimen flat and parallel matters, because any bend or twist in the strip narrows the channels and reports a capacity the product does not actually have.
Water temperature moves the result more than most operators expect, since viscosity falls as water warms and a warmer sample flows faster through the same channel. The onboard tank heats or cools the supply water and holds it there, so two specimens tested on different days remain comparable. Steady applied pressure completes the picture, reproducing the load the drain carries in the ground and showing how much of the open channel area survives under it.
