Drainage Intensity
Drainage intensity (DI) is the rate of water movement through the soil into the drain pipe when water table midway between laterals is at the soil surface.

This value can be determined from Drain Spacing Tool, here.

Type of lateral drain pipe affects the effective radius.
3-inch 4-row regular-perf = 0.8 cm
3-inch 4-row sand-slot = 0.6 cm
3-inch pipe with knitted sock = 4.5 cm
4-inch 4-row regular-perf = 0.6 cm
4-inch 8-row regular-perf = 1.9 cm
4-inch 4-row sand-slot = 0.5 cm
4-inch 8-row sand-slot = 1.6 cm
4-inch pipe with knitted sock = 5.8 cm
Please cite this reference: Ghane (2022).

This value can be determined from the Drain Spacing Tool, here.