Manning's roughness coefficient (n):

For smooth-wall inside corrugated plastic, n=0.012

For 3, 4, 5 and 6 inch single-wall corrugated plastic, n=0.015
For 8 inch single-wall corrugated plastic, n=0.016
For 10 inch single-wall corrugated plastic, n=0.017
For 12 and 15 inch single-wall corrugated plastic, n=0.018
For 18 and 24 inch single-wall corrugated plastic, n=0.020

Source: Corrugated Polyethylene Pipe Association (2000) and ASABE EP260.5 FEB2015 (R2019)

The rate of water movement through the drainage pipe network. Set this value greater than or equal to drainage intensity.

Use the Drain Spacing Tool too estimate the optimum drain spacing. Click here.

For the "Both sides" selection, consider the two laterals on both sides of the main as one long lateral. Thus, enter the total length of the two laterals as one long lateral.

For example, if the length of the main from last lateral to outlet is 500 ft and the nonperforated section of the main is 100 ft, enter 400 ft of perforated section of the main in this box.