Drainage Capacity

Pipe material

Manning's roughness coefficient (n):

For smooth-wall interior 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

For clay or concrete drain tile, n=0.013

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

Pipe diameter
(in)

Pipe grade
(%)

Soil Texture	Maximum velocity (ft/s) WITH sock or sand-slot pipe	Maximum velocity (ft/s) WITHOUT sock or sand-slot pipe
Sand, loamy sand, sandy loam	5.0	-
Silt, silt loam	6.0	5.0
Loam, silty clay, silty clay loam, sandy clay, sandy clay loam	7.0	6.0
Clay, clay loam	-	7.0