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Culvert Size Guidelines

Acres Drained Light Soils (Sands) Medium Soils Heavy Soils (Clay)
Flat Mod. Steep Flat Mod. Steep Flat Mod. Steep
0-5% 5-15% 15%+ 0-5% 5-15% 15%+ 0-5% 5-15% 15%+
Culvert diameter in inches
5 18 18 18 18 18 21 21 21 24
10 18 18 18 21 24 27 27 27 36
20 18 18 18 24 27 36 36 36 42
30 18 18 18 27 30 36 36 42 48
40 18 18 18 27 36 42 42 48 -
50 18 18 18 30 36 48 48 48 -
75 18 21 21 36 42 - - - -
100 21 21 24 36 48 - - - -
150 21 24 24 42 - - - - -
200 24 30 30 48 - - - - -
250 27 30 30 - - - - - -
300 30 36 36 - - - - - -
350 30 36 42 - - - - - -
400 36 36 42 - - - - - -

Data Source: Texas Best Management Practices for Silviculture, Texas Forestry Association