Example sizing information for riprap energy dissipators at culvert outlets. Source: Kentucky Division of Water
Link to this table

Culvert size Avg. rock diameter Apron width1 Apron length2 Apron length3
8" 3" 2–3 ft. 3–5 ft. 5–7 ft.
12" 5" 3–4 ft 4–6 ft. 8–12 ft.
18" 8" 4–6 ft. 6–8 ft. 12–18 ft.
24" 10" 6–8 ft. 8–12 ft. 18–22 ft.
30" 12" 8–10 ft. 12–14 ft. 22–28 ft.
36" 14" 10–12 ft. 14–16 ft. 28–32 ft.
42" 16" 12–14 ft. 16–18 ft. 32–38 ft.
48" 20" 14–16 ft. 18–25 ft. 38–44 ft.

1Apron width at the narrow end (pipe or channel outlet)
2Apron length for slow-flow (no pressure head) culverts
3Apron length for high flow (pressure head) culverts

This page was last modified on 21 October 2016, at 14:53.

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